Electric shower replacement questions

[JohnW2]

I'm probably just a wuss! I know there is no reason to, but I always worry with a circuit run right at the limit the problems caused down the line. Such as when someone adds an extra layer to the loft insulation, which seems to be fashionable at the moment, the cable might start getting rather warm, a cable sized less close to the edge will be much less likely to be affected.

That's obviously all true but, as often discussed, one wonders how far one can/should go in trying to anticipate 'incorrect'/stupid, and possibly harmful, things that others might do in the future. Let's face it, although it's possible that someone might add insulation in the future, a more likely scenario is probably that they will 'upgrade' their shower to a higher power one. The OP in this thread has, sensibly, asked about this, but many might not even think about the issue.

I've certainly removed shower cables that have been thermally damaged where they pass through insulation. Cables can take quite a lot though and for the conductors to exceed 70°c would certainly take some time.

It does rather surprise me that you have seen such damage, unless the cable concerned was seriously under-rated. As often discussed here, there clearly are some substantial 'safety margins' built into the figures we work with. Let's face it, the specification of OPDs implicitly deems a cable with a CCC of, say, only 30A to be able to carry a current of 43.5A (30A x 1.45) for an hour without coming to any harm. Even that undoubtedly includes a generous 'safety margin' and, of course, it would be pretty unusual for a shower to be used continuously for anything like an hour (unless, perhaps, there were teenagers in the house ).

Looking through the regs book I still wouldn't be comfortable doing it!

As I said, I would be perfectly comfortable doing it in my own house, but I wouldn't do it in anyone else's house, and nor would I 'advise' anyone else to do it. However, I do think it reasonable to explain the 'facts', as I see them, to an intelligent person (which the OP in this thread appears to be) so that they are able to make a judgement/decision for themselves, based on what I and others have said. Others, particularly an 'other' who is no longer participating in this forum (plus at least one who occasionally participates), might well not agree with that approach!

Kind Regards, John

 

[600rob]

Fair enough. If there is no insulation, then that (in conduit within a cavity wall, but with no insulation) is, for some reason, one installation method which is not explicitly mentioned in the regs. However, as far as I can see it is no 'worse' (thermally speaking) than situations accepted by the regs as "Method B" ('38A max' for 6mm cable), so my previous ('personal') comments would still apply.
Again, fair enough. You will realise from what has been said (particularly by me) that it's likely to come down to your decision as regards whether you want to be 'strictly compliant' with regulations.

Kind Regards, John

Managed to have a look today and there is no insulation in the wall. I couldn't see anything else to suggest why the conduit might have been used but it doesn't appear to go anywhere near as far down to where the cut out in the wall has been made for the cable to enter the bathroom .
If i get a chance ill get in the loft and remove it to asses how much has actually been used.

Ive been looking at the different options available and i reckon ill go somewhere in between the old unit and the one i was looking at initially with a unit rated at 9.0kw.

 

[JohnW2]

Managed to have a look today and there is no insulation in the wall. I couldn't see anything else to suggest why the conduit might have been used but it doesn't appear to go anywhere near as far down to where the cut out in the wall has been made for the cable to enter the bathroom . If i get a chance ill get in the loft and remove it to asses how much has actually been used.

Fair enough. You might find that it is just a very short piece of conduit just to protect the cable where it goes through the top plate of the wall. If so, I really do think that you can ignore it.

Ive been looking at the different options available and i reckon ill go somewhere in between the old unit and the one i was looking at initially with a unit rated at 9.0kw.

There's nothing like a compromise

Kind Regards, John