I a CU is exchanged and it is found that some of the existing
installation doesnt quite reach where it needs to, what is the
correct/acceptable method of extending the existing cable(s)?.

joe

On Wed, 01 Dec 2004 08:21:31 +0000, tarquinlinbin
wrote:

I a CU is exchanged and it is found that some of the existing
installation doesnt quite reach where it needs to, what is the
correct/acceptable method of extending the existing cable(s)?.

joe
PS is it normal practice just to have just the lights on the isolator
side of a split CU?. Is there legislation/directive to specify what
goes on the CB side and what goes on the isolator side??

ta

joe

I a CU is exchanged and it is found that some of the existing
installation doesnt quite reach where it needs to, what is the
correct/acceptable method of extending the existing cable(s)?.

Use a correct sized insulated crimp applied with a proper ratchet crimping
tool. Cover the lot with heatshrink tubing, preferably remembering to slide
it on before crimping the ends!

PS is it normal practice just to have just the lights on the isolator
side of a split CU?. Is there legislation/directive to specify what
goes on the CB side and what goes on the isolator side??

The legislation is mostly silent except that some bathroom electrics and
sockets likely to be used outdoors must have an RCD. If you don't have
specific outdoor electrics, then general purpose socket circuits on the
ground floor are regarded as being likely to be so used.

However, as a general rule with no legal foundation, I'd divide up the
circuits as follows:

Definitely NOT RCD side:
Lights
Alarms
Fridge/Freezer
Central Heating*
Cooker
Fixed heating appliances

* = except when boiler installed in a bathroom

Definitely RCD side:
All general purpose socket circuits
Electric shower

Personal preference/by convenience:
Immersion Heater
Dedicated laundry circuit. (i.e. washing machine+tumble+dishwasher)
Other fixed appliances

Specical cases:
Exterior, garage and shed circuits should be RCDed but should never share an
RCD with circuits used within the house. Therefore, they should have a
separate RCBO, or come off the non-RCD side and into a dedicated RCD in a
separate housing or consumer unit.

Note that in the case of TT earthing, all circuits must be RCD protected.
However, this is achieved by using the same method as standard TN earthing,
but swapping the main incoming isolator switch with a 100mA time delayed
RCD. Alternatively, RCBOs on every single circuit is an expensive, but
convenient way to achieve this.

Christian.

Christian McArdle wrote:

Specical cases:
Exterior, garage and shed circuits should be RCDed but should never share an
RCD with circuits used within the house. Therefore, they should have a
separate RCBO, or come off the non-RCD side and into a dedicated RCD in a
separate housing or consumer unit.

That begs a question:

I was wondering if there is a preference for location of the RCD on shed
circuits? My current arrangement is:

Meter - Henley - 30mA RCD - SWA to outbuildings - conventional CU in
each.

That does have the disadvantage that when you borrow a dodgy electric
cement mixer from the neighbours that likes tripping RCDs on damp days,
you have to trapse throught the house to turn the RCD back on. So when I
replace the CU shortly (with two as below) I could go for:

Meter - Henley - SWA to outbuildings - CU with 30mA RCD in each

This would be more convienient, although that means the SWA itself (or
the heavy T&E that feeds it through the house) would no longer have RCD
protection.

Note that in the case of TT earthing, all circuits must be RCD protected.
However, this is achieved by using the same method as standard TN earthing,
but swapping the main incoming isolator switch with a 100mA time delayed
RCD. Alternatively, RCBOs on every single circuit is an expensive, but
convenient way to achieve this.

Or two separate CUs, one with a 30mA RCD, and the other with a normal
(i.e. non time delayed) 100mA RCD.

--
Cheers,

John.

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

"John Rumm" wrote in message
...
Christian McArdle wrote:

Specical cases:
Exterior, garage and shed circuits should be RCDed but should never
share an
RCD with circuits used within the house. Therefore, they should have a
separate RCBO, or come off the non-RCD side and into a dedicated RCD in
a
separate housing or consumer unit.

That begs a question:

I was wondering if there is a preference for location of the RCD on shed
circuits? My current arrangement is:

Meter - Henley - 30mA RCD - SWA to outbuildings - conventional CU in
each.

That does have the disadvantage that when you borrow a dodgy electric
cement mixer from the neighbours that likes tripping RCDs on damp days,
you have to trapse throught the house to turn the RCD back on. So when I
replace the CU shortly (with two as below) I could go for:

Meter - Henley - SWA to outbuildings - CU with 30mA RCD in each

This would be more convienient, although that means the SWA itself (or
the heavy T&E that feeds it through the house) would no longer have RCD
protection.

Note that in the case of TT earthing, all circuits must be RCD
protected.
However, this is achieved by using the same method as standard TN
earthing,
but swapping the main incoming isolator switch with a 100mA time delayed
RCD. Alternatively, RCBOs on every single circuit is an expensive, but
convenient way to achieve this.

Or two separate CUs, one with a 30mA RCD, and the other with a normal
(i.e. non time delayed) 100mA RCD.



In this case, however, won't you lose discrimination in the event of a
current imbalance in the end circuit of 100mA?

For non-TT, shouldn't the house-side RCD be time-delayed (at 100mA it's not
going to provide shock protection, so it's primary purpose must surely be
circuit protection?) For TT it's protected by the 100mA time delayed
mandatory RCD anyway.


--
Richard Sampson

mail me at
richard at olifant d-ot co do-t uk

For non-TT, shouldn't the house-side RCD be time-delayed (at 100mA it's
not
going to provide shock protection, so it's primary purpose must surely be
circuit protection?) For TT it's protected by the 100mA time delayed
mandatory RCD anyway.

I'm not sure you've understood the proposed solution. You have 2 consumer
units, with either a 30mA instant RCD (for protected circuits) or a 100mA
instant RCD (for less protected circuits). There is no loss of
discrimination. A fault on high risk 30mA circuits will not trip the 100mA
RCD, as the current doesn't pass through the 100mA RCD as well. You only
need the time delay one if the current goes through both the 30mA and the
100mA one, such as would happen with a split load consumer unit. This is
required to prevent the lights going out upon fault in a socket circuit.

Note that for a TT system, the consumer units must be insulated (i.e.
plastic) type.

Christian.

RichardS wrote:

In this case, however, won't you lose discrimination in the event of a
current imbalance in the end circuit of 100mA?

With my setup, there is no need to discriminate since there are no
cascaded RCDs. The outbuildings are fed from a submain split off the
incoming supply before the house CU. Currently there is a RCD that
protects the outbuilding supply but it is on the source end of the
cable. I shall move this to the other end.

For non-TT, shouldn't the house-side RCD be time-delayed (at 100mA it's not
going to provide shock protection, so it's primary purpose must surely be
circuit protection?) For TT it's protected by the 100mA time delayed
mandatory RCD anyway.

An RCDs main purpose is shock protection (since it has no (intentional)
over current detection built in). A shock limited to 100mA is still far
safer than an unlimited one!

AIUI, you only need a time delay RCD if you are going to cascade other
RCDs from it, otherwise in the event of a trip condition (with a trip
current above the trip threshold of both RCDs) you would loose
discrimination.

For a TT install, it is mandatory that the whole installation is
protected by an RCD. The reason a time delayed one is typically used is
down to the topology of the wiring... if you have a split load CU and
replace the main incomer with a 100mA RCD then you now have the RCD side
of the CU powered from another RCD. This is when you use the time
delayed RCD as the incomer.

In my case, space restrictions prevent me installing a big enough split
load CU, and hence I need to install two. This does however mean I can
dispense with the need for the time delay RCD since the CUs are not
cascaded.

--
Cheers,

John.

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

I was wondering if there is a preference for location of the RCD on shed
circuits?

I prefer the RCD in the outbuilding.

This would be more convienient, although that means the SWA itself (or
the heavy T&E that feeds it through the house) would no longer have RCD
protection.

There is no requirement to do so, provided that the cables have been
correctly calculated to have sufficiently low earth loop impedence. You
already have plenty of cables within the house (i.e. lighting/freezer
circuits) and buried under the ground (i.e. your main incoming supply)
without RCD protection.

Or two separate CUs, one with a 30mA RCD, and the other with a normal
(i.e. non time delayed) 100mA RCD.

Indeed.

Christian.

"John Rumm" wrote
| Meter - Henley - 30mA RCD - SWA to outbuildings - conventional CU in
| each.
| That does have the disadvantage that when you borrow a dodgy electric
| cement mixer from the neighbours that likes tripping RCDs on damp days,
| you have to trapse throught the house to turn the RCD back on

It also has the disadvantage that you cannot discriminate between lights and
tools in the outbuilding; an RCD trip could leave you in sudden darkness
with power tools spinning down.

Owain

It also has the disadvantage that you cannot discriminate between lights
and
tools in the outbuilding; an RCD trip could leave you in sudden darkness
with power tools spinning down.

Especially as the RCD trip is likely to occur as a result of your power tool
being out of control and chopping a cable.

Christian.

"Christian McArdle" wrote in message .net...

Use a correct sized insulated crimp applied with a proper ratchet crimping
tool. Cover the lot with heatshrink tubing, preferably remembering to slide
it on before crimping the ends!

DO NOT under any circumstances use insulated crimps on solid drawn
copper conductors, such as used in Flat Twin & Earth.
Crimps are for 7 core+ cable only.
There are some manufacturers who claim that you can use their crimps
on solid drawn cable, they are misleading you.
BS 7671 implies that all parts of an installation should consist of
British Standard parts, their is no british standard for "insulated"
crimps used in domestic solid copper conductor wiring systems.
If it comes to the crunch and this type of connection results in a
fire, your insurance company may refuse to pay out.
regards
Bob

In article , bob
writes
"Christian McArdle" wrote in message
x.net...

Use a correct sized insulated crimp applied with a proper ratchet crimping
tool. Cover the lot with heatshrink tubing, preferably remembering to slide
it on before crimping the ends!

DO NOT under any circumstances use insulated crimps on solid drawn
copper conductors, such as used in Flat Twin & Earth.
Crimps are for 7 core+ cable only.
There are some manufacturers who claim that you can use their crimps
on solid drawn cable, they are misleading you.
BS 7671 implies that all parts of an installation should consist of
British Standard parts, their is no british standard for "insulated"
crimps used in domestic solid copper conductor wiring systems.
If it comes to the crunch and this type of connection results in a
fire, your insurance company may refuse to pay out.
regards
Bob

Well I've just had a rewire done in a house by a NICEC approved
electrical firm, thats been around many years and works for local
authorities etc, and they have used these for joining 2.5 T&E....
--
Tony Sayer

Well I've just had a rewire done in a house by a NICEC approved
electrical firm, thats been around many years and works for local
authorities etc, and they have used these for joining 2.5 T&E....

Well get them back to put it right before your house burns down,
Any smart arse reply will be quoted at your funeral
Bob

bob wrote:

There are some manufacturers who claim that you can use their crimps
on solid drawn cable, they are misleading you.

I find if you make a crimp with a decent ratchet crimping tool then even
with solid core cable you still get a very solid joint. You will not
easily pull the wire appart.

If it comes to the crunch and this type of connection results in a
fire, your insurance company may refuse to pay out.

Seems like one of the less likely things to cause a fire. I assume that
you would have tested the circuit (i.e. low ohms continuity, 500V
insulation resistance etc) before use anyway.

--
Cheers,

John.

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

In article ,
bob wrote:
DO NOT under any circumstances use insulated crimps on solid drawn
copper conductors, such as used in Flat Twin & Earth.
Crimps are for 7 core+ cable only.
There are some manufacturers who claim that you can use their crimps
on solid drawn cable, they are misleading you.
BS 7671 implies that all parts of an installation should consist of
British Standard parts, their is no british standard for "insulated"
crimps used in domestic solid copper conductor wiring systems.

That's interesting. I have also rather a dislike for these things, even
although they seem to be available everywhere. I have a decent cantilever
crimp tool, but find that if you use flex at the smaller end of the range
with red ones, the connection ain't that good. This is mainly with car
1/4" spade connectors. I therefore no longer use them, and bought a very
expensive crimp tool for the correct sort of connectors you get on maker's
car looms. They also look rather better...

If I've needed to extend a wire within a CU when replacing one, I've used
a single choc block large enough to allow the wires to overlap, so they
are gripped by both terminals.

If I were moving a CU so some didn't reached, I'd be inclined to bite the
bullet and rewire as necessary, or use conventional junction boxes at a
convenient place for those which it was too awkward to replace. The cost
of the materials are, after all, pennies.

--
*Everyone has a photographic memory. Some just don't have film.

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

On Wed, 1 Dec 2004 09:48:17 -0000, "Christian McArdle"
wrote:

I a CU is exchanged and it is found that some of the existing
installation doesnt quite reach where it needs to, what is the
correct/acceptable method of extending the existing cable(s)?.

Use a correct sized insulated crimp applied with a proper ratchet crimping
tool. Cover the lot with heatshrink tubing, preferably remembering to slide
it on before crimping the ends!

PS is it normal practice just to have just the lights on the isolator
side of a split CU?. Is there legislation/directive to specify what
goes on the CB side and what goes on the isolator side??

The legislation is mostly silent except that some bathroom electrics and
sockets likely to be used outdoors must have an RCD. If you don't have
specific outdoor electrics, then general purpose socket circuits on the
ground floor are regarded as being likely to be so used.

[snip]

So if I install some specific sockets (or socket) for outdoor use
(including a built in 30mA RCD) can I avoid having to install a 30mA
RCD within the CU?

I ask because I have a rented house where there is a small 6 way CU
with all circuits protected by a 100mA RCD. Clearly, this avoids the
problems with lights tripping the 30mA RCD when they blow, and could
be argued to be safer than no RCD at all but it does not provide a
30mA RCD protection for outdoor supply.

I could fit a 30mA RCBO I guess except that the downstairs has two
circuits for sockets so that could get expensive. Installing one of
the double sockets with built in 30mA RCD into the garage or just
inside the back door and being designated for external equipment use
would solve the problem.

If it is allowed of course. If not, what other suggestions?

Rob



Replace 'spam' with 'org' to reply

"Kalico" wrote in message
...
On Wed, 1 Dec 2004 09:48:17 -0000, "Christian McArdle"
wrote:

snipped

I could fit a 30mA RCBO I guess except that the downstairs has two
circuits for sockets so that could get expensive. Installing one of
the double sockets with built in 30mA RCD into the garage or just
inside the back door and being designated for external equipment use
would solve the problem.

If it is allowed of course. If not, what other suggestions?

Rob


That sounds a good idea if you know that the RCD protected sockets are the
closest ones to an exit. But beware of someone using an extension through
an open window.

On Wed, 01 Dec 2004 23:13:46 +0000, Kalico wrote:


The legislation is mostly silent except that some bathroom electrics and
sockets likely to be used outdoors must have an RCD. If you don't have
specific outdoor electrics, then general purpose socket circuits on the
ground floor are regarded as being likely to be so used.

So the exisitng setup is old metalclad CU with troublesome buitl in
mains incomer RCD which nuisance trips occasionally,no apparent
fault,perhaps 3 times a year.

Old rewireable fuses have been replaced in the past with plug in MCBs

2x6A for lights,1x6A for central heating system, 1x16A for immersion
heater, 1x30A for ring main,1x30A for cooker (gas cooker now fitted!).

What would be the best configuration for a split load CU?. Shuodl i
just ditch the RCD and wire them all up through the isolator?

J

"tarquinlinbin" wrote in message
...
I a CU is exchanged and it is found that some of the existing
installation doesnt quite reach where it needs to, what is the
correct/acceptable method of extending the existing cable(s)?.

joe

IMHO Crimps are best, done with a proper crimp tool.

Solder is occasionally argued for.

Anything with a screw terminal (choc block / junction box)
must be (a) accessible (b) not under strain i.e. hanging

HTH,
Al