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[geofff]

I am needing to replace an old 7.5kw electric shower. This is run using 6mm cable direct from its own fuse over a distance of approx 21 metres.
Can anyone advise as to what the maximum kw shower that i can change to - will this cabling take 8 or 8.5kw?

[Jeffmo]

Hi depends on a few things
a.) Installation method
b.) What fuse or circuit breaker you have
If cable clipped to wall and clear of any external influences then the cable is rated at 47amps before voltage drop which should not exceed 9.2 volts.My advice to you is to upgrade cable to 10mm then most showers would be available for you to fit . 21 metres is a long way from home for the little 6mm.Regards jeff.But your part p leckie will work all this out for you

[boomboom]

what size fuse are you using, 50 amp is good for a 8.5, voltage drop of 7.24

[Jeffmo]

load currents are:-
8.5kw = 36.9 amps
9kw = 39.1 amps
9.5kw = 41.3 amps
10.5 kw = 45.65 amps

Protective devices obviously need to be greater than load current therefore
8.5 kw = 40 amp
9 kw = 40 amp ( just )
9.5 kw = 45 amp
10.5 kw = 50 amp.

This gives you the protective device for the individual shower load currents

cable capacity :-
6mm = 46 amp
10mm = 63 amp

As you can see cable capacity of 6mm is greater than upto 9.5kw shower however this does not take account of any correction factors ie: Temp , install method,grouping or thermal insulation along cable run ,so you running close to the mark even if installed just clipped direct with no correction taken into account ..
My advice would be to upgrade your cable to 10mm with a capacity of 63 amp then plenty in the bag for increased shower load .

Hope this helps Regards Jeff