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Taking the Ph too CPC as:
Ph cpc
1.0mm 1 mm2
1.5mm 1 mm2
2.5mm 1.5 mm2
4.0mm 1.5 mm2
6.0mm 2.5 mm2
10mm 4 mm2
16mm 6 mm2

Why suddenly do we need a 4mm CPC for a lighting circuit taking into account that the CPC in T&E is only single insulated by way of the sheath and can be run inside a stud wall without any additional protection, seems a bit of a nonsense to me.
 
Not ideal but 4mm cpc from socket to switch is ok. Don't love this as anyone working on sockets circuit with lighting live is inadvertently removing cpc to the switch. Leave a sticker on CU
Agree it’s like going back to the old days…why not use a Class II fitting & switch…& if this is the case on other areas recommend a rewire of the lights..far better job by.
 
Why suddenly do we need a 4mm CPC for a lighting circuit taking into account that the CPC in T&E is only single insulated by way of the sheath and can be run inside a stud wall without any additional protection, seems a bit of a nonsense to me.
It is one more of those never quite explained aspects of the regs, assumed to be due to mechanical strength of it (probably more how it is fixed at the accessories) compared to thinner single-core options.

I had wondered if it was influenced by the standard 4mm / single core 1-2.5mm as you see in T&E but most singles I have seen are stranded?
 
There may possibly be a difference in UK and ROI regs here. If running a separate cpc in attic for a lighting circuit I must use a 2.5mm. If running a separate cpc for a socket circuit I must use a 4mm
It is a difference. BS7671 doesn't have the same reduced requirement for a lighting circuit that ET101/I.S. 10101 does. Therefore the minimum under BS7671 is 4mm^2 regardless of whether it's lighting or otherwise.
 
if the single cpc conductor is sheathed, is that not mechanicall protection of a sort and thus 2.5mm can be used????
 
Nice and clear this isn’t it! The wording is identical for supplementary bonding. I’ve always just used 4mm, don’t know what others do?
 
Nice and clear this isn’t it! The wording is identical for supplementary bonding. I’ve always just used 4mm, don’t know what others do?
There comes a point when it is simpler to have a couple of rules and stock of wire to make life easier, sort of:
  • Supplementary bonding = 4mm
  • Extraneous bonding = 10mm
  • Main earth = 16mm
Which is going to be fine in almost all cases (unless industrial with supplies over 100A of course). Then again, if you have a roll of 16mm to hand and it is 3 flights of stairs to the van then its going to be 16mm all round!
 
if the single cpc conductor is sheathed, is that not mechanicall protection of a sort and thus 2.5mm can be used????
I like your thinking. I've never seen green/yellow with a sheath, but you could use brown or blue sheathed 2.5, or even 1.5, with g/y sleeving at both ends.

Edited to make clear I was thinking of brown or blue insulation, with a grey sheath. Which is in common use. And that I'm not advocating this as a solution, just agreeing it could be done.
 
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I like your thinking. I've never seen green/yellow with a sheath, but you could use brown or blue sheathed 2.5, or even 1.5, with g/y sleeving at both ends.
You could I guess, but who normally has that to hand (outside of some folk building control panels, etc)?
 
Some contractors use sheathed singles all the time for lighting.
Interesting.

I would have thought if you are using singles then it is in trunking or conduit so no sheath needed, otherwise you want a CPC along with it anyway so using T&E, Flexishield, SWA, etc, depending on environment.
 
I remember a few years back visiting two sites for a client where they had two office buildings completely gutted and refurbished. All the wiring for the lighting in the ceiling voids was done in 1.5 6181Y and a separate unenclosed 1.5 cpc. It was all run through spacer bar saddles and was extremely neat, bit like singles in conduit but the conduit had disappeared. I questioned this but have no idea the outcome.
 
Interesting.

I would have thought if you are using singles then it is in trunking or conduit so no sheath needed, otherwise you want a CPC along with it anyway so using T&E, Flexishield, SWA, etc, depending on environment.
There are whole housing estates with the lighting circuits wired in sheathed singles in many areas.
I usually keep a roll of brown or blue 1mm², as it can come in handy if you need to pull in an extra core down to a switch. Though I prefer twin and earth for general use.
 
I don't see anything wrong with using the sheathed singles, I just don't see any advantage in it for the sort of cases I have seen in my own limited experience.
 
You can get 1 core and CPC sheathed cables.
I have seen that advertised but never used it.

For some cases it would make sense to save a bit of unused copper, but equally a lot of systems are as simple to do in T&E or 3&E.

Same argument for the twin-brown T&E for light switches. Theoretically it saves you the time for sleeving the neutral on normal T&E but I don't quite know at what point it makes it worth carrying various different reels to a job. Also it is harder to tell which is which, unlike sleeved T&E where the feed and return are more obvious.
 
An earth wire is totally useless, right up to the point that it is needed, so a broken one may not be noticed, or even if it is seen, the damage may be ignored.
I've always taken the reasons to be exactly for that reason. A 2.5mm2 wire is considered the minimum size that may get damaged if it is reasonably well protected, and a 4.0mm2 wire is considered strong enough to survive if it is strung across a loft, and some clumsy individual trips over it.
 

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