Finally got round to looking at the upstairs lights in this place, and discovered that all the chased-in cable uses 15mm copper as conduit containing 1 or 2 1.5mm cables (well, could be 1.0)
My understanding is that this doesn't need earthing (it isn't) because it contains normal T+E, so double insulated.
My concern is that when I pull new cable through it, I run the risk of damaging it, particularly if I'm running two cables. I can deburr as much as possible - it's already deburred - and tape over the edges - but is there anything else to help matters?
Metal capping does not need an earth so I guess the pipe would not either, but you need more expert advice. You may run into problems if using 3core + earth for two way lighting and if you are planning to loop in at the switches the pipe is woefully inadequate. If you have loft insulation and the cables will run either across or through it you may have to uprate the cable to 1.5mm2 which make for a tighter fit.
Are you worried about the insides of corners etc? How is it assembled at corners, surely not like a water pipe with fittings? I don't think I've ever come across this sort of thing, most conduits I've seen are jointed black painted tubes with a thread on the end which is often not used for fixing it seems. Brian
Unless I want to chase out some more - and I really don't if I don't have to (and SWMBO *really* doesn't)- then aren't I tied to JBs (maintenance free, obvs)? For the first floor lights I'll try to put them outside the floor area of the planned loft conversion. Ground floor is less critical, because it's not affected by the planned works.
1.0mm T&E has a CCC of 16A so if we have to derate this by 50% it can still be covered with a 6A MCB. Further say we then had to apply another
0.7 derating due to it been say 50deg then you still have 5.6A to play with. That is 1.29kW. Now only if the OP has a load somewhere in that region do you need to consider upping the cable size.
It matters not that in this case we are running the cable at a CCC rating below the MCBs rating as the known load "should" be a lot lower.
If the OPs load is in that range then he would probably have to swap to
They do look nice. I was planning on using Ashley boxes, but at £5 per light/switch connection, the SureWire stuff will work out cheaper. I'll lose some on longer runs - but I need those anyway because I want all the JBs to be accessible from the eaves storage areas. I'll give them a go.
Finally got around to putting a Building Notice for the full rewire. Was supposed to start last year but work got in the way.
Pulled up some floorboards today (and split one of them :( ), and in the course of putting a temporary run in, discovered the existing wiring is stranded. Discovered some tags for 3/029 under the floor. This is quite fun. So presumably it was rewired in T+E in (presumably) the early 70s - at which point they appear to have surface mounted all the cables they couldn't hide in the original copper "conduit". Also found some of the original VIR in a copper pipe (I say copper. It looks like copper. Was 1/2" copper common in 1935??).
Also some twin-core (not in service, so far as I've been able to determine) and an obviously retrofitted 6mm (maybe) earth which I'm a bit worried about since it's still connected to the CU, and heading off in the direction of the bathroom. Surely someone hasn't connected the supplementary bonding back to the CU.... Or perhaps it's a main bond for the cast iron waste?
The wiring is still in good nick - but we plan on being in this house for a good while, so we'll gut the lot and then get on with decorating. If I can get hold of the guy inspecting it, I'll ask how he feels about calling the copper tube "capping" - otherwise I've decided to just rip it out and pick a different battle.
Wiring the lot in 1.0mm since loads won't approach anywhere near 6A. Planning to run a neutral to all the switches while I'm there.
The downstairs will be the fun bit. I want to insulate underfloor, I so I need to lift every floorboard. Not to mention 20sqm of laminate.
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