CU replacement with earthed conduit and singles

[Dartlec]

Just carried out an EICR on a flat that was wired in the 70s - with singles run in earthed conduit to each point and the trunking providing the earth at each socket/light point.

Ground floor flat, so needs RCD protection on sockets at least and seems due a CU change, but I have no experience with metal trunking so would appreciate the benefit of those with more experience...



Upper board can go as there is now a combi and central heating - no off peak circuits being used....

The lower board has approx 8 conduit lengths coming up, and 2 from above...All seem to be correctly glanded to the board - and the ZS readings at all sockets/fittings seem to be fine...

Obviously the chances are nil of finding a board to exactly match what's there - but I'd rather minimise the work - not to mention not having the skill or experience on metal conduit work (and this not being an empty flat where I could learn on the job).

What's the best way to ensure continuity with a new board?

1 option I can see is to leave the existing board in place purely as a 'junction box' for the earths and singles.... and fit a new one above it - leaving only the two upper conduits to deal with.

Another would be to replace the lower board with plastic trunking - terminating all the lower conduit with their existing bushes , but then I'd need to find a way to ensure continuity across the trunking - really don't want to have to cut metal trunking to do the job as it maybe 'should' be done.

If they are cut back, is there an approved clamp or similar to earth them, without needing to thread them for the correct glanding? I've found what is called a bonding nipple that looks like it would still allow space for the singles to exit.

Follow up question - all the sockets I checked have adequate Zs, but are getting that through the socket screws to the earthed back box (with the trunking glanded into each box). There are no fly leads from the box to the earth terminal on sockets. Some of the boxes have a terminal, to make that easy but others do not - but could be screwed, and drilled with self tapping and ring terminals used to make fly leads....

That is apart from the one more recently added socket which had a plasterboard backbox and earth cut short ? (Currently out of use until I can fix it)

In terms of an EICR on an existing installation, would you consider it essential to add the fly leads, a recommend, or not necessary at all as long as the earthing is satisfactory?

Final Question - Easycert has the option to choose 'conduit' for the earthing sizing on the test list. Is there any check that needs to be done to ensure equivalent sizing, or is pretty much all conduit greater than the equivalent T&E sizing?

 

[ChipFanDave]

I don't do domestic but finding this in a more industrial setting is not uncommon. Turminate conduits into into galvanised trunking then into DB or try using existing cables to pull in new ones including a CPC.

Not sure if they exist but a cosumer unit without knockouts would be ideal !!

 

[i=p/u]

Maybe consider din rail connectors in galv boxes, maybe use loop of galv trunking

Cpc is good on conduit

 

[littlespark]

Did you write all that just so you could use the term "bonding nipples"?

If you can find a new board that is less height, you could fill the gaps with nipples and couplings?
or you might find the lower conduits have a bit of play and can be pushed down a little within the wall

 

[Pete999]

Just carried out an EICR on a flat that was wired in the 70s - with singles run in earthed conduit to each point and the trunking providing the earth at each socket/light point.

Ground floor flat, so needs RCD protection on sockets at least and seems due a CU change, but I have no experience with metal trunking so would appreciate the benefit of those with more experience...

View attachment 86492

Upper board can go as there is now a combi and central heating - no off peak circuits being used....

The lower board has approx 8 conduit lengths coming up, and 2 from above...All seem to be correctly glanded to the board - and the ZS readings at all sockets/fittings seem to be fine...

Obviously the chances are nil of finding a board to exactly match what's there - but I'd rather minimise the work - not to mention not having the skill or experience on metal conduit work (and this not being an empty flat where I could learn on the job).

What's the best way to ensure continuity with a new board?

1 option I can see is to leave the existing board in place purely as a 'junction box' for the earths and singles.... and fit a new one above it - leaving only the two upper conduits to deal with.

Another would be to replace the lower board with plastic trunking - terminating all the lower conduit with their existing bushes , but then I'd need to find a way to ensure continuity across the trunking - really don't want to have to cut metal trunking to do the job as it maybe 'should' be done.

If they are cut back, is there an approved clamp or similar to earth them, without needing to thread them for the correct glanding? I've found what is called a bonding nipple that looks like it would still allow space for the singles to exit.

Follow up question - all the sockets I checked have adequate Zs, but are getting that through the socket screws to the earthed back box (with the trunking glanded into each box). There are no fly leads from the box to the earth terminal on sockets. Some of the boxes have a terminal, to make that easy but others do not - but could be screwed, and drilled with self tapping and ring terminals used to make fly leads....

That is apart from the one more recently added socket which had a plasterboard backbox and earth cut short ? (Currently out of use until I can fix it)

In terms of an EICR on an existing installation, would you consider it essential to add the fly leads, a recommend, or not necessary at all as long as the earthing is satisfactory?

Final Question - Easycert has the option to choose 'conduit' for the earthing sizing on the test list. Is there any check that needs to be done to ensure equivalent sizing, or is pretty much all conduit greater than the equivalent T&E sizing?

Run a cpc with every circuit don't rely on the conduit, if you haven't tested the conduit for continuity etc.

 

[mattg4321]

Do you have the depth to take the cover off the existing board and mount the new one on top?

 

[Dartlec]

Do you have the depth to take the cover off the existing board and mount the new one on top?

Sadly not, it's in a cupboard in the internal wall, so not a whole lot of depth above what is already there....

 

[Dartlec]

Did you write all that just so you could use the term "bonding nipples"?

If you can find a new board that is less height, you could fill the gaps with nipples and couplings?
or you might find the lower conduits have a bit of play and can be pushed down a little within the wall

I wasn't going to miss an opportunity to use the term "bonding nipples" once my googling found it, now was I!

No way to tell exactly how firm they are, but the back of the conduit is accessible from the outside cupboard that reverses onto this, with the main fuse in - and they seem to be pretty firm - solid concrete floor and ceiling I think...

The existing CU is 185 high, so unlikely I'll find one that's less than that.

No doubt it would be easy for someone with the tools and experience who does conduit all the time, but I'd rather not have to learn it and get all the bits just for the one job...

How likely is it that the bushes etc that have likely been there 45 years old will come undone without a lot of hassle?

If I have to cut the upper conduit back, I was hoping there was some sort of approved clamps that could be fitted to the existing conduit to maintain the earth - and chained in 6mm or something of suitable size from the MET...

Flat is currently on long term let, so not likely to be empty any time soon to consider a full rewire - and cabling all seems in good condition..

 

[Dartlec]

I don't do domestic but finding this in a more industrial setting is not uncommon. Turminate conduits into into galvanised trunking then into DB or try using existing cables to pull in new ones including a CPC.

Not sure if they exist but a cosumer unit without knockouts would be ideal !!

I'd rather not have to get into cutting galv trunking, conduit etc for one job if I can avoid it, though it's definitely the best way to do this I agree...

No idea how likely it is to all come apart easily either, after 45 years....

Pulling a CPC through might be an option, but no way to access conduit other than at fittings and source (buried in walls/concrete floor) and I can see one getting stuck half way and leaving me worse off than I am now....

 

[ChipFanDave]

I'd rather not have to get into cutting galv trunking, conduit etc for one job if I can avoid it, though it's definitely the best way to do this I agree...

No idea how likely it is to all come apart easily either, after 45 years....

Pulling a CPC through might be an option, but no way to access conduit other than at fittings and source (buried in walls/concrete floor) and I can see one getting stuck half way and leaving me worse off than I am now....

You won't need any extra tools for the galvanised trunking just a marker pen, hacksaw/grinder and a hole saw. Also a good dose of washing up liquid/expensive conduit lube would get them through ok. If the conduits are 45 years old may be worth getting some bushes that swap between imperial and metric.

 

[i=p/u]

Maybe someone on here can do for you dartlec, and you can watch.. and take 2%

 

[timhoward]

This is certainly a good challenge! A few reckless random ideas...

Last resort - plug in MCB's and up front RCD?!

Or using the old board as a template for cutting holes in the new board for the the lower circuits, maybe clean up and re-use old bushes if imperial. Very Very carefully shorten the top two, use bonding nipples to earth them and copex to get them to the new CU with separate CPCs.

OR how about replacing the lower board with two pieces of larger metal trunking and solder/crimp heat shrink new longer wires on them. You at least get multiple goes at the hole spacing then.

Or how about getting a fabricator to make a new front for the Wylex and it can just be a joint box.

 

[Pretty Mouth]

If the conduit is metric, then presumably earthing nuts would fit the threads? Not sure that's of any help or not.

Is there a reason BS951 clamps couldn't be used to earth the conduit? This article from PE lists their intended uses, and kind of leads me to believe they would be okay for this:

Clamps, Earthing and Bonding: Correct Selection and Installation

BS 951 specifies the performance and important mechanical requirements for metal clamps that are used to provide mechanically and electrically sound earthing and bonding connections to metal tubes. The

tinyurl.com

 

[Vortigern]

I am not clear as to whether you have an earth/cpc on the circuit, yes or no? So what you can do is cut the conduit back and use flexible conduit to go to the new box. That would need a cpc already in the circuit. If not then can you pull one in? As to the conduit being earthed, at the junction boxes such as where the lights are and inspection T's and 90 degrees etc you can put a fly lead joined to your cpc if this is not already done, secured with a round crimp and brass pan head screw. If there is no cpc then you need special tester to ensure continuity of the conduit earth. It puts out a high current and where the joins are it sparks if they are loose (forget what it is called) If this is not an option then you will have to draw in a cpc if you can access the inspection boxes??? Getting out the bushes requires a tool for the brass bush that you can buy at denmans. I have never found a jammed or impossible bush when doing this sort of thing but it does require the right tool. CK do one, bush spanner I would think it is called but it is not like a spanner. Oh and the best way to draw in an extra cable is to pull out one of the existing (one single) and attach two singles taped on to the one you are pulling out.

 

[westward10]

If you have space to the left terminate the upper conduits to a steel adaptable box, fit 20mm serrated washers, assuming they are metric to maintain continuity and bolt a separate cpc to the box again with serrated washers and connect to board with flexible or solid conduit. Do the same with the opposite lower conduits then fit the new board left of these direct to the other remaining lower conduits again with serrated washers. If they are imperial you need imperial entries metric will be oversized. Yes accessories need cpcs to the back boxes.