On Thu, 8 Mar 2018 19:48:14 +0000
John Rumm wrote:

On 08/03/2018 16:44, SteveE wrote:
My 89 y/o mother can no longer reach the switch above the mirror
and I want to change it for a LED pullcord light.

The old light was installed by a bathroom fitter and was not
earthed.

This light requires an earth connection but further investigation
has revealed that her upstairs lighting circuit has no earth.

Can I borrow an earth from an accessible ring-circuit in these
circumstances?

Its not a good idea to borrow conductors from other circuits.

Thanks, this is why I was uneasy about doing it.


If you must* take a feed from another circuit, then take the Line and
Neutral from there as well (via a FCU). Remember to include the earth
for the new circuit into the bathroom's equipotential bonding.

I think I'll take this approach as it will be as easy as just taking a
single earth wire down.

* One could argue that for a pull cord switch, where any metallic
part of the switch is out of reach, one could omit the earthing
without too much risk. Better choose a lamp fitting that is double
insulated and does not require an earth.


Yes, the pull cord will provide some isolation and she is under
instruction not to touch the metallic part until it's sorted.

On 09/03/18 05:42, SteveE wrote:

I think I'll take this approach as it will be as easy as just taking a
single earth wire down.


You could legitimately take a single earth to the nearest light on the
same circuit that does have an earth. For this, it would be preferable
to use a single insulated earth wire with green/yellow insulation. Often
called "singles" and available from all good electrical wholesalers
(some like TLC should be able to sell a length rather than a reel).

I don't have the regs to hand so not 100% sure if a CPC (earth) in this
scenario *must* be insulated, but it shows the purpose clearly which is
worthwhile.

In article ,
Tim Watts wrote:
You could legitimately take a single earth to the nearest light on the
same circuit that does have an earth. For this, it would be preferable
to use a single insulated earth wire with green/yellow insulation. Often
called "singles" and available from all good electrical wholesalers
(some like TLC should be able to sell a length rather than a reel).

Chances are since it's old wiring there is no earth to any lighting
circuit.

--
*Very funny Scotty, now beam down my clothes.

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

On 09/03/2018 11:29, Tim Watts wrote:
On 09/03/18 05:42, SteveE wrote:

I think I'll take this approach as it will be as easy as just taking a
single earth wire down.


You could legitimately take a single earth to the nearest light on the
same circuit that does have an earth. For this, it would be preferable
to use a single insulated earth wire with green/yellow insulation. Often
called "singles" and available from all good electrical wholesalers
(some like TLC should be able to sell a length rather than a reel).

I don't have the regs to hand so not 100% sure if a CPC (earth) in this
scenario *must* be insulated, but it shows the purpose clearly which is
worthwhile.


It's worse than that. It would have to be 4mm green/yellow and follow
the route/cable run of the live conductor unless that circuit is RCD
protected.

It's a while since this one came up at work but I am sure that was the
outcome.

--
Adam

On 09/03/18 19:24, ARW wrote:
On 09/03/2018 11:29, Tim Watts wrote:
On 09/03/18 05:42, SteveE wrote:

I think I'll take this approach as it will be as easy as just taking a
single earth wire down.


You could legitimately take a single earth to the nearest light on the
same circuit that does have an earth. For this, it would be preferable
to use a single insulated earth wire with green/yellow insulation.
Often called "singles" and available from all good electrical
wholesalers (some like TLC should be able to sell a length rather than
a reel).

I don't have the regs to hand so not 100% sure if a CPC (earth) in
this scenario *must* be insulated, but it shows the purpose clearly
which is worthwhile.


It's worse than that. It would have to be 4mm green/yellow

Is that coming from the same rules that govern the size of a lone earth
rod conductor (mechanical strength)?

and follow
the route/cable run of the live conductor unless that circuit is RCD
protected.

I wouldn't even know where to start looking that one up!


It's a while since this one came up at work but I am sure that was the
outcome.

On 09/03/2018 20:33, Tim Watts wrote:
On 09/03/18 19:24, ARW wrote:
On 09/03/2018 11:29, Tim Watts wrote:
On 09/03/18 05:42, SteveE wrote:

I think I'll take this approach as it will be as easy as just taking a
single earth wire down.


You could legitimately take a single earth to the nearest light on
the same circuit that does have an earth. For this, it would be
preferable to use a single insulated earth wire with green/yellow
insulation. Often called "singles" and available from all good
electrical wholesalers (some like TLC should be able to sell a length
rather than a reel).

I don't have the regs to hand so not 100% sure if a CPC (earth) in
this scenario *must* be insulated, but it shows the purpose clearly
which is worthwhile.


It's worse than that. It would have to be 4mm green/yellow

Is that coming from the same rules that govern the size of a lone earth
rod conductor (mechanical strength)?

And supplementary bonding

and follow the route/cable run of the live conductor unless that
circuit is RCD protected.

I wouldn't even know where to start looking that one up!

I am pretty sure that it is in one of my NICEIC snags and solutions
books. I'll take them to work today as I really will be doing nothing at
all when I get there apart from getting paid.


--
Adam

On 10/03/18 07:02, ARW wrote:
and follow the route/cable run of the live conductor unless that
circuit is RCD protected.

I wouldn't even know where to start looking that one up!

I am pretty sure that it is in one of my NICEIC snags and solutions
books. I'll take them to work today as I really will be doing nothing at
all when I get there apart from getting paid.



I've got one of those - I'll have a look...

On 09/03/2018 20:33, Tim Watts wrote:
On 09/03/18 19:24, ARW wrote:
On 09/03/2018 11:29, Tim Watts wrote:
On 09/03/18 05:42, SteveE wrote:

I think I'll take this approach as it will be as easy as just taking a
single earth wire down.


You could legitimately take a single earth to the nearest light on
the same circuit that does have an earth. For this, it would be
preferable to use a single insulated earth wire with green/yellow
insulation. Often called "singles" and available from all good
electrical wholesalers (some like TLC should be able to sell a length
rather than a reel).

I don't have the regs to hand so not 100% sure if a CPC (earth) in
this scenario *must* be insulated, but it shows the purpose clearly
which is worthwhile.


It's worse than that. It would have to be 4mm green/yellow

Is that coming from the same rules that govern the size of a lone earth
rod conductor (mechanical strength)?



543.1.1 The cross-sectional area of every protective conductor SNIP
If the protective conductor
(iii) is not an integral part of a cable, or
(iv) is not formed by conduit, ducting or trunking, or
(v) is not contained in an enclosure formed by a wiring system.

the cross-sectional area shall not be less than 2.5mm^2 copper
equivalent if protection against mechanical damage is provided, and
4mm^2 copper equivalent if mechanical damage is not provided


and follow the route/cable run of the live conductor unless that
circuit is RCD protected.

I wouldn't even know where to start looking that one up!

543.6.1 Where overcurrent protective devices are used for fault
protection, the protective conductor shall be incorporated in the same
wiring system as the live conductors or in their immediate proximity

I do believe that should answer your questions.

I dunno where the RCD bit came into it.

--
Adam

On 10/03/18 10:17, ARW wrote:
On 09/03/2018 20:33, Tim Watts wrote:
On 09/03/18 19:24, ARW wrote:

Is that coming from the same rules that govern the size of a lone
earth rod conductor (mechanical strength)?



543.1.1 The cross-sectional area of every protective conductor SNIP
If the protective conductor
(iii) is not an integral part of a cable, or
(iv) is not formed by conduit, ducting or trunking, or
(v) is not contained in an enclosure formed by a wiring system.

the cross-sectional area shall not be less than 2.5mm^2 copper
equivalent if protection against mechanical damage is provided, and
4mm^2 copper equivalent if mechanical damage is not provided


Ah - thank you

On 10/03/2018 10:17, ARW wrote:
On 09/03/2018 20:33, Tim Watts wrote:
On 09/03/18 19:24, ARW wrote:
On 09/03/2018 11:29, Tim Watts wrote:
On 09/03/18 05:42, SteveE wrote:

I think I'll take this approach as it will be as easy as just taking a
single earth wire down.


You could legitimately take a single earth to the nearest light on
the same circuit that does have an earth. For this, it would be
preferable to use a single insulated earth wire with green/yellow
insulation. Often called "singles" and available from all good
electrical wholesalers (some like TLC should be able to sell a
length rather than a reel).

I don't have the regs to hand so not 100% sure if a CPC (earth) in
this scenario *must* be insulated, but it shows the purpose clearly
which is worthwhile.


It's worse than that. It would have to be 4mm green/yellow

Is that coming from the same rules that govern the size of a lone
earth rod conductor (mechanical strength)?



543.1.1 The cross-sectional area of every protective conductor SNIP
If the protective conductor
(iii) is not an integral part of a cable, or
(iv) is not formed by conduit, ducting or trunking, or
(v) is not contained in an enclosure formed by a wiring system.

the cross-sectional area shall not be less than 2.5mm^2 copper
equivalent if protection against mechanical damage is provided, and
4mm^2 copper equivalent if mechanical damage is not provided

So it doesn't specify it has to follow the cable run of the live conductor?

and follow the route/cable run of the live conductor unless that
circuit is RCD protected.

I wouldn't even know where to start looking that one up!

543.6.1 Where overcurrent protective devices are used for fault
protection, the protective conductor shall be incorporated in the same
wiring system as the live conductors or in their immediate proximity

Is a wiring system in this case the 'whole house'?