Upgrading a existing electric shower

20 Jan 2007
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United Kingdom
Hi there.

I am wanting to replace an existing Gainsborough 8500 electric shower unit which I am presuming is 8.5kW. The supply to this unit is 10mm cable, surface mounted, approximately 11 metres from the consumer unit protected by a 40Amp MCB with double pole isolating switch in the bathroom.

I have read the postings on cable sizing etc and still find myself confused.

Am I correct in assuming that I can fit a 9.5kW shower on this circuit as it stands or if I change the MCB to 45A I could even have a 10.5kW unit instead?

The current consumer unit is a standard 100A unit. How do I determine how much power is being supplied to the house so I know there will be enough when demand dictates?

I want to avoid having to replace the cable if possible for the obvious reasons and get the best shower unit possible with minimum change.

Thanks for any advice in advance...
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Yes you are correct - you could fit a 9.5kw shower using the 10mm^2 cable and with an MCB upgrade a 10.5kw shower too.

There's no definite way to determine the size of the main fuse without actually breaking the seals but for the short length of time a shower is on there should be no problem because the main fuse can take a fair bit over the rated capacity for more than enough for you to finish in the shower.


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