New new wiring guide has been printed
and is now available - anyone got it yet?

Items dispatched on 5 Sep 2008:
Delivery estimate: 11 Sep 2008
1 package via Royal Mail 1 of
: IEE On-site Guide; BS 7671 : 2008 IEE Wiring Regulations 17th Edition
Sold by: Amazon EU S.a.r.L.
£16.15






--

[george]

~

George (dicegeorge) wrote:
New new wiring guide has been printed
and is now available - anyone got it yet?

not got mine yet...


--
Cheers,

John.

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John Rumm wrote:

not got mine yet...

Nor me, but Amazon sayeth:

- Order Placed: 3 May 2008
- Dispatch estimate: 5 Sep 2008
- Delivery estimate: 11 Sep 2008

--
Andy

I wrote:

[...] but Amazon sayeth:

- Order Placed: 3 May 2008
- Dispatch estimate: 5 Sep 2008
- Delivery estimate: 11 Sep 2008

- Arrived this morning.

Max. circuit length for a 32 A ring protected by a Type B MCB is now 106
metres.

Where Part M applies (re. height of sockets and switches) the consumer
unit should be readily accessible.

Fig. 7.3 indicates what could be considered the preferred core colours
for 2-way switching: brown for the permanently live line strapper, black
for common-common, grey for the switched line strapper.

--
Andy

"Andy Wade" wrote in message
...
I wrote:

[...] but Amazon sayeth:

- Order Placed: 3 May 2008
- Dispatch estimate: 5 Sep 2008
- Delivery estimate: 11 Sep 2008

- Arrived this morning.

Max. circuit length for a 32 A ring protected by a Type B MCB is now 106
metres.

What was it?

Doctor Drivel wrote:

Max. circuit length for a 32 A ring protected by a Type B MCB is now
106 metres.

What was it?

84 metres. Acceptable voltage drop is now 5% for power and 3% for
lighting circuits, as opposed to a blanket 4% before. Table 7.1 in the
new OSG includes a new section for lighting circuits (3% drop &
distributed load), as distinct from radial circuits (5% drop and
terminal load).

--
Andy

"Andy Wade" wrote in message
...
Doctor Drivel wrote:

Max. circuit length for a 32 A ring protected by a Type B MCB is now 106
metres.

What was it?

84 metres. Acceptable voltage drop is now 5% for power and 3% for
lighting circuits, as opposed to a blanket 4% before. Table 7.1 in the
new OSG includes a new section for lighting circuits (3% drop &
distributed load), as distinct from radial circuits (5% drop and terminal
load).

So, a watering down From 84m to 106 is hell of a percentage hype.

"Andy Wade" wrote in message
...
Doctor Drivel wrote:

Max. circuit length for a 32 A ring protected by a Type B MCB is now 106
metres.

What was it?

84 metres. Acceptable voltage drop is now 5% for power and 3% for
lighting circuits, as opposed to a blanket 4% before. Table 7.1 in the
new OSG includes a new section for lighting circuits (3% drop &
distributed load), as distinct from radial circuits (5% drop and terminal
load).

I suppose nobody plugs lights into a ring circuit so the extra 2% drop
doesn't matter.
And since it doesn't matter why the difference in the first place?
I would love the committee to answer that one.


--
Andy

dennis@home wrote:

I suppose nobody plugs lights into a ring circuit so the extra 2% drop
doesn't matter.

Cynic :-) A little more voltage drop won't matter too much for mood
lighting. In any case most domestic rings are nowhere near fully loaded
for the great majority of the time.

And since it doesn't matter why the difference in the first place?
I would love the committee to answer that one.

Surely it's obvious that lighting - tungsten lighting at least - is
considerably more voltage sensitive than most other loads.

--
Andy

Andy Wade wrote:

And since it doesn't matter why the difference in the first place?
I would love the committee to answer that one.

Surely it's obvious that lighting - tungsten lighting at least - is
considerably more voltage sensitive than most other loads.

Slightly ironic they think of this now, given the govt sponsored push to
try and get people using other forms of lighting ;-)

--
Cheers,

John.

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John Rumm wrote:

Slightly ironic they think of this now, given the govt sponsored push to
try and get people using other forms of lighting ;-)

Yes, but perhaps we should have gone back to the old 2.5% voltage drop
limit anyway in the interest of energy efficiency. Except that it might
use more copper. What's the embedded energy in a 100 m reel of 2.5 T&E,
I wonder...

--
Andy

On Mon, 08 Sep 2008 23:54:37 +0100, Andy Wade
wrote:

John Rumm wrote:

Slightly ironic they think of this now, given the govt sponsored push to
try and get people using other forms of lighting ;-)

Yes, but perhaps we should have gone back to the old 2.5% voltage drop
limit anyway in the interest of energy efficiency. Except that it might
use more copper. What's the embedded energy in a 100 m reel of 2.5 T&E,
I wonder...

I seem to think there is a problem in the regs, as if you work out
using 2.5mm for a ring main, its just not quite big enough for the MCB
protecton, so you will have to use 4mm. Its only very marginal.

The only trouble is i cannot remember where, but I remember on the
regs course it being highlighted.

floosy wrote:
On Mon, 08 Sep 2008 23:54:37 +0100, Andy Wade
wrote:

John Rumm wrote:

Slightly ironic they think of this now, given the govt sponsored push to
try and get people using other forms of lighting ;-)
Yes, but perhaps we should have gone back to the old 2.5% voltage drop
limit anyway in the interest of energy efficiency. Except that it might
use more copper. What's the embedded energy in a 100 m reel of 2.5 T&E,
I wonder...

I seem to think there is a problem in the regs, as if you work out
using 2.5mm for a ring main, its just not quite big enough for the MCB
protecton, so you will have to use 4mm. Its only very marginal.

The only trouble is i cannot remember where, but I remember on the
regs course it being highlighted.

The only times I can think of that being a problem is either with old
cables that have 1.0mm^2 CPCs on circuits with rewireable fuses, where
spurs may be insufficiently protected, and perhaps on current installs
where the supply impedance is *very* low and a fault close to the CU
would result in a prospective short circuit current that could exceed
the breaking capacity of a typical MCB.

--
Cheers,

John.

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\================================================= ================/

"John Rumm" wrote in message
et...
floosy wrote:
On Mon, 08 Sep 2008 23:54:37 +0100, Andy Wade
wrote:

John Rumm wrote:

Slightly ironic they think of this now, given the govt sponsored push
to try and get people using other forms of lighting ;-)
Yes, but perhaps we should have gone back to the old 2.5% voltage drop
limit anyway in the interest of energy efficiency. Except that it might
use more copper. What's the embedded energy in a 100 m reel of 2.5 T&E,
I wonder...

I seem to think there is a problem in the regs, as if you work out
using 2.5mm for a ring main, its just not quite big enough for the MCB
protecton, so you will have to use 4mm. Its only very marginal.

The only trouble is i cannot remember where, but I remember on the
regs course it being highlighted.

The only times I can think of that being a problem is either with old
cables that have 1.0mm^2 CPCs on circuits with rewireable fuses, where
spurs may be insufficiently protected, and perhaps on current installs
where the supply impedance is *very* low and a fault close to the CU would
result in a prospective short circuit current that could exceed the
breaking capacity of a typical MCB.

I wonder if the poster was thinking about this...

http://www2.theiet.org/Publish/WireR...c ircuits.pdf

but then you already knew that, didn't you?

Jim A

Jim Alexander wrote:

I wonder if the poster was thinking about this...
http://www2.theiet.org/Publish/WireR...c ircuits.pdf
but then you already knew that, didn't you?

Well, yes, that's old hat now. Nothing's changed in the 17th ed. apart
from the RCD requirements. So far as cable current rating is concerned
there are two principal requirements to meet:

(i) the as-installed current rating must be at least 20 A everywhere in
the circuit, with all relevant derating factors taken into account, and

(ii) under the reasonably foreseeable load conditions the _actual_
as-installed rating at any point should not be exceeded for long periods.

The second of these only comes into play when you have a cluster of
heavier current loads (i.e. a kitchen, usually) at one end of the ring.

It's worth noting that some of the tabulated ratings for 2.5 T&E in
Table 4D5 (Table 6F in the new OSG) are below 20 A. The two particular
cases a

- ref. method 101 - cable above and in contact with a plasterboard
ceiling with 100 mm thermal insulation above (rating 17 A);

- ref. method 103 - cable in a stud wall with cable not touching the
inner wall surface (rating 13.5 A).

In these cases 4 mm^2 cable would have to be used unless a different
cable installation method could be chosen. 30/32 A rings with 4 mm^2
cable (1.5 mm^2 CPC) are now included in table 7.1 in the new OSG.

--
Andy

"Andy Wade" wrote in message
...

- ref. method 103 - cable in a stud wall with cable not touching the inner
wall surface (rating 13.5 A).

Shame that most modern houses would be like that.
So now we have been building houses for 30 years where rings are dangerous
according to the 17th edition?

What does it say about dropping it behind the plaster board when its stuck
to brick work using dabs?

BTW I suspect that the rating assumes the stud wall is full of insulation
and that the cable is therefore wrapped in it, not all stud walls have
insulation in them but someone could put foam in them for some obscure
reason.

dennis@home wrote:

- ref. method 103 - cable in a stud wall with cable not touching the
inner wall surface (rating 13.5 A).

Shame that most modern houses would be like that.
So now we have been building houses for 30 years where rings are
dangerous according to the 17th edition?

There's nothing new in the 17th ed. there, except for the rating being
explicitly tabulated. 13.5 A is exactly half of the clipped direct
rating and a 50% derating has long applied for cables completely
surrounded in thermal insulation. Doubtless there are quite a few
non-compliant installations but I'd hope that the great majority have
the cabling clipped to the studwork (rating 21 A) or run in oval conduit
in contact with the studwork or the wall (rating 20 A).

What does it say about dropping it behind the plaster board when its
stuck to brick work using dabs?

The closest installation method I can see for that is no. 40 (assuming
it's not insulated plasterboard) - multicore cable in a building void.
Ref. method B applies, giving a rating of 23 A according to Table 4D2A.

BTW I suspect that the rating assumes the stud wall is full of
insulation and that the cable is therefore wrapped in it, not all stud
walls have insulation in them but someone could put foam in them for
some obscure reason.

Some contain a form of fibreglass quilt to reduce sound transmission.

--
Andy

If RCBOs are fiited in a CU on all circuits, is there really any real need
for an earth wire, apart from backup in case the RCBO fails?

Doctor Drivel wrote:
If RCBOs are fiited in a CU on all circuits, is there really any real
need for an earth wire, apart from backup in case the RCBO fails?

Of course, if there were no earthing, then a live to normally earthed metal
casing fault in, say, a toaster would not trip the breaker until you touched
it and provided a path to earth!

"Doctor Drivel" wrote in message
...
If RCBOs are fiited in a CU on all circuits, is there really any real need
for an earth wire, apart from backup in case the RCBO fails?

Yes.

In article ,
"Toby" writes:
Doctor Drivel wrote:
If RCBOs are fiited in a CU on all circuits, is there really any real
need for an earth wire, apart from backup in case the RCBO fails?

Of course, if there were no earthing, then a live to normally earthed metal
casing fault in, say, a toaster would not trip the breaker until you touched
it and provided a path to earth!

Also, RCDs/RCBOs are not fail-safe devices. If the electronic
circuitry inside stops work (as happens sometimes), they generally
stay switched on and fail to trip when required. Relying on one as
the primary means of protection would thus be rather foolish.
Remember to test them from time to time too!

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 10 Oct, 10:56, "Doctor Drivel" wrote:
If RCBOs are fiited in a CU on all circuits, is there really any real need
for an earth wire, apart from backup in case the RCBO fails?

Yes, you muppet.

The RCCD triggers if there's a current imbalance, which requires the
difference in current to pass through some earth connection somewhere.
One of the functions of a deliberate earth connection is to provide
this (thus tripping the RCCD at the time the faults occurs) rather
than having to wait for you to come along personally and stick a fork
in the toaster, earthing it through yourself.

I prefer my faulty appliances disconnected early, without having to
use myself as a current path.

In article
,
Andy Dingley wrote:
If RCBOs are fiited in a CU on all circuits, is there really any real
need for an earth wire, apart from backup in case the RCBO fails?

Yes, you muppet.

The RCCD triggers if there's a current imbalance, which requires the
difference in current to pass through some earth connection somewhere.
One of the functions of a deliberate earth connection is to provide
this (thus tripping the RCCD at the time the faults occurs) rather
than having to wait for you to come along personally and stick a fork
in the toaster, earthing it through yourself.

I prefer my faulty appliances disconnected early, without having to
use myself as a current path.

Perhaps dribble is looking for cheaper cable given the sink estate he
lives in where everything gets nicked.

--
*A journey of a thousand sites begins with a single click *

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

"Dave Plowman (News)" wrote in message
...
In article
,
Andy Dingley wrote:
If RCBOs are fiited in a CU on all circuits, is there really any real
need for an earth wire, apart from backup in case the RCBO fails?

Yes, you muppet.

The RCCD triggers if there's a current imbalance, which requires the
difference in current to pass through some earth connection somewhere.
One of the functions of a deliberate earth connection is to provide
this (thus tripping the RCCD at the time the faults occurs) rather
than having to wait for you to come along personally and stick a fork
in the toaster, earthing it through yourself.

I prefer my faulty appliances disconnected early, without having to
use myself as a current path.

Perhaps

Please eff off you are stupid idiot.

"Andy Dingley" wrote in message
...
On 10 Oct, 10:56, "Doctor Drivel" wrote:
If RCBOs are fiited in a CU on all circuits, is there really any real
need
for an earth wire, apart from backup in case the RCBO fails?

Yes, you muppet.

The RCCD triggers if there's a current imbalance, which requires the
difference in current to pass through some earth connection somewhere.

Which is invariably not down the supplied earth wire, Plantpot.

Doctor Drivel wrote:
If RCBOs are fiited in a CU on all circuits, is there really any real
need for an earth wire, apart from backup in case the RCBO fails?

Its not permissible to use a RCD as the only form of protection... so
earthing is as much required as ever.

--
Cheers,

John.

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\================================================= ================/

Doctor Drivel wrote:

"Andy Dingley" wrote
[...] which requires the difference in current to pass through some
earth connection somewhere.

Which is invariably not down the supplied earth wire,

Incorrect statement: the current path frequently is through the circuit
earth wire (properly called circuit protective conductor). Indeed in
TN-earthed installations it's recommended that disconnection in the
event of an earth fault to an exposed-conductive-part should not rely on
the presence of any RCD in the circuit. IOW the earth fault loop
impedance (Zs) should be low enough to ensure that the overcurrent
protective device (fuse or MCB) operates within the relevant permitted
disconnection time. Fault protection is then maintained, even if the
RCD is faulty. The RCD provides additional protection against the less
common situation where the current path is through someone's body.

Plantpot.

That's not a recommended method of earthing...

--
Andy

Doctor Drivel coughed up some electrons that declared:


"Andy Dingley" wrote in message
...
On 10 Oct, 10:56, "Doctor Drivel" wrote:
If RCBOs are fiited in a CU on all circuits, is there really any real
need
for an earth wire, apart from backup in case the RCBO fails?

Yes, you muppet.

The RCCD triggers if there's a current imbalance, which requires the
difference in current to pass through some earth connection somewhere.

Which is invariably not down the supplied earth wire, Plantpot.

How does your Class I appliance find it's earth without a supplied earth
wire then?

Obviously not through your head, for a vacuum is a near perfect insulator.

:-)


Cheers

Tim

"Andy Wade" wrote in message
...

Plantpot.

That's not a recommended method of earthing...

It should be.

"John Rumm" wrote in message
...
Doctor Drivel wrote:
If RCBOs are fiited in a CU on all circuits, is there really any real
need for an earth wire, apart from backup in case the RCBO fails?

Its not permissible to use a RCD as the only form of protection... so
earthing is as much required as ever.

That is rules. Would an RCD only offer the same protection?

In article ,
Doctor Drivel wrote:

"John Rumm" wrote in message
...
Doctor Drivel wrote:
If RCBOs are fiited in a CU on all circuits, is there really any real
need for an earth wire, apart from backup in case the RCBO fails?

Its not permissible to use a RCD as the only form of protection... so
earthing is as much required as ever.

That is rules. Would an RCD only offer the same protection?

There's not much point in explaining things to you, is there, since you
obviously don't understand plain English.

--
*No sentence fragments *

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

Doctor Drivel wrote:

"John Rumm" wrote in message
...
Doctor Drivel wrote:
If RCBOs are fiited in a CU on all circuits, is there really any real
need for an earth wire, apart from backup in case the RCBO fails?

Its not permissible to use a RCD as the only form of protection... so
earthing is as much required as ever.

That is rules. Would an RCD only offer the same protection?

No. For example a wire breaking loose in a metal lamp fitting (not
uncommon) on an earthed circuit would cause an immediate disconnection
of the supply, and an inability to reset the MCB while the fault is
present. The RCD acting on its own would only be able to offer any
protection when you actually got a shock, rather than before.

--
Cheers,

John.

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\================================================= ================/

"Dave Plowman (News)" wrote in message
...
In article ,
Doctor Drivel wrote:

"John Rumm" wrote in message
...
Doctor Drivel wrote:
If RCBOs are fiited in a CU on all circuits, is there really any real
need for an earth wire, apart from backup in case the RCBO fails?

Its not permissible to use a RCD as the only form of protection... so
earthing is as much required as ever.

That is rules. Would an RCD only offer the same protection?

There's

Please eff off as you are a plantpot.

"John Rumm" wrote in message
...
Doctor Drivel wrote:

"John Rumm" wrote in message
...
Doctor Drivel wrote:
If RCBOs are fiited in a CU on all circuits, is there really any real
need for an earth wire, apart from backup in case the RCBO fails?

Its not permissible to use a RCD as the only form of protection... so
earthing is as much required as ever.

That is rules. Would an RCD only offer the same protection?

No. For example a wire breaking loose in a metal lamp fitting (not
uncommon) on an earthed circuit would cause an immediate disconnection of
the supply, and an inability to reset the MCB while the fault is present.
The RCD acting on its own would only be able to offer any protection when
you actually got a shock, rather than before.

That is the point. An RCD is supposed to cut off so quick you will not get
a fatal shock. If that is the case then all this earthing wiring is just
backup if the RCD is faulty. When an RCD is fitted that the prime
protection mechanism, not the earthing.

John,
I don't understand this paragraph, (though I've read it 6 times)
could you please explain it a bit more?



That is rules. Would an RCD only offer the same protection?

No. For example a wire breaking loose in a metal lamp fitting (not
uncommon) on an earthed circuit would cause an immediate disconnection
of the supply, and an inability to reset the MCB while the fault is
present. The RCD acting on its own would only be able to offer any
protection when you actually got a shock, rather than before.

--
Cheers,

John.

Doctor Drivel wrote:

No. For example a wire breaking loose in a metal lamp fitting (not
uncommon) on an earthed circuit would cause an immediate disconnection
of the supply, and an inability to reset the MCB while the fault is
present. The RCD acting on its own would only be able to offer any
protection when you actually got a shock, rather than before.

That is the point. An RCD is supposed to cut off so quick you will not
get a fatal shock. If that is the case then all this earthing wiring is

The key issues here are really the "supposed to" and the "fatal" bits.
The RCD is an inherently more complex device, and there are more reasons
why it may fail to operate (not only due to its being faulty). Secondly,
many faults in an earthed system will be cleared without anyone
receiving a shock. While the RCD *should* render a shock non fatal
(assuming its a 30mA trip device or lower), that does not mean it is
always non fatal, and it also does not mean you will escape injury. That
could be directly - pain, localised burns, maybe even arc flash injuries
in some extreme cases, or consequential - recoiling and bruising /
lacerating yourself, falling etc.

just backup if the RCD is faulty. When an RCD is fitted that the prime
protection mechanism, not the earthing.

Its the first acting protection in the minority of typical fault
conditions.

I am not denigrating RCDs in any way - they do a very worthwhile job and
are certainly an added level of protection in a number of cases if used
properly. However, personally I would want to rely only on them as the
only protection.

(its rather a moot point really given the regulatory requirements)


--
Cheers,

John.

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\================================================= ================/

George (dicegeorge) wrote:

John,
I don't understand this paragraph, (though I've read it 6 times)
could you please explain it a bit more?

I can try ;-)

No. For example a wire breaking loose in a metal lamp fitting (not
uncommon) on an earthed circuit would cause an immediate disconnection
of the supply,

Say you have some appliance with earthed metalwork - I chose the example
of a metal lamp fitting. Many of these will have the bulb holders wired
in fairly flimsy wire that is vulnerable to being twisted and pulled
from its terminations when someone ends up screwing round the whole bulb
fitting trying to free a stuck bulb.

Should a live wire come free and make contact with the metalwork, this
would cause a large current surge to flow to earth next time you turn
the lamp on. This will blow the fuse or open the circuit breaker. If you
happened to be changing the bulb while the fitting is powered, the
earthing would also limit the voltage rise on the metal (the circuit
breaker / fuse / RCD can only limit the time that power remains
connected, and hence only the duration of the shock not its magnitude)

and an inability to reset the MCB while the fault is
present.

With the faulty earthed appliance, the MCB will react any time that
power is applied. Hence if you try resetting the MCB it will fail to do
so. A RCD however would only usually be responding to a transient event
- say someone touching the appliance. So you could go reset it, and come
back for another go.

(you may think that having got a belt off something the once, people
would be reluctant to try it again until they have worked out why and
fixed it, but that only seems to be the mindset of the engineer or DIY
enthusiast!)

The RCD acting on its own would only be able to offer any
protection when you actually got a shock, rather than before.

With earthing, many faults will be detected and cleared by the fuse /
MCB or RCD when they happen. You also have two devices acting in your
defence (e.g. MCB and RCD) - you would need a cascade of failures for
then to not clear the fault between them. If all you have is the RCD,
then a fault may lay in wait for the next unlucky person to complete a
circuit. They may well live to tell the tale, but would presumably
rather not have had a shock in the first place.

--
Cheers,

John.

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