Shower wiring melted

[smelly]

Could a prolonged shower, say 15 mins or even more, overheat new shower wiring to the point where it melts the insulation?

It's a newish bathroom, fitted only last May by a reputable builder. The shower wiring was upgraded of course, as the previous shower wiring insulation had melted too. We asked the builder to fit wiring suitable for a much more powerful shower than the present one (8.5 or 9.5 Kw), in case we upgrade that in the future as well.

Other than a bad installation, I can only think taking prolonged showers is causing the problem.

TIA

[ransley]

Sounds like a short, it is a tankless eclectric? But why didnt the fuse blow unless the wire was improper gauge, i would not even use that shower, if its a short and you are showering, well you get the idea. Get a real pro out.

[Andrew Gabriel]

No, only bad installation, either using wrong materials, or not using them correctly. The shower should be able to run continuously.

Where has it melted? It usually happens at a connection because the connection was poorly made for the current involved, or because the wiring accessory was low quality and has worn out quickly.

[fred]

In article , smelly writes

A correctly rated cable should not overheat no matter how long the shower is on so it looks like a badly designed installation.

Is the overheating insulation in the open air, in trunking or as it is passing through some insulation? Any kind of confinement or insulation changes the rating of the cable. Take a look at this cable calculator and see what it recommends:

can take a guess at the current cable rating from its outer dimensions:

6mm2 cable is nominal O.D - 13.5mm x 7mm 10mm2 cable is nominal O.D - 17.1mm x 10mm Figures courtesy of TLC, note that basic ratings quoted on their site apply in free air only.

If you're not sure how much power the shower is using then check it on your electricity meter with say a 10min run and use a bit of arithmetic to get the kW usage.

[cynic]

Did the builder use an electrician who knew what he was doing or did he install the shower himself?

[smelly]

He installed everything himself. We've been in touch with the bathroom co. who recommended him and they say he will call later today (Sat). He let us down 4 times, over the fitting of a radiator; he just never turned up each time. So, I haven't much confidence. We'll see! Meanwhile, I'm getting smellier (no bath!)

Thanks for the replies

[smelly]

It's fed from the cold water tank in the loft. I don't know why the circuit breaker didn't trip. It's a 50amp (a Wylex, marked BD50) - is that the correct rating for a shower?

[smelly]

It appears to have melted inside the shower isolation switch(? - sorry, don't know all the terminology). I mean the switch outside the bathroom, with a mains neon.

The power to the shower had gone off while I was showering so I checked the switch. I couldn't even press it to turn it off; it was solid inside :-s. I took the cover off and could see melted insulation.

[smelly]

The wiring is inside a stud wall, plasterboarded and tiled on one side. There's no insulation in there. It's very difficult to see inside the switch as the cover will only come away from the back box very slightly, so it's hard to see the wires. With a torch, you can see they are melted though!

I remember now, asking the builder to fit 10mm cable in case we wanted to fit a powerful shower in the future.

[John]

Could be an under-rated isolation switch. Can you see the rating on it?

[Andrew Gabriel]

Most likely the electrical connections to the switch were not made well enough. Very common problem, and many installers (particularly if not a well experianced electrician) just don't know how to make high quality high current connections.

Next most likely is that the switch was low quality and/or defective. This is one place where you really do need a good quality high current switch, and not the cheapest one on the shelf.

This should be repaired by an electrician, noto the person who did the original installation.

[fred]

If they are only melted at the switch then the cause may be a loose connection or fault at the switch.. I imagine you want to narrow down the cause of the problem before approaching the builder but to do that you will need to find a point where you can inspect the cable and see if it is adequate. You could remove the cover of the shower or the consumer unit and inspect the cable to estimate the rating from the sizes I gave before. Turn off the main switch before removing the CU cover.

[Dave Plowman (News)]

They do have the appropriate calculator to take all others into account in their technical section.

[fred]

In article , Dave Plowman (News) writes

Is that the one I linked to 6 lines higher in the same post ;-)

[Dave Plowman (News)]

So you did. ;-)

[Tim]

Really? Much more usual for electric showers to be mains fed, not from a header tank.

Tim

[ARWadsworth]

And the elecrtician should of course check all the other terminals on the shower circuit. The ones in the CU and the shower will probably only be finger tight as well.

Adam

[geoff]

In message , Andrew Gabriel writes

Or it was incorrectly fused

[smelly]

Right, problem is sorted. The builder didn't turn up (as expected) so I called an knowledgeable friend. He says all the connections were good, so the problem was either a duff switch or the builder had overtightened the screws and caused it to crack (it just fell to pieces in his hand)

Only the brown live was melted and only for a couple of inches along its length from the switch, so a fairly quick and simple repair. I'm relieved. New switch now fitted, I'm off for a shower.

Cheers.

[Peter Parry]

Quite common, either the switch was faulty or the connections not well made. In either situation the normal current flowing in the circuit will cause local heating around the poor joint or faulty switch and this will melt the cable insulation. The only difference a long shower makes is it gives the poor contact more time to heat up and damage everything around it.