Is a borrowed earth allowed?

[a-z electrics]

Funnily enough, I made a similar mistake a couple months ago.. I put in a socket spur from a socket on the rfc which was being covered over.. after plasterer had been I retested and found there wad no earth at new socket! I had to cut out an inspection hole and found the new cpc had actually snapped off inside the terminal for some reason (possibly a hurried stripping operation).. so it DOES happen!

 

[Midwest]

You not inferring you plastered over a joint?

 

[a-z electrics]

You not inferring you plastered over a joint?

Not me.. that was the builder

 

[a-z electrics]

But it was MF..

 

[SparkyChick]

But it was MF..

Just out of interest... what sort of joint was it?

 

[Midwest]

Hope it wasn't one of these;

 

[Pete999]

But it was MF..

What type of connector was used?

 

[mrloy99]

There are other concerns too..maybe there could be another radial in the kitchen with a 'lost ' earth and the previous spark has already borrowed the cooker earth......So new cooker circuit in /old cooker circuit out might leave another circuit unprotected...Full test might identify that..I suppise...I dont really see a problem with just installing a new separate earth..Why does it need to be in the same cable.

 

[Midwest]

Why does it need to be in the same cable.

We were arguing that last weekend. You'll have to read the posts yourself.

 

[Deleted member 9648]

Funnily enough, I made a similar mistake a couple months ago.. I put in a socket spur from a socket on the rfc which was being covered over.. after plasterer had been I retested and found there wad no earth at new socket! I had to cut out an inspection hole and found the new cpc had actually snapped off inside the terminal for some reason (possibly a hurried stripping operation).. so it DOES happen!

GASP!

 

[a-z electrics]

Just out of interest... what sort of joint was it?

Push in Wagos .. but I have a feeling the cpc wire was nicked whilst stripping, hence snapped off whilst being pushed into the box..

 

[alasdairp]

Sorry this is late, I only usually look once a week when the summary comes around. I have carried quite a few 'serious' Grounding / Earthing related works in the past. In one case, in a very large shopping and business complex in the upper Midlands, with its own substation in the basement, I determined (and they eventually admitted after legal pressure) that they had failed !!!!! to reconnect the Earth to the whole building after they had tested and commissioned the substation! So much for the "professionals" in the DNO's.

Another case was a multiply-supplied (with originally 6 separate meters) industrial/scientific starter-unit complex (with a different DNO) that eventually had one pharmaceutical owner and had really high EMF magnetic fields in their labs (like 50 microteslas) from stray currents which were affecting the biological research results. I determined what the problem was. It was in the local distribution network and not their own supply cables. The only way to sort it was to remove all but one of the network protective Earths and rely on that and the buildings steel structures into the ground (like super Earth Rods). That sorted the problem and the DNO agreed with me that it was the only practical solution. So we did that BUT also affixed signed warning notices at all the incoming supply points to say what we had done in some detail and why.

I agree with SparkyChic that ideally the CPC should be of adequate size, but, if as you say, it is a dual RCD protected installation then all any CPC needs to carry will be 30 mA (or possibly 100 mA). This is not yet reflected in BS7571 - even in the latest 18th Edition.

I think, if you leave it that way, you should stick a notice near the CU saying that is what you have done. It should be safe, but it should not be un-noted. I would have done what you did.

 

[alasdairp]

Sorry this is late, I only usually look once a week when the summary comes around. I have carried quite a few 'serious' Grounding / Earthing related works in the past. In one case, in a very large shopping and business complex in the upper Midlands, with its own substation in the basement, I determined (and they eventually admitted after legal pressure) that they had failed !!!!! to reconnect the Earth to the whole building after they had tested and commissioned the substation! So much for the "professionals" in the DNO's.

Another case was a multiply-supplied (with originally 6 separate meters) industrial/scientific starter-unit complex (with a different DNO) that eventually had one pharmaceutical owner and had really high EMF magnetic fields in their labs (like 50 microteslas) from stray currents which were affecting the biological research results. I determined what the problem was. It was in the local distribution network and not their own supply cables. The only way to sort it was to remove all but one of the network protective Earths and rely on that and the buildings steel structures into the ground (like super Earth Rods). That sorted the problem and the DNO agreed with me that it was the only practical solution. So we did that BUT also affixed signed warning notices at all the incoming supply points to say what we had done in some detail and why.

I agree with SparkyChic that ideally the CPC should be of adequate size, but, if as you say, it is a dual RCD protected installation then all any CPC needs to carry will be 30 mA (or possibly 100 mA). This is not yet reflected in BS7571 - even in the latest 18th Edition.

I think, if you leave it that way, you should stick a notice near the CU saying that is what you have done. It should be safe, but it should not be un-noted. I would have done what you did.

The secod one was was due to PME problems in the area.

 

[SparkyChick]

Push in Wagos .. but I have a feeling the cpc wire was nicked whilst stripping, hence snapped off whilst being pushed into the box..

Were the Wago's in a Wagobox by any chance?

 

[buzzlightyear]

Just out of interest... what sort of joint was it?

a smoking one why

 

[gerry whitwham]

I would say that borrowed earths are not good practice ……..one alternative may have been to run a separate 4 0r 6mm cpc back to the consumer unit.

 

[Intoelectrics]

I would say that borrowed earths are not good practice ……..one alternative may have been to run a separate 4 0r 6mm cpc back to the consumer unit.

I don't think anybody is arguing that it is good practice. The op was about whether it was an acceptable alternative in the circumstances he/she faced. If you are going to the trouble of running a new single cpc back to the CU, I suspect in this case you may as well run in a new twin & earth.