7kw shower upgrade

[lauriekinguk]

Hello,

I have a broken 7kw electric shower that I need to replace, however I can find any 7kw showers to replace it with. There are lots 7.5kw, will the feed from the consumer box be ok. I know not to risk a 8.5kw, but wondered if a extra 0.5kw would make that much difference?
Thanks

 

[ELZ4742]

unless you can give the cable size and fuse size its impossible to say.

 

[riveralt]

Hello,

I have a broken 7kw electric shower that I need to replace, however I can find any 7kw showers to replace it with. There are lots 7.5kw, will the feed from the consumer box be ok. I know not to risk a 8.5kw, but wondered if a extra 0.5kw would make that much difference?
Thanks

For 7.5kw shower it will depend on what the manufacturers instructions say and the voltage they have used to describe their product. Normally it would be a 40Amp MCB with 6mm2 cable and they will insist on additional protection from an RCD.

However, 7.5kw @ 240v is 31.25Amps which means you could have got away with a 4mm2 cable on a 32Amp MCB (assuming no derating factors on the cable).

While 7.5kw @ 230v is 32.6 Amps still a 4Amp cable but a 40Amp MCB( assuming no derating factors on the cable).

As BS7671 uses 230v as the standard I would always fit a minimum of 6mm cable and 40Amp MCB - you would be able to run a 8.5kw shower of this arrangement - and have a more powerful shower.

 

[plugwash]

Check the specs on those showers carefully, whether it is 7.5KW@230V or 7.5KW@240V makes a significant difference.

Showers can be treated as resitive loads (they probablly aren't perfectly resistive but close enough) therefore

A shower rated at 7.5KW@230V will draw 32.6A on a 230V supply and 34.0A on a 240V supply.

A shower rated at 7.5KW@240V will draw 31.3A on a 240V supply and 29.9A on a 230V supply

 

[lauriekinguk]

Thank you to the above, very helpful. Appart from ELZ4742, guess you don't need a crystal ball .

 

[ELZ4742]

Thank you to the above, very helpful. Appart from ELZ4742, guess you don't need a crystal ball .

its my sig, you only need a brain not a crystal ball to realise that

on the basis of the info, you still need a cable size... which is?