Steel conduits acceptable for earthing in domestic property ?

[NEB Electrical]

Evening

Just been to quote for a consumer unit upgrade. Found that the board was from circa 1960 and wiring looked original also. No alterations have been made with exception of a few faceplates renewed in the kitchen. Red and black single cores going into an adaptable box at the back and then down the relevant conduits. No CPC's for any circuit. The only thing providing an earth is the conduits themselves.

My question is does this provide an adequate earth and would this be deemed acceptable once the new 18th edition unit is installed ?

I am of the opinion that it does not as there is technically only one earth point at the main board and if that were to fail, nothing in the house would be earthed, there is also no guarantee that the conduit system is 100% complete, although a long lead test could verify continuity ?

Any advice/opinions welcome.

Thanks in advance.

Nick
NEB Electrical Ltd

 

[NEB Electrical]

You can't, but earthed metallic containment used as a CPC is specifically exempted from the requirement for the CPC of a ring to be in the form of a ring also. Therefore no test is required beyond providing a suitably low-resistance earth at each point.

Yes as there is no CPC ring

An n/a would suffice in the box then ..

Thanks

 

[davesparks]

Reason behind a suggested rewire is because my client is in the process of redecorating the house. So would be a good time to get this done.

But if it is wired in conduit then a straight point for point rewire wouldn't touch the decorating, you'd just pull new brown and blue singles in using the old as draw wires.

 

[Kidsolo]

Question.... was the ring system used back when steel conduit was used.

 

[Lucien Nunes]

Steel conduit introduced around 1890s, evolving out of the re-use of gas piping as conduit when gas lighting was converted to electric. Ring final circuits introduced 1947.

In the low-rise domestic sector, there was a negative correlation between rings and conduit due to the post-WW2 rebuilding and modernisation phase in which economy and speed were paramount. This pushed domestic installations away from conduit in favour of sheathed cables, while RFCs and BS1363 fittings were introduced at the same time for the same purpose.

In industrial and commercial work, steel conduit has been the normal wiring system of choice for much of the history of the RFC.

 

[l4urence]

As stated previously this method is perfectly acceptable, I’ve worked on a couple (in bungalows for some reason). Be mindful that in my cases the conduit was joined in many places (no bends), these screwed connections and conduit buried in the wall can become loose or corrode quite badly - creating a risk. I test at each point and check condition of the backbox - which in one case revealed severe corrosion problems. It’s this arrangement that reminds us the purpose of the earthing lug in the backbox was to provide the earth to the socket - not like we do today with T&E and bond to it. In another case the bungalow was rewired, not because it failed any testing - but because the conduit ran up into the bungalow ceiling quite high (8” above the beams) and ran it’s way directly to the various rooms. The client wanted to use this space for storage and the raised conduit prevented sensible flooring.

 

[ipf]

I test at each point and check condition of the backbox - which in one case revealed severe corrosion problems. It’s this arrangement that reminds us the purpose of the earthing lug in the backbox was to provide the earth to the socket - not like we do today with T&E and bond to it.

We're earthing the backbox not bonding it.

 

[l4urence]

We're earthing the backbox not bonding it.

Correct. My mistake, well spotted. I think I was getting to direction and went off at a tangent. With conduit we take the earth from the backbox with T&E we take an earth to it.

 

[littlespark]

Rewiring through the old conduits could be a problem.
Last one I worked on had a central box with pipes running out to all the sockets.
This box was just under the floorboards, and no access hatch. Had to cut one.

Give the customer the idea that decorating now would be wrong. Go for a rewire first. There won’t be enough sockets for them even changing all the singles to doubles.