Using cpc as neutral

[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 ..