Hypothetical question to ease my troubled brow

[Pete999]

Recently there was a post regarding separate cpc sizes, Consider a circuit of socket outlet that need to have high integrity earthing, wired in Twin and Earth as a Radial, where by you need to run the cpc in the form of a ring using the integral cpc of the Tand E and you need to run a further cpc to form the ring.
Easy enough you may say, now in PVC trunking or conduit it is a simple job, same size cpc as the main cpc, say 2.5mm2 as it's protected by mechanical protection ie the trunking or conduit.
What size would you use if you had wired the Radial, not in trunking or conduit but under the floor boards or in a ceiling void as an example, if my memory serves me well it use to be, if the extra cpc was enclosed in trunking or conduit it has Mechanical protection so the min size is 2., however if the cpc is not protected then the min size would be 4mm2, is this still the case or has it recently changed?

 

[telectrix]

think you are correct with that last bit, but i'm not 100% certain. they change the regs more often than their underpants.

 

[westward10]

I think the minimum size of an unenclosed cpc being 4.0mm harks back to the days when solid 2.5mm single conductors were still commonly used. Being solid they would be more prone to breakage when used on exposed supplementary bonding. That could be total garbage but I seem to recall this from somewhere.

 

[Andy78]

543.1.1 says 2.5mm minimum if mechanically protected and 4mm minimum if not. This is in copper or copper equivalent.
The reg also says that this minimum only applies if the cpc is not contained in an enclosure formed by a wiring system.

 

[Pete999]

543.1.1 says 2.5mm minimum if mechanically protected and 4mm minimum if not. This is in copper or copper equivalent.
The reg also says that this minimum only applies if the cpc is not contained in an enclosure formed by a wiring system.

Thanks Andy, thought that was the case. So using another analogy, if you needed to run a cpc for a lighting circuit that had been wired in twin cable, you would run 4mm2?

 

[Andy78]

Thanks Andy, thought that was the case. So using another analogy, if you needed to run a cpc for a lighting circuit that had been wired in twin cable, you would run 4mm2?

Yes if it was unprotected in the building fabric.
I have never done this though, just rewired in t+e as it makes more sense in many ways.

 

[Deleted member 26818]

Insulated and sheathed cable can be 2.5mm2.

 

[buzzlightyear]

it would be better if you take out the existing cable out and replace if possible .you might find it hard to put the 4mm cpc down the conduit or capping if there.

 

[SparkyChick]

Thanks Andy, thought that was the case. So using another analogy, if you needed to run a cpc for a lighting circuit that had been wired in twin cable, you would run 4mm2?

I recently ran a 4mm earth from a socket outlet to a metallic light fitting. The lighting was wired in twin.

As Andy said rewiring would be the best bet, but they had just decorated and newly fitted carpets so it wasn't an option.

 

[Pete999]

I recently ran a 4mm earth from a socket outlet to a metallic light fitting. The lighting was wired in twin.

As Andy said rewiring would be the best bet, but they had just decorated and newly fitted carpets so it wasn't an option.

Nice one SC

 

[buzzlightyear]

I recently ran a 4mm earth from a socket outlet to a metallic light fitting. The lighting was wired in twin.

what about the switch ?

 

[SparkyChick]

what about the switch ?

The switch cable was T+E, so the metallic switch was properly earthed as well. Clearly some work had been undertaken but the main loop of the lighting circuit was twin.

They were advised that I wouldn't be able to continue with the other changes they wanted (more metallic switches, metallic light fittings) and that they should change to double insulated fittings and plastic switches, or go through the upheaval of lifting carpets and boards etc. to bring an earth to the rooms with metallic fittings.

 

[Pete999]

The switch cable was T+E, so the metallic switch was properly earthed as well. Clearly some work had been undertaken but the main loop of the lighting circuit was twin.

They were advised that I wouldn't be able to continue with the other changes they wanted (more metallic switches, metallic light fittings) and that they should change to double insulated fittings and plastic switches, or go through the upheaval of lifting carpets and boards etc. to bring an earth to the rooms with metallic fittings.

Sorry SC how would the switch be earthed if the loop as you say was just a twin cable, or am I being hypercritical?

 

[SparkyChick]

Sorry SC how would the switch be earthed if the loop as you say was just a twin cable, or am I being hypercritical?

Basically, the loop in/out were in twin, so the CPC on the switch wire was just floating until I dragged an earth to the fitting using 4mm from a nearby socket circuit. At that point I properly terminated the switch CPC and lamp body earth strapper to the newly supplied earth.

Not hypercritical, just I probably wasn't completely clear.

 

[Dave OCD]

I've used 1.5mm single green/yellow stranded to earth a kitchen flourescent before, had no 4mm and better than no earth. And it was run in such a way as to avoid damage [under insulation]. And I can't find my tin hat either.

 

[Pete999]

Basically, the loop in/out were in twin, so the CPC on the switch wire was just floating until I dragged an earth to the fitting using 4mm from a nearby socket circuit. At that point I properly terminated the switch CPC and lamp body earth strapper to the newly supplied earth.

Not hypercritical, just I probably wasn't completely clear.

Ahh all clear now, thanks SC

 

[Pete999]

Basically, the loop in/out were in twin, so the CPC on the switch wire was just floating until I dragged an earth to the fitting using 4mm from a nearby socket circuit. At that point I properly terminated the switch CPC and lamp body earth strapper to the newly supplied earth.

Not hypercritical, just I probably wasn't completely clear.

Ahh all clear now, thanks SC, I just knew it wasn't what I was thinking it might be, just my mind is on over drive this evening. On a roll some may say.