Using cpc as neutral

[Andy78]

Thanks for the regs help! I can't think of a circuit without a cpc either, that would certainly not comply and i have not suggested it.


"Where overcurrent protective devices are used for fault protection, the protective conductor shall be be incorporated into the same wiring system as the live conductors or in their immediate proximity."
Same wiring system, but not necessarily the same cable, as i understand it.
The latter reg is talking about the special case of rings which are not under discussion but it states that the cpc should also be a ring.

Same wiring system does not necesarilly mean the same cable, but can do, and in the case of the question posed here, a multicore cable was mentioned, which is the wiring system in this case.

Rings are not under discussion, but they might be as the OP gave sparse information. You did bring up quite a few points yourself which were not under discussion.

 

[Richard Burns]

The most relevant regulation for providing a cpc to a circuit that is protected by ADS is probably 411.3.1.1 fourth paragraph: a circuit protective conductor shall be run to and terminated at each point in wiring and at each accessory except a lampholder having no exposed conductive parts and suspended from such a point.

 

[johnduffell]

Same wiring system does not necesarilly mean the same cable,

Agree, that's basically what i meant when i was saying each cable didn't have to have a cpc as long as there was one available at every termination.

You did bring up quite a few points yourself which were not under discussion.

Sorry, i didn't mean to, as far as i can see from rereading my posts every single one was either addressing the question the op originally posted or attempting to clarify information provided by others, together with informative examples for further clarification.

 

[Rpa07]

‘Or Immediate proximity’ I read as 6491 singles in conduit or trunking taking the same complete route as both or all lives. This is in order to terminate at each accessory.

Thanks for the regs help! I can't think of a circuit without a cpc either, that would certainly not comply and i have not suggested it.


"Where overcurrent protective devices are used for fault protection, the protective conductor shall be be incorporated into the same wiring system as the live conductors or in their immediate proximity."
Same wiring system, but not necessarily the same cable, as i understand it.
The latter reg is talking about the special case of rings which are not under discussion but it states that the cpc should also be a ring.

 

[Adam W]

No offence, unfortunately i can't do any more detailed explanation at that point! But i was addressing a part of your post not your usual excellent standards!
I do think that when people are asking this kind of question, we should be precise about why it's not allowed, and appeal to both the regs and to common sense specifically where appropriate.i think a lot of things that are uncommon in domestic are actually within the regs, and sometimes the boundary between what is allowed and what isn't seems to defy common sense, but as long as we discuss properly we will help everyone to learn something new.

There are reasons we work to a standard, primarily for safety.
I don't believe it is helpful for anyone, especially someone who has just begun learning about the subject to routinely challenge the way everything is done seemingly in an attempt to push boundaries and think outside the box.

Unconventional installation methods, or as I call it "doing it weird" is a tell-tale sign of someone who doesn't know what they're doing; the more I've learned about electrics the more I've been able to appreciate that a lot of consideration and knowledge goes into the writing of BS7671 and that deviating from the standard should only be done in exceptional circumstances and not as a norm "because you can".

In this instance the CPC in a T&E is not suitable to use as a neutral because it is not the same size as the other (line) conductors and could overheat, the outer sheath of a T&E is intended for mechanical protection and not electrical insulation; sleeving is intended for identification and not electrical insulation - it is not fixed to the conductor so can easily slide off to reveal a live part where the outer sheath is stripped back or could fall off altogether.

This is basic stuff.

As a minimum it should be enough to say that we don't do it, at a push that regs forbid it, and leave it as that.

 

[johnduffell]

‘Or Immediate proximity’ I read as 6491 singles in conduit or trunking taking the same complete route as both or all lives. This is in order to terminate at each accessory.

Interesting didn't think about that re wiring systems:, so if two 3 core flexes routed together you could do it in one of them but not if they went via different routes? Or is that only if they are in the same containment rather than being sheathed?
That's more strict then i was originally thinking.

 

[Rpa07]

@johnduffell you call it strict - I call it safe, as all installations should be.
We all need to sleep at night and installing safely to regulations, that are set in place for a reason, make my pillow feel like a cloud!

 

[johnduffell]

.

@johnduffell you call it strict - I call it safe, as all installations should be.
We all need to sleep at night and installing safely to regulations, that are set in place for a reason, make my pillow feel like a cloud!

I meant strict in the mathematical sense of more tightly defined, not in the sense that i disagreed with it.
Anyway thanks for helping!

 

[Colin33]

Hi - I'm struggling to think of installing a circuit without a cpc. Some have been installed historically, but I don't think that's been since the '60s. As I've started to practice for the regs exam ( ) the two regs I could find that seem relevant are 543.6.1 and 543.2.9 .

Not so long ago I was wiring up an underfloor heating system. The controls for the heating were all downstairs, along with domestic hot water controls. The zone valves, along with the water tank and gas boiler were all in the loft. To complicate things, there was also a solar thermal input and a 'warm loop' system. I had a twin n earth cable feeding the system and supplying a large junction box with its cpc. I also had two 5 core flex going up to the JB in the loft. Therefore, I had two green/yellow cores which were not required as a cpc. I did need to use one of these as a live conductor and oversleeved it at each end accordingly. Isn't this an example of when an unused cpc is legitimately used as a live conductor?

 

[davesparks]

Not so long ago I was wiring up an underfloor heating system. The controls for the heating were all downstairs, along with domestic hot water controls. The zone valves, along with the water tank and gas boiler were all in the loft. To complicate things, there was also a solar thermal input and a 'warm loop' system. I had a twin n earth cable feeding the system and supplying a large junction box with its cpc. I also had two 5 core flex going up to the JB in the loft. Therefore, I had two green/yellow cores which were not required as a cpc. I did need to use one of these as a live conductor and oversleeved it at each end accordingly. Isn't this an example of when an unused cpc is legitimately used as a live conductor?

No, that’s an example of very poor workmanship, the correct cables should have been installed for the job.

Where were the 5 core cables coming from? Did that point not need a cpc?

 

[johnduffell]

junction box with its cpc. I also had two 5 core flex going up to the JB in the loft

So based on the discussion so far, whether it's within the regs depends whether the pair of flexes are run together in close proximity.

the correct cables should have been installed for the job

Youre assuming in your assertion that those are not the correct cables. According to the earlier discussion, as long as the cables are in close proximity it looks like they are correct.

Where were the 5 core cables coming from? Did that point not need a cpc?

He said the large junction box, which had a cpc:

twin n earth cable feeding the system and supplying a large junction box with its cpc

 

[Adam W]

.

I meant strict in the mathematical sense of more tightly defined, not in the sense that i disagreed with it.
Anyway thanks for helping!

Yes. All of the figures we work to were calculated by the boffins at the IET and are given for a reason - the maximum Ze on a particular system, minimum CSA of cables, maximum tripping times, touch voltage, CSA of bonding conductors... They don't just pluck figures out of thin air for you to come along and decide it's easier to make a deviation.

As far as I'm concerned the electronics inside my mobile phone works by means of witchcraft, I mean I have absolutely no idea how it works, it's like electronic circuits and that. I don't need to know how it works and I'm not really going to benefit from doing a degree in electronics just so that I can say I understand how it works, the explanation of 'witchcraft' is good enough for me as long as I can make phone calls and send texts.
Same with the maths in the regs book - just because you don't understand it doesn't mean you can deviate, in fact that's more of a reason not to, but for the purposes of pulling in circuits you need to accept that the figures work.

 

[elsparko]

Not so long ago I was wiring up an underfloor heating system. The controls for the heating were all downstairs, along with domestic hot water controls. The zone valves, along with the water tank and gas boiler were all in the loft. To complicate things, there was also a solar thermal input and a 'warm loop' system. I had a twin n earth cable feeding the system and supplying a large junction box with its cpc. I also had two 5 core flex going up to the JB in the loft. Therefore, I had two green/yellow cores which were not required as a cpc. I did need to use one of these as a live conductor and oversleeved it at each end accordingly. Isn't this an example of when an unused cpc is legitimately used as a live conductor?

a yellow/green sleeved conductor should only be used as a cpc, i think the regulations are pretty cut and dry on this subject

 

[johnduffell]

a yellow/green sleeved conductor should only be used as a cpc, i think the regulations are pretty cut and dry on this subject

True but when he said "oversleeved accordingly" presumably that wouldn't be oversleeved green yellow over green yellow insulation

 

[Toneyz]

We all know he means oversleeve with brown or blue sleaving to use it as a live or neutral.

 

[Toneyz]

We all know he means oversleeve with brown or blue sleaving to use it as a live or neutral.

I was hoping that the idiots that were using a CPC in a T&E/3 core and E cable as live or neutral had well and truly gone from the profession.

 

[elsparko]

True but when he said "oversleeved accordingly" presumably that wouldn't be oversleeved green yellow over green yellow insulation

and what happens when that brown or blue oversleeve falls off the green yellow core of the flex and someone assumes that naturally its an earth for something?

multicore exists for a reason, this reason.

 

[Rpa07]

and what happens when that brown or blue oversleeve falls off the green yellow core of the flex and someone assumes that naturally its an earth for something?

multicore exists for a reason, this reason.

In any situation, that is where voltage indicators come into the part of our job @elsparko - assuming makes an ‘Aaargh that wire is live!’

 

[elsparko]

In any situation, that is where voltage indicators come into the part of our job @elsparko - assuming makes an ‘Aaargh that wire is live!’

its still not to be used as a live conductor, oversleeving or not.

 

[Rpa07]

That’s not what you implied though @elsparko was it? Safety first, the world second!

 

[elsparko]

That’s not what you implied though @elsparko was it? Safety first, the world second!

if its used as a neutral you wont get voltage across it at all times will you though? which is what this thread is about , "live conductor" is a vague-ish term for both live/switched lives and neutrals in use.

 

[elsparko]

That’s not what you implied though @elsparko was it? Safety first, the world second!

if its used as a neutral you wont get voltage across it at all times will you though? which is what this thread is about , "live conductor" is a vague-ish term for both live/switched lives and neutrals in use, if its not in use and you test between the neutral and cpc its going to be 0v

so when the sleeving falls off and he tests it between a live (brown) and the percieved earth he may well get the 240v, but its not to earth, its to neutral, and he connects that bugger up to earth, then pop goes the fuse

 

[johnduffell]

and what happens when that brown or blue oversleeve falls off the green yellow core of the flex and someone assumes that naturally its an earth for something?

multicore exists for a reason, this reason.

doors over sleeving fall off often?
I think this thread is on a bit of a repeat, i still agree it wouldn't be great design for new work but unless the regs are badly drafted, they consider over sleeving is sufficient to reliably identify conductors at their ends, although being identified throughout is preferable

 

[elsparko]

doors over sleeving fall off often?
I think this thread is on a bit of a repeat, i still agree it wouldn't be great design for new work but unless the regs are badly drafted, they consider over sleeving is sufficient to reliably identify conductors at their ends, although being identified throughout is preferable

well it must do the amount of cpcs i come across with none

 

[Richard Burns]

The identification of the cpc in a twin and earth cable as a live conductor is not permissible because the cpc is not of sufficient csa to avoid overheating in all cases and the cpc is not provided with insulation which is the basic protection required for live conductors.

The identification of a single core cable that is coloured green and yellow along its length cannot be oversleeved as a live conductor because the cable could be accessed at a non termination part of the circuit, such as when opening a trunking lid, and then misidentified as a cpc.

The identification of any green and yellow insulated core of a multicore cable as a live conductor is not good practise as inadvertent misidentification of a core as an earth conductor can be dangerous to life. It is not expressly forbidden by the regulations though.

Where a circuit is protected by ADS a cpc must be present at every point, this cpc can be part of a cable (as a core or armour) or can be a separate cable adjacent to the live conductors, such as singles in containment, a separate earth run beside an SWA or a single core cable run beside a multicore cable. There should be a cpc adjacent to every part of the circuit at any position to allow the possibility of a fault on a live conductor being directed to earth more easily.

I am sure there used to be a requirement for identification of cores to be irremovable without a tool, but I can find no reference for this, maybe just dreamt it.

 

[Darkwood]

Coming at this from a different angle, the sheath on a T&E cable is there for environmental protection, its purpose is to resist what the cable may be subjected to in normal storage and installation conditions, the fact it also has insulating properties is mostly for redundancy.
The copper itself has an insulating sheath which is designed for the primary purpose of insulation, it may also posses many of the qualities of the sheath too but this can change dramatically when you look into specialised cables.
The fact that the earth in T&E has no basic insulation in itself should suggest it cannot be utilised as a functional live conductor, simply dressing the ends is not adequate because you assume and rely on the fact the sheath is designed to the exact same properties of that of the insulation of the other cores, this is of course ignoring other obvious issues like difference in csa etc.

I can understand reaction to such a question as it would seem very strange not to realise it is a definite no no, but we all start somewhere and if we don't ask what may seem a very basic question to seasoned sparks then we hinder the next generation from becoming fully knowledged and competent trade persons.
The opening question to be fair expressed the understanding it wasn't safe but was only asking for other reasons, maybe he was asked this very question and on thinking about a reply wondered if there was a better way to explain or show why it is indeed a no no.

 

[johnduffell]

Excellent post, thanks!

cpc in a twin and earth cable as a live conductor is not permissible because the cpc is not of sufficient csa to avoid overheating in all cases and the cpc is not provided with insulation

I agree with the latter point about insulation, but regarding the csa that's no reason to disallow it alone. Look at 6a lighting circuit wired in 1.5 or 1mm t&e. That would be no problem purely on the basis of csa.
I think it could be more correctly expressed as the CSA would need to be taken into account.
However before i get misquoted, i don't think the insulation issue is surmountable anyway.

There should be a cpc adjacent to every part of the circuit at any position to allow the possibility of a fault on a live conductor being directed to earth more easily.

That's interesting, i thought it was just to make it easy to understand which CPC is protecting the circuits present, and reduce the risk of a separate Cpc being damaged or removed.
What you you mean by diverted to earth more easily? By who or what?

 

[Richard Burns]

Excellent post, thanks!
I think it could be more correctly expressed as the CSA would need to be taken into account.

This is why I said in all cases, if someone looks at a cable and sees 1.5/1.0 T&E then they may decide they can convert this circuit to a 20A circuit, however if at a later part of the circuit the cpc is used as a live conductor it may overheat.

That's interesting, i thought it was just to make it easy to understand which CPC is protecting the circuits present, and reduce the risk of a separate Cpc being damaged or removed.
What you you mean by diverted to earth more easily? By who or what?

There are many good reasons for an adjacent cpc, identification is useful, prevention of removal because it is unidentified is useful, damage is probably not so relevant as it could be damaged anywhere.
If you were to cut through a standard multicore cable then you would contact the cpc at some point, if you were to cut through a cable with no cpc but with one attached to the outside then you would also contact the cpc, if it were 2m away it is less likely there would be an earth path available to provide ADS at the point of damage.

 

[Pete999]

68 post when we all know it's not permissible, just don't do it end of, nothing to discuss really is there?

 

[Toneyz]

68 post when we all know it's not permissible, just don't do it end of, nothing to discuss really is there?

What reg is this Pete?

 

[Pete999]

What reg is this Pete?

Not got a clue, common sense really Ant

 

[Toneyz]

Not got a clue, common sense really Ant

Agree good workmanship/common sense etc. I am sure there was a reg that said could not be used but can't seem to find it now.

 

[Colin33]

No, that’s an example of very poor workmanship, the correct cables should have been installed for the job.

Where were the 5 core cables coming from? Did that point not need a cpc?

The 5 core cables were coming from the controls downstairs, as already explained. As was the cpc contained within supply cable. I'll have to remember to ask the wholesaler for a 5 core which doesn't contain a green/yellow covered conductor next time.

 

[Colin33]

and what happens when that brown or blue oversleeve falls off the green yellow core of the flex and someone assumes that naturally its an earth for something?

multicore exists for a reason, this reason.

Firstly, how can it when it's terminated? And in this case it's highly unlikely to because I use heat shrink. Takes time, but I believe it's good practice to do so.

 

[Colin33]

I was hoping that the idiots that were using a CPC in a T&E/3 core and E cable as live or neutral had well and truly gone from the profession.

I agree, hopefully they have.

 

[Toneyz]

The 5 core cables were coming from the controls downstairs, as already explained. As was the cpc contained within supply cable. I'll have to remember to ask the wholesaler for a 5 core which doesn't contain a green/yellow covered conductor next time.

You can get YY flex or 7 core flex.

 

[Colin33]

You can get YY flex or 7 core flex.

I'm not sure the wholesaler has 7 core flex, needed some to wire up a Rayburn once and it was a nightmare to find. That was a few years ago mind. Not heard of YY flex, does it not have a green/yellow core? Anyway, I'm sure there's nothing wrong with using the cpc in a multicore flex as long as it's identified properly, and it's not specifically prohibited in 7671 like an un-insulated cpc is. I go to great lengths to ensure that identification stays put

 

[Spoon]

It will be hard to find YY cable that doesn't have the below comment in their specs. All depends on what you are using the YY cable for.

 

[Toneyz]

The 5 core cables were coming from the controls downstairs, as already explained. As was the cpc contained within supply cable. I'll have to remember to ask the wholesaler for a 5 core which doesn't contain a green/yellow covered conductor next time.

You can get YY flex or 7 core flex.

It will be hard to find YY cable that doesn't have the below comment in their specs. All depends on what you are using the YY cable for.
View attachment 43825

I thought he was using it as control wiring?

 

[Octopus]

I Work on the basis that it's best to have a CPC in every cable I run ..