Using the earth wire in a switch

[motorbiking]

I've just replaced the external PIR wall lights and found the junction box that has been used to feed the single PIR sensor switch. It confused the hell out of me, until I'd worked out they had used the earth cable as live for the switch (rather than using two bits of cable or a 3 core and earth). I've no idea if the old PIR needs an earth, but surely that isn't safe?

Is this common/acceptable? I will likely re-cable it and replace it with 2 cables. Just thought it was odd.

 

[EFLImpudence]

If it is three-core flex, i.e. with the 'earth wire' insulated throughout its length, then it's fine (not so for Twin & bare Earth).

It should, though be identified - as you have discovered.


A regulation states that a CPC (earth wire) should be run to all points even if not required - just in case one is needed.

 

[motorbiking]

Yes it was flex external grade flex rather than twin and earth. Further pain as the new style push fit junction boxes don’t like stranded cable. So I ended up putting a choc block in with the correct cable colours. There was also a single live running to the other side of the garage with local neutral. I can see the logic, but it’s not easy to follow when cables aren’t run how you expect. Would hardly be any effort to run both L and N to the same box.

 

[mattylad]

If the earth wire is green/yellow then it is not fine!
A green/yellow wire should not be used for anything except earthing/cpc.

Your suggestion to replace the cable is the way to go.

 

[plugwash]

they had used the earth cable as live for the switch (rather than using two bits of cable or a 3 core and earth). I've no idea if the old PIR needs an earth, but surely that isn't safe? Is this common/acceptable?

As I understand it, there are several issues here.

1. Is the conductor adequately insulated and sheathed? for T&E the answer is clearly no, for flex the answer is generally yes.
2. Is the conductor correctly identified? the wording in BS7671 is a little unclear, and there was a thread arguing about this a while back, the NICEIC argue that it is ok to use a green/yellow core in a multicore cable for something else if it is oversleeved, not everyone agrees with that interpretation https://www.diynot.com/diy/threads/niceic-snags-and-solutions-book.549589/page-2.
3. Have the BS7671 requirements to take a CPC (earth) to every point and every accessory been satisfied? If the PIR is not "current using equipment" then it's an accessory and needs a CPC taken to it. If the PIR is current using equipment then the termination of the fixed wiring feeding it is a point. You could argue that a short loop of flex from an outlet box is not fixed wiring, but once you start fixing wiring to the building, running it through holes in the building, running it through conduits attatched to the building etc then I think it's pretty clearly fixed wiring.

Further pain as the new style push fit junction boxes don’t like stranded cable.

Pure push-in terminals don't like fine stranded wire, because it's not rigid enough to force it's way into the terminal. Push button terminals like in the Hager/Ashley J803/J804 will accept it though it can be a bit fiddly as you have to hold the very stiff button down while you insert the wire. Lever terminals like the Wago 221 and 222 series are absolutely fine with fine stranded wire.

The classic Wagobox doesn't really give enough room to work with when used with lever terminals, but the Wagobox 221-4 solves that problem with 3 slots rather than 2 and with a special position for a 5 way block for the earths.

 

[JohnW2]

If the earth wire is green/yellow then it is not fine! A green/yellow wire should not be used for anything except earthing/cpc.

As EFLI has said, as far as the regs are concerned (and provided it is not a G/Y single), it is 'compliant' to use a G/Y-insulated conductor as a live conductor, provided it is identified as such (e.g. by over-sleeving) at both ends.

However, as EFLI also wrote, the catch is that there is a reg which requires an earth/CPC to be run to every 'point' (including accessories such as a switch) in an installation. Hence, the overall situation of using a G/Y for some other purpose (with appropriate identification) is, strictly speaking, not compliant unless an earth/CPC gets to the switch in some other cable (or other conductor).

Your suggestion to replace the cable is the way to go.

That is obviously the ideal, and the 'nice/decent' solution. However, I suspect that a significant proportion of people have 'done the other thing' at least occasionally, in the name of convenience/expediency!

Kind Regards, John

 

[mattylad]

I really do not care what 7671 say about it if it can somehow allow it's use.
60204 certainly bans its use for anything else.
To use the earth/cpc for any voltage is IMHO a stupid thing to do, it's prompting someone else to get a shock.

Anyone that does this is IMHO being a damn cowboy/lazy barstewerd.
My MD suggested doing it ion a job once, I told him in no uncertain words not to - he did not after that.

 

[JohnW2]

I really do not care what 7671 say about it if it can somehow allow it's use. 60204 certainly bans its use for anything else. To use the earth/cpc for any voltage is IMHO a stupid thing to do, it's prompting someone else to get a shock.

I can understand (and sympathise with) that view, but I think it's also appropriate to inform people of what BS7671 actually says/requires/allows - given how obsessed some people are about compliance/non-compliance with BS7671 in other contexts.

How would you feel if (as is quite possible) a G/Y-insulated conductor was over-sleeved with heatshrink at its ends in such a manner that no G/Y (only the sleeving colour) were visible?

Kind Regards, John

 

[mattylad]

What about the rest of it's length?
IMO should not be used for anything else - end of.

 

[Simon35]

I really do not care what 7671 say about it if it can somehow allow it's use.
60204 certainly bans its use for anything else.
To use the earth/cpc for any voltage is IMHO a stupid thing to do, it's prompting someone else to get a shock.

Anyone that does this is IMHO being a damn cowboy/lazy barstewerd.
My MD suggested doing it ion a job once, I told him in no uncertain words not to - he did not after that.

What 60204 says is irrelevant in this instance, though.

 

[JohnW2]

What about the rest of it's length?

The 'not normally visible' insulation would obviously remain G/Y.

In the sort of situations in which this is most likely to be done, it is incredibly unlikely that someone would 'break into' a length of flex with a view to connecting things to the conductors. However, even if they did, to assume (without verification) that a G/Y-insulated conductor was a CPC/'earth' would not be much (if at all) less silly than to assume (without verification) that a blue- or black-insulated conductor (which might be over-sleeved at its terminations) was a neutral.

IMO should not be used for anything else - end of.

As I said, I can understand, and sympathise with, that "O", even though I believe any risk to be minimal. It is certainly not a practice that I would advocate, or often (if ever) use myself, but nor would I be particularly scathing about anyone who did.

Kind Regards, John

 

[Gasguru]

Glad to see your regs are as shambolic as the Gas regs
We're the most regs on Earth but so often written to be ambiguous (on purpose).

 

[JohnW2]

Glad to see your regs are as shambolic as the Gas regs We're the most regs on Earth but so often written to be ambiguous (on purpose).

There's a lot which is less-than-ideal sometimes ambiguous, in other cases seemingly 'plain wrong'!) about BS76671 but, in terms of the issue were discussing, although many/most of us regard it as a fairly undesirable practice, BS7671 is pretty clear and unambiguous in allowing oversleeving (or otherwise 'identifying') of a G/Y-insulated conductor at its terminations (for use as something else), provided only that it is not a 'single' G/Y.

Kind Regards, John