"David Ward" wrote in message
om...
Hello,

We need to replace our electric shower. It's currently 9kW and we were
thinking of upgrading to 10.8kW. Its connected directly to the main
fuse box on a 30amp trip. A quick calculation shows that 30amp isnt
really enough for the current shower: 9000/240 = 37.5 amp. I'm quite
surprised it has never tripped.

So it looks like we would need to upgrade to a 40amp or 45amp fuse.
However, our main circuit board is only rated at 60 amp total. We have
a gas cooker so i doubt we'd ever draw 60amp, but I guess we would
need to upgrade to a 100amp to be on the safe side?

I also need to check the rating of the cable. Is there anywhere which
tells me roughly how the external dimensions of cable correspond to
the core sizes?

Thanks.

David.

The first thing I'm going to ask is, "Is the cable large enough to take this
size of heating element ?"

You will have to reinforce the cable to at least a 10mm Two Core and Earth
if it already isn't.

The reason the fuse hasn't blown is more than likely to be that it is a
rewireable fuse with the wrong size fuse wire in it. An MCB (miniature
circuit breaker) would not have been able to take the current load and would
have tripped off at the first switch on of the shower.

You consumer unit (fuse box) is rated at 60 amps on the main switch and BUS
bar and you should probably never reach this load even with everything in
the house switched on.

More information about the whole installation as it is now, would help us
make a better diagnosis of any problems you may get if you go ahead with the
your proposed changes.


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