Earthing

[Piotr1000]

Hi guys,is it ok to borrow earth from socket to light switch which is unearthed.It is all about changing plastic switch to metal one.The socket is underneath and probably the easiest way to do this if you do not want to rewire the whole circuit.Thank you in advance for all the answers.

 

[westward10]

Yes but it would have to be 4.0 as I assume it wouldn't be enclosed. Sounds like a whole load of hassle for a switch change, are cpcs absent throughout the circuit.

 

[timhoward]

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

 

[Piotr1000]

Thanks,yes there is no cpc through lighting circuit and customer wants brass switch in that room.

 

[loz2754]

Thanks,yes there is no cpc through lighting circuit and customer wants brass switch in that room.

Technically a 4mm² cable from a nearby circuit would be ok. But not a good idea, as already stated.

I would refuse the job personally. Too much risk of it going wrong. In fact I did, a few months ago, exactly the same type of request. The customer was fine with my refusal once I explained the risks.

 

[Zerax]

What's the logic/regs on using 4mm ?

 

[loz2754]

What's the logic/regs on using 4mm ?

Minimum size of CPC allowed unless part of another cable, or in conduit or trunking

 

[LastManOnline]

What's the logic/regs on using 4mm ?

It's subjective logic . A 2.5mm would be perfectly fine from an electrical point of view. From a mechanical protection point of view though the powers that be, deem a "lone" wire needs to be larger than it would be if enclosed in a cable. In principle though a mechanically secured 2.5mm (or even 1.5mm) would be perfectly safe.

 

[brianmoooore]

Last time I looked at the regs., 2.5mm2 is fine as long as its enclosed, as inside a wall cavity. 4.0mm2 is the minimum for an exposed cable.

 

[timhoward]

Last time I looked at the regs., 2.5mm2 is fine as long as its enclosed, as inside a wall cavity. 4.0mm2 is the minimum for an exposed cable.

I didn’t think “contained in an enclosure formed by a wiring system” included inside a wall. Section 2 definitions for “enclosure” and “wiring system” seem to agree?
So I think we end up with 4mm for non mechanically protected conductor.
It’s still far too much hassle for a switch change however we read the regs!

 

[LastManOnline]

I didn’t think “contained in an enclosure formed by a wiring system” included inside a wall.

You are correct in what you state. But this discussion highlights the failings in some of our regs. We are permitted to run a single 2.5mm earth along with 2 x 1.5 pvc/pvc singles from an attic down through a stud partition to a light switch. Yet in a similar stud on the opposite side of the room with an unearthed switch (OP, s scenario), we are now obliged to run a 4mm from a socket to said switch. Despite the exact same physical conditions. Something does not add up here!!

 

[timhoward]

You are correct in what you state. But this discussion highlights the failings in some of our regs. We are permitted to run a single 2.5mm earth along with 2 x 1.5 pvc/pvc singles from an attic down through a stud partition to a light switch.

I admit to being rather confused now! Tin hat ready....
If singles, I'm assuming you mean in some form of containment for double insulation which therefore isn't the same conditions and tail end of 543.1.1 wouldn't apply, and cpc can just match the line conductor and be 1.5mm.
If you meant a loose 2.5mm cpc doesn't that contravene the same regulation as it's not integral, not in conduit/trunking/ducting and not in enclosure/wiring system so needs to be 2.5 if mechanically protected or 4 if not?

 

[brianmoooore]

IMHO, inside the cavity of a stud wall is mechanically protected.

 

[timhoward]

IMHO, inside the cavity of a stud wall is mechanically protected.

Ah ok, I see how you got to 2.5mm now.
I thought the external influences bit (Impact) waffled about mechanical protection sufficient to protect against nails and screws or something similar. But I might have dreamed that up.
I still think the customer in this case needs to be told "sorry, no earth, no metal light switch"

 

[brianmoooore]

I still think the customer in this case needs to be told "sorry, no earth, no metal light switch"

I'm not disagreeing with that bit. The wiring's likely to be at least half a century old.

 

[LastManOnline]

I admit to being rather confused now! Tin hat ready....
If singles, I'm assuming you mean in some form of containment for double insulation which therefore isn't the same conditions and tail end of 543.1.1 wouldn't apply, and cpc can just match the line conductor and be 1.5mm.
If you meant a loose 2.5mm cpc doesn't that contravene the same regulation as it's not integral, not in conduit/trunking/ducting and not in enclosure/wiring system so needs to be 2.5 if mechanically protected or 4 if not?

I realise that I could have been a little clearer in my description. We may use a 1.5mm T&E (3 cores in one cable) or two 1.5 single pvc/pvc plus a 2.5mm earth (3 individual cores) to wire a lighting circuit. I may run these individual cores along an attic and down a stud partition to a switch. And it's all hunky dorrey.
Now the OP is required according to regs to run a 4mm earth (not 2.5mm) in a similar stud partition from a socket to a switch. Does, nt make sense to me

 

[timhoward]

or two 1.5 single pvc/pvc plus a 2.5mm earth (3 individual cores) to wire a lighting circuit. I may run these individual cores along an attic and down a stud partition to a switch. And it's all hunky dorrey.

I'm probably frustrating you but this still isn't going ding in my head.
I'm reading that as two double insulated singles, and one single insulated 2.5mm cpc. If I've got that wrong ignore the rest!
I'm happy to be corrected but my understanding is that the salient points are:
1) whether the sperate cpc is mechanically protected if loose in the attic (if no 4mm needed?)
2) While I take 522.6.204 [iv] to mean that a stud wall isn't mechanical protection, if a view was held that it is sufficient mechanical protection (as expressed by others) and the three cores are all loose in the wall then cpc can be 2.5mm. And so could the OP's case.

 

[nicebutdim]

I realise that I could have been a little clearer in my description. We may use a 1.5mm T&E (3 cores in one cable) or two 1.5 single pvc/pvc plus a 2.5mm earth (3 individual cores) to wire a lighting circuit. I may run these individual cores along an attic and down a stud partition to a switch. And it's all hunky dorrey.
Now the OP is required according to regs to run a 4mm earth (not 2.5mm) in a similar stud partition from a socket to a switch. Does, nt make sense to me

This would be a single with CPC or single and separate CPC?


Edit: Cross posted with above.


Aslo; as it'll take me a considerable time to find the correct regulation - does BS7671 stipulate mechanical protection of CPC or suitable containment?

 

[timhoward]

Aslo; as it'll take me a considerable time to find the correct regulation - does BS7671 stipulate mechanical protection of CPC or suitable containment?

In summary we only get into this territory if iii,iv and v apply, and then we end up with 2.5 if mechanically protected and 4 if not. So if 'contained' by either of the 3 methods the normal cpc sizing stuff can apply.
(My current view is that the wall is not enclosure/wiring system and not mechanical protection)

 

[LastManOnline]

I'm probably frustrating you but this still isn't going ding in my head.
I'm reading that as two double insulated singles, and one single insulated 2.5mm cpc. If I've got that wrong ignore the rest!

Not at all. And your description of the cables is spot on.

I'm happy to be corrected but my understanding is that the salient points are:
1) whether the sperate cpc is mechanically protected if loose in the attic (if no 4mm needed?)

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

2) While I take 522.6.204 [iv] to mean that a stud wall isn't mechanical protection, if a view was held that it is sufficient mechanical protection (as expressed by others) and the three cores are all loose in the wall then cpc can be 2.5mm. And so could the OP's case.

I would agree with all of the above. But I must say in conclusion that it's one of these "splitting hairs" discussions. "Should it be 4mm or should it be 2.5mm"? Bearing in mind that it's all based on a concept of a perceived mechanical threat to the integrity of the cpc. (completely unexplained in the regs as far as I am aware) What could happen to threaten a 2.5 cpc but would allow a 4mm cpc to remain unharmed? I think if I was a member the electrical fraternity responsible for producing the electrical regs I would not want it to be part of my legacy

 

[Mike Johnson]

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.

 

[cliffed]

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.

 

[pc1966]

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?

 

[Risteard]

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.

 

[telectrix]

if the single cpc conductor is sheathed, is that not mechanicall protection of a sort and thus 2.5mm can be used????

 

[timhoward]

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?

 

[pc1966]

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!

 

[loz2754]

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.

 

[pc1966]

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)?

 

[loz2754]

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. I edited my other post to make clear I meant grey sheath, with brown or blue cores.

 

[pc1966]

A quick check on Superlec site has:

• 1.5mm sheathed 6181Y at £21.91 for 100m (+VAT)
• 2.5mm sheathed for £43.25
• 4mm single 6491X for £36.79

 

[pc1966]

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.

 

[westward10]

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.

 

[loz2754]

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.

 

[pc1966]

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.

 

[loz2754]

otherwise you want a CPC along with it anyway

You can get 1 core and CPC sheathed cables.

 

[westward10]

You can get 1 core and CPC sheathed cables.

6241Y.

 

[pc1966]

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.

 

[LastManOnline]

if the single cpc conductor is sheathed, is that not mechanicall protection of a sort and thus 2.5mm can be used????

Bit late back to the party here. Just curious to know if anyone knows WHY this extra mechanical protection is required for an unenclosed earth? or WHAT circumstances merit it?

 

[brianmoooore]

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.

 

[LastManOnline]

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.

That is the only scenario I can envisage, although my thought was that rather than a "clumsy individual" tripping over and dragging an earth wire, (though conceivable) I could more easily picture a suitcase been retrieved from the attic for the annual holiday and dragging a cable with it. In whatever scenario though I cannot imagine a 4 mm earth providing any advantage over a 2.5mm earth.
In fact I could not possibly see someone breaking a 2.5mm earth by dragging it with their foot, no matter how hard they tried. It would surely be pulled free from the ceiling rose or switch it was connected to before physically breaking itself.

 

[LastManOnline]

I've always taken the reasons to be exactly for that reason......... 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.

I think all of us would be inclined to agree that such a scenario must be the reasoning, be it "a clumsy individual" or the "suitcase" scenario. Then by definition there should be no requirement for having to increase the earth size when running the cable in a ceiling void or a wall cavity, stud etc

 

[timhoward]

I think all of us would be inclined to agree that such a scenario must be the reasoning, be it "a clumsy individual" or the "suitcase" scenario. Then by definition there should be no requirement for having to increase the earth size when running the cable in a ceiling void or a wall cavity, stud etc

It's been helpful discussing this - thanks.
I'm (now) inclined to agree that "mechanical protection" in this context could be taken to mean "no one can easily get to it", so at least the smaller size can be used.
In other contexts in the regs the level of "mechanical protection" is more precisely specified, e.g. "be provided with mechanical protection against damage sufficient to prevent penetration of the cable by nails, screws and the like".
The fact that the earthing section (and the supplementary bonding section) don't define the level of mechanical protection probably gives us license to apply common sense.

 

[Mike Johnson]

Today we mourn the passing of a beloved old friend, Common Sense, who has been with us for many years. No one knows for sure how old he was, since his birth records were long ago lost in bureaucratic red tape. He will be remembered as having cultivated such valuable lessons as:

• Knowing when to come in out of the rain;
• Knowing not to stick a screwdriver into a socket;
• Why the early bird gets the worm;
• Life isn't always fair; and
• Maybe it was my fault.

Common Sense lived by simple, sound financial policies (don't spend more than you can earn) and reliable strategies (adults, not children, are in charge).

His health began to deteriorate rapidly when well-intentioned but overbearing regulations were set in place.

Reports of a 6-year-old boy charged with sexual harassment for kissing a classmate; teens suspended from school for using mouthwash after lunch; and a teacher fired for reprimanding an unruly student, only worsened his condition.

Common Sense lost ground when parents attacked teachers for doing the job that they themselves had failed to do in disciplining their unruly children.

It declined even further when schools were required to get parental consent to administer sun lotion or an aspirin to a student; but could not inform parents when a student became pregnant and wanted to have an abortion.

Common Sense lost the will to live as the churches became businesses; and criminals received better treatment than their victims.

Common Sense took a beating when you couldn't defend yourself from a burglar in your own home and the burglar could sue you for assault.

Common Sense finally gave up the will to live, after a woman failed to realise that a steaming cup of coffee was hot. She spilled a little in her lap, and was promptly awarded a huge settlement.

Common Sense was preceded in death, by his parents, Truth and Trust, by his wife, Discretion, by his daughter, Responsibility, and by his son, Reason.

He is survived by his 4 stepbrothers;

• I Know My Rights
• I Want It Now
• Someone Else Is To Blame
• I'm A Victim

Not many attended his funeral because so few realised he was gone. If you still remember him, pass this on. If not, join the majority and do nothing.

 

[LastManOnline]

In other contexts in the regs the level of "mechanical protection" is more precisely specified, e.g. "be provided with mechanical protection against damage sufficient to prevent penetration of the cable by nails, screws and the like".

Agreed. There appear to be 2 concepts of mechanical protection catered for in the regs.
The first is what you mention above. It's easy for us to relate to the need for protection of cables against damage from penetration, impact etc.
The second is a little more abstract and is based on the perception of the powers that be, for a need for greater mechanical strength in the earthing conductor. This perception is a vague and unexplained (in my experience at least) and is the reason for this thread.
For example, I have seen the earthingc cable to the earth electrode go from 2.5mm to 4mm to 6mm to 10mm.
2.5mm is all that's required electrically. . So what's changed over the years that's required the enlarged size? Soil conditions are the same. The earth electrode is the same. It's the "perception" among the powers that be that's altered. It would be helpful to know what fed into that perception

 

[littlespark]

A bit late in the day, but how about this;

OP wants to take a cpc from a socket to earth a metal switch when there is no cpc on the lights?
Suggestions of a 4mm unsheathed, unprotected single core. Ok. That makes sense and I’m sure it’s been done like that many times.

Going to the lesser size extreme, could a length of 1.5 t&e, or 6241 single and earth be used, and the live cores cut short?
The cpc would be no lesser size than it would be if the lights were wired in t&e, and it’s sheathed.

the remarks about whether cables are mechanically protected in a stud wall? No, they’re not… they would catch on splintered wood, sticking out nails and whatever else the wood butcher decided to leave in there…

apologies of this has already been covered, just scan read through previous messages.

 

[Mike Johnson]

Am I loosing the plot, why can't the OP use 6491X in GY in what ever c\c he wants, we just seem to be making the whole thing very complicated?