On Wed, 12 Feb 2014 08:36:44 +0000, Tim Watts
wrote:

On Wednesday 12 February 2014 03:44 Johny B Good wrote in uk.d-i-y:


====snip====


Well, not being an electrician by trade, I've been unable to find any
references to the regulations, only anecdotes regarding 10A lighting
circuits (including the use of a ring lighting circuit) so I can't
quote 'chapter and verse' as to whether this is an acceptable
departure from the regulations or not (I know some leaway exists
within the regulations but this seems to be quite a large departure to
my mind).

10A lighting circuits are "standard" (by the wiring regs) as are 16A
(though the latter are almost unheard of domestically).

I have designed my house with 2 x 10A lighting circuits, type C breakers
on 1.5mm2 cable to make the system a) able to cope with upto quite a lot
of lighting; b) more trip resistant when lamps fail.

I saw no real disadvantages to doing it that way - I prefer 1.5mm2 cable
over 1mm2 as I find the latter a little flimsy.

I guess I used 1.5mm at the behest of my "Consultant", probably on
account of the fact that we'd need well in excess of 100m of cabling.

According to my "Consultant", the maximum fusing value for lighting
circuits was 5A and I accepted this as gospel. Since this protects the
ceiling rose and pendant fittings (cordage and lamp holders) as well
as the cabling and switches, it seemed to be a logical and sensible
restriction (the lower the fuse rating you can use without risking
frequent 'fuse blowing' events, the safer it is).

In the past 3 decades since I re-wired the house, I've not had to
change a lighting fuse and, afair, only one ring main fuse the one
time I carelessly refitted a socket plate onto a new socket I'd added
to the ring main (framing fault).

TBH, I can't see the point of mcbs which can have their own peculiar
'failure' modes. A good "Old Fashioned Wylex CU with fuse bridges does
the job perfectly fine.

When it's just a matter of resetting a mcb to deal with a mystery
intermittent overload, you're more inclined to let things slide than
when you have to keep changing fuse links (and rewire the blown fuse
links to keep pace with demand).

Fuse protection inclines you to "Do The Right Thing" straight away
and fix the actual problem rather than to put it off until you get
hold of a "Round Tuit" or have saved up enough money to pay a
'professional' electrician to sort it out for you.

If, like most householders over the past 15 years or so, you have
changed a good portion of your tungsten filament GLS lamps over to CFL
or LED lamps, you might find that a 6A mcb will now suffice for the
reduced loading.

It's certainly worth checking out this possibility since the lower
trip value mcb will reduce the risk of a house fire from very small to
vanishingly small and it is _this_ hazard such protection is designed
to eliminate in the first place.
--
Regards, J B Good

In article ,
Tim Watts wrote:
10A lighting circuits are "standard" (by the wiring regs) as are 16A
(though the latter are almost unheard of domestically).

Quite - my ground floor lighting circuit has been 10 amp since I installed
it some 40 years ago. Due to a rather large load on it. ;-) The feeds are
all 1.5mm - switch drops 1mm.

--
*If at first you don't succeed, destroy all evidence that you tried *

Dave Plowman London SW
To e-mail, change noise into sound.

On 12/02/2014 03:44, Johny B Good wrote:
On Tue, 11 Feb 2014 23:53:15 +0000, John Rumm
wrote:

On 11/02/2014 20:43, Johny B Good wrote:
On Tue, 11 Feb 2014 10:42:42 +0000, John Rumm
wrote:

On 11/02/2014 04:47, Bill Wright wrote:

Use a 1A or 3A fuse then.

Indeed... although it does depend on what the main circuit is protected
with. There are some 10A lighting circuits about which will offer more
scope.

I suspect such circuits would only qualify for the higher 10A rating
when completely wired up with Pyro cabling and appropriate fittings. a

10A is well within the capability of even 1.0mm T&E in some cases, and
1.5mm T&E in most.

There used to be a restriction on not using SBC and SES lamp fittings on
such circuits, but that was deleted with the issue of the 17th edition.

more likely scenarion in commercial premises rather than in premises
of the domestic persuasion (i.e. a house) where the limit has always
been 6A fusing at the CU panel afair.

10A is used domestically as well... I have certainly met it a few times.

Well, not being an electrician by trade, I've been unable to find any
references to the regulations, only anecdotes regarding 10A lighting
circuits (including the use of a ring lighting circuit) so I can't
quote 'chapter and verse' as to whether this is an acceptable
departure from the regulations or not (I know some leaway exists
within the regulations but this seems to be quite a large departure to
my mind).

Its not a departure at all - its one of the standard circuits listed in
the On Site Guide:

http://wiki.diyfaq.org.uk/images/2/2...g-Circuits.jpg

(you will note there is also a standard 16A lighting circuit - although
that is very unlikely to be used in a domestic situation)

All my knowledge comes from when, with the assistance of a retired
electrician (a family relative), I totally rewired this 3 story 6 bed
Victorian semi-detached house back around 1983.

This is where I learned about the CU fusing regulations with regard
to ring mains, lighting circuits, high power spur feeds to things like
cooker points and power showers as well as to the requirement to
provide a dedicated 15A fused feed to the immersion heater (classified
as a fixed connected load requiringa high temp flex connection between
the heater element terminals and the switched terminal box on the end
of said dedicated feed).

Sounds like a very useful learning experience. Keep in mind though that
for subtle details that was several issues of BS7671 ago, and stuff has
(and will continue to) evolve.

Plus I also learned about the earth bonding
requirements of all exposed metalwork (pipework, stainless steel sinks
etc).

Alas in those days many professional electricians had very little clue
about equipotential bonding (even the term "earth bonding" is a misnomer
when you think about it - earthing and bonding are two different systems
designed to add protection in two different ways). Not aided much by the
15th edition regs that also over egged the requirements somewhat.

You may find this useful:

http://wiki.diyfaq.org.uk/index.php?...ng_and_Bonding

The key requirement in situations where EQ bonding is used is to
establish if the metalwork in question is capable of bringing a
potential into the equipotential zone. If its not, then there is no
point in bonding it. Hence why things like sinks and bath do not require
bonding in spite of so many electricians believing they do.

It isn't exactly rocket science for someone experienced with
electronics kit and a well founded knowledge of electrical theory.
Once you understand that the fundamental protection provided by the
fuse links (MCBs) in a CU is essentially to protect the permanent
cabling and fittings it's easy to see why 5A was chosen for lighting
and up to 30A for ring mains with 45A protecting 4mm FT&E cabling to a
cooker point and other similar heavy duty loads.

Many of these things are chosen for backward compatibility as much as
fundamental theory.

A small 3 bed semi can manage with just a single ring main circuit
and a single lighting circuit plus cooker point and immersion heater
feeds so could be nicely served by a 4 fuse CU with a set of fuses
comprising of 5A for the lighting, 15A for the immersion, 30A for the
ring main and a 45A for the cooker point.

Depends on how you define "manage". It an installation that does not
provide adequate discrimination[1] in the event of a fault

[1] i.e. the requirement that the effect of a fault be localised to it.
Plunging an entire house into darkness due to a lamp failing and
tripping a MCB is not acceptable today. (it never really was, but the
implications of it had not really been considered at the time)

In a bigger property, you'd be well advised to fit a 6 way CU so you
can split the lighting across two circuits, each with their own 5A
fuse rather than the ill advised use of a 10A fuse on a single circuit

I sense an anti 10A fuse agenda here ;-)

(even when 1.5mm cabling is used - the ratings on the fittings are all
based on the protection of a 5A fused supply). Obviously, the second
extra fuse position will allow two seperate ring mains to be provided.

I think you will find that modern lighting accessories are fine on 10A
circuits (note that even the limitation on the "small" version of the
normal lamp holders was removed).

(and TBH a 6 way CU is woefully inadequate for many places these days)

When we first moved into the current property, it didn't have a
cooker point so I was able to wire up three seperate ring mains
(ground floor, first floor and second floor mains socket supplies).

If doing it now, it would be quite common to do that, and also add an
extra ring circuit for the kitchen / utility room - since the modern
compliment of kitchen appliances can rapidly use all 7.2kW capacity of a
ring circuit.

The basement was catered for by fitting 3 single outlet 13A sockets
onto the CU backboard each fed off the 3 ring main circuits so that
the freezer we kept in the basement could be readily powered from any
one of the ring main circuits as an insurance against any protracted
outage that might arise due to faults or planned changes in the ring
main wiring.

Would it not have been simpler to provide a dedicated circuit for this
purpose? Then you would *know* its not going to be tripped regardless of
what happens elsewhere.

The freezer no longer resides in the basement but the 'diversity' of
this setup is still very handy although I have installed an extra twin
outlet wall socket away from the CU, connected most likely to the 1st
floor ring main circuit (but I'd have to take a gander at the fuse
cover labelling to confirm this - but it seems the most logical choice
of ring main so I'd be surprised if it were otherwise since the same
logic would have dictated my original choice).

When it came to replacing all the VIR cabling in conduit lighting
wiring, we knew it had to be split across two lighting circuits. As it
happened I bought a couple of 100m reels of 1.5mm FT&E for this job
and used nearly all of it.

The Mortgage company had held back £1000 of the loan on account of
the state of the lighting circuit wiring but when I delved a little
deeper into the state of the rest of the wiring, I discovered the
house had two ring circuits and a mix of spur fed outlets randomly
distributed about the property (one ring main fed half the ground
floor sockets and half the first floor sockets and the other ring main
fed all the 2nd floor sockets but with a length of heavy duty rubber
sheathed appliance cord being used instead of the regulation FT&E.

Its not uncommon to find all sorts of strange stuff in existing
installations - especially if they are ageing and have been hacked about
a bit in the following years.

(I recall digging a 5A circular junction box out of the plaster above
the sink in the kitchen of a neighbour's property. (yes it was the screw
terminal type that is intended to remain accessible for maintenance))

What had started out as just a lighting circuit 'rewire' developed
into a complete rewiring of the whole house. The job was essentially
an exercise in re-organising the randomly fed sockets into 3 distinct
ring mains.

Since the top floor was the only proper ring main in the whole house,
I replaced the rubber sheathed flex with 2.5mm FT&E to bring it up to
standard then dropped a very long mains extension down to the kitchen
with another extension lead into the basement to power the freezer
whilst I stripped out most of the 'ring main' wiring to the ground and
first floor sockets, sorting out the recovered lengths of FT&E so I
could rebuild the ring main circuits using shortest lengths first.

This minimised the need to add extra cable to the point where I was
able to beg the extra 20 or so metres from my dad thus reducing the
cable costs to nil with only the new dual gang 13A sockets as the main
parts cost.

It was a lot of work to sort it out but I felt it just had to be done
in the interest of safety (it's not good having sockets in the same
room powered from different fuses in the CU). needless to say (after
sorting out the earth bonding) I had no trouble getting the job
certified and the extra grand released by the Mortgage company.

I would expect that as long as you fill in the test results correctly
they will be happy (they probably don't even look at the name of the
contractor on top of the page!)

I suspect anyone trying to get their house wiring certified whilst
they have a 10A fused lighting circuit in the mix will have a hard
time trying to convince an inspector that it is within regs and
standard wiring practice.

Your suspicion is this case is unfounded - or at least not for this
reason. Needless to say Part P has complicated the "certification"
process somewhat in subsequent years.

With many house owners now using CFLs and LED lamps in place of most
of the originally fitted 60 and 100 watt incandescent lamps, I think
any such 10A lighting circuits could now be 'downgraded' to 5A fuse or
6A mcb protected circuits without any problems.

Quite possibly, although you would need to consider what you are
attempting to achieve, and also the unintended consequences of the change.

Keep in mind that when providing over current protection for any
circuit, there are two discrete issues that need to be addressed:
overload, and fault handling. (i.e. long term over current resulting
from applying more load than the circuit design current, and the very
short term effects from massive over current caused by someone nailing
through the cable etc). Traditionally these two functions are provided
by the same protective device at the origin of the circuit[2]. If you
are using one of the standard circuits, then both of these are allowed
for in the design; The protective device nominal rating is lower than
that of the "as installed" cable current carrying capacity[3], and
someone has already done the sums to make sure the cable won't melt
while carrying 1000A for the few ms necessary to open the MCB on its
magnetic trip).

So for example changing a "whole house" 10A lighting circuit to a
"normal" type B 6A MCB on the grounds that modern lamps no longer
require the current may be fine. But you are starting with a circuit
that was already adequately protected. As consequence of changing the
protective device, you have also reduced the fault current tolerance of
the MCB from 50A to 30A (type B MCBs need 5x nominal current to trip on
the "instant" part of their response curve)[4]. A result you may now
find is that when one of the few remaining incandescent lamps does fail,
its far more likely to trip the whole circuit. (and trips and falls in
the house kill orders of magnitude more people each year than are
electrocuted!) (note that this is easy enough to mitigate in this
particular example since you could use a type C MCBs instead)


[2] this does not always have to be the case - fault current protection
must be provided at the origin, while overload protection may be
delegated elsewhere or in some cases may not be required at all.

[3] Remember that the "clipped direct" current carrying capacity of even
1.0mm T&E is 16A

http://wiki.diyfaq.org.uk/index.php?...es#Cable_Sizes

[4] http://wiki.diyfaq.org.uk/index.php?...e-MCBTypeB.png

Other than 'special cases' I think anyone with a 10A fuse protected
lighting circuit should downgrade to a 5A fuse for their own peace of
mind just on safety grounds alone.

While that all sounds nice and warm and fuzzy, can you actually justify
it on technical merit?

Using a 10A fuse, even in a larger
domestic property is probably unnecessary with modern lamps these
days.

Agreed in most cases... although keep in mind the increasing use of
ancillary loads on lighting circuits - e.g. extractor fans for forced
ventilation in kitchens, loos, bath/shower rooms etc, localised space
heating with "heater" lamps etc.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 12/02/2014 14:27, Johny B Good wrote:

I guess I used 1.5mm at the behest of my "Consultant", probably on
account of the fact that we'd need well in excess of 100m of cabling.

According to my "Consultant", the maximum fusing value for lighting
circuits was 5A and I accepted this as gospel. Since this protects the
ceiling rose and pendant fittings (cordage and lamp holders) as well

If you think about it, the drop lead to most BC lamp holders is in 3A
flex...

(you are correct however in that it is "protected". This is one of those
situations I alluded to in my previous post, where overload protection
may be delegated or dispensed with in certain circumstances)

http://wiki.diyfaq.org.uk/index.php?...abatic _Check

TBH, I can't see the point of mcbs which can have their own peculiar
'failure' modes. A good "Old Fashioned Wylex CU with fuse bridges does
the job perfectly fine.

They are still acceptable, however you would be very unlikely to use one
in a new installation for several reasons.

Modern trends in insulating properties makes their use more difficult.
The big downside with a BS3036 rewireable is the slower fusing time.
This requires a x 0.725 de-rating factor be applied to the current
carrying capacity of the cables used in the circuit they protect. With
the effects of the extra thermal insulation added to the equation, you
would frequently find that you would need to increase the conductor CSA
to compensate - hence unnecessary cost in both materials and time spent
wiring.

Old style fuse boxes typically don't have any provision for RCDs, hence
you would need to house these separately, and also use multiple fuse
boxes to provide adequate discrimination.

When it's just a matter of resetting a mcb to deal with a mystery
intermittent overload, you're more inclined to let things slide than
when you have to keep changing fuse links (and rewire the blown fuse
links to keep pace with demand).

Much depends on who is doing the resetting... Its much harder for
someone to wrap tinfoil round a tripped MCB or stick a nail in it
instead ;-)

Fuse protection inclines you to "Do The Right Thing" straight away
and fix the actual problem rather than to put it off until you get
hold of a "Round Tuit" or have saved up enough money to pay a
'professional' electrician to sort it out for you.

Alas, outside the shrinking population in places like this group, the
number of them that can DIY seems to be ever diminishing.

If, like most householders over the past 15 years or so, you have
changed a good portion of your tungsten filament GLS lamps over to CFL
or LED lamps, you might find that a 6A mcb will now suffice for the
reduced loading.

It's certainly worth checking out this possibility since the lower
trip value mcb will reduce the risk of a house fire from very small to
vanishingly small and it is _this_ hazard such protection is designed
to eliminate in the first place.

Its a difficult assertion to validate one way or the other. However it
might be worth considering that the vast majority of house fires started
"electrically" are actually the result of the misuse of appliances, or
use of faulty appliances. Fixed wiring faults come *way* down the list.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 12/02/2014 01:32, Bill Wright wrote:

The amp had not blown the plug fuse, which was 3A. The smell had alerted
the customer when he came home and he had disconnected the power.

When you consider that many a 3A fuse will happily supply nearly 5A
indefinitely, that's over 1kW of available power ;-)

Incidentally I've told this before on here, but there was the young mum
who, offended by the smell coming from the masthead amplifier power
supply, and concerned that it might burn the baby's fingers, wrapped it
in towels.

Hmmm nice bit of logic.... oh, that's really hot - let's insulate it and
make it much hotter - using flammable insulation!



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 12/02/2014 15:20, Dave Plowman (News) wrote:
In article ,
Tim Watts wrote:
10A lighting circuits are "standard" (by the wiring regs) as are 16A
(though the latter are almost unheard of domestically).

Quite - my ground floor lighting circuit has been 10 amp since I installed
it some 40 years ago. Due to a rather large load on it. ;-) The feeds are
all 1.5mm - switch drops 1mm.

Shame whoever wired this place did not think of that... they did one 5A
(Type 1 MCB) and then worked out it was not going to hack the 40 or so
lamp fittings on the ground floor, then split of two rooms on a second
one. Even then the first circuit would not tolerate all the lights on
for long!


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Wednesday 12 February 2014 16:19 John Rumm wrote in uk.d-i-y:


Its a difficult assertion to validate one way or the other. However it
might be worth considering that the vast majority of house fires
started "electrically" are actually the result of the misuse of
appliances, or use of faulty appliances. Fixed wiring faults come
*way* down the list.

Indeed.

When designing my circuits to work with a 10A Type C breaker, I require
the trip times (loop impedances) and max current capacity of the wiring
to meet the standards for 10A type C lighting *right to the lamp
fitting*.

If the lamp fitting itself is sub standard, then it is usually a
negligible risk as

a) it tends to be self protecting (hard to fit a lamp that will overload
it);

b) unlikely to be a danger even if it smoked (the exception being flush
mount ceiling fittings or you live in a hippy den with fabric all over
the ceiling!);

c) As John suggested, if you look at the wires in many fittings, they
would not even be adequately protected by a 6A Type B breaker.

d) The bits that are most at risk of causing a fire (cables running
thorough the building often via bits of wood, piles of fluff and sawdust
etc) are designed and protected correctly.

Then you come to bathroom fans and other things that are commonly fed
from a lighting circuit and they all want a 3A FCU fitted regardless of
circuit protection!

Cheers,

Tim

--
Tim Watts Personal Blog: http://squiddy.blog.dionic.net/

http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal
coverage

In article ,
John Rumm wrote:
On 12/02/2014 15:20, Dave Plowman (News) wrote:
In article ,
Tim Watts wrote:
10A lighting circuits are "standard" (by the wiring regs) as are 16A
(though the latter are almost unheard of domestically).

Quite - my ground floor lighting circuit has been 10 amp since I installed
it some 40 years ago. Due to a rather large load on it. ;-) The feeds are
all 1.5mm - switch drops 1mm.

Shame whoever wired this place did not think of that... they did one 5A
(Type 1 MCB) and then worked out it was not going to hack the 40 or so
lamp fittings on the ground floor, then split of two rooms on a second
one. Even then the first circuit would not tolerate all the lights on
for long!

I was just thinking the 'Grand Designs' usual of thousands of low voltage
downlighters must need some thinking about - certainly before LEDs. When I
wired my place the usual was a single bulb pendant per room. ;-)

--
*What happens when none of your bees wax? *

Dave Plowman London SW
To e-mail, change noise into sound.

On 12/02/2014 16:29, John Rumm wrote:
On 12/02/2014 15:20, Dave Plowman (News) wrote:
In article ,
Tim Watts wrote:
10A lighting circuits are "standard" (by the wiring regs) as are 16A
(though the latter are almost unheard of domestically).

Quite - my ground floor lighting circuit has been 10 amp since I
installed
it some 40 years ago. Due to a rather large load on it. ;-) The feeds are
all 1.5mm - switch drops 1mm.

Shame whoever wired this place did not think of that... they did one 5A
(Type 1 MCB) and then worked out it was not going to hack the 40 or so
lamp fittings on the ground floor, then split of two rooms on a second
one. Even then the first circuit would not tolerate all the lights on
for long!



You need less lights and use the CH to heat the place.

On 12/02/2014 17:43, Dave Plowman (News) wrote:
In article ,
John Rumm wrote:
On 12/02/2014 15:20, Dave Plowman (News) wrote:
In article ,
Tim Watts wrote:
10A lighting circuits are "standard" (by the wiring regs) as are 16A
(though the latter are almost unheard of domestically).

Quite - my ground floor lighting circuit has been 10 amp since I installed
it some 40 years ago. Due to a rather large load on it. ;-) The feeds are
all 1.5mm - switch drops 1mm.

Shame whoever wired this place did not think of that... they did one 5A
(Type 1 MCB) and then worked out it was not going to hack the 40 or so
lamp fittings on the ground floor, then split of two rooms on a second
one. Even then the first circuit would not tolerate all the lights on
for long!

I was just thinking the 'Grand Designs' usual of thousands of low voltage
downlighters must need some thinking about - certainly before LEDs. When I
wired my place the usual was a single bulb pendant per room. ;-)

People here before were fond of the multi armed dangly thing with three
or five spokes and a lamp on each... they soon ramp up the lamp count if
not used sparingly!

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 12/02/2014 18:45, dennis@home wrote:
On 12/02/2014 16:29, John Rumm wrote:
On 12/02/2014 15:20, Dave Plowman (News) wrote:
In article ,
Tim Watts wrote:
10A lighting circuits are "standard" (by the wiring regs) as are 16A
(though the latter are almost unheard of domestically).

Quite - my ground floor lighting circuit has been 10 amp since I
installed
it some 40 years ago. Due to a rather large load on it. ;-) The feeds
are
all 1.5mm - switch drops 1mm.

Shame whoever wired this place did not think of that... they did one 5A
(Type 1 MCB) and then worked out it was not going to hack the 40 or so
lamp fittings on the ground floor, then split of two rooms on a second
one. Even then the first circuit would not tolerate all the lights on
for long!



You need less lights and use the CH to heat the place.

Judicious use of low energy lamps, and a few fitting changes, and bulb
wattage reductions has tamed the excess a little. Lots of high ceilings
though, so they take a reasonable amount of lighting to be comfortable.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Wed, 12 Feb 2014 16:00:02 +0000, John Rumm
wrote:

On 12/02/2014 03:44, Johny B Good wrote:
On Tue, 11 Feb 2014 23:53:15 +0000, John Rumm
wrote:

On 11/02/2014 20:43, Johny B Good wrote:
On Tue, 11 Feb 2014 10:42:42 +0000, John Rumm
wrote:

On 11/02/2014 04:47, Bill Wright wrote:

Use a 1A or 3A fuse then.

Indeed... although it does depend on what the main circuit is protected
with. There are some 10A lighting circuits about which will offer more
scope.

I suspect such circuits would only qualify for the higher 10A rating
when completely wired up with Pyro cabling and appropriate fittings. a

10A is well within the capability of even 1.0mm T&E in some cases, and
1.5mm T&E in most.

There used to be a restriction on not using SBC and SES lamp fittings on
such circuits, but that was deleted with the issue of the 17th edition.

more likely scenarion in commercial premises rather than in premises
of the domestic persuasion (i.e. a house) where the limit has always
been 6A fusing at the CU panel afair.

10A is used domestically as well... I have certainly met it a few times.

Well, not being an electrician by trade, I've been unable to find any
references to the regulations, only anecdotes regarding 10A lighting
circuits (including the use of a ring lighting circuit) so I can't
quote 'chapter and verse' as to whether this is an acceptable
departure from the regulations or not (I know some leaway exists
within the regulations but this seems to be quite a large departure to
my mind).

Its not a departure at all - its one of the standard circuits listed in
the On Site Guide:

http://wiki.diyfaq.org.uk/images/2/2...g-Circuits.jpg

(you will note there is also a standard 16A lighting circuit - although
that is very unlikely to be used in a domestic situation)

Well thanks for that revealing information. It's additional knowledge
I can retain for future reference. Obviously, I'm not going to uprate
the fusing on my owm lighting circuits since the efficacy of the 5A
fusing has amply proved itself in my case over the past 3 decades.


All my knowledge comes from when, with the assistance of a retired
electrician (a family relative), I totally rewired this 3 story 6 bed
Victorian semi-detached house back around 1983.

This is where I learned about the CU fusing regulations with regard
to ring mains, lighting circuits, high power spur feeds to things like
cooker points and power showers as well as to the requirement to
provide a dedicated 15A fused feed to the immersion heater (classified
as a fixed connected load requiringa high temp flex connection between
the heater element terminals and the switched terminal box on the end
of said dedicated feed).

Sounds like a very useful learning experience. Keep in mind though that
for subtle details that was several issues of BS7671 ago, and stuff has
(and will continue to) evolve.

Plus I also learned about the earth bonding
requirements of all exposed metalwork (pipework, stainless steel sinks
etc).

Alas in those days many professional electricians had very little clue
about equipotential bonding (even the term "earth bonding" is a misnomer
when you think about it - earthing and bonding are two different systems
designed to add protection in two different ways). Not aided much by the
15th edition regs that also over egged the requirements somewhat.

You may find this useful:

http://wiki.diyfaq.org.uk/index.php?...ng_and_Bonding

The key requirement in situations where EQ bonding is used is to
establish if the metalwork in question is capable of bringing a
potential into the equipotential zone. If its not, then there is no
point in bonding it. Hence why things like sinks and bath do not require
bonding in spite of so many electricians believing they do.

It isn't exactly rocket science for someone experienced with
electronics kit and a well founded knowledge of electrical theory.
Once you understand that the fundamental protection provided by the
fuse links (MCBs) in a CU is essentially to protect the permanent
cabling and fittings it's easy to see why 5A was chosen for lighting
and up to 30A for ring mains with 45A protecting 4mm FT&E cabling to a
cooker point and other similar heavy duty loads.

Many of these things are chosen for backward compatibility as much as
fundamental theory.

A small 3 bed semi can manage with just a single ring main circuit
and a single lighting circuit plus cooker point and immersion heater
feeds so could be nicely served by a 4 fuse CU with a set of fuses
comprising of 5A for the lighting, 15A for the immersion, 30A for the
ring main and a 45A for the cooker point.

Depends on how you define "manage". It an installation that does not
provide adequate discrimination[1] in the event of a fault

[1] i.e. the requirement that the effect of a fault be localised to it.
Plunging an entire house into darkness due to a lamp failing and
tripping a MCB is not acceptable today. (it never really was, but the
implications of it had not really been considered at the time)

Still and all, the whole point of a single fuse at the CU to protect
a lighting circuit is essentially to minimise the risk of a house
fire. Being 'plunged into darkness' is very rarely as fatal as smoke
inhalation or worse.

Of course there is always the counter argument in the automotive case
where it is (or at least, was) deemed preferable to eliminate a sudden
blackout of the headlamps due to a fuse fault by foregoing any
protective fusing whatsoever, making the risk of an electrical vehicle
fire higher as a result. The idea being that it is better to still be
able to safely navigate along a narrow country road on a dark night
for as long as it takes to bring the vehicle safely to rest and permit
a rapid bailout.

I believe modern practice with vehicular wiring is to fuse each
headlight independantly now that the fusebox is housed within the less
harsher environment of the passenger compartment, usually just under
the dashboard over the driver's footwell.


In a bigger property, you'd be well advised to fit a 6 way CU so you
can split the lighting across two circuits, each with their own 5A
fuse rather than the ill advised use of a 10A fuse on a single circuit

I sense an anti 10A fuse agenda here ;-)

Well yes but you _know_ why. Even now, the idea of using a 10A fuse
over a 5A fuse for lighting circuit protection still leaves me with a
feeling of uneasiness.


(even when 1.5mm cabling is used - the ratings on the fittings are all
based on the protection of a 5A fused supply). Obviously, the second
extra fuse position will allow two seperate ring mains to be provided.

I think you will find that modern lighting accessories are fine on 10A
circuits (note that even the limitation on the "small" version of the
normal lamp holders was removed).

I'm familiar with the 'moving goalposts' syndrome. Obviously a fine
tuning of the safety versus utlity compromise. At least you still have
the option 'to make it safer'.


(and TBH a 6 way CU is woefully inadequate for many places these days)

When we first moved into the current property, it didn't have a
cooker point so I was able to wire up three seperate ring mains
(ground floor, first floor and second floor mains socket supplies).

If doing it now, it would be quite common to do that, and also add an
extra ring circuit for the kitchen / utility room - since the modern
compliment of kitchen appliances can rapidly use all 7.2kW capacity of a
ring circuit.

Funny you should mention that. :-)

We needed to have a downstairs toilet and shower room extension just
after moving in for the benefit of the XYL's elderly parents whom we
had moved in with us (the whole reason for buying such a capacious
property in the first place).

What we landed up doing was to convert the woefully inadequate
kitchen (probably an earlier conversion from a cloakroom) into the
downstairs shower room and use the extension to create a new kitchen.

I remember recovering the 2.5mm FT&E cable and sockets (along with a
redundent porcelain DC fuse holder and fuses that had simply been left
in situ) after the old kitchen space had been gutted prior to its
conversion.

In the meantime once the kitchen extension had been completed, the
electrical contractor added a 2 way wylex fuse box to extend a
seperate kitchen ring main and supply a cooker point feed. The
lighting was served by the addition of one extra fluorescent tube
luminary to the existing ground floor lighting circuit.

Overloading the kitchen ring main has never been a problem. I suppose
it is just possible to overload it if we were to switch the 3KW kettle
on whilst using the "George Formby", toasting bread , microwaving some
food and 'Brevelling' some tasty sandwiches whilst we (the XYL & I)
each run a Dyson over the respective halves of the kitchen dining room
floor areas when the noise of the dishwasher will be nicely drowned
out. We may even have enough 13A sockets without having to disconnect
the fridge and the freezer nor cheat by plugging into the 13A cooker
point socket.

I'm sure that would be a good 8 or 9KW's worth right there (maybe
even 10). The strange thing is, we've never felt impelled to "Work so
hard at cooking and cleaning as to make our eyes bleed" Not even at
Christmas time when it was 'our turn' to host the 'christmas family
do'.

Perhaps we simply don't posses enough of the latest energy consuming
'Must Have' kitchen gadgets to bless us with such overloading
problems.


The basement was catered for by fitting 3 single outlet 13A sockets
onto the CU backboard each fed off the 3 ring main circuits so that
the freezer we kept in the basement could be readily powered from any
one of the ring main circuits as an insurance against any protracted
outage that might arise due to faults or planned changes in the ring
main wiring.

Would it not have been simpler to provide a dedicated circuit for this
purpose? Then you would *know* its not going to be tripped regardless of
what happens elsewhere.

Think it through. What's important? having a dedicated circuit that
can still go faulty despite its splendid isolation from the other ring
mains or a choice of three alternative sockets less than an extension
lead's length away. Remember, this sort of eventuality ideally should
never happen or at least no more than once in a lifetime so there's no
good reason to over engineer a solution when a perfectly good one is
already to hand.


The freezer no longer resides in the basement but the 'diversity' of
this setup is still very handy although I have installed an extra twin
outlet wall socket away from the CU, connected most likely to the 1st
floor ring main circuit (but I'd have to take a gander at the fuse
cover labelling to confirm this - but it seems the most logical choice
of ring main so I'd be surprised if it were otherwise since the same
logic would have dictated my original choice).

When it came to replacing all the VIR cabling in conduit lighting
wiring, we knew it had to be split across two lighting circuits. As it
happened I bought a couple of 100m reels of 1.5mm FT&E for this job
and used nearly all of it.

The Mortgage company had held back £1000 of the loan on account of
the state of the lighting circuit wiring but when I delved a little
deeper into the state of the rest of the wiring, I discovered the
house had two ring circuits and a mix of spur fed outlets randomly
distributed about the property (one ring main fed half the ground
floor sockets and half the first floor sockets and the other ring main
fed all the 2nd floor sockets but with a length of heavy duty rubber
sheathed appliance cord being used instead of the regulation FT&E.

Its not uncommon to find all sorts of strange stuff in existing
installations - especially if they are ageing and have been hacked about
a bit in the following years.

(I recall digging a 5A circular junction box out of the plaster above
the sink in the kitchen of a neighbour's property. (yes it was the screw
terminal type that is intended to remain accessible for maintenance))

What had started out as just a lighting circuit 'rewire' developed
into a complete rewiring of the whole house. The job was essentially
an exercise in re-organising the randomly fed sockets into 3 distinct
ring mains.

Since the top floor was the only proper ring main in the whole house,
I replaced the rubber sheathed flex with 2.5mm FT&E to bring it up to
standard then dropped a very long mains extension down to the kitchen
with another extension lead into the basement to power the freezer
whilst I stripped out most of the 'ring main' wiring to the ground and
first floor sockets, sorting out the recovered lengths of FT&E so I
could rebuild the ring main circuits using shortest lengths first.

This minimised the need to add extra cable to the point where I was
able to beg the extra 20 or so metres from my dad thus reducing the
cable costs to nil with only the new dual gang 13A sockets as the main
parts cost.

It was a lot of work to sort it out but I felt it just had to be done
in the interest of safety (it's not good having sockets in the same
room powered from different fuses in the CU). needless to say (after
sorting out the earth bonding) I had no trouble getting the job
certified and the extra grand released by the Mortgage company.

I would expect that as long as you fill in the test results correctly
they will be happy (they probably don't even look at the name of the
contractor on top of the page!)

I suspect anyone trying to get their house wiring certified whilst
they have a 10A fused lighting circuit in the mix will have a hard
time trying to convince an inspector that it is within regs and
standard wiring practice.

Your suspicion is this case is unfounded - or at least not for this
reason. Needless to say Part P has complicated the "certification"
process somewhat in subsequent years.

With many house owners now using CFLs and LED lamps in place of most
of the originally fitted 60 and 100 watt incandescent lamps, I think
any such 10A lighting circuits could now be 'downgraded' to 5A fuse or
6A mcb protected circuits without any problems.

Quite possibly, although you would need to consider what you are
attempting to achieve, and also the unintended consequences of the change.

Keep in mind that when providing over current protection for any
circuit, there are two discrete issues that need to be addressed:
overload, and fault handling. (i.e. long term over current resulting
from applying more load than the circuit design current, and the very
short term effects from massive over current caused by someone nailing
through the cable etc). Traditionally these two functions are provided
by the same protective device at the origin of the circuit[2]. If you
are using one of the standard circuits, then both of these are allowed
for in the design; The protective device nominal rating is lower than
that of the "as installed" cable current carrying capacity[3], and
someone has already done the sums to make sure the cable won't melt
while carrying 1000A for the few ms necessary to open the MCB on its
magnetic trip).

So for example changing a "whole house" 10A lighting circuit to a
"normal" type B 6A MCB on the grounds that modern lamps no longer
require the current may be fine. But you are starting with a circuit
that was already adequately protected. As consequence of changing the
protective device, you have also reduced the fault current tolerance of
the MCB from 50A to 30A (type B MCBs need 5x nominal current to trip on
the "instant" part of their response curve)[4]. A result you may now
find is that when one of the few remaining incandescent lamps does fail,
its far more likely to trip the whole circuit. (and trips and falls in
the house kill orders of magnitude more people each year than are
electrocuted!) (note that this is easy enough to mitigate in this
particular example since you could use a type C MCBs instead)


[2] this does not always have to be the case - fault current protection
must be provided at the origin, while overload protection may be
delegated elsewhere or in some cases may not be required at all.

[3] Remember that the "clipped direct" current carrying capacity of even
1.0mm T&E is 16A

http://wiki.diyfaq.org.uk/index.php?...es#Cable_Sizes

[4] http://wiki.diyfaq.org.uk/index.php?...e-MCBTypeB.png

Other than 'special cases' I think anyone with a 10A fuse protected
lighting circuit should downgrade to a 5A fuse for their own peace of
mind just on safety grounds alone.

While that all sounds nice and warm and fuzzy, can you actually justify
it on technical merit?

Just the fact that lower fuse ratings result in lower fire hazard
risks. I wasn't concerned over the electric shock hazard which remains
unchanged when simple fuses provide the protection.


Using a 10A fuse, even in a larger
domestic property is probably unnecessary with modern lamps these
days.

Agreed in most cases... although keep in mind the increasing use of
ancillary loads on lighting circuits - e.g. extractor fans for forced
ventilation in kitchens, loos, bath/shower rooms etc, localised space
heating with "heater" lamps etc.

If my floor standing cooling fan is anything to go by, I'd imagine a
small vent axia type of fan wouldn't draw much more than 50 watts. As
for 'heater lamps' you're probably looking at 500W max (in a suitable
lamp fitting) or else 1KW for a radiant 'bathroom heater' that's
mounted high up and operated by the obligatory pull cord.

The more powerful radiant heater would be better served by a 5A fused
junction box spur tapped off the ring main. Quite frankly, I wouldn't
feed such loads from a lighting circuit other than maybe a vent axia
fan or two. You seem to be trying to justify the higher 10A fuse
rating with extra appliances that would be better served from a ring
main supply (via a suitably fused connection box).

My own personal view is that the the primary function of a CU is
safety and, to this end, selecting a lower fuse rating option over a
higher one when conditions allow maximises its effectiveness at
minimising the risk of a house fire.

The risk can never be totally eliminated whatever size fuse is chosen
but the risk does become more improbable as you lower the fuse rating
used on any existing circuit. Take my 15A ring main as an example of
this. I've never ever had to replace the 15A fuse link with a 30A one
because of 'overload' issues (nor for any other reason).

The 15A fuse link has sufficed quite nicely for the loading this
particular ring main is subjected to. IOW, its utility hasn't suffered
as a result of the lower fuse rating so I've gained an extra margin of
safety 'for free' by this simple expedient.

I suspect that most domestic 10A lighting circuits could be just as
well served by a 5A fuse link or 6A MCB these days simply by virtue of
the extensive use of CFL lamps in place of the tungsten filament GLS
lamps they'd originally been sized for. It's certainly worthy of some
consideration if you have 10A lighting circuits in your home.
--
Regards, J B Good

On Thursday, February 13, 2014 1:25:03 AM UTC, Johny B Good wrote:

Still and all, the whole point of a single fuse at the CU to protect
a lighting circuit is essentially to minimise the risk of a house
fire. Being 'plunged into darkness' is very rarely as fatal as smoke
inhalation or worse.
Of course there is always the counter argument in the automotive case
where it is (or at least, was) deemed preferable to eliminate a sudden
blackout of the headlamps due to a fuse fault by foregoing any
protective fusing whatsoever, making the risk of an electrical vehicle
fire higher as a result. The idea being that it is better to still be
able to safely navigate along a narrow country road on a dark night
for as long as it takes to bring the vehicle safely to rest and permit
a rapid bailout.
I believe modern practice with vehicular wiring is to fuse each
headlight independantly now that the fusebox is housed within the less
harsher environment of the passenger compartment, usually just under
the dashboard over the driver's footwell.

The oldest vehicle I had had no fusing whatever. The original fusebox with space for 2 fuses was present, but not connected.


Overloading the kitchen ring main has never been a problem. I suppose
it is just possible to overload it if we were to switch the 3KW kettle
on whilst using the "George Formby", toasting bread , microwaving some
food and 'Brevelling' some tasty sandwiches whilst we (the XYL & I)
each run a Dyson over the respective halves of the kitchen dining room
floor areas when the noise of the dishwasher will be nicely drowned
out. We may even have enough 13A sockets without having to disconnect
the fridge and the freezer nor cheat by plugging into the 13A cooker
point socket.
I'm sure that would be a good 8 or 9KW's worth right there (maybe
even 10). The strange thing is, we've never felt impelled to "Work so
hard at cooking and cleaning as to make our eyes bleed" Not even at
Christmas time when it was 'our turn' to host the 'christmas family
do'.
Perhaps we simply don't posses enough of the latest energy consuming
'Must Have' kitchen gadgets to bless us with such overloading
problems.

Exceeding 30A on a ring circuit isnt a problem, theyre designed to deliver much more for limited periods. 30A is the continuous rating. We regularly used to heavily exceed 30A at the last house, but nothing got hot or blew.


NT

On 13/02/2014 01:25, Johny B Good wrote:
On Wed, 12 Feb 2014 16:00:02 +0000, John Rumm
wrote:

On 12/02/2014 03:44, Johny B Good wrote:
On Tue, 11 Feb 2014 23:53:15 +0000, John Rumm
wrote:

On 11/02/2014 20:43, Johny B Good wrote:
On Tue, 11 Feb 2014 10:42:42 +0000, John Rumm
wrote:

10A is used domestically as well... I have certainly met it a few times.

Well, not being an electrician by trade, I've been unable to find any
references to the regulations, only anecdotes regarding 10A lighting
circuits (including the use of a ring lighting circuit) so I can't
quote 'chapter and verse' as to whether this is an acceptable
departure from the regulations or not (I know some leaway exists
within the regulations but this seems to be quite a large departure to
my mind).

Its not a departure at all - its one of the standard circuits listed in
the On Site Guide:

http://wiki.diyfaq.org.uk/images/2/2...g-Circuits.jpg

(you will note there is also a standard 16A lighting circuit - although
that is very unlikely to be used in a domestic situation)

Well thanks for that revealing information. It's additional knowledge
I can retain for future reference. Obviously, I'm not going to uprate
the fusing on my owm lighting circuits since the efficacy of the 5A
fusing has amply proved itself in my case over the past 3 decades.

I don't think anyone was suggesting that you do. Just highlighting that
it is an allowable and properly designed option.

[1] i.e. the requirement that the effect of a fault be localised to it.
Plunging an entire house into darkness due to a lamp failing and
tripping a MCB is not acceptable today. (it never really was, but the
implications of it had not really been considered at the time)

Still and all, the whole point of a single fuse at the CU to protect
a lighting circuit is essentially to minimise the risk of a house
fire. Being 'plunged into darkness' is very rarely as fatal as smoke
inhalation or worse.

Missing the point I think... fusing good; single lighting circuit bad!

The chances of any lighting circuit causing a fire in the first place
are vanishingly small, but having a pair of them (and in consequence a
lower average current load on each) can only improve the odds further.

So if a house is wired with a single 10A circuit, you would get a much
greater improvement in safety by splitting it into two circuits (of
whatever rating), rather than just keeping it as it is and lowering the
fuse size.

Of course there is always the counter argument in the automotive case
where it is (or at least, was) deemed preferable to eliminate a sudden
blackout of the headlamps due to a fuse fault by foregoing any
protective fusing whatsoever, making the risk of an electrical vehicle
fire higher as a result. The idea being that it is better to still be
able to safely navigate along a narrow country road on a dark night
for as long as it takes to bring the vehicle safely to rest and permit
a rapid bailout.

There are a few permitted cases where fusing may be omitted on similar
grounds - i.e. where failure of the supply is more dangerous than the
circuit being damaged by over heating etc. (unlikely to crop up
domestically though!)

I sense an anti 10A fuse agenda here ;-)

Well yes but you _know_ why. Even now, the idea of using a 10A fuse
over a 5A fuse for lighting circuit protection still leaves me with a
feeling of uneasiness.

Whilst I agree with the general principle of using protective thresholds
of no bigger than they need to be, I also recognise that the absolute
size of the fuse is not the sole guide to how safe a circuit is.

(even when 1.5mm cabling is used - the ratings on the fittings are all
based on the protection of a 5A fused supply). Obviously, the second
extra fuse position will allow two seperate ring mains to be provided.

I think you will find that modern lighting accessories are fine on 10A
circuits (note that even the limitation on the "small" version of the
normal lamp holders was removed).

I'm familiar with the 'moving goalposts' syndrome. Obviously a fine
tuning of the safety versus utlity compromise. At least you still have
the option 'to make it safer'.

Possibly - but that does not always equate to a lower current protective
device. Nuisance trips from "close to tripping" protective devices can
in themselves harbour dangers.

If doing it now, it would be quite common to do that, and also add an
extra ring circuit for the kitchen / utility room - since the modern
compliment of kitchen appliances can rapidly use all 7.2kW capacity of a
ring circuit.

Funny you should mention that. :-)

[snip]

Overloading the kitchen ring main has never been a problem. I suppose
it is just possible to overload it if we were to switch the 3KW kettle
on whilst using the "George Formby", toasting bread , microwaving some
food and 'Brevelling' some tasty sandwiches whilst we (the XYL & I)
each run a Dyson over the respective halves of the kitchen dining room
floor areas when the noise of the dishwasher will be nicely drowned
out. We may even have enough 13A sockets without having to disconnect
the fridge and the freezer nor cheat by plugging into the 13A cooker
point socket.

With kitchens you can generally ignore the kettle and microwave etc -
they are not usually on long enough to pose a problem. The big white
things with heater elements like washing machine, dishwasher, tumble
drier etc can swallow more "long term" capacity. Some single ovens are
also often plugged into a kitchen ring circuit these days.

I'm sure that would be a good 8 or 9KW's worth right there (maybe
even 10). The strange thing is, we've never felt impelled to "Work so
hard at cooking and cleaning as to make our eyes bleed" Not even at
Christmas time when it was 'our turn' to host the 'christmas family
do'.

Keep in mind the circuit is *designed* to be able to cope with short
term overloads of several kW without any damage. A normal 32A MCB will
happily supply 45A for some time, and even 50A for 10 mins or so. This
reflects the case that the wiring itself also requires some time to
reach a temperature where it will start to suffer damage.

Perhaps we simply don't posses enough of the latest energy consuming
'Must Have' kitchen gadgets to bless us with such overloading
problems.

Most people don't. Although many have enough that it would become an
issue if the kitchen was sharing a circuit with large parts of the rest
of the house as well.

The basement was catered for by fitting 3 single outlet 13A sockets
onto the CU backboard each fed off the 3 ring main circuits so that
the freezer we kept in the basement could be readily powered from any
one of the ring main circuits as an insurance against any protracted
outage that might arise due to faults or planned changes in the ring
main wiring.

Would it not have been simpler to provide a dedicated circuit for this
purpose? Then you would *know* its not going to be tripped regardless of
what happens elsewhere.

Think it through. What's important? having a dedicated circuit that
can still go faulty despite its splendid isolation from the other ring
mains or a choice of three alternative sockets less than an extension
lead's length away.

Whichever ring you power it from, its sharing with other appliances,
which may cause a nuisance trip. Without sharing, there is no possible
cause for a trip other than catastrophic failure of the freezer itself!

(it would also allow the provision of a freezer supply that does not
have RCD protection, which eliminates another set of trip scenarios from
an application where enhanced shock protection is not an issue)

[big snip]

Using a 10A fuse, even in a larger
domestic property is probably unnecessary with modern lamps these
days.

Agreed in most cases... although keep in mind the increasing use of
ancillary loads on lighting circuits - e.g. extractor fans for forced
ventilation in kitchens, loos, bath/shower rooms etc, localised space
heating with "heater" lamps etc.

If my floor standing cooling fan is anything to go by, I'd imagine a
small vent axia type of fan wouldn't draw much more than 50 watts. As
for 'heater lamps' you're probably looking at 500W max (in a suitable

Yup fans are typically no more than tens of watts at most. Most heater
lamps are usually under 750W. Although there are a few over 1kW. E.g:

http://www.tlc-direct.co.uk/Products/SHHL1.html

A 6A circuit gives you 1380W to play with. So that would only allow
another two lamps (allowing the required 100W per lighting position) on
the circuit if using a 6A one.

Other common reasons for larger capacity circuits would be a largish
bank of strip lights - since they can have a fairly heavy switch on surge.

The more powerful radiant heater would be better served by a 5A fused
junction box spur tapped off the ring main. Quite frankly, I wouldn't
feed such loads from a lighting circuit other than maybe a vent axia
fan or two. You seem to be trying to justify the higher 10A fuse
rating with extra appliances that would be better served from a ring
main supply (via a suitably fused connection box).

I find no need to "justify" the circuit - they exist, and are
appropriate for some situations. I was just pointing out some of the
reasons that the "normal" 1380W may not offer the required capacity.

My own personal view is that the the primary function of a CU is
safety and, to this end, selecting a lower fuse rating option over a
higher one when conditions allow maximises its effectiveness at
minimising the risk of a house fire.

Nothing wrong with the logic... although you need to focus attention on
the right things. Adding RCD protection would give a much more
significant reduction in the likelihood of of house a fire cause by an
electrical source than say worrying about (properly installed and
configured) 10A lighting circuits. As would Fitting mains powered
interlinked smoke alarms.

The risk can never be totally eliminated whatever size fuse is chosen
but the risk does become more improbable as you lower the fuse rating
used on any existing circuit. Take my 15A ring main as an example of
this. I've never ever had to replace the 15A fuse link with a 30A one
because of 'overload' issues (nor for any other reason).

Any circuit is capable of supplying ample current to heat something
enough to cause a fire... Quality of terminations and cable insulation
are more relevant.

Your 15A rewireable will supply 28A pretty much indefinitely anyway - in
these days of central heating, most ring circuits outside a kitchen are
less heavily loaded in the past (lots of small appliances rather than
heavy load space heating etc)

The 15A fuse link has sufficed quite nicely for the loading this
particular ring main is subjected to. IOW, its utility hasn't suffered
as a result of the lower fuse rating so I've gained an extra margin of
safety 'for free' by this simple expedient.

I suspect that most domestic 10A lighting circuits could be just as
well served by a 5A fuse link or 6A MCB these days simply by virtue of
the extensive use of CFL lamps in place of the tungsten filament GLS
lamps they'd originally been sized for. It's certainly worthy of some
consideration if you have 10A lighting circuits in your home.

Personally I don't have any 10A ones, although as I alluded to
elsewhere, one would have actually been a quite a good choice here due
to the huge number of lamps employed on the ground floor! (when we moved
in, turning on half the downstairs lights all at once would trip the 5A
MCB after about 10 mins) (I have replaced the CU since)

Now I have three 6A Type C MCB circuits for the house, another for the
outside lights, another in the garage / workshop. (I also have battery
backed emergency lighting fed from the adjacent normal lighting
circuits, since there are no street lights here, and it can be *very* dark)





--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In message , Johny B Good
writes

I like the principle that you can replace a large fuse link in an
existing fuse carrier with smaller rated fuse links (Wylex CU) since
it makes it very simple to downgrade the ciruit capacity on an as
needed basis without compromising safety (in this case, boosting
safety), since it's a trivial exercise to refit the original larger
fuse should the smaller one blow due to unanticipated overload.

Of course the opposite is also easy....
--
Chris French

On Wed, 12 Feb 2014 18:13:03 -0800 (PST), wrote:

On Thursday, February 13, 2014 1:25:03 AM UTC, Johny B Good wrote:

Still and all, the whole point of a single fuse at the CU to protect
a lighting circuit is essentially to minimise the risk of a house
fire. Being 'plunged into darkness' is very rarely as fatal as smoke
inhalation or worse.
Of course there is always the counter argument in the automotive case
where it is (or at least, was) deemed preferable to eliminate a sudden
blackout of the headlamps due to a fuse fault by foregoing any
protective fusing whatsoever, making the risk of an electrical vehicle
fire higher as a result. The idea being that it is better to still be
able to safely navigate along a narrow country road on a dark night
for as long as it takes to bring the vehicle safely to rest and permit
a rapid bailout.
I believe modern practice with vehicular wiring is to fuse each
headlight independantly now that the fusebox is housed within the less
harsher environment of the passenger compartment, usually just under
the dashboard over the driver's footwell.

The oldest vehicle I had had no fusing whatever. The original fusebox with space for 2 fuses was present, but not connected.

The manufacturer probably decided the risk with 6 or 12 volt wasn't
worth the expense and trouble of 'fuse protection' (plenty of other
hazards to consider) in a box on wheels that could be rather more
swiftly evacuated than a typical house (plus, one might hope, at least
one of the occupants would be wide awake and alert to such a danger).


Overloading the kitchen ring main has never been a problem. I suppose
it is just possible to overload it if we were to switch the 3KW kettle
on whilst using the "George Formby", toasting bread , microwaving some
food and 'Brevelling' some tasty sandwiches whilst we (the XYL & I)
each run a Dyson over the respective halves of the kitchen dining room
floor areas when the noise of the dishwasher will be nicely drowned
out. We may even have enough 13A sockets without having to disconnect
the fridge and the freezer nor cheat by plugging into the 13A cooker
point socket.
I'm sure that would be a good 8 or 9KW's worth right there (maybe
even 10). The strange thing is, we've never felt impelled to "Work so
hard at cooking and cleaning as to make our eyes bleed" Not even at
Christmas time when it was 'our turn' to host the 'christmas family
do'.
Perhaps we simply don't posses enough of the latest energy consuming
'Must Have' kitchen gadgets to bless us with such overloading
problems.

Exceeding 30A on a ring circuit isnt a problem, theyre designed to deliver much more for limited periods. 30A is the continuous rating. We regularly used to heavily exceed 30A at the last house, but nothing got hot or blew.


ISTR, that 2.5mm FT&E has a continuous rating of 27A (depends on how
the cables are routed (trunking with other cables versus single run
clipped onto beams and joists with adequate air space).

The 27A rating is only 3A shy of the full 30A fuse rating but on a
ring main it would be difficult to persuade more than 27A to flow over
the shortest section between the CU and the nearest socket (but not
impossible under the right (wrong?) circumstances).

The remaining 3A is modest enough that in most installations this
would be supplied over the 'scenic route' via the rest of the ring
main wiring.

What helps is the 13A fusing of the plugtops limiting the current
draw from a twin gang outlet to 26A (the regs might have something to
say in regard of the use of 3 and 4 gang outlets - I just don't know).

In most domestic properties, the risk of overloading the shortest run
to the socket nearest the CU is vanishingly small so the use of 27A
rated cabling in a 30A fused ring circuit is deemed acceptable in the
regs (it's only a 10% overload at its worst after all).
--
Regards, J B Good

On 2014-02-11, wrote:

On Tuesday, February 11, 2014 8:32:39 PM UTC, Johny B Good wrote:


If you're fitting a 13A socket in the loft or attic, it's usually for
the purposes of providing power to something like a masthead amp or TV
aerial distribution amp both of which would be more than amply served
by a half amp fuse[1] which minimises the risk of a house fire should
a fault develop on the (now fused) 13A socket spur.

2A and below suffer much more frequent failure, I expect one of the reasons for the choice of 3A fuses in the 40s.

Has fuse manufacturing not improved in the past 70 years?

On Thu, 13 Feb 2014 06:54:30 +0000, John Rumm
wrote:

On 13/02/2014 01:25, Johny B Good wrote:
On Wed, 12 Feb 2014 16:00:02 +0000, John Rumm
wrote:

On 12/02/2014 03:44, Johny B Good wrote:
On Tue, 11 Feb 2014 23:53:15 +0000, John Rumm
wrote:

On 11/02/2014 20:43, Johny B Good wrote:
On Tue, 11 Feb 2014 10:42:42 +0000, John Rumm
wrote:

10A is used domestically as well... I have certainly met it a few times.

Well, not being an electrician by trade, I've been unable to find any
references to the regulations, only anecdotes regarding 10A lighting
circuits (including the use of a ring lighting circuit) so I can't
quote 'chapter and verse' as to whether this is an acceptable
departure from the regulations or not (I know some leaway exists
within the regulations but this seems to be quite a large departure to
my mind).

Its not a departure at all - its one of the standard circuits listed in
the On Site Guide:

http://wiki.diyfaq.org.uk/images/2/2...g-Circuits.jpg

(you will note there is also a standard 16A lighting circuit - although
that is very unlikely to be used in a domestic situation)

Well thanks for that revealing information. It's additional knowledge
I can retain for future reference. Obviously, I'm not going to uprate
the fusing on my owm lighting circuits since the efficacy of the 5A
fusing has amply proved itself in my case over the past 3 decades.

I don't think anyone was suggesting that you do. Just highlighting that
it is an allowable and properly designed option.

I appreciate that. I was pointing out that just because I could
uprate to 10A fuses without violating the regs, I wasn't about to do
so (you're not obliged to fuse up to the allowable limits if you don't
need to).

If I'd been aware that use of 10A fusing was permitted on lighting
circuits when I was rewiring the house, I'd probably have chosen that
option (but I've no doubt, after replacing all bar one incandescent
lamp with CFLs, I'd have long since downrated to 5A fusing by now
anyway).


[1] i.e. the requirement that the effect of a fault be localised to it.
Plunging an entire house into darkness due to a lamp failing and
tripping a MCB is not acceptable today. (it never really was, but the
implications of it had not really been considered at the time)

Still and all, the whole point of a single fuse at the CU to protect
a lighting circuit is essentially to minimise the risk of a house
fire. Being 'plunged into darkness' is very rarely as fatal as smoke
inhalation or worse.

Missing the point I think... fusing good; single lighting circuit bad!

I agree that there's more to having two lighting circuits simply to
limit the maximum current draw. It's just that there are a lot of
quite modern 3 bedroom properties (less than 40 years old) relying on
only a single lighting circuit (along with a single ring main) and I
thought this was standard practice. I suppose it was by the cost
concious "Barret Homes" of the building industry at the time.


The chances of any lighting circuit causing a fire in the first place
are vanishingly small, but having a pair of them (and in consequence a
lower average current load on each) can only improve the odds further.

So if a house is wired with a single 10A circuit, you would get a much
greater improvement in safety by splitting it into two circuits (of
whatever rating), rather than just keeping it as it is and lowering the
fuse size.

You'll get the same safety benefit regardless of whether you simply
replace the 10A fuse with a 5A one or split the lighting into two
seprately fused circuits, each fused at 5A. In the latter case you'll
have improved utility over the single circuit and retain the same
safety level against faults in the fittings and lamp cordage.

If we ignore the bare faced lie that CFLs have 5 times the luminous
efficiency and assume a more reasonable 4 times improvement, a total
relamping of the original filament lamps with equivilent light power
CFLs will reduce the load current to only 25% of the original
requirements used to define the size of fuse.

For anyone who has replaced most of their incandescent filament lamps
with CFLs or LEDs, they can probably simply replace the 10A fuse with
a 5A one without detriment to the utility of the lighting circuit.


Of course there is always the counter argument in the automotive case
where it is (or at least, was) deemed preferable to eliminate a sudden
blackout of the headlamps due to a fuse fault by foregoing any
protective fusing whatsoever, making the risk of an electrical vehicle
fire higher as a result. The idea being that it is better to still be
able to safely navigate along a narrow country road on a dark night
for as long as it takes to bring the vehicle safely to rest and permit
a rapid bailout.

There are a few permitted cases where fusing may be omitted on similar
grounds - i.e. where failure of the supply is more dangerous than the
circuit being damaged by over heating etc. (unlikely to crop up
domestically though!)

There _just_ might be a reference to life support system power in the
home but other than that I wouldn't have thought the regs would allow
any such 'dispensation' whatsoever.


I sense an anti 10A fuse agenda here ;-)

Well yes but you _know_ why. Even now, the idea of using a 10A fuse
over a 5A fuse for lighting circuit protection still leaves me with a
feeling of uneasiness.

Whilst I agree with the general principle of using protective thresholds
of no bigger than they need to be, I also recognise that the absolute
size of the fuse is not the sole guide to how safe a circuit is.

I'm aware of this.


(even when 1.5mm cabling is used - the ratings on the fittings are all
based on the protection of a 5A fused supply). Obviously, the second
extra fuse position will allow two seperate ring mains to be provided.

I think you will find that modern lighting accessories are fine on 10A
circuits (note that even the limitation on the "small" version of the
normal lamp holders was removed).

I'm familiar with the 'moving goalposts' syndrome. Obviously a fine
tuning of the safety versus utlity compromise. At least you still have
the option 'to make it safer'.

Possibly - but that does not always equate to a lower current protective
device. Nuisance trips from "close to tripping" protective devices can
in themselves harbour dangers.

"House Owner Rage"?


If doing it now, it would be quite common to do that, and also add an
extra ring circuit for the kitchen / utility room - since the modern
compliment of kitchen appliances can rapidly use all 7.2kW capacity of a
ring circuit.

Funny you should mention that. :-)

[snip]

Overloading the kitchen ring main has never been a problem. I suppose
it is just possible to overload it if we were to switch the 3KW kettle
on whilst using the "George Formby", toasting bread , microwaving some
food and 'Brevelling' some tasty sandwiches whilst we (the XYL & I)
each run a Dyson over the respective halves of the kitchen dining room
floor areas when the noise of the dishwasher will be nicely drowned
out. We may even have enough 13A sockets without having to disconnect
the fridge and the freezer nor cheat by plugging into the 13A cooker
point socket.

With kitchens you can generally ignore the kettle and microwave etc -
they are not usually on long enough to pose a problem. The big white
things with heater elements like washing machine, dishwasher, tumble
drier etc can swallow more "long term" capacity. Some single ovens are
also often plugged into a kitchen ring circuit these days.

I'm sure that would be a good 8 or 9KW's worth right there (maybe
even 10). The strange thing is, we've never felt impelled to "Work so
hard at cooking and cleaning as to make our eyes bleed" Not even at
Christmas time when it was 'our turn' to host the 'christmas family
do'.

Keep in mind the circuit is *designed* to be able to cope with short
term overloads of several kW without any damage. A normal 32A MCB will
happily supply 45A for some time, and even 50A for 10 mins or so. This
reflects the case that the wiring itself also requires some time to
reach a temperature where it will start to suffer damage.

Perhaps we simply don't posses enough of the latest energy consuming
'Must Have' kitchen gadgets to bless us with such overloading
problems.

Most people don't. Although many have enough that it would become an
issue if the kitchen was sharing a circuit with large parts of the rest
of the house as well.

Well, it helps that the kitchen's ring main is not cursed with the
washing machine and tumble drier loads, they live in the utility room
right next to the downstairs shower/toilet and are plugged into the
ground floor ring main circuit.


The basement was catered for by fitting 3 single outlet 13A sockets
onto the CU backboard each fed off the 3 ring main circuits so that
the freezer we kept in the basement could be readily powered from any
one of the ring main circuits as an insurance against any protracted
outage that might arise due to faults or planned changes in the ring
main wiring.

Would it not have been simpler to provide a dedicated circuit for this
purpose? Then you would *know* its not going to be tripped regardless of
what happens elsewhere.

Think it through. What's important? having a dedicated circuit that
can still go faulty despite its splendid isolation from the other ring
mains or a choice of three alternative sockets less than an extension
lead's length away.

Whichever ring you power it from, its sharing with other appliances,
which may cause a nuisance trip. Without sharing, there is no possible
cause for a trip other than catastrophic failure of the freezer itself!

I see your point but my setup is protected by simple fuses with no
ELCBs in sight so I don't have the problem of 'nuisance trips' to
contend with. In any case, a freezer can go unattended for 24 hours
before it just has to be powered back up.

I think we'd notice a ring main outage well within that time limit
and pay the basement a visit if only to check the fuse box, allowing
us to swap the freezer to an adjacent working socket if need be which
is not even one step away from the fuse board.

That chest freezer has long since been sent to the council tip. I
don't think we even bothered to relocate it to the newly built kitchen
(BICBW on this point) electing instead to simply buy a new more energy
efficient unit more in keeping with our 'brand new' kitchen.


(it would also allow the provision of a freezer supply that does not
have RCD protection, which eliminates another set of trip scenarios from
an application where enhanced shock protection is not an issue)

As I said, not an issue in my case.


[big snip]

Using a 10A fuse, even in a larger
domestic property is probably unnecessary with modern lamps these
days.

Agreed in most cases... although keep in mind the increasing use of
ancillary loads on lighting circuits - e.g. extractor fans for forced
ventilation in kitchens, loos, bath/shower rooms etc, localised space
heating with "heater" lamps etc.

If my floor standing cooling fan is anything to go by, I'd imagine a
small vent axia type of fan wouldn't draw much more than 50 watts. As
for 'heater lamps' you're probably looking at 500W max (in a suitable

Yup fans are typically no more than tens of watts at most. Most heater
lamps are usually under 750W. Although there are a few over 1kW. E.g:

http://www.tlc-direct.co.uk/Products/SHHL1.html

A 6A circuit gives you 1380W to play with. So that would only allow
another two lamps (allowing the required 100W per lighting position) on
the circuit if using a 6A one.

Other common reasons for larger capacity circuits would be a largish
bank of strip lights - since they can have a fairly heavy switch on surge.

The more powerful radiant heater would be better served by a 5A fused
junction box spur tapped off the ring main. Quite frankly, I wouldn't
feed such loads from a lighting circuit other than maybe a vent axia
fan or two. You seem to be trying to justify the higher 10A fuse
rating with extra appliances that would be better served from a ring
main supply (via a suitably fused connection box).

I find no need to "justify" the circuit - they exist, and are
appropriate for some situations. I was just pointing out some of the
reasons that the "normal" 1380W may not offer the required capacity.

Well, you're offering a justification regardless. I'm not saying
you're wrong to provide such justification, just pointing out that
such justification doesn't apply in my case since, like most homes
connected to the gas main we enjoy the benefit of central heating
which makes such additional loads redundent.

For those with electric only homes, I can see the justification to
use 10A fusing on the lighting circuits to increase the utility over
and above the bare minimum of lighting only.

I might even consider uprating the fuse to allow the use of such a
heating lamp if I decided to improve the comfort of taking a bath
whilst a CH fault had forced us back to using the immersion element
for heating the water. TBH, I think I'd forego such luxuries on the
grounds that it'll 'help concentrate the mind' on getting the CH
repaired in a timely fashion.

I made sure to include such redundency when the CH was installed but
it did rather help that the previous owner had installed a hot water
tank designed for both immersion and central heating which reduced the
parts cost significantly of the CH installation - it was only a matter
of plumbing the heat exchanger coils into the CH system.

My own personal view is that the the primary function of a CU is
safety and, to this end, selecting a lower fuse rating option over a
higher one when conditions allow maximises its effectiveness at
minimising the risk of a house fire.

Nothing wrong with the logic... although you need to focus attention on
the right things. Adding RCD protection would give a much more
significant reduction in the likelihood of of house a fire cause by an
electrical source than say worrying about (properly installed and
configured) 10A lighting circuits. As would Fitting mains powered
interlinked smoke alarms.

We've got plenty of the stand alone battery powered smoke alarms
scattered throughout the house. That's a 'last line of defence'
measure to protect life and limb (but not goods and chattels - any
saving of those would simply be a side effect of the primary
protection).

The risk can never be totally eliminated whatever size fuse is chosen
but the risk does become more improbable as you lower the fuse rating
used on any existing circuit. Take my 15A ring main as an example of
this. I've never ever had to replace the 15A fuse link with a 30A one
because of 'overload' issues (nor for any other reason).

Any circuit is capable of supplying ample current to heat something
enough to cause a fire... Quality of terminations and cable insulation
are more relevant.

Your 15A rewireable will supply 28A pretty much indefinitely anyway - in
these days of central heating, most ring circuits outside a kitchen are
less heavily loaded in the past (lots of small appliances rather than
heavy load space heating etc)

You make a very good argument for my case. :-)


The 15A fuse link has sufficed quite nicely for the loading this
particular ring main is subjected to. IOW, its utility hasn't suffered
as a result of the lower fuse rating so I've gained an extra margin of
safety 'for free' by this simple expedient.

I suspect that most domestic 10A lighting circuits could be just as
well served by a 5A fuse link or 6A MCB these days simply by virtue of
the extensive use of CFL lamps in place of the tungsten filament GLS
lamps they'd originally been sized for. It's certainly worthy of some
consideration if you have 10A lighting circuits in your home.

Personally I don't have any 10A ones, although as I alluded to
elsewhere, one would have actually been a quite a good choice here due
to the huge number of lamps employed on the ground floor! (when we moved
in, turning on half the downstairs lights all at once would trip the 5A
MCB after about 10 mins) (I have replaced the CU since)

Now I have three 6A Type C MCB circuits for the house, another for the
outside lights, another in the garage / workshop. (I also have battery
backed emergency lighting fed from the adjacent normal lighting
circuits, since there are no street lights here, and it can be *very* dark)

You've built a system that meets your requirements, seemingly taking
the more cautious approach with the lighting circuits. I guess you've
been playing "Devil's Advocate" in offering the counter argument to my
assertions which were initially prompted by my ignorance of the regs
in regard of permissable lighting circuit fuse ratings.

I've learnt something new so the whole discussion hasn't been a
pointless waste of time and I'm sure it's given others something to
ponder upon which might prove to be of some use in the future.
--
Regards, J B Good

Johny B Good wrote:
On Thu, 13 Feb 2014 06:54:30 +0000, John Rumm
wrote:

On 13/02/2014 01:25, Johny B Good wrote:
On Wed, 12 Feb 2014 16:00:02 +0000, John Rumm
wrote:

On 12/02/2014 03:44, Johny B Good wrote:
On Tue, 11 Feb 2014 23:53:15 +0000, John Rumm
wrote:

On 11/02/2014 20:43, Johny B Good wrote:
On Tue, 11 Feb 2014 10:42:42 +0000, John Rumm
wrote:

10A is used domestically as well... I have certainly met it a few times.

Well, not being an electrician by trade, I've been unable to find any
references to the regulations, only anecdotes regarding 10A lighting
circuits (including the use of a ring lighting circuit) so I can't
quote 'chapter and verse' as to whether this is an acceptable
departure from the regulations or not (I know some leaway exists
within the regulations but this seems to be quite a large departure to
my mind).

Its not a departure at all - its one of the standard circuits listed in
the On Site Guide:

http://wiki.diyfaq.org.uk/images/2/2...g-Circuits.jpg

(you will note there is also a standard 16A lighting circuit - although
that is very unlikely to be used in a domestic situation)

Well thanks for that revealing information. It's additional knowledge
I can retain for future reference. Obviously, I'm not going to uprate
the fusing on my owm lighting circuits since the efficacy of the 5A
fusing has amply proved itself in my case over the past 3 decades.

I don't think anyone was suggesting that you do. Just highlighting that
it is an allowable and properly designed option.

I appreciate that. I was pointing out that just because I could
uprate to 10A fuses without violating the regs, I wasn't about to do
so (you're not obliged to fuse up to the allowable limits if you don't
need to).

If I'd been aware that use of 10A fusing was permitted on lighting
circuits when I was rewiring the house, I'd probably have chosen that
option (but I've no doubt, after replacing all bar one incandescent
lamp with CFLs, I'd have long since downrated to 5A fusing by now
anyway).


[1] i.e. the requirement that the effect of a fault be localised to it.
Plunging an entire house into darkness due to a lamp failing and
tripping a MCB is not acceptable today. (it never really was, but the
implications of it had not really been considered at the time)

Still and all, the whole point of a single fuse at the CU to protect
a lighting circuit is essentially to minimise the risk of a house
fire. Being 'plunged into darkness' is very rarely as fatal as smoke
inhalation or worse.

Missing the point I think... fusing good; single lighting circuit bad!

I agree that there's more to having two lighting circuits simply to
limit the maximum current draw. It's just that there are a lot of
quite modern 3 bedroom properties (less than 40 years old) relying on
only a single lighting circuit (along with a single ring main) and I
thought this was standard practice. I suppose it was by the cost
concious "Barret Homes" of the building industry at the time.


The chances of any lighting circuit causing a fire in the first place
are vanishingly small, but having a pair of them (and in consequence a
lower average current load on each) can only improve the odds further.

So if a house is wired with a single 10A circuit, you would get a much
greater improvement in safety by splitting it into two circuits (of
whatever rating), rather than just keeping it as it is and lowering the
fuse size.

You'll get the same safety benefit regardless of whether you simply
replace the 10A fuse with a 5A one or split the lighting into two
seprately fused circuits, each fused at 5A. In the latter case you'll
have improved utility over the single circuit and retain the same
safety level against faults in the fittings and lamp cordage.

If we ignore the bare faced lie that CFLs have 5 times the luminous
efficiency and assume a more reasonable 4 times improvement, a total
relamping of the original filament lamps with equivilent light power
CFLs will reduce the load current to only 25% of the original
requirements used to define the size of fuse.

For anyone who has replaced most of their incandescent filament lamps
with CFLs or LEDs, they can probably simply replace the 10A fuse with
a 5A one without detriment to the utility of the lighting circuit.


Of course there is always the counter argument in the automotive case
where it is (or at least, was) deemed preferable to eliminate a sudden
blackout of the headlamps due to a fuse fault by foregoing any
protective fusing whatsoever, making the risk of an electrical vehicle
fire higher as a result. The idea being that it is better to still be
able to safely navigate along a narrow country road on a dark night
for as long as it takes to bring the vehicle safely to rest and permit
a rapid bailout.

There are a few permitted cases where fusing may be omitted on similar
grounds - i.e. where failure of the supply is more dangerous than the
circuit being damaged by over heating etc. (unlikely to crop up
domestically though!)

There _just_ might be a reference to life support system power in the
home but other than that I wouldn't have thought the regs would allow
any such 'dispensation' whatsoever.


I sense an anti 10A fuse agenda here ;-)

Well yes but you _know_ why. Even now, the idea of using a 10A fuse
over a 5A fuse for lighting circuit protection still leaves me with a
feeling of uneasiness.

Whilst I agree with the general principle of using protective thresholds
of no bigger than they need to be, I also recognise that the absolute
size of the fuse is not the sole guide to how safe a circuit is.

I'm aware of this.


(even when 1.5mm cabling is used - the ratings on the fittings are all
based on the protection of a 5A fused supply). Obviously, the second
extra fuse position will allow two seperate ring mains to be provided.

I think you will find that modern lighting accessories are fine on 10A
circuits (note that even the limitation on the "small" version of the
normal lamp holders was removed).

I'm familiar with the 'moving goalposts' syndrome. Obviously a fine
tuning of the safety versus utlity compromise. At least you still have
the option 'to make it safer'.

Possibly - but that does not always equate to a lower current protective
device. Nuisance trips from "close to tripping" protective devices can
in themselves harbour dangers.

"House Owner Rage"?


If doing it now, it would be quite common to do that, and also add an
extra ring circuit for the kitchen / utility room - since the modern
compliment of kitchen appliances can rapidly use all 7.2kW capacity of a
ring circuit.

Funny you should mention that. :-)

[snip]

Overloading the kitchen ring main has never been a problem. I suppose
it is just possible to overload it if we were to switch the 3KW kettle
on whilst using the "George Formby", toasting bread , microwaving some
food and 'Brevelling' some tasty sandwiches whilst we (the XYL& I)
each run a Dyson over the respective halves of the kitchen dining room
floor areas when the noise of the dishwasher will be nicely drowned
out. We may even have enough 13A sockets without having to disconnect
the fridge and the freezer nor cheat by plugging into the 13A cooker
point socket.

With kitchens you can generally ignore the kettle and microwave etc -
they are not usually on long enough to pose a problem. The big white
things with heater elements like washing machine, dishwasher, tumble
drier etc can swallow more "long term" capacity. Some single ovens are
also often plugged into a kitchen ring circuit these days.

I'm sure that would be a good 8 or 9KW's worth right there (maybe
even 10). The strange thing is, we've never felt impelled to "Work so
hard at cooking and cleaning as to make our eyes bleed" Not even at
Christmas time when it was 'our turn' to host the 'christmas family
do'.

Keep in mind the circuit is *designed* to be able to cope with short
term overloads of several kW without any damage. A normal 32A MCB will
happily supply 45A for some time, and even 50A for 10 mins or so. This
reflects the case that the wiring itself also requires some time to
reach a temperature where it will start to suffer damage.

Perhaps we simply don't posses enough of the latest energy consuming
'Must Have' kitchen gadgets to bless us with such overloading
problems.

Most people don't. Although many have enough that it would become an
issue if the kitchen was sharing a circuit with large parts of the rest
of the house as well.

Well, it helps that the kitchen's ring main is not cursed with the
washing machine and tumble drier loads, they live in the utility room
right next to the downstairs shower/toilet and are plugged into the
ground floor ring main circuit.


The basement was catered for by fitting 3 single outlet 13A sockets
onto the CU backboard each fed off the 3 ring main circuits so that
the freezer we kept in the basement could be readily powered from any
one of the ring main circuits as an insurance against any protracted
outage that might arise due to faults or planned changes in the ring
main wiring.

Would it not have been simpler to provide a dedicated circuit for this
purpose? Then you would *know* its not going to be tripped regardless of
what happens elsewhere.

Think it through. What's important? having a dedicated circuit that
can still go faulty despite its splendid isolation from the other ring
mains or a choice of three alternative sockets less than an extension
lead's length away.

Whichever ring you power it from, its sharing with other appliances,
which may cause a nuisance trip. Without sharing, there is no possible
cause for a trip other than catastrophic failure of the freezer itself!

I see your point but my setup is protected by simple fuses with no
ELCBs in sight so I don't have the problem of 'nuisance trips' to
contend with. In any case, a freezer can go unattended for 24 hours
before it just has to be powered back up.

I think we'd notice a ring main outage well within that time limit
and pay the basement a visit if only to check the fuse box, allowing
us to swap the freezer to an adjacent working socket if need be which
is not even one step away from the fuse board.

That chest freezer has long since been sent to the council tip. I
don't think we even bothered to relocate it to the newly built kitchen
(BICBW on this point) electing instead to simply buy a new more energy
efficient unit more in keeping with our 'brand new' kitchen.


(it would also allow the provision of a freezer supply that does not
have RCD protection, which eliminates another set of trip scenarios from
an application where enhanced shock protection is not an issue)

As I said, not an issue in my case.


[big snip]

Using a 10A fuse, even in a larger
domestic property is probably unnecessary with modern lamps these
days.

Agreed in most cases... although keep in mind the increasing use of
ancillary loads on lighting circuits - e.g. extractor fans for forced
ventilation in kitchens, loos, bath/shower rooms etc, localised space
heating with "heater" lamps etc.

If my floor standing cooling fan is anything to go by, I'd imagine a
small vent axia type of fan wouldn't draw much more than 50 watts. As
for 'heater lamps' you're probably looking at 500W max (in a suitable

Yup fans are typically no more than tens of watts at most. Most heater
lamps are usually under 750W. Although there are a few over 1kW. E.g:

http://www.tlc-direct.co.uk/Products/SHHL1.html

A 6A circuit gives you 1380W to play with. So that would only allow
another two lamps (allowing the required 100W per lighting position) on
the circuit if using a 6A one.

Other common reasons for larger capacity circuits would be a largish
bank of strip lights - since they can have a fairly heavy switch on surge.

The more powerful radiant heater would be better served by a 5A fused
junction box spur tapped off the ring main. Quite frankly, I wouldn't
feed such loads from a lighting circuit other than maybe a vent axia
fan or two. You seem to be trying to justify the higher 10A fuse
rating with extra appliances that would be better served from a ring
main supply (via a suitably fused connection box).

I find no need to "justify" the circuit - they exist, and are
appropriate for some situations. I was just pointing out some of the
reasons that the "normal" 1380W may not offer the required capacity.

Well, you're offering a justification regardless. I'm not saying
you're wrong to provide such justification, just pointing out that
such justification doesn't apply in my case since, like most homes
connected to the gas main we enjoy the benefit of central heating
which makes such additional loads redundent.

For those with electric only homes, I can see the justification to
use 10A fusing on the lighting circuits to increase the utility over
and above the bare minimum of lighting only.

I might even consider uprating the fuse to allow the use of such a
heating lamp if I decided to improve the comfort of taking a bath
whilst a CH fault had forced us back to using the immersion element
for heating the water. TBH, I think I'd forego such luxuries on the
grounds that it'll 'help concentrate the mind' on getting the CH
repaired in a timely fashion.

I made sure to include such redundency when the CH was installed but
it did rather help that the previous owner had installed a hot water
tank designed for both immersion and central heating which reduced the
parts cost significantly of the CH installation - it was only a matter
of plumbing the heat exchanger coils into the CH system.

My own personal view is that the the primary function of a CU is
safety and, to this end, selecting a lower fuse rating option over a
higher one when conditions allow maximises its effectiveness at
minimising the risk of a house fire.

Nothing wrong with the logic... although you need to focus attention on
the right things. Adding RCD protection would give a much more
significant reduction in the likelihood of of house a fire cause by an
electrical source than say worrying about (properly installed and
configured) 10A lighting circuits. As would Fitting mains powered
interlinked smoke alarms.

We've got plenty of the stand alone battery powered smoke alarms
scattered throughout the house. That's a 'last line of defence'
measure to protect life and limb (but not goods and chattels - any
saving of those would simply be a side effect of the primary
protection).

The risk can never be totally eliminated whatever size fuse is chosen
but the risk does become more improbable as you lower the fuse rating
used on any existing circuit. Take my 15A ring main as an example of
this. I've never ever had to replace the 15A fuse link with a 30A one
because of 'overload' issues (nor for any other reason).

Any circuit is capable of supplying ample current to heat something
enough to cause a fire... Quality of terminations and cable insulation
are more relevant.

Your 15A rewireable will supply 28A pretty much indefinitely anyway - in
these days of central heating, most ring circuits outside a kitchen are
less heavily loaded in the past (lots of small appliances rather than
heavy load space heating etc)

You make a very good argument for my case. :-)


The 15A fuse link has sufficed quite nicely for the loading this
particular ring main is subjected to. IOW, its utility hasn't suffered
as a result of the lower fuse rating so I've gained an extra margin of
safety 'for free' by this simple expedient.

I suspect that most domestic 10A lighting circuits could be just as
well served by a 5A fuse link or 6A MCB these days simply by virtue of
the extensive use of CFL lamps in place of the tungsten filament GLS
lamps they'd originally been sized for. It's certainly worthy of some
consideration if you have 10A lighting circuits in your home.

Personally I don't have any 10A ones, although as I alluded to
elsewhere, one would have actually been a quite a good choice here due
to the huge number of lamps employed on the ground floor! (when we moved
in, turning on half the downstairs lights all at once would trip the 5A
MCB after about 10 mins) (I have replaced the CU since)

Now I have three 6A Type C MCB circuits for the house, another for the
outside lights, another in the garage / workshop. (I also have battery
backed emergency lighting fed from the adjacent normal lighting
circuits, since there are no street lights here, and it can be *very* dark)

You've built a system that meets your requirements, seemingly taking
the more cautious approach with the lighting circuits. I guess you've
been playing "Devil's Advocate" in offering the counter argument to my
assertions which were initially prompted by my ignorance of the regs
in regard of permissable lighting circuit fuse ratings.

I've learnt something new so the whole discussion hasn't been a
pointless waste of time and I'm sure it's given others something to
ponder upon which might prove to be of some use in the future.

Seems to be a case of extreme verbal diarrhoea!

On Thursday, February 13, 2014 3:03:21 PM UTC, Johny B Good wrote:
On Wed, 12 Feb 2014 18:13:03 -0800 (PST), wrote:
On Thursday, February 13, 2014 1:25:03 AM UTC, Johny B Good wrote:

The oldest vehicle I had had no fusing whatever. The original fusebox with space for 2 fuses was present, but not connected.

The manufacturer probably decided the risk with 6 or 12 volt wasn't
worth the expense and trouble of 'fuse protection' (plenty of other
hazards to consider) in a box on wheels that could be rather more
swiftly evacuated than a typical house (plus, one might hope, at least
one of the occupants would be wide awake and alert to such a danger).

Maybe. But I doubt it following a convo I had with them Trying to find out what the engine was, the oldest guy that had been there forever said 'we used to put whatever was lying around in those, could be anything.' I dont think vehicle hazards were considered much in postwar designs.


Exceeding 30A on a ring circuit isnt a problem, theyre designed to deliver much more for limited periods. 30A is the continuous rating. We regularly used to heavily exceed 30A at the last house, but nothing got hot or blew..

ISTR, that 2.5mm FT&E has a continuous rating of 27A (depends on how
the cables are routed (trunking with other cables versus single run
clipped onto beams and joists with adequate air space).
The 27A rating is only 3A shy of the full 30A fuse rating but on a
ring main it would be difficult to persuade more than 27A to flow over
the shortest section between the CU and the nearest socket (but not
impossible under the right (wrong?) circumstances).
The remaining 3A is modest enough that in most installations this
would be supplied over the 'scenic route' via the rest of the ring
main wiring.
What helps is the 13A fusing of the plugtops limiting the current
draw from a twin gang outlet to 26A (the regs might have something to
say in regard of the use of 3 and 4 gang outlets - I just don't know).
In most domestic properties, the risk of overloading the shortest run
to the socket nearest the CU is vanishingly small so the use of 27A
rated cabling in a 30A fused ring circuit is deemed acceptable in the
regs (it's only a 10% overload at its worst after all).

Its routine, but not a problem. Think about it, washing machine dishwasher kettle microwave... we often exceed 30A.


NT

On Thursday, February 13, 2014 4:03:39 PM UTC, Adam Funk wrote:
On 2014-02-11, wrote:
On Tuesday, February 11, 2014 8:32:39 PM UTC, Johny B Good wrote:

If you're fitting a 13A socket in the loft or attic, it's usually for
the purposes of providing power to something like a masthead amp or TV
aerial distribution amp both of which would be more than amply served
by a half amp fuse[1] which minimises the risk of a house fire should
a fault develop on the (now fused) 13A socket spur.

2A and below suffer much more frequent failure, I expect one of the reasons for the choice of 3A fuses in the 40s.

Has fuse manufacturing not improved in the past 70 years?

AFAIK fuse wire is still the same material (tinned copper) it was 100 years ago. Its drawn differently, but afaik the result is the same. 3/13A cartridges have only changed in very minor details since their design in the 40s. BICBW.


NT

On 13/02/2014 19:09, Capitol wrote:

Seems to be a case of extreme verbal diarrhoea!

Used to be an AOL subscriber I take it? ;-)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 13/02/2014 17:25, Johny B Good wrote:

There are a few permitted cases where fusing may be omitted on similar
grounds - i.e. where failure of the supply is more dangerous than the
circuit being damaged by over heating etc. (unlikely to crop up
domestically though!)

There _just_ might be a reference to life support system power in the
home but other than that I wouldn't have thought the regs would allow
any such 'dispensation' whatsoever.

433.3.3 does indeed include life support systems, but it also includes
supplies to the exciter of a rotating machine, to a lifting magnet, the
secondary circuit of a current transformer, a supply to a fire
extinguisher system, and ones to safety systems like smoke or gas alarms.

(these are in addition to the overload exceptions permitted for other
reasons)

Possibly - but that does not always equate to a lower current protective
device. Nuisance trips from "close to tripping" protective devices can
in themselves harbour dangers.

"House Owner Rage"?

that and falling down the stairs in the dark etc.

I see your point but my setup is protected by simple fuses with no
ELCBs in sight so I don't have the problem of 'nuisance trips' to

A lamp tripping a MCB when it fails, is still a "nuisance trip", and not
RCD related... (one area where BS3036 rewireable fuses have an advantage
over MCBs)

(Not having *any* ECD protection kind of renders any worries about
fusing somewhat moot, since you are forgoing the single biggest
contribution to shock and fire protection to have come about as a result
of electrical regulation changes in quite a number of years).


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On Thu, 13 Feb 2014 15:02:32 +0000, chris French
wrote:

In message , Johny B Good
writes

I like the principle that you can replace a large fuse link in an
existing fuse carrier with smaller rated fuse links (Wylex CU) since
it makes it very simple to downgrade the ciruit capacity on an as
needed basis without compromising safety (in this case, boosting
safety), since it's a trivial exercise to refit the original larger
fuse should the smaller one blow due to unanticipated overload.

Of course the opposite is also easy....

If you mean fitting a larger fuse carrier in place of the smaller
fuse carrier (e.g. fitting a 15A fuse carrier into a 5A fuse bridge)
it's actually impossible without the assistance of a "Birmingham
Screwdriver".

Perhaps I'm a little out of the ordinary in keeping a set of
correctly wired fuse carriers spare to facilitate fuse replacement.
Perhaps I'm also a little unusual in only re-wiring a blown fuse with
the correct fusewire.

The practice of miswiring fuses with the wrong fuse wire seems to be
one only followed by those aiming to earn a "Darwin Award". The fuse
carriers are clearly marked with their fuse rating amperage and the
fusewire card clearly identifies each wrap of fusewire and it's not
exactly 'Rocket Science' to figure how to rewire a Wylex fuse carrier.

The fact that Niglon cards of replacement fusewire were readily
available from almost any hardware store or chandlers does suggest
that this was a job that was deemed to be within the competence of the
typical literate householder of the day.
--
Regards, J B Good

On Thu, 13 Feb 2014 11:43:20 -0800 (PST), wrote:

On Thursday, February 13, 2014 3:03:21 PM UTC, Johny B Good wrote:
On Wed, 12 Feb 2014 18:13:03 -0800 (PST), wrote:
On Thursday, February 13, 2014 1:25:03 AM UTC, Johny B Good wrote:

The oldest vehicle I had had no fusing whatever. The original fusebox with space for 2 fuses was present, but not connected.

The manufacturer probably decided the risk with 6 or 12 volt wasn't
worth the expense and trouble of 'fuse protection' (plenty of other
hazards to consider) in a box on wheels that could be rather more
swiftly evacuated than a typical house (plus, one might hope, at least
one of the occupants would be wide awake and alert to such a danger).

Maybe. But I doubt it following a convo I had with them Trying to find out what the engine was, the oldest guy that had been there forever said 'we used to put whatever was lying around in those, could be anything.' I dont think vehicle hazards were considered much in postwar designs.


Exceeding 30A on a ring circuit isnt a problem, theyre designed to deliver much more for limited periods. 30A is the continuous rating. We regularly used to heavily exceed 30A at the last house, but nothing got hot or blew.

ISTR, that 2.5mm FT&E has a continuous rating of 27A (depends on how
the cables are routed (trunking with other cables versus single run
clipped onto beams and joists with adequate air space).
The 27A rating is only 3A shy of the full 30A fuse rating but on a
ring main it would be difficult to persuade more than 27A to flow over
the shortest section between the CU and the nearest socket (but not
impossible under the right (wrong?) circumstances).
The remaining 3A is modest enough that in most installations this
would be supplied over the 'scenic route' via the rest of the ring
main wiring.
What helps is the 13A fusing of the plugtops limiting the current
draw from a twin gang outlet to 26A (the regs might have something to
say in regard of the use of 3 and 4 gang outlets - I just don't know).
In most domestic properties, the risk of overloading the shortest run
to the socket nearest the CU is vanishingly small so the use of 27A
rated cabling in a 30A fused ring circuit is deemed acceptable in the
regs (it's only a 10% overload at its worst after all).

Its routine, but not a problem. Think about it, washing machine dishwasher kettle microwave... we often exceed 30A.

Not in this house. :-)
--
Regards, J B Good

In article , Johny B Good
scribeth thus
On Thu, 13 Feb 2014 15:02:32 +0000, chris French
wrote:

In message , Johny B Good
writes

I like the principle that you can replace a large fuse link in an
existing fuse carrier with smaller rated fuse links (Wylex CU) since
it makes it very simple to downgrade the ciruit capacity on an as
needed basis without compromising safety (in this case, boosting
safety), since it's a trivial exercise to refit the original larger
fuse should the smaller one blow due to unanticipated overload.

Of course the opposite is also easy....

If you mean fitting a larger fuse carrier in place of the smaller
fuse carrier (e.g. fitting a 15A fuse carrier into a 5A fuse bridge)
it's actually impossible without the assistance of a "Birmingham
Screwdriver".

Perhaps I'm a little out of the ordinary in keeping a set of
correctly wired fuse carriers spare to facilitate fuse replacement.
Perhaps I'm also a little unusual in only re-wiring a blown fuse with
the correct fusewire.

The practice of miswiring fuses with the wrong fuse wire seems to be
one only followed by those aiming to earn a "Darwin Award". The fuse
carriers are clearly marked with their fuse rating amperage and the
fusewire card clearly identifies each wrap of fusewire and it's not
exactly 'Rocket Science' to figure how to rewire a Wylex fuse carrier.

The fact that Niglon cards of replacement fusewire were readily
available from almost any hardware store or chandlers does suggest
that this was a job that was deemed to be within the competence of the
typical literate householder of the day.


Theres people I know who'd have to get a man in to "change a damm light
bulb";!...


--
Tony Sayer

In article ,
tony sayer wrote:
In article , Johny B Good
scribeth thus
On Thu, 13 Feb 2014 15:02:32 +0000, chris French
wrote:

In message , Johny B Good
writes

I like the principle that you can replace a large fuse link in an
existing fuse carrier with smaller rated fuse links (Wylex CU) since
it makes it very simple to downgrade the ciruit capacity on an as
needed basis without compromising safety (in this case, boosting
safety), since it's a trivial exercise to refit the original larger
fuse should the smaller one blow due to unanticipated overload.

Of course the opposite is also easy....

If you mean fitting a larger fuse carrier in place of the smaller
fuse carrier (e.g. fitting a 15A fuse carrier into a 5A fuse bridge)
it's actually impossible without the assistance of a "Birmingham
Screwdriver".

Perhaps I'm a little out of the ordinary in keeping a set of
correctly wired fuse carriers spare to facilitate fuse replacement.
Perhaps I'm also a little unusual in only re-wiring a blown fuse with
the correct fusewire.

The practice of miswiring fuses with the wrong fuse wire seems to be
one only followed by those aiming to earn a "Darwin Award". The fuse
carriers are clearly marked with their fuse rating amperage and the
fusewire card clearly identifies each wrap of fusewire and it's not
exactly 'Rocket Science' to figure how to rewire a Wylex fuse carrier.

The fact that Niglon cards of replacement fusewire were readily
available from almost any hardware store or chandlers does suggest
that this was a job that was deemed to be within the competence of the
typical literate householder of the day.


Theres people I know who'd have to get a man in to "change a damm light
bulb";!...

A friend had a local handyman in to hang her Christmas lights since her
husband was still recovering from a hip operation.

--
From KT24

Using a RISC OS computer running v5.18

In article ,
Johny B Good wrote:
On Thu, 13 Feb 2014 15:02:32 +0000, chris French
wrote:

In message , Johny B Good
writes

I like the principle that you can replace a large fuse link in an
existing fuse carrier with smaller rated fuse links (Wylex CU) since
it makes it very simple to downgrade the ciruit capacity on an as
needed basis without compromising safety (in this case, boosting
safety), since it's a trivial exercise to refit the original larger
fuse should the smaller one blow due to unanticipated overload.

Of course the opposite is also easy....

If you mean fitting a larger fuse carrier in place of the smaller
fuse carrier (e.g. fitting a 15A fuse carrier into a 5A fuse bridge)
it's actually impossible without the assistance of a "Birmingham
Screwdriver".

Perhaps I'm a little out of the ordinary in keeping a set of
correctly wired fuse carriers spare to facilitate fuse replacement.
Perhaps I'm also a little unusual in only re-wiring a blown fuse with
the correct fusewire.

what's wrong with a 6" nail?

--
From KT24

Using a RISC OS computer running v5.18

In message , charles
writes
In article ,
Johny B Good wrote:
On Thu, 13 Feb 2014 15:02:32 +0000, chris French
wrote:

In message , Johny B Good
writes

I like the principle that you can replace a large fuse link in an
existing fuse carrier with smaller rated fuse links (Wylex CU) since
it makes it very simple to downgrade the ciruit capacity on an as
needed basis without compromising safety (in this case, boosting
safety), since it's a trivial exercise to refit the original larger
fuse should the smaller one blow due to unanticipated overload.

Of course the opposite is also easy....

If you mean fitting a larger fuse carrier in place of the smaller
fuse carrier (e.g. fitting a 15A fuse carrier into a 5A fuse bridge)
it's actually impossible without the assistance of a "Birmingham
Screwdriver".

Perhaps I'm a little out of the ordinary in keeping a set of
correctly wired fuse carriers spare to facilitate fuse replacement.
Perhaps I'm also a little unusual in only re-wiring a blown fuse with
the correct fusewire.

what's wrong with a 6" nail?

Back in the good old days a brass volume control shaft was a good
replacement for any value of fuse in a 13A plug. Never seen one blow.


--
Bill

In article ,
Bill wrote:
In message , charles
writes
In article ,
Johny B Good wrote:
On Thu, 13 Feb 2014 15:02:32 +0000, chris French
wrote:

In message , Johny B Good
writes

I like the principle that you can replace a large fuse link in an
existing fuse carrier with smaller rated fuse links (Wylex CU) since
it makes it very simple to downgrade the ciruit capacity on an as
needed basis without compromising safety (in this case, boosting
safety), since it's a trivial exercise to refit the original larger
fuse should the smaller one blow due to unanticipated overload.

Of course the opposite is also easy....

If you mean fitting a larger fuse carrier in place of the smaller
fuse carrier (e.g. fitting a 15A fuse carrier into a 5A fuse bridge)
it's actually impossible without the assistance of a "Birmingham
Screwdriver".

Perhaps I'm a little out of the ordinary in keeping a set of
correctly wired fuse carriers spare to facilitate fuse replacement.
Perhaps I'm also a little unusual in only re-wiring a blown fuse with
the correct fusewire.

what's wrong with a 6" nail?

Back in the good old days a brass volume control shaft was a good
replacement for any value of fuse in a 13A plug. Never seen one blow.

knew them well.

--
From KT24

Using a RISC OS computer running v5.18