In message ,
"Charles Middleton" wrote:

Hi,

My current electric shower does say anywhere its KW rating. I intend to
replace this next week and am wondering if I can determine the rating from
either...


There have been some very interesting and accurate posts on this thread,
but I suspect that the "real world" answer to your problem is much
simpler.

If the shower has been there some time, chances are that it will be
wired in 6mm2 T&E (this stuff is about half an inch wide altogether) and
fed from a 30A fuse or 32A MCB. If the shower has been rated at 240V
then it *should* be at most 7.6kW (32A*240V) though it is common to see
showers up to 8.5kW run in this way: a 32A MCB isn't going to trip for
that amount of overload, and it is highly likely that the cable will
handle it fine, depending on route and length. (Note that I would *not*
recommend installing an 8.5kW shower on a 32A MCB, or worse still a 30A
rewireable).

I am told that 7.5kW really doesn't do the job for much of the year.

When you buy your new shower you really need to get the most powerful
one you can afford so you should also be factoring in the cost of
running a new length of 10mm2 cable (it's about an inch wide: while you
are in B&Q (or wherever) looking for your shower, check out the cable in
the electrical aisle) and upgrading the MCB (and possibly your supply)
to accommodate the new shower.

While you're at it, you need to think about the shower disconnection
times and whether or not an RCD is required for it. This will largely
depend on the type of earthing your system has and the length of cable
from CU to shower. Don't forget to make sure your supplementary bonding
is up to scratch too.

One thing I'm surprised people often don't think about though is the
possibility of hanging a shower from the existing hot water system. It
seems that if there's an electric shower already installed many people
think that more of the same is their only option. Not so; most
combi boilers (should you have one) will give showers at least as good,
and in most cases better than most electric showers because a combi
might be putting 24kW into the water whereas the biggest practical
electric shower is only 10kW or so. Do invest in a thermostatic mixer
though.

Even if you have a hot water cylinder system it is possible to run a
very good shower from that. If it is one of the rare (at the moment)
mains pressure systems just bung on a thermostatic mixer. If it is
gravity fed then a shower pump will cost about the same as a new
electric shower and potentially give a better result. The difficulty is
re-arranging the plumbing.

For both the above though, the electrics are simplified. None at all are
needed for a thermostatic on combi or mains, and for a pumped system,
the pump takes a very small amount of power and can easily be run from
an existing sockets circuit.

Erm... sorry. I wrote a lot more there than I was intending.

Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
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