missing lighting cpc

[gts860]

Good Evening,
I have failed an EIC test, C1 lighting circuit has induced voltage on light switch screws.
The lighting circuit is on a split load CU non RCD side only MCB fitted.
All switches and pendants have a connected R2 however the CPC conductor present does not connect to any Earth, its floating.
The break or disconnection is probably under the floorboards.
Is there any reason why one cannot take from a tested radial socket cct, on 20A RCD, which is 1.5M distant from one of the light pendants in this failed cct, run it through the loft and connect it to the pendant ? I am told one cannot do this and the electrician wants to drill holes through the walls, run an extra CPC from the CU, up a wall surface, within trunking and tap it into one of the light switches on this circuit.
He tells me my suggestion cannot be done "the cpc must come from the same cct" Surely the many and various cpc on the other circuits are all connected to the same Earthing point so i do not see the logic in his explanation
The entire house is rewired to 16th Edition

 

[i=p/u]

C3, if plastic fittings. Rcd it , take switch away and add microwave sensor fitting of some sort or replace cpc, but not from the socket

 

[gts860]

Hello i=,
they are plastic fittings, but because the cpc is physically present but not connected to a earth then it is subject to an induced >100v potential on the light switch screws,taking the switch away is not an option all light switches on this circuit have "live" fascia screws. What I would like to know is the reason why one cannot take from another cpc, surely its all the same point.
Which REG is contravened ?

 

[westward10]

There is nothing preventing an earth being shared by multiple circuits providing it is suitably selected. How long did they spend looking for the fault.

 

[i=p/u]

I'd need a look myself haha, if its only going to light switch, disconnect it at light maybe.

 

[Lucien Nunes]

C1 lighting circuit has induced voltage on light switch screws.

Surely that would be a C2 - it's merely a symptom of the missing CPC rather than a separate fault. I would give a C1 if the screws were live from a spurious connection of the CPC to line.

The break or disconnection is probably under the floorboards.

A concealed damaged cable or junction that has an open-circuit CPC could be defective in other ways too. E.g. It might be a cable with a screw through where the CPC has blown itself clear on one side but the screw is still live. I would not be content to supply a replacement CPC, from the board or another circuit, without attempting to locate and rectify, or bypass completely, the cable segment with the open-circuit CPC.

All switches and pendants have a connected R2 however the CPC conductor present does not connect to any Earth, its floating.

You say they have a resistance value that indicates they are connected, but then say they are not connected. Am I missing something?

 

[gts860]

There is nothing preventing an earth being shared by multiple circuits providing it is suitably selected. How long did they spend looking for the fault.

Hello Westward, i do not know i was not there. I suspect i am being given the run around if what i suggested is a viable and according to regs acceptable solution then it probably would not take more than 15 mins and 2M of eth cable. I have already pointed out to them that the ETH arrangements in the house are not what they wrote on the form, that the Ze value is too high, (incoorectly filled in form) a suspected C2 on a workshop with 20 sockets because open grommets have been used on the knock outs and more than 3mm gap is present. This is quite a time consuming job taking all the socket faces off disconnecting all the conductors, fitting closed grommets and putting it all back. When questioned they decided it was not a C2 but a C3 so easy fix for them different tick box.
Anyway, what do you mean by "suitably selected"

 

[gts860]

hello Lucien,
to clarify, all the components of the lighting circuit ETH points, switches and pendants are connected together. This is the R2 test performed, However this conductor is not actually connected to an earthing point, perhaps it has always been missing,

 

[westward10]

I think you need an electrician who can actually fault find to give you a clear opinion as to what is going on.

 

[gts860]

I think you need an electrician who can actually fault find to give you a clear opinion as to what is going on.

 

[gts860]

i thought i had of one those, he has all the certificates but clearly non of the answers

 

[westward10]

I would ask where the fault is through the circuit any competent electrician would be able to tell you after some fundamental testing.

 

[Lucien Nunes]

R2 is specifically the resistance of the CPC from the furthest point back to the CU. But if your CPC is not connected to the CU, you cannot have a valid result for R2.

If the CPCs of all points (bar none) are interconnected, but not connected to the CU, then the break must be in the 'home run' of the cable. If that cable is accessible at a point so that it can be disconnected, my suggestion would be to run not just a CPC but a complete new cable to the CU, and thereby isolate the faulty section completely.

 

[westward10]

R2 is specifically the resistance of the CPC from the furthest point back to the CU. But if your CPC is not connected to the CU, you cannot have a valid result for R2.

If the CPCs of all points (bar none) are interconnected, but not connected to the CU, then the break must be in the 'home run' of the cable. If that cable is accessible at a point so that it can be disconnected, my suggestion would be to run not just a CPC but a complete new cable to the CU, and thereby isolate the faulty section completely.

Problem is the electricians description is a bit vague. I believe they are saying there is a cpc at all accessories but an earth fault loop test indicates 100v and subsequently will not perform the test but I could be wrong. Nine times out of ten this is an incorrectly connected cpc.

 

[gts860]

R2 is specifically the resistance of the CPC from the furthest point back to the CU. But if your CPC is not connected to the CU, you cannot have a valid result for R2.

If the CPCs of all points (bar none) are interconnected, but not connected to the CU, then the break must be in the 'home run' of the cable. If that cable is accessible at a point so that it can be disconnected, my suggestion would be to run not just a CPC but a complete new cable to the CU, and thereby isolate the faulty section completely.

Sorry but i have mislead you here by using the terminology supplied by the tester. What is more accurate to say is that all of the earthing points of the lighting circuit components are connected to one-another with a 1.0mm eth cable (not an R2) This (at this moment) is a completely isolated run of cable and is not connected to a central earthing point either at or connected to the CU earth block. So I see why you were confused.
This is why i suggested taking a short spur from a known good CPC adjacent to one of the light pendants and effectively connecting a verifiable earth to the failing light circuit. This I am told is not possible however his solution is effectively the same fix, only he takes the earth not from a remote socket box but from the CU earth via a run of trunking up a wall to pick up on the same circuit, in a light switch.

 

[gts860]

Problem is the electricians description is a bit vague. I believe they are saying there is a cpc at all accessories but an earth fault loop test indicates 100v and subsequently will not perform the test but I could be wrong. Nine times out of ten this is an incorrectly connected cpc.

actually the description is simply that 160V is present on the fascia screws. I think i will be looking to get a second opinion and for him to quote which Regulation does not permit taking a cpc from one circuit and using it for another circuit. If it is of any value the L/E insulation test on this cct passes

 

[westward10]

Has he verified the fault is from the consumer unit to the first light.

 

[gts860]

, my suggestion would be to run not just a CPC but a complete new cable to the CU, and thereby isolate the faulty section completely.

this however is exactly what i want to avoid if at all possible. All cables are either under floorboards or buried and i would prefer not to have trunking running over the surfaces.

 

[gts860]

Has he verified the fault is from the consumer unit to the first light.

i personally do not think he has verified anything, i will ask him to detail what fault finding steps he has applied and what the results where, but based on his performance to date i have little confidence in his thoroughness. Incidently the cct in question incorporates a 3 way hall /landing arrangement and a two way landing/loft lighting switch arrangement.

 

[i=p/u]

Yh , let him do.his job and trust him or get someone.else..