"TonyK" wrote in message
...
I have a number of electric storage heaters on a single ring covred by a
30A
MCB. The heaters are 3 x 1.7Kw and a single 3.3Kw. These are all on 24hr
fused spur timers and set to come on at times that offset the load, i.e.
the
3.3 and a single 1.7, then two 1.7's etc etc. So in theory the max load is
a
3.3 and 1.7 or 5Kw which according to my understanding is 5000/240 =
20.8333
or 21amps? So... why does it trip out occasionally (once every 24 horus) ?
No other loading on the circuit but the MCB buzzes and the buzzing gets
louder the higher the load, ie. put another .17kw heater on.

So, is there something fundamentally wrong with my understanding or what?

Thanks



Thanks for the pointers. I'm pretty well stuck with the way the heaters are
installed and this is one of three sets of heaters in the building. The
others are fine so I feel the problem is with this one circuit. The timers
are programmed with the heaters set to go on and off in groups so (in
theory) there is never more than 5Kw draw at any one time however 2 heaters
do switch on pretty simultaneously so I'll offset them by a couple of
minutes and see. Plus I'll exchange to MCB with another and see if that is
faulty in any way.