Is a borrowed earth allowed?

[a-z electrics]

Done an EICR yday on an old house and all ok apart from 2 issues..
1) 32A cooker circuit had high resistance pec continuity (over2kohms) ALTHO it did buzz out on my voltage probes. Hence not able to get a Zs reading and no rcd tripping. The dual rcd consumer unit was fitted 10 yrs ago and those test readings all available and fine. 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.
.. I've put in an earth wire link from an immediately adjacent rfc socket into the cooker switch and this solves this problem.
Question .. is this ok as a permanent solution if i label up what ive done?
2) lowish IR readings 1.75M L-E and N-E on light circuits and one rfc but possibly in hindsight due to some bulbs, fan and appliances still plugged in. Could this account for it?

 

[Wilko]

We can speculate what the fault is and the condition of the cooker circuit cable, but we don't know. It could just be the cpc was not jointed properly somewhere, or at there could be a bit of cable that's been crushed and heat stressed (by those Xmas cooking events).
Back in olden days I worked somewhere where the mantra was "if there is a doubt, there is no doubt".

 

['mr2'gd4u]

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.

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

 

['mr2'gd4u]

End of discussion??

 

[Midwest]

End of discussion??

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

 

['mr2'gd4u]

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

My bad

 

[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.