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?

 

[Dartlec]

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

I did wonder that.

That article only mentions 'bonding conductors' to metal tubes, and earthing conductors to rods, but can't see any reason why they wouldn't be functional - just not sure enough of the way they are normally done...

There are really only 4 circuits needed, so I may be able to fit an RCBO board to the top left in place of the off peak one - and then use the existing board merely as a junction box....

 

[Dartlec]

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 the existing )one single and attach two singles taped on to the one you are pulling out.

No CPCs at any fitting - just live conductor singles pulled to each point - with the conduit acting as the earth...

From documents on site it looks like this was done by SEB in 1976, so it in theory should be metric - just never seen one still in place in a domestic property - usually its the even older (thinner) piping that wasn't earthed - and has had twin and earth pulled through after that...

As far as I can see there are no inspection boxes or access to any of the conduit - it appears to be in the concrete floor/ceiling or buried entirely in the walls...

Each back box does appear to be properly fitted with bushes though, and the standard Hi Zs test gave acceptable results at each point I tested....

 

[telectrix]

You need to test R2 at every point to ensure conduit is electrically connected throughout, then use conduit as cpc. flyleads may be required for any new accessories fitted.

 

[Dartlec]

Update on this:

I managed to just squeeze a Fusebox CU in the gap so left the Wylex board as a junction box. Still need to find a suitable permanent cover for it - I'm thinking maybe the lid of an adaptable box screwed into the existing cover with self tapping... Or possibly even just a suitable size bit of PVC sheet or similar?

Had to run some SWA externally to supply the cooker and hob that had been bodged by the same kitchen fitter who screwed the sockets up in my dodgy trade pics post...

Not ideal - but also not the job where there was time (or budget) for me to get into cutting and finishing conduit - which would have been a nightmare anyway with the space and access I think...

Since the photo I added a label stating the conduit was essential earthing so should not be removed.

Maybe if/when it's next empty I'll have a chance to sort it all out properly....

 

[westward10]

Should have done something like I suggested in #15 time and budget should not be relevant although my suggestion would not really have compromised either.

 

[MJPD29]

I can't help but notice that with everyone's fusebox installs the mcbs/rcbos all seem to have a bit of tilt tk them. Did you find that when fitting this? I haven't used one yet and probably never will If they suffer from the mk or mcg slant I can't stand it

 

[Dartlec]

I can't help but notice that with everyone's fusebox installs the mcbs/rcbos all seem to have a bit of tilt tk them. Did you find that when fitting this? I haven't used one yet and probably never will If they suffer from the mk or mcg slant I can't stand it

Yes I think it is a problem inherent with them. Torquing the lower terminals to 2.5Nm seems to instill a slightly lean, though it's not quite as bad as MK at its worst. They use a similar busbar to MK so maybe something to do with that design, or the clips.

I did try a couple of times to improve it, and to be honest it was slightly worse before the cover went on.

They are nice at the price and the enclosures seem pretty strong compared to some, so happy to use them when I can get them. Waiting for my CEF to get Click in, and may give those a go....

 

[timhoward]

If you make some spacers so it clears the switch, you could just maybe just drill, tap and use machine screws.
Or remove the switch and pop-rivet two smaller plates on.
Probably 100 ways to do it!

In the meantime (being over-paranoid) I wonder if a label saying "Isolate Above Not Here" might be a thought in case someone pulls back the tape thinking some wally has taped over the switch!
Nothing is fool-proof for a sufficiently talented fool...

 

[ipf]

You could get some 2 pack araldite epoxy adhesive. Remove switch, etc for a flat face and just glue a suitable piece of steel to the steel. Screwfix do some for about a fiver.
Call at some small fabrication works or garage, maybe. I'm sure someone will cut and provide a suitable piece of steel from a cut off for next to nothing.

 

[Lucien Nunes]

It's a tidy (and popular) solution to convert the existing board into a marshalling box, but in this case it only worked because of the small number of ways required in the board that would fit in the available space. Had there been three more circuits, that would have been a problem.

This is a situation where I would have used Conlok fittings for the top two conduits The downward conduits could have been dealt with very quickly with a length of 50x50 trunking. Take the old board off, put the trunking against the bottom of it and draw the hole positions through. A few minutes with a drill and a Q-Max and you have a replica that should just drop straight on. But the top two conduits are in the way and assuming they can't be unscrewed, need to be cut back in situ.

If there is enough room to slide some protective hose over the cables and up inside the conduit, you can get rid of 80% of the cross-section of steel with a mini grinder / Dremel disc and snap the rest off. But then you have a plain unthreaded end of conduit for which a Conlok coupling is the obvious solution. It feels like cheating but why not indeed?

 

[i=p/u]

Soon as you do it, always a better way to improve.
But a steel plate or something and screw it up, jobs a gooden...

Any chance a look inside you junction box.. show the boys its not a mess?

 

[Dartlec]

It's a tidy (and popular) solution to convert the existing board into a marshalling box, but in this case it only worked because of the small number of ways required in the board that would fit in the available space. Had there been three more circuits, that would have been a problem.

This is a situation where I would have used Conlok fittings for the top two conduits The downward conduits could have been dealt with very quickly with a length of 50x50 trunking. Take the old board off, put the trunking against the bottom of it and draw the hole positions through. A few minutes with a drill and a Q-Max and you have a replica that should just drop straight on. But the top two conduits are in the way and assuming they can't be unscrewed, need to be cut back in situ.

If there is enough room to slide some protective hose over the cables and up inside the conduit, you can get rid of 80% of the cross-section of steel with a mini grinder / Dremel disc and snap the rest off. But then you have a plain unthreaded end of conduit for which a Conlok coupling is the obvious solution. It feels like cheating but why not indeed?

I did wonder about Conlock, but it seemed to have a poor reputation in the places I searched....

One of the top conduits was actually no longer in use but naturally it was the right hand one, so not helpful...

Circumstances in this one required a fairly fast turn around - tenant off work and at home, needing EICR done, etc - and most of the time was needed fixing the other issues in the property...

I'll maybe get some conduit and conlok when I have some free time and have a play around until I'm confident I could do a competent job.

Alternatively if it was empty I'd probably try drawing a CPC through the conduit, or even suggest a rewire...

For now, there is unlikely to ever be need for more circuits (small 1 bed flat). The only real compromise was the lack of an SPD.

 

[timhoward]

I did wonder about Conlock, but it seemed to have a poor reputation in the places I searched....

One of the top conduits was actually no longer in use but naturally it was the right hand one, so not helpful...

Circumstances in this one required a fairly fast turn around - tenant off work and at home, needing EICR done, etc - and most of the time was needed fixing the other issues in the property...

I'll maybe get some conduit and conlok when I have some free time and have a play around until I'm confident I could do a competent job.

Alternatively if it was empty I'd probably try drawing a CPC through the conduit, or even suggest a rewire...

For now, there is unlikely to ever be need for more circuits (small 1 bed flat). The only real compromise was the lack of an SPD.

I also wondered about Conlock (having never used it).
The thing that cast lingering doubts is that I believe a small hex grub screw is used to tighten up the fitting, and this doesn't feel adequate to confirm a joint in a CPC. I might be totally wrong, just a gut reaction.

 

[WallaceP]

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?

Are you sure the ‘bonding nipples’ ? are the correct thread?
I like the idea of pulling new cabling through the existing conduit but it could be risky. For me converting the existing fusebox to a j-box din rail, new lid etc and t+e or kopex to the new board is the way.
I have an MICC board change next week but luckily they all come into the top of the board ?

 

[DefyG]

Think I would try to maintain the good cpc continuity and save time by not disconnecting/reconnecting the 8/9 conduits and incorporate existing box into new consumer unit/trunking.