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

 

[7029 dave]

IMO, if it is a full conduit installation then it will be ok, do some continuity testing, having said that I used run in cpc on all my installs. (even on rewires)

 

[davesparks]

Yes steel conduit is still just as acceptable as a CPC today as it was when that was installed, see regulation 543.2.1 (vi)
Also note the requirement of regulation 543.2.7 must be complied with in this case, so an earth flylead must be taken from the backbox to every accessory with an earth terminal.

How you test the continued integrity of the conduit is up to you, you need to apply your technical knowledge to decide this as there is no 'paint by numbers' method as far as I know. personally I would use a high current Zs test as a bare minimum but would much prefer to test with a high current milliohmmeter (aka ductor) wherever possible.

 

[NEB Electrical]

IMO, if it is a full conduit installation then it will be ok, do some continuity testing, having said that I used run in cpc on all my installs. (even on rewires)

Yes i think it is a full conduit install.

Just gives me the heeby jeebys looking at a board and there is no earths connected to the bar!

Thanks for your reply

 

[MJPD29]

If it's from 1960 check what kind of cable it is whether it's pvc or rubber

 

[NEB Electrical]

Yes steel conduit is still just as acceptable as a CPC today as it was when that was installed, see regulation 543.2.1 (vi)
Also note the requirement of regulation 543.2.7 must be complied with in this case, so an earth flylead must be taken from the backbox to every accessory with an earth terminal.

How you test the continued integrity of the conduit is up to you, you need to apply your technical knowledge to decide this as there is no 'paint by numbers' method as far as I know. personally I would use a high current Zs test as a bare minimum but would much prefer to test with a high current milliohmmeter (aka ductor) wherever possible.

Dave

Superb, yes i carry out a complete test of the installation any time a consumer unit upgrade is done. I think in this case thought every switch/socket will have to be opened to make sure fly leads are in place.

I appreciate your advice on this matter.

Nick
[automerge]1572380229[/automerge]

If it's from 1960 check what kind of cable it is whether it's pvc or rubber

Matthew

Is there a way to tell the difference ? As it just looks like old single core wiring. I suppose just by the feel of it ?

If it is rubber does this constitute a non-compliance ? In my eyes it should be fully rewired due to the age of the system, but customer only wants it done if it is absolutely necessary.

Nick

 

[davesparks]

Just gives me the heeby jeebys looking at a board and there is no earths connected to the bar!

Why? there's plenty of boards out there with no cpcs, or far less cpcs than the number of circuits connected.
Circuits wired in steel conduit, trunking, SWA or MICC can all result in no,or very few, cpcs in the earth bar.

 

[NEB Electrical]

Why? there's plenty of boards out there with no cpcs, or far less cpcs than the number of circuits connected.
Circuits wired in steel conduit, trunking, SWA or MICC can all result in no,or very few, cpcs in the earth bar.

Dont know why, think its just the way i was taught.

Not everything is black and white though as i have learned over the past 5 years running by business

 

[7029 dave]

Why? there's plenty of boards out there with no cpcs, or far less cpcs than the number of circuits connected.
Circuits wired in steel conduit, trunking, SWA or MICC can all result in no,or very few, cpcs in the earth bar.

The best method because it at mass, in my day no fly leads etc, get your file out an give it a bloody good clean down to the metal.

 

[davesparks]

Superb, yes i carry out a complete test of the installation any time a consumer unit upgrade is done.

Is there a way to tell the difference ? As it just looks like old single core wiring. I suppose just by the feel of it ?

If it is rubber does this constitute a non-compliance ? In my eyes it should be fully rewired due to the age of the system, but customer only wants it done if it is absolutely necessary.

Its possible to carry out a complete test without effectively testing the conduits, for example carrying out only low current/anti trip type Zs test instead of a high current test may well result in a false pass result.

VIR singles look very different to any pvc insulated cable, i'm sure you could find many pictures if you search but the dead give away would be the woven fabric outer surface of VIR. Also the smell, waxy feel and high chance that it has perished and gone crispy should give it away.

Why would you rewire purely due to the age of the system? There are good valid reasons why you might rewire if there were a lot of additions to be made or significant alterations, altering a flush mounted steel conduit system isn't all that convenient,
but just because it is old it doesn't necessarily mean it must be replaced.

 

[MJPD29]

Dave

Superb, yes i carry out a complete test of the installation any time a consumer unit upgrade is done. I think in this case thought every switch/socket will have to be opened to make sure fly leads are in place.

I appreciate your advice on this matter.

Nick
[automerge]1572380229[/automerge]

Matthew

Is there a way to tell the difference ? As it just looks like old single core wiring. I suppose just by the feel of it ?

If it is rubber does this constitute a non-compliance ? In my eyes it should be fully rewired due to the age of the system, but customer only wants it done if it is absolutely necessary.

Nick

Generally you can tell from the look of it, if you get a chance even send a pic in and we can try and help

 

[NEB Electrical]

Its possible to carry out a complete test without effectively testing the conduits, for example carrying out only low current/anti trip type Zs test instead of a high current test may well result in a false pass result.

VIR singles look very different to any pvc insulated cable, i'm sure you could find many pictures if you search but the dead give away would be the woven fabric outer surface of VIR. Also the smell, waxy feel and high chance that it has perished and gone crispy should give it away.

Why would you rewire purely due to the age of the system? There are good valid reasons why you might rewire if there were a lot of additions to be made or significant alterations, altering a flush mounted steel conduit system isn't all that convenient,
but just because it is old it doesn't necessarily mean it must be replaced.

Dave

Yes i understand that. What i mean is that this will get its full test with the addition of continuity tests for the conduit system.

The wiring is not VIR as i know that stuff from the look and feel of it. I was more concerned about one of the other comments that asked if it was PVC or RUBBER cabling.

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.

Thanks again

Nick

 

[Lucien Nunes]

Rubber = VIR for most conduit wiring (Vulcanised India-Rubber)
Rubber = TRS for T+E (Tough Rubber Sheathed)

There are a few situations where plain unbraided rubber cables were pulled into conduit, they look like the cores of rubber flex, but not for ordinary domestic. If it's 1960 it will be ordinary XLPE or PVC-insulated imperial tinned copper singles.

Beware hidden sections of conduit that have been cut and not re-joined, or corroded at the joints in damp areas. If it's never been tested, I would do a wander-lead test if not an actual high-current ductor test, as this will give a clearer indication of any bad joints than R1+R2 or Zs as excessive conduit resistance will not be masked by differences in the resistance of the line conductor at different points.

In general, steel conduit offers an excellent CPC provided it is done properly and not left incomplete by later careless work. That is the unknown you have to deal with at this stage, instead of the different unknowns typical of T+E installs (Hidden joints, nails through cables, rodent damage).

 

[NEB Electrical]

Rubber = VIR for most conduit wiring (Vulcanised India-Rubber)
Rubber = TRS for T+E (Tough Rubber Sheathed)

There are a few situations where plain unbraided rubber cables were pulled into conduit, they look like the cores of rubber flex, but not for ordinary domestic. If it's 1960 it will be ordinary XLPE or PVC-insulated imperial tinned copper singles.

Beware hidden sections of conduit that have been cut and not re-joined, or corroded at the joints in damp areas. If it's never been tested, I would do a wander-lead test if not an actual high-current ductor test, as this will give a clearer indication of any bad joints than R1+R2 or Zs as excessive conduit resistance will not be masked by differences in the resistance of the line conductor at different points.

In general, steel conduit offers an excellent CPC provided it is done properly and not left incomplete by later careless work. That is the unknown you have to deal with at this stage, instead of the different unknowns typical of T+E installs (Hidden joints, nails through cables, rodent damage).

Lucian

Thank you for clearing that up. I would agree that a wander lead would be the most effective method of proving continuity to each point in the system.

Yeah conduit is a dying art, i was lucky enough to do alot of it in my early career, although the industrial/commercial side of it. We would always run CPC's though.

On a side note, if you are using the conduit as CPC what do you record for your ring r2 readings ?

Nick

 

[Lucien Nunes]

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.

 

[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.