Heard a sort of chattering sound from the MCB (30A) supplying one of the
ring mains in our house this afternoon. Turn of the MCB, turn it back on
again, all is ok for a little while (maybe 10 minutes?) then it starts
The circuit in question is one of four ring mains in the house, it
supplies the sitting room, one bedroom , a socket in the hall, in the
conservatory and the dressing room. generally lightly loaded - a few
table/standard lamps, TV, VCR, DVD etc.
Whilst investigating this problem I noticed that when this circuit was
switched on the disc on the meter started fair whizzing round - 30
rev/minute up from the say about 3 rev/minute is was doing normally.
My quick calcs indicate that 30 rev/min implies something like 10kW/h
being consumed - around 40A? , or have I made some big boo-boo?
Anyway, there is nothing on the circuit drawing anything like that (no
we don't have any secret electric showers, or unknown immersion heaters
etc.) These symptoms continue to occur once everything on the circuit
has been disconnected.
I've not had time today to investigate this more thoroughly, the circuit
is isolated now via the MCB pending time tomorrow.
So, my thought so far is that there is some fault in the fixed wiring,
causing a high current draw, and that the MCB is faulty in some way,
hence the noise rather than tripping.
Does the above sound a reasonable diagnosis?
I can check out the MCB by swopping it with others in the CU I guess, if
it is faulty then I'm not sure if replacing it is going to be a problem
The CU is a pretty old Crabtree one, you can see a couple of piccies
Does anyone know if I will be able to find something to fit?
- posted 12 years ago