"Set Square" wrote in message
...
In an earlier contribution to this discussion,
TonyK wrote:

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?

Almost... It does depend on the type of load. These will be broadly
resistive so yes, BUT I'd say it would be a slight inductive load that is
causing this problem.

So... why does it trip out occasionally (once

I'm wondering if you need an MCB with a different swiching characteristic -
type C or D. Basically you get a slight short circuit on switch on which
could be knocking out the MCB, a C/D type will allow for this before
tripping.

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.

Now that is odd...

Scott




I would say that upon switch on they