CU change in ex council flat

[Naz]

Hi all

further to my prev thread, thanks for the advise from the members.

The old CU is a metal box size 265*135*85mm, re-wirable fuse's. The wiring is run in steel conduit and this also acts as the CPC. The conduit is bushed to the metal CU box and everything is fixed firmly against the back wall.

I have a few worries doing this job and hope that you all may be able to suggest the best way forward.

1. Any new CU will be larger than than the unit being taken out meaning I may have to to cut the conduit to size. Im not sure how I would cut conduit held firm against the wall.
2. I would loose the thread and hence the bush fitting arrangement and thus my earth continuity.

I would like to put in a small CU ie 8 way and give the customer the benefit of rcd protection but with out circuit cpc's this will not be the case.
The customer also wants a cooker cable run to the Kitchen, running the 6mm cable will not be a problem and would ideally be run to a new CU with 32m mcb.

I will attempt to attach a pic to clarify

I have not suggested rewiring yet since I had not considered this originally and it would mean an extra cost implication. Also from some threads it is suggested rewiring steel conduit systems can be a nightmare.

regards
Naz

 

[lamb]

Kill the supply, strip out the fusebox, terminate existing tubes into 2x 50mm steel trunking runs (one for top, one bottom).
Join the two trunkings with 90' bends right hand side.
Extend lower trunking to the left and mount a modern metal clad consumer unit above it with a slot and grommet strip.
Extend the circuit conductors with thru crimps, run an earth to the trunking which will earth the conduits. Test and cert, job done.

 

[malcolmsanford]

That is a good way Lamb.

Just another take would be strip the guts out of the existing board and make it a "glorified Junction Box" fit a din rail and some 55amp Klippons and then terminate the circuit cables.

Then next to it, you seem to have room piggy back a new metal glad CU via a couple of 32mm brass bushes and lock nuts and away you go.

Lambs way is good, mine is that there is very little extra work involved.

As I said in a previous post though make sure you have CPC continuity at every point if you using the conduit as your CPC. Because of the earthed conduit you should be able to have some circuits non rcd protected, unless of course if the system is TT, but I agree RCDs are safer, but it could cut costs.

 

[lamb]

Malcolm, thats a good idea if the client wants to save money, as long as the old fuse box lid requires the use of a tool to gain access.

 

[telectrix]

and send me the old CU. i need to upgrade mine at home.

 

[Naz]

many thanks for the rapid replies,

going through them now to make sure I understand properly

regards

 

[Naz]

Hi Lamb
do you infer that I rip out the old cu and put the trunking in place to allow circuit cables to be run along to the new CU? I understand about then bushing the conduit to the trunking and then earthing all this to the new CU sitting on top of the extended trunking. Thanks for the suggest
Hi Malc, I will ensure continuity all the way as you have indicated, the system is TNS, I prefer RCDs as well, I think going the rewire route will be a mare and Im sure customer will not want the extra cost.
again many thanks
Telectrix- more than welcome u having old unit? didnt think it was any good in todays age?

 

[Knobhead]

Just to add to Malcolm’s suggestion of turning the old CU in to a JB, I personally would add banjo’s to each of the conduits so continuity isn’t reliant on the metal box.

 

[telectrix]

i was only joking, Naz. don't think i could sleep at night if i fitted that thing

 

[Knobhead]

i was only joking, Naz. don't think i could sleep at night if i fitted that thing

You would have to collect it, can’t send asbestos through the post

 

[Naz]

Hi Tel

Ha ha ha ha !

 

[Naz]

ps

have to be cash on collection

 

[Naz]

many thanks all

off for sun roast now

latas

 

[Engineer54]

That is a good way Lamb.

Just another take would be strip the guts out of the existing board and make it a "glorified Junction Box" fit a din rail and some 55amp Klippons and then terminate the circuit cables.

Then next to it, you seem to have room piggy back a new metal glad CU via a couple of 32mm brass bushes and lock nuts and away you go.

Lambs way is good, mine is that there is very little extra work involved.

As I said in a previous post though make sure you have CPC continuity at every point if you using the conduit as your CPC. Because of the earthed conduit you should be able to have some circuits non rcd protected, unless of course if the system is TT, but I agree RCDs are safer, but it could cut costs.

That would be the course i would take with this installation too. But i would remove the the hinged door and replace with a lid made of galvanised sheet steel. Can't have a gaping hole where access to the main switch once was!! As Tony stated i would also add banjo's or piranha nuts to the conduits entering the old CU. Also i'd be getting rid of those earth clamps to the conduit, and especially that SWA cable, and create a pukka MET.

I don't like these split RCD CU's, although more expensive, i would always favour RCBOs. Thus making the CU far more secure and adaptable in the future, and without these multi circuit RCD problems, that seem to be the subject of threads here, on a daily occurance on the forums these day's.

 

[Welchyboy]

I have actually seen conduit couplers where you can cut the conduit in place and knock them on the end of the existing conduit, i dont know if they do them in imperial sizes though, also dont know how good the earth continuity would be through them but maybe its worth a look???
then you could loose that old cu alltogether

 

[malcolmsanford]

That would be the course i would take with this installation too. But i would remove the the hinged door and replace with a lid made of galvanised sheet steel. Can't have a gaping hole where access to the main switch once was!! As Tony stated i would also add banjo's or piranha nuts to the conduits entering the old CU. Also i'd be getting rid of those earth clamps to the conduit, and especially that SWA cable, and create a pukka MET.

I don't like these split RCD CU's, although more expensive, i would always favour RCBOs. Thus making the CU far more secure and adaptable in the future, and without these multi circuit RCD problems, that seem to be the subject of threads here, on a daily occurance on the forums these day's.

Yes mate spot on you need to remove the existing board face plate and knock up another one but done it many times and it can look quite good, especially if you have a mate who owns a metal workshop with a press and guillotine lol

 

[Engineer54]

I have actually seen conduit couplers where you can cut the conduit in place and knock them on the end of the existing conduit, i dont know if they do them in imperial sizes though, also dont know how good the earth continuity would be through them but maybe its worth a look???
then you could loose that old cu alltogether

Welchyboy, i've seen a couple of these as submitted samples on my projects, i don't believe they can be relied on for long term continuity, they are not particually too clever even when new. Systems using such push-fits would in my opinion require a separate CPC to ensure ongoing long term earth continuity....

 

[Knobhead]

I have actually seen conduit couplers where you can cut the conduit in place and knock them on the end of the existing conduit, i dont know if they do them in imperial sizes though, also dont know how good the earth continuity would be through them but maybe its worth a look???
then you could loose that old cu alltogether

Have you just wandered in off the plumber’s forum? Those things are awful!

 

[Welchyboy]

Have you just wandered in off the plumber’s forum? Those things are awful!

Ok ok fair enough! just throwing ideas about no need for an insult of that magnitude!

 

[Knobhead]

Sorry