shower plumbing & electrics

[Fred]

Yes, that's what I was thinking of. I just wondered whether it needed clipping to a stud at certain intervals. That would be easy to do if you were building the wall from scratch but since the wall is already there, I will not be able to do this. I wasn't sure whether the pipe might "kick" when switched on and off and whether over time this might make it loosen any compression joints. Hopefully I am being far too pessimistic. Thanks.

[Fred]

Thanks to the table in the UK.DIY FAQ, and thanks to ARW for posting the link, I think it is 6mm^2 cable that is in place.

It is red and black cable. Was that fatter than the blue and brown? I had a small off cut of blue and brown 6mm^2 with me and it did look smaller overall. Perhaps the insulation is thinner on the new coloured stuff?

I measured the overall size as being 13.4mm x 7.5mm. The FAQ says

6mm^2 cable is 13.1mm x 6.8 mm. So this one is slightly thicker than expected. Do the cables vary by manufacturer? If so, this might explain the difference.

The table says that a 2.5mm^2 CPC would have a diameter of 1.78mm, so let's call that 1.8mm to one decimal place. I measured 1.9mm on a vernier calliper, so that's pretty close to the expected result. So far so good.

I measured the diameter of the neutral (once the circuit had been disconnected). I measured an overall diameter of 3.0mm but I am not sure how accurate this was as I guess it depends how the individual cores lie. I measured a single core and it was 1.0mm. The table says it should be 1.04 but I would not have been able to see the 0.04, so I guess my result matches the table.

I am pretty confident this is 6mm^2 T&E. Is there any reason to doubt this now?

The table gives much bigger values for the various dimensions of

10mm^2 T&E so I am sure it is not that.

The only thing that concerns me now is the path of the cable. All the cables leave the CU and go up the wall in sort of trunking. Does this count as clipped direct to the wall? I was worrying that the trunking makes it count as being in conduit. I'll have to take a closer look at what it actually is and how the cables are grouped inside it. I suspect they are just all thrown in together.

The cables then appear under the bathroom floorboards. They then run

3' or so all next to each other and where there are joists in the way, the cables go through one big hole in the middle of the joist. I thought you were supposed to have a separate hole for each cable and space the holes by three times their diameter?

But since this is "red and black" wiring, perhaps the regs. were more relaxed then? Were they? It was rewired by a pro, so I hope it was done properly at the time.

It's crazy really because the cable is not far from the corner with the shower cubicle and all that needed to be done was for the cable to go up the wall to a pull switch on the bathroom ceiling. For reasons I cannot understand (perhaps he didn't want to chaser the wall nor have cable clipped or trunked or otherwise visible), the cable does not do this; instead it turns and runs away from the cubicle!

The cable runs to the airing cupboard in the opposite corner of the room and then runs up the inside of the cupboard and into the loft. I don't know whether the cable is buried under any insulation because that part of the loft is inaccessible. Because it is inaccessible, there shouldn't be any insulation there but who knows?!

It is a little old lady living on her own, so I don't expect the wiring ever gets near full load but all the same, should I derate the shower cable on the basis that it runs close to everything else and may or may not be under insulation in the loft?

If so, what should I derate it to?

I think, but will check, that there is another 6mm^2 cable for the electric cooker and there is an immersion heater (2.5mm^2 ?). Quite often she has an electric fire plugged in to a socket downstairs. These are the only big loads I can think of that exist in the house.

That said, the cooker is only on for short periods of time at meal times and the boiler rather than the immersion is used for HW, and a ring main can cope comfortably with an electric heater, so I don't think any of these would be on at the same time as the shower and I doubt any of the loads would be on long enough to cause any heating of the cables. That only leave the insulation to worry about.

What do you all think? I could lay the cable in a more sensible route but I'd prefer to avoid the hassle if necessary.

TIA

[andrew]

I hadn't noticed that. I posted it because it explains the principle well. The other 2 brands I've seen (Trevi Boost and Newteam) both handle small negative heads. Replacing the electric does sound like the simplest option though.

A