shower overheating at consumer unit!!!

22 Jun 2004
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United Kingdom
Hi there,I fitted an electric shower in my bathroom about 10 years ago,I have now redecorated my bathroom and put in a new shower just wiring it in on the same wiring as the old one,the problem is that everytime the shower is in use it is overheating the fuse at the consumer unit,but it is not blowing the fuse.the fuse in the consumer unit is 30amp as recommended,the shower is a gainsborough energy 2000x,I think its more powerful that the old unit,would this be causing the problem,should the fuse be blowing if its overheating,it was actually smoking when I realised the problem.HELP!!!There were never any problems with my old shower I really dont know what it could be.
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If the new shower is more powerful than the old, the supply current will be higher. Is the wiring sufficiently beefy to take the current? Is the wiring connection well made at the CU?

(there's a calculator somewhere on this forum which will calculate the required wire thibkness for a particular current and run length)
How powerful was the old shower, how powerful is the new one? Quantitative information is required here!

What thickness is the cable? How long is the cable run?
the cable run is 10m and the shower is 10.8kw,I have just brought some 10mm sq twin and earth cable,will this do it?The old cable is 6mm sq
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30A rewireable fuses will stand 40A for a long time without blowing

also if it is a rewireable it may well not be 30A fusewire in it

what brand is the CU?
what rating is the main isolator on the CU?
can we have a photo of the CU arangement?
phil_ballard said:
Just about. Use the calculator at

What's more concerning is why the 30A fuse isn't blowing - 10.8kW at 240V is over 40A. And for a shower installation you should have an RCD ....
And 10.8kW at the 230V you should use for the calcs is 47A.

If I'm reading this correctly, a 30A rewireable will withstand 47A indefinitely:

but it will get a bit hot. 45A would be a much better choice, but then you wouldn't be able to use 10mm cable because you need to derate it if you're using those fuses.

And given that you should have an RCD, installing a mini-shower CU would be the best bet.

Hopefully when plugwash turns up he'll just post a link to the reference section, rather than pasting in the entire speil again.... :LOL:
That's an interesting graph! I knew wired fuses ran well above their rating but I never realised they were that tolerant ..... thanks for posting that Ban

PS WHY would you want to ban all sheds? :confused:
Sheds as in wickes, b+q, focus, homebase, etc, he means, not the wooden thing at the end of your garden.

shed story: I was told this by the person it happened to, he went and bought a 45A cooker isoloater, it turned to be the wrong product in the packet it was actually a 20A isolator, on returning it the ******* on the returns desk tried to argue that it doesn't make a difference, and it took ages argueing that the rateings are there for a reason before the return would be accepted

I dislike the sheds, but they can be good places for DIYers. If only they were more responsible.

B & Q: Poor quality unbranded products due to poor employment ethics, poor environmental ethics (that's probably another story).. though they do seem to reccomend MK if you ask them.

Wickes: The DIY Gas boiler installation kit speaks for itself.

Homebase: How much??!!
apparently corgi registration is only needed to do gas work for reward

still i wouldn't fancy diy gas
CORGI website said:
93% of gas work carried out by non-registered installers has been found to have serious safety defects.


Unregistered installers and DIYers are not only breaking the law but can also put yourself, your friends and your family at risk.

It would appear that for residential use, DIY gas installation is legal if the rules are kept to 100%, however these rules are too complex to be covered in a small leaflet included with a kit. It's about as good as illegal to DIY. It isn't a case of reward, anywhere in business use it is illegal to DIY gas.
To rupture a rewireable fuse instantaneously requires twice the rated current. IE 60A to blow a 30A fuse.

If your CU is brown, or has a main switch less than 100A, then you should not be running any circuit over 30 (or 32) A.

The CU needs replacement.
Trouble is, for those of us who work at something else all day/week, the 'sheds' are the only places open (at 8pm, or on Sundays etc)

The internet is useful (screwfix etc) but sometimes you want to actually pick stuff up and look at it to decide whether it'll do ...

Ah well.... :(

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