Discuss Steel conduit used as CPC in flat, can’t find bonding, can’t find ring main CPC at C.U in the Electrical Forum area at ElectriciansForums.net

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ZEDEZ

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I’ve been asked to add a couple of extra points to the single ring main in a flat. Building fabric is concrete, all of the electrical installation is steel conduit buried in the concrete.

I opened the consumer unit and could only see one CPC for a radial socket, as well as the main Earth. No other CPC’s visible.

There was no supply head, just the incoming line conductors (looked like 16mm) coming through an opening behind the C.U, no bonding for gas or water. All of the cables disappear down into this opening and I can’t see any other CPC’s or connections down there, plus as it’s all in concrete I can’t get down behind there to look.

I’m guessing the C.U is being fed from a locked cupboard in the communal hallway on that floor, but I couldn’t gain access to it today to check.

I was also hoping that the gas and water would be bonded here or on the incoming to the entire block of flats itself, but again I couldn’t check that today.

The only ring main in the flat (the one I want to add spurs to) has continuity on all conductors, but I couldn’t test the CPC of the ring main at the C.U as there is no visible connection there for the CPC’s, which are present at the socket outlets. I tested at a socket though, and the CPC appears to be continuous as well as being connected to the Earthing - somewhere.

There is no CPC in the lighting circuit either, but the conduit seems to be being used as the CPC. I’ve done a wandering R2 to each light switch and fittings, all have low readings for R2 well within reason.

So my questions are, how do I approach adding the additional sockets in light of what I found, is the steel conduit used as CPC acceptable for the light switches and fittings, and if the gas and water is bonded on the incoming to the block of flats itself / at the communal supplies, is this sufficient?
 
I’ve been asked to add a couple of extra points to the single ring main in a flat. Building fabric is concrete, all of the electrical installation is steel conduit buried in the concrete.

I opened the consumer unit and could only see one CPC for a radial socket, as well as the main Earth. No other CPC’s visible.

There was no supply head, just the incoming line conductors (looked like 16mm) coming through an opening behind the C.U, no bonding for gas or water. All of the cables disappear down into this opening and I can’t see any other CPC’s or connections down there, plus as it’s all in concrete I can’t get down behind there to look.

I’m guessing the C.U is being fed from a locked cupboard in the communal hallway on that floor, but I couldn’t gain access to it today to check.

I was also hoping that the gas and water would be bonded here or on the incoming to the entire block of flats itself, but again I couldn’t check that today.

The only ring main in the flat (the one I want to add spurs to) has continuity on all conductors, but I couldn’t test the CPC of the ring main at the C.U as there is no visible connection there for the CPC’s, which are present at the socket outlets. I tested at a socket though, and the CPC appears to be continuous as well as being connected to the Earthing - somewhere.

There is no CPC in the lighting circuit either, but the conduit seems to be being used as the CPC. I’ve done a wandering R2 to each light switch and fittings, all have low readings for R2 well within reason.

So my questions are, how do I approach adding the additional sockets in light of what I found, is the steel conduit used as CPC acceptable for the light switches and fittings, and if the gas and water is bonded on the incoming to the block of flats itself / at the communal supplies, is this sufficient?
What were the Zs readings at the sockets and lighting points?
 
I personally haven’t worked on that many properties with buried steel conduit acting as the cpc.
But in the few cases that I have the earth readings have all been good and I have managed to add extra points without too many problems.
 
Pete I see where you’re going with this.

Ok so given that those readings are fine, what about the bonding situation?
You will need to ensure the bonding is in place if it isn't then install it
 
It is perfectly acceptable to use the containment as the cpc providing it is still has its integrity so check for corrosion on parts you can see. I suspect if you poke a long screwdriver through the back of the consumer unit you will hit an adaptable conduit box in the wall. As for bonding this requires investigating as there may be a common bond so you are going to need access to the risers and intake before you can proceed. Does the existing CU have additional rcd protection.
 
Any update on this one Zedez?
 
why not get a wander lead from the CU to the gas and water. see what the reading is. if it's fractions of an ohm, it will be bonded.
 

Reply to Steel conduit used as CPC in flat, can’t find bonding, can’t find ring main CPC at C.U in the Electrical Forum area at ElectriciansForums.net

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