Is a borrowed earth allowed?

[Midwest]

But if the cpc is connected from the appliance to new cpc plus old cpc as well as the CU end the cpc should be continuous up to the point of loss of contact... But on both ends. Although if there were 2 losses in contact along the length..
Obviously the op said it would be easy to replace so has done a bit of service by providing protection against exposed parts so therefore is a reasonably good temp fix

Your assuming the old cpc is good until the old connection. It might have failed 100mm from the CU.

 

['mr2'gd4u]

Your assuming the old cpc is good until the old connection. It might have failed 100mm from the CU.

That's true but the new cpc connected at the switch side of the old cpc with be connected back to cu...

 

['mr2'gd4u]

Hence cpc present up until 100mm from cu.. Then the 100mm cpc is connected also

 

[Midwest]

Hence cpc present up until 100mm from cu.. Then the 100mm cpc is connected also

But the rest is not, old cable is not compliant with reg 543.6.1.

 

[SparkyChick]

Don't be silly, I've got another hour before jelly & ice-cream.

Is it strawberry jelly???

 

[johnduffell]

the CPC for the circuit will be routed with the live conductors (or in close proximity - in back boxes) along it's entire length.

Kitchen was refitted 3 yrs ago and no docs available so they extended original cooker cable prob from the switch which is now tiled over somewhere.

This suggests the two cables don't share the same routing. I don't think anyone making the alternative cpc connection can say for sure.

As for sleeving yellow/green with brown in a flex... that's not weird, it's plain wrong. If you need three live cores you should be using an appropriate 4 core flex

Have you got a reg for that? The only one i know of forbids over sleeving of a single green yellow. The only way it would be forbidden for multi core would be if the two flexes run together were considered separate wiring systems and the cpc in the other not being in close proximity.
Even then, you could theoretically run a separate cpc like you would with swa sub mains, although i doubt it's done ever!

if the cooker circuit had no cpc whatsoever, would taking a connection from the RFC to provide a cpc be correct, according to the regs mentioned?

Possibly, if they run together throughout the circuit, assuming two t&e together are considered the same wiring system.

 

[Midwest]

Is it strawberry jelly???

Blackcurrant I hope, although there's talk of a bar for the older kids!

 

[SparkyChick]

This suggests the two cables don't share the same routing. I don't think anyone making the alternative cpc connection can say for sure.

I disagree, his post suggests the cable was extended at the original switch meaning there are two cable segments, one from the CU to the switch and another from the switch to the cooker. Both segments will be wired in T+E (valid assumption) meaning the CPC is contained within the wiring system (the cable, again... valid assumption).

And thus, it's not breaking any regulations.

Have you got a reg for that?

No, I don't have a reg for that. It's my personal take on what I consider to be good practice. If there is an earth in the cable, use it for the CPC or don't use it, don't sleeve it and use it for something else. There's not many occasions I can think of where you'd have an earth in a cable and not use/require it as an earth/CPC. The only one that springs to mind is light fittings and supplying class two equipment. In all other cases I would use x+1 core cable where x is the number of live conductors I required.

For the most part, these appear to be matters of opinion and interpretation. You've got your interpretation and opinion and I've got mine, it's unlikely we are going to agree, but then I don't have to agree with you, I just have to be happy with my interpretation of the regulations and their subsequent application.

So, as usual I think you and I are going to have to agree to disagree.

 

[Midwest]

Possibly, if they run together throughout the circuit, assuming two t&e together are considered the same wiring system.

But there's no way of confirming that; therefore you should assume they don't and act accordingly.

 

[Midwest]

I disagree, his post suggests the cable was extended at the original switch meaning there are two cable segments, one from the CU to the switch and another from the switch to the cooker. Both segments will be wired in T+E (valid assumption) meaning the CPC is contained within the wiring system (the cable, again... valid assumption).

And thus, it's not breaking any regulations.
.

But you are assuming the break/fault is at the original switch, it could be elsewhere. You would have to assume it is not continuous from the CU. Therefore it is not complaint.

 

[johnduffell]

I think

But you are assuming the break/fault is at the original switch, it could be elsewhere. You would have to assume it is not continuous from the CU. Therefore it is not complaint.

I think the confusion is that sparky chick considers that there has to be "a" cpc present throughout the wiring system, whereas my interpretation is that "the" cpc must be present throughout the wiring system.
Although i think everyone agrees it's not ideal!

 

[SparkyChick]

But you are assuming the break/fault is at the original switch, it could be elsewhere. You would have to assume it is not continuous from the CU. Therefore it is not complaint.

But it is continuous in that he can get a resistance reading end to end. It's just not a very good connection. So assuming it's a single break... both ends are earthed and the CPC will do it's job. Where it becomes a concern is if there are mulitple breaks... if there were two breaks, theoretically there could be a segment of the CPC that does not provide a sufficient good Zs to allow the protective devices to operate should a fault occur on that segment.

In essence, this is assumption... some of it can be proved (by inspection and testing) and some cannot (but we accept it because if we didn't some things would be a mare, like an EICR for example. We have to assume the CPC is continuous and running as expected in the same cable because we have no way of actually proving it.

This is just a theoretical discussion about a less than ideal situation. My personal preference would be to find and fix the fault or replace it. End of. But, I don't believe the solution breaks the regs, at least none that have been quoted so far.

Anyhow, blackcurrant jelly you say... Yum A bar for the big kids is even better... enjoy

 

[Intoelectrics]

my main concern is that, although the bypass cpc provides protection to the point of use, the original cable with it's damaged cpc is not, in itself, protected, so I lean towards the find and fix option.

I can see your point but I don't think this is the intended function of a cpc.
"Circuit Protective Conductor (cpc). A protective conductor connecting exposed-conductive-parts of equipment to the main earthing terminal".

So for example based on your point one could argue that a twin core flex has no protection because there is no cpc present.

Though what the OP has done is not "best practice" no reg has been broken and it has improved the safety of the circuit.
By which it could now be down coded from a C1 / C2 to CFI or C3 if the OP felt that further improvement was needed.

 

[buzzlightyear]

we can all give the good points and the bad, it is down to the op what is conscience tells him he is the one work on it .if was doing it in which I'm not .new feed if possible .

 

[johnduffell]

I can see your point but I don't think this is the intended function of a cpc.

Agree. The cpc in a flex or t&e is not an exposed conductive part it is just a conductor. In swa and metallic conduit the two functions do happen to be combined.
Indeed in my interpretation the regs would allow, if you somehow had an insulating joint in some conduit, you could indeed run a single cpc inside or alongside and use it to ensure the whole length was earthed.
The intent of the reg mentioned earlier is surely to make sure the cpc isn't removed by mistake when another circuit is decommissioned or abandoned?

 

[Lucien Nunes]

I agree that the earth borrowed from the RFC is probably quite adequate to provide the necessary protection to the cooker circuit. However I would not accept the practice as an actual solution specifically for two of the reasons already mentioned:

a) The original cooker cable is either damaged to an unknown extent, or connected in a defective manner. It is impossible to say what other danger exists from this problem, but borrowing the CPC conceals the original defect and is likely to prejudice its timely repair. This is a different scenario to borrowing a CPC for a circuit that was installed without one, where nothing is otherwise defective.

b) In a domestic situation, confusion is likely to arise from the non-standard configuration, especially as one of the circuits involved is an RFC, and erroneous future test results and inferences from them can reasonably be anticipated.

This latter point does not in my mind stand comparison to a metallic containment providing the CPC for multiple circuits, which is a normal and expected configuration, nor the deliberate design of a wiring system with one CPC cable serving multiple circuits. This occurs quite commonly in entertainment lighting, where cabling often runs in blocks of 6, 12, or 24 identical circuits to a single point of use. There's no point running 24 CPCs in parallel to the same box, one cable will do, but it is plainly obvious which CPC serves which circuits even without documentation and the circuits can be tested without unexpected side-effects from cross-connections.

By contrast, this ad-hoc arrangement is anything but obvious. Part of the cooker circuit cable is protected by the usual CPC from the CU, the other part terminating in an unknown location, and neither properly connected to, nor insulated from, the first part, is back-fed along with the cooker itself, from a CPC consisting of two legs of a functionally unrelated RFC.

All that said, I might be tempted to do this as a fix but I'd make it visible and ugly, so that the problem wouldn't get swept under a rug!

 

[johnduffell]

Part of the cooker circuit cable is protected by the usual CPC from the CU, the other part terminating in an unknown location

I agree with the general thrust of your post, but I'm intrigued about this need to protect t&e cable with a cpc. As i understand it the regs only require the earth at every termination, and cpcs in the same wiring system would not provide any protection unless the cpc was also an exposed conductive part eg SWA or metallic conduit.
I appreciate that nailing t&e has a chance of hitting the cpc but what protection is actually given by that?

 

[BruvDunk]

Im with the replace cable side !
Too many unknowns and guesses...

 

[Lucien Nunes]

Johnduffell you're right, I didn't word that very well. What I meant to say was that any accessory inserted into the cable, such as the putative bypassed isolator which may have a metal back box, would be protected by... rather than the T+E cable itself.

 

[a-z electrics]

I disagree, his post suggests the cable was extended at the original switch meaning there are two cable segments, one from the CU to the switch and another from the switch to the cooker. Both segments will be wired in T+E (valid assumption) meaning the CPC is contained within the wiring system (the cable, again... valid assumption).
.

Yes the cable from DB is red and black. At switch it's brown and blue.. I understand the original switch position is in the wall less than 3M from the DB. The new switch is about 2m as crow flies from DB, albeit thru a thick wall with lots of cables and pipes along it. I'd say it was a good chance the cpc join at the original switch isn't sound .. there is ecery infication the live cable joins are sound. The test readings match almost exactly those done 10 yrs ago after I did the cpc repair..