Alterations involving buried metal conduit

[Doug]

The property in question is an ex-council flat with brick walls and concrete floor and ceiling. Most wiring is buried in steel conduit. The conduit is in good condition and it's been rewired in singles including a CPC. All in all, the wiring is pretty good.

The householders would like a lot of alterations including fittings moved, points added and single sockets changed for doubles. For example, they would like pendant lights moved from near the windows to the centres of the rooms. They don't want surface wiring.

One method would be to chase across the ceiling from the original point, cut a notch in the side of the metal box, join the wires then plaster over. Although the ceiling is structural, I wouldn't be going any deeper than the original conduit.

If the original conduit happens to cross the centre of the ceiling then an alternative could be to chop out a piece of conduit to pick up the wires. I probably wouldn't have enough slack to join onto though. I also wondered if the wires could come from different directions, with live from switch and neutral from previous light.

A third option would be to give up and fit a new circuit. This would mean a lot of chasing.

None of this will be straightforward. Are there any tips for modifying circuits buried in metal conduit?

 

[Deleted member 9648]

The property in question is an ex-council flat with brick walls and concrete floor and ceiling. Most wiring is buried in steel conduit. The conduit is in good condition and it's been rewired in singles including a CPC. All in all, the wiring is pretty good.

The householders would like a lot of alterations including fittings moved, points added and single sockets changed for doubles. For example, they would like pendant lights moved from near the windows to the centres of the rooms. They don't want surface wiring.They may have to,they need to understand the difficulties with this

One method would be to chase across the ceiling from the original point, cut a notch in the side of the metal box, join the wires then plaster over. Although the ceiling is structural, I wouldn't be going any deeper than the original conduit.You would need to use earthed steel conduit or SWA as it would not be in a safe zone...I doubt the original conduit would be on the underside of the ceiling,they are normally run over the floor above in the screed and drop through,you should seek advise from a structural engineer before cutting a chase........Quite frankly they may be better off putting in a false ceiling and extending from the original boxes in T/E

If the original conduit happens to cross the centre of the ceiling then an alternative could be to chop out a piece of conduit to pick up the wires. I probably wouldn't have enough slack to join onto though. I also wondered if the wires could come from different directions, with live from switch and neutral from previous light.NO!!not an option

A third option would be to give up and fit a new circuit. This would mean a lot of chasing.

None of this will be straightforward. Are there any tips for modifying circuits buried in metal conduit...Even changing a single to a twin is not as simple as you would think...the problem with a flush box bushed to steel is removing the box and refitting a twin without damaging the wires where they exit the tube.One option is to chop down below the box position to give enough space for the box to be dropped away from the pipe before being manouvered out/in....Another if this is not an option is to leave the existing alone and cut a second box alongside....third and easiest ,if they will sanction it ,is to use one of those nasty converter sockets.

.........

 

[Doug]

Thanks for your advice. That's a good point about the conduit possibly being buried in the floor above.

One of the sockets they want changed from single to double has conduit bolted into the top AND the rear. I was already thinking that it would be best to add the new back box alongside.

They are considering a suspended ceiling in the kitchen to allow downlights. It would make the wiring easier if they did this throughout the flat.

 

[Knobhead]

As Wirepuller says the conduit will drop down from the top screed to BESA boxes.
Chasing the ceiling is not an option you will find the reinforcing mat about 1” above the level of the ceiling, cut through that and the structural integrity is compromised. The mat will be in tension cut a bar and “twang” cut the next and the next and I hope you’ve got strong arms.
Don’t even think about it!

 

[Doug]

Thanks for your comments Tony. I knew knew this would not be a straightforward job and it's good to hear from others who have tried this before.

Light switches have round boxes behind, with the 2 imperial screw holes in a diagonal line. The modern square switches have been fitted using shallow pattresses. Is there an easy way to mount the switches flush with the wall?

 

[Knobhead]

You will find all the circuits come downwards. For the ceilings the shuttering is erected first followed by the reinforcing. Then the conduit and boxes, Conduit leapfrogs from the top of one box to the next. The floor is then poured followed by the final screed.
As to the light switches you’ll have to do as Wirepuller suggested with the sockets and chop out below the box and slide the new box on to the conduit
You’ve got your work cut out kid.

 

[Engineer54]

What can i say, ...i've never seen power/socket circuit conduits run from above, in an all concrete or concrete frame, block/brick infill building, they are always run on the floor slab of the level they are serving. They are then covered by the float/screed... Lighting wise yes, generally installed into the slab re-bar system before pouring...

Not saying that they can't be or are never run from above, but material wise it doesn't make much sense!!

Oppppps ... this was meant to be posted in the Concrete ceiling walls floors,, thread!! ...lol!!!

 

[GLENNSPARK]

Thanks for your advice. That's a good point about the conduit possibly being buried in the floor above.

One of the sockets they want changed from single to double has conduit bolted into the top AND the rear. I was already thinking that it would be best to add the new back box alongside.

They are considering a suspended ceiling in the kitchen to allow downlights. It would make the wiring easier if they did this throughout the flat.

yes, dont count this scenario out....as i seem to remember a thread in here a while back involving a damaged cable in conduit in a flat....yep you guessed it..builders in the flat above with a stihlsaw and jiggypick had been the culprits....