armoured cpc problem | on ElectriciansForums

Discuss armoured cpc problem in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

K

karakoram

Hi, this one is stumping me.

I have been asked to look at a swiming pool installation. The supply to house is tns, with a submain running out to a pool plant building, the installer has atempted to put the pool side on a seperate TT, however the gas pipe running to the pool building is in copper from house so introduces the TNS into TT. Ok i can live with that its not on a PME.

My main problem is the submain. The installer extended an existing 2 core armoured, however they decided in not to conect the armour up in the underground joint. so in effect we have a submain that only a CPC (armour) for half its length that is earthed.

Digging up the submain or the joint is not an option, my only solution is running an additional CPC ie green n yellow, from one end of the submain to the other. this would follow a different root to the submain.

Anyones thoughts would be great
 
The problem is the only physical earth at the plant building is the copper gas pipe....in my mind not suitable. The submain would have provided the earth if the plant room is made TT. But then the copper gas pipe introduces TNS, so we have to make plant building tns.

"The submain would have provided the earth if the plant room is made TT"
Sorry ment Submain would have provided earth if plant room on tns, or cpc for the submain if we put plant room on TT. But we cant do that becouse gas pipe introduces tns anyway!
 
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i think u need to run seperate earth to plant room and earth armour from plant room end i allways either run seperate earth wire with armoured cadle or get cable with extra core for earth
 
This was my thought aswell, Not being our work, we have just been asked to put this right. Although this is a bit unorthodox, do you think it satisfies regs, running another earth from one end to another to join the break, bearing in mind it will take a completly different route to the submain?
 
Im not sure why you dont make the plant room TT and bond the gas pipe to the plant room.

No different from a domestic TT.

Thanks
unfortunatly we cant do that because the gas is bonded back at house on TNS, and is copper through out.

We would still end up with the half the submain arrmour(CPC) on TNS and Half on TT. If we had an earth fault on the TT side of submain it would not meet disconnection time as would be going through earth stack down stream, to trip mcb upstream, if that makes sence
 
Too much fussin.

You do need to make sure that the armour is connected to earth on the pool side. As you cannot dig up you have got to assume.

As for the pipework it is simply being a 'new' extraneous part (assuming it is buried in the ground between the house and pool) on the pool side. Yes it may be giving a better return to earth than any rod, but it needs to be connected to the MET on the pool side to remove the pottential.

DO NOT disconnect bond in house.

And put an earth rod on the pool incomer.
 
Last edited by a moderator:
Too much fussin.

You do need to make sure that the armour is connected to earth on the pool side. As you cannot dig up you have got to assume.

As for the pipework it is simply being a 'new' extraneous part (assuming it is buried in the ground between the house and pool) on the pool side. Yes it may be giving a better return to earth than any rod, but it needs to be connected to the MET on the pool side to remove the pottential.

DO NOT disconnect bond in house.

And put an earth rod on the pool incomer.

Hey thanks for this, my concern is that doing this relies on the extraneous part in this case the gas pipe bringing the same earth potential at the origen (tns) to the other end of the armour(due to the break in armour).regardless of stake at pool end.
This is why i was asking if it was worth running an a dditional earth cable?
 
If you run a seperate cpc then it would become a TNS in the pool house. If that was the case the cpc would have to be minimum the equipotential bond for the house (10mm?) as the equipotential bond to the gas would have to be that of the incomer, not your new TT supply.

The gas pipe will bring a similar pottential, but as it is not an 'electrical' conductor it should not be seen as one. There is a chance you can split the gas with an insulated joint, but you will have to speak to a gas fitter about that.

Yes you will get parralel paths when bonding the gas, but that is less of a concern than bringing in either different pottentials to the house or the pool. Just make sure any Ze is taken with the main earth connected to the rod only and you must protect with minimum 100mA RCD (as it is a swimming pool instalation you may as well stick a 30mA one in!) and you get readings below the tabulated values.
 
hi

just a thought.... could you make the whole installation a tt? pool side and supply side? provide 100ma at supply and 30ma at pool, then bond gas at each end?

cheers
 

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