Discuss Is a borrowed earth allowed? in the Electrical Forum area at ElectriciansForums.net

a-z electrics

Regular EF Member
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387
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Exeter area
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?
 

buzzlightyear

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Electrician's Arms
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star command
no this the answer rewire the circuit in full if possible .borrowing a earth from some where else .it will cause problems down the line if was a main fault .
 

Midwest

Electrician's Arms
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11,175
Location
Oxfordshire
I'd say;
1) No, as each circuit must have its own cpc, as I recall.
2) Further investigation required

I don't do EICR's, but I recall you report, but not carry out the remedial work?
 

freddo

Regular EF Member
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1,155
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Devon
1 I wouldn't do it.

2 Could be anything, light bulbs shouldn't be causing L/N - E insulation faults!

Edit: Wow I was way too slow.
 

Midwest

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Oxfordshire
I do if it removes immediate danger! Client not on site..
I'd just isolated the circuit, with clients permission of course.

You've not really done a permanent repair, and now your liable, should anything go wrong. If it was young family or someone frail, then as a temporary fix ok.
 

westward10

In echoed steps I walk across an empty dream.
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Not right now Westy, but go ahead fill yer boots
What I am saying is that he has done nothing wrong, it is permitted provided it is adequate for a cpc to serve more than one circuit. What he has done may seem unorthodox but I was asking for those who disagree with his actions to back it up with a Regulation.
 

Pete999

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What I am saying is that he has done nothing wrong, it is permitted provided it is adequate for a cpc to serve more than one circuit. What he has done may seem unorthodox but I was asking for those who disagree with his actions to back it up with a Regulation.
Ah right, I don't have a copy of BS 7671, so in all honesty I can't confirm if there is a regulation.
 

Kamikaze

I do what the voices in my head tell me.
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All long as he complies with regulations: 543.1.2, 543.1.3 and 543.1.4 then I can’t see nothing wrong with that.
 

Wilko

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Berkshire
Anyone want to quote a Regulation where this is not permitted providing the borrowed cpc is adequate for fault protection requirements.
Question - what is the state of the cpc for the cable, along its length? Cables in walls 522.6.202 has me thinking about a screw being driven into the cable. If CPC is 2K then it should be sufficient to trip a 30mA RCD but the screw may exceed the 50V max target (1667 Ohms).
 

Midwest

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Ok I give up, I'm orrffh to cook a curry is my excuse.

My thoughts were that the cpc must remain effective throughout the life of the install. Therefore, if the RFC is altered or removed subsequently, the installer altering/removing may not know the other circuit is reliant on its cpc.
 

buzzlightyear

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What I am saying is that he has done nothing wrong, it is permitted provided it is adequate for a cpc to serve more than one circuit. What he has done may seem unorthodox but I was asking for those who disagree with his actions to back it up with a Regulation.
so Westy is like borrowing a neutral .;)
 

westward10

In echoed steps I walk across an empty dream.
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Ok I give up, I'm orrffh to cook a curry is my excuse.

My thoughts were that the cpc must remain effective throughout the life of the install. Therefore, if the RFC is altered or removed subsequently, the installer altering/removing may not know the other circuit is reliant on its cpc.
You could argue if the problem cpc has only one break it is now effectively connected to earth from either end. I think it would be prudent to fit some form of info at the CU.
 

Andy-1960

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Wolverhampton
I agree with Westy, the circuits cannot now be independently isolated, anyone working on the RFC in the future could potentially get a shock from the cooker circuit in the event of a fault on the cooker.
It is as BL says like borrowing a neutral, as soon as that link is disconnected there could be a potential difference between the two earth conductors.
Big problem with temporary repairs is that they have a nasty habit of become permanent repairs!
Also, what has now been done must surely screw the test results for the RFC, so how do you document that in the EICR?
Correct thing to do would be to isolate the cooker circuit and label it saying it is not to be used until remedial action has been carried out and document that to the client.
 

Kamikaze

I do what the voices in my head tell me.
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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?
If you got those readings of the same lighting circuit, then I would say there is a fault on that circuit. Did you disconnect the earth and neutral for that circuit out of the board before testing?
 

'mr2'gd4u

Regular EF Member
Messages
180
Location
Farnham
Trouble is the diffence in size of cpc. 1.5mm on a 2.5mm ring (essentially 3mm) the cooker if in a 10mm t&e.. With a 4mm cpc... 6mm t&e is fine at 2.5mm cpc
 

happyhippydad

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Gloucestershire
As some of the more experienced have said... It is fine to use a CPC common to two or more circuits, and it complies with a regulation 543.1.2 (as long as it's CSA is sufficient).

I do find it worrying when members, some are even trusted members, give the wrong advice and give it out so quickly without giving proper thought. We all get it wrong at times, but at least lets give it some thought before we get it wrong.
 

buzzlightyear

please let me back in to the prison cell.
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It is as BL says like borrowing a neutral, as soon as that link is disconnected there could be a potential difference between the two earth conductors.
Big problem with temporary repairs is that they have a nasty habit of become permanent repairs!
Different scenario Buzz.
how can it be a different . are you saying its ok to borrow a earth knowing if their is fault to earth It want clear quicker. IMO the op needs to ring his scam and get clarification.
 

Midwest

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As some of the more experienced have said... It is fine to use a CPC common to two or more circuits, and it complies with a regulation 543.1.2 (as long as it's CSA is sufficient).

I do find it worrying when members, some are even trusted members, give the wrong advice and give it out so quickly without giving proper thought. We all get it wrong at times, but at least lets give it some thought before we get it wrong.
Thats told me then. Still think its so wrong though. :)
 

Andy-1960

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506
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Wolverhampton
I agree with Westy, the circuits cannot now be independently isolated, anyone working on the RFC in the future could potentially get a shock from the cooker circuit in the event of a fault on the cooker.
It is as BL says like borrowing a neutral, as soon as that link is disconnected there could be a potential difference between the two earth conductors.
Big problem with temporary repairs is that they have a nasty habit of become permanent repairs!
Also, what has now been done must surely screw the test results for the RFC, so how do you document that in the EICR?
Correct thing to do would be to isolate the cooker circuit and label it saying it is not to be used until remedial action has been carried out and document that to the client.
I agree with Westy.
I meant Midwest... sorry Westy!
 

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