230v or 240v??

[nabby68]

Hi fellas just something im mulling over at the moment and would be grateful for any advice.

I am thinking of putting a 9.5kw shower in my bathroom, i already have 10mm cable installed via method 4which equals 43amps.

so next is to decide what size mcb to put in place to protect the cable.
Depending on what size voltage you divide the power by depends on what breaker i can put in ie 9500 over 240= 39.58 amps quite ok for the cable size, but tight for a 40amp mcb
and
9500 over 230= 41.30 amps, again ok for the cable, but if i put a 45amp mcb in then this cannot protect the cable in a current overload?

I hope this makes sense and would welcome any replies to either tell me i am wrong or to explain a way round it.

Me thinks i maybe missing something obvious!

 

[plugwash]

it may be even worse than you think!

british mains is officially 230V (with quite a wide tollerance band) but realistically closer to 240V.

you should carefully read the ratings for your shower. if it says its 9.5KW at 240V you are fine using 240V in your calcuation. If it says its rated 9.5KW at 230V then it will draw more than that at 240V so even your calculation using 230V will be an underestimate of the current it will draw from british mains. Lukilly in practice breakers don't trip the instant you go over thier rated current and cables don't die the instant you go over thier rated current either so this isn't too much of a problem in practice.

 

[nabby68]

ok, thanks plugwash.

So worst case scenario would be 9500 over 230v ?
So what size breaker would protect the cable, bearing in mind how it is installed?

 

[plugwash]

fit a 45A breaker. The shower is a fixed load anyway so there is little danger of a moderate overcurrent (showers seem to tend to fail violently) and in any case cables can go a fair bit over thier rated current for quite a long time without catestrophic failure.