How to change from conduit to T&E in celing void

[SJD]

Scenario:
In an old house, the main fuse board is next to the supply intake, which feeds sockets, cooker, immersion.
For the lighting, there is a separate sub-board in the centre of the house, fed by a 2.5mm T&E distribution circuit from the main board.
This 4-way sub-board is antique, cast iron with porcelain fuses, above a ground floor door - and has to go prior to renovation work.
The lighting is singles in metal conduit, with the conduit used as the CPC, but is in very nice condition, no need to replace any of it.
Intent is to run the 4 circuits in T&E individually back to the main board (which is being replaced by a modern CU).
There's not a lot of room in the ceiling void.

Question:
Ideally I'd like to cut off the conduits in the ceiling void, and connect the T&E to each circuit.
Any suggestions for the best way to do this, nicely terminating the conduits/singles, and all maintenance free and meeting regs?

 

[telectrix]

if you can fit the T/E into the conduit, you could use the singles as draw wires, then no joints. otherwise, fit boxes to the cut conduit and join in the boxes, stuffing glands on the T/E.

 

[guest119]

Is I.R. ok?
You will be using rcd/rcbos wont you?

Boydy

 

[Lucien Nunes]

If the conduit is 3/4" screwed, you might use imperial/metric adaptors at the nearest existing joints to allow you to extend the conduits to meet at an adaptable box, where you can connect the singles to the new T+E. If you can retain access for inspection, then even flexible conduit with earth terminals on the adaptors might suit, to take the earth to the beginning of the solid conduits. If it is 5/8" or you have to saw through without room to thread, it will be more of a problem to attach to the ends of the existing, I am not sure if you can still get 5/8" fittings.

You can make a custom adaptor to flex conduit out of a conduit adaptor and a decent compression gland (to fit the steel) connected in a coupler. However you must bush the cut end of the steel - I use thick-wall adhesive heatshrink and pop the outer end in on itself inside the tube so that it shrinks 'outwards' and totally covers the end. But for continuity you will then need a bonding clamp to a bared area on the tube and hence access for maintenance.

Also, are you sure there are no slip fittings in the conduit work? I would not trust these for continued use as the CPC.

 

[SJD]

Thanks for the replies so far.

Tel: There have to be joints, I'm not planning to disturb most of the lighting circuits, unless any faults show up on testing.

Boydy: Yes, IR is excellent (tens to hundreds MOhm depending on the circuit) and yes new CU will be dual RCD with all circuits protected.

Lucien: Yes, the conduit is screwed imperial and the bits I can access don't have any slip fittings, but I'm not able to inspect it all. I'll be testing for continuity at each fitting. The access for inspection if that is needed will be under a floorboard in a doorway, that's the best that's going to be available, though I'm sure some will say this doesn't count. Some custom adapter and bonding clamp along the lines you suggest might work.

 

[Lucien Nunes]

Because you don't need much mechanical protection you might even find a thin-wall nylon flex conduit that will push snugly inside the end of the steel, and seal them together with heavy duty adhesive heatshrink. That might sound like a bodge but it can be as strong as the nylon conduit if you use good quality heatshrink and get a good purchase on both sides.

If you can draw as far as the first point, then maybe it's worth taking the T+E that far or adding a CPC to there and using that to earth the conduit. This might enable you to make the plastic / steel connection inaccessible if the T+E is connected with MF terminals.

BTW if the old fuse box has a glass front or is very unusual don't skip it - museum it! Threaded steel for domestic lighting seems to pinpoint good class work with nice fittings.

 

[Jay Sparks]

Is the conduit used as the cpc?

 

[guest119]

Is the conduit used as the cpc?

Should have gone to Specsavers Jay.

Boydy

 

[Jay Sparks]

Should have gone to Specsavers Jay.

Boydy

Ha ha Ha lol......Totally missed that bit in the OP. My bad, didn't read it all!!! Serves me right.

 

[johnboy6083]

If you have a box nearby, get another terminal box, bush the threaded entry and drill out the back of the box. Take the twin into the box below & join away. Drill 5mm holes in the back of the top box, using the lid you removed as a guide. Then screw the top box onto the small one.

this is a method I've used lots when I've needed to add to conduit systems, but can't switch off the circuits contained in it to break into it!

when doing this to add to the conduit, I set the tube back down to the same level as the bottom box and it looks neat.

 

[brizospark]

Conlok through box stuffing gland for t and e ring crimp on earth and earthed to through box earthing terminal. Wagos for l&n.

 

[Lucien Nunes]

Is the Conlok earth continuity guaranteed with imperial conduit sizes? And, as I've never used it, are Conlok joints rated as MF when used for CPC?

 

[Dave 85]

Is I.R. ok?
You will be using rcd/rcbos wont you?

Boydy

Great answer. Very informative. Thanks.

 

[SJD]

You can make a custom adaptor to flex conduit out of a conduit adaptor and a decent compression gland (to fit the steel) connected in a coupler. However you must bush the cut end of the steel - I use thick-wall adhesive heatshrink and pop the outer end in on itself inside the tube so that it shrinks 'outwards' and totally covers the end. But for continuity you will then need a bonding clamp to a bared area on the tube and hence access for maintenance.

Just tried this. Using adhesive heatshrink to bush the ends (5/8 conduit), it works really well. I was a bit concerned the heatshrink inside would close up, but not so. I used a tapered screwdriver shaft to press the folded over heatshrink tube onto the inside wall of the conduit while hot.

 

[Lucien Nunes]

I used a tapered screwdriver shaft to press the folded over heatshrink tube onto the inside wall of the conduit while hot.

Glad it worked, this sounds like a good precaution. Another thing that helps make sticky heatshrink bond well to metalwork is to pre-heat the metal before putting the tube over it, but then you must hit the spot first time as it sticks immediately.