Main breaker won't reset

[Giblets46]

My circuit board has two main breakers, each has 4 branch circuits. Recently one of the main breakers went ( not any of the branch), so I reset it. seemed OK for a while but went again this evening. I suspected the circuit in the kitchen, and turning that on seems to trip the main breaker, however now it seems the other branches are also causing the main breaker to trip ( ie the kitchen circuit is off).
Do the breakers happen to die?

 

[JohnD]

no.

show us photos please, close enough that we can see the ratings printed on all the breakers, and the descriptions of each circuit on the label above or below each breaker.

BTW, guessing (in ignorance pending the photos) it is very likely a "watery" appliance such as a dishwasher, immersion-heater, electric shower, washing machine, kettle, coffee-maker, steam iron, tea-urn or boiler. Sometimes it will be an electric heating element, like in an oven.

Unplug all of these (the appliance switch is not sufficient, and an MCB is not sufficient).

If the boiler has no plug, turn off its wall switch and show us a photo of that switch.

 

[oldbutnotdead]

Guessing til the photos appear but suspect your 'main breakers' are RCDs, somewhere in the circuits fed by that 'main breaker' there is a neutral to earth fault. Pics......

 

[Giblets46]

Thanks for replies, seems I've unplugged everything off the circuit that was initially causing the problem, essentially I can turn on any of the branch circuits on individually, but as soon as any current is drawn through it trips the main breaker.

 

[ericmark]

That is a RCD and likely it is detecting an inbalance which means some thing is leaking to earth, first switch off manually all the small MCB's and then try resetting the RCD then if it resets switch on the MCB's one by one to work out what is causing it to trip.

You can also try switching off the water heater at the local isolator/fused connection unit(FCU) and unplugging every thing that will unplug.

 

[bernardgreen]

Fault finding is complicated by the fact that the MCB supplying a circuit with a Neutral to Earth can be switched OFF and the fault still triggers a trip of the RCD

however now it seems the other branches are also causing the main breaker to trip ( ie the kitchen circuit is off).

Neutral_Earth_trip

• bernardgreen
• 16 Jan 2011
• 48

 

[Giblets46]

That is a RCD and likely it is detecting an inbalance which means some thing is leaking to earth, first switch off manually all the small MCB's and then try resetting the RCD then if it resets switch on the MCB's one by one to work out what is causing it to trip.

.

Cheers
The problem is any of the small MCBs will trip the main RCD if there is any current running on their circuit.
Tried one at a time, as soon as any current flows, the main RCD trips. Wondering if the main RCD is screwed.

 

[bernardgreen]

The RCD has a sensor that compares the current on the Live wire going to the load with the current returning from the load on the Neutral. If they are different then the RCD will trip.

These currents can only be diffent if some current is "leaking" to Earth. As shown in the diagram any Neutral to Earth fault will provide a path for some of the current on the Neutral and hence the currents through the sensor are not the same and the RCD will trip.

Most important when fault finding is to realise that the RCD can trip when the MCB supplying the faulty circuit / appliance is OFF but current from another MCB is flowing through a appliance that is not faulty.

EDITED last paragraph

 

[JohnD]

IF you have taken my advice about unplugging all the appliances from all the circuits protected by the RCD, then you can plug them back in and turn them on, one at a time, and you may find which appliance is at fault. Try the boiler first. Then the immersion heater. Then any outdoor lighting exposed to rain. Unplug each appliance after you have tried it before trying the next. Turning off the MCB is not enough.

Otherwise, you will need a qualified electrician to search for the fault.

 

[AndyPRK]

has any work been done recently? that may of caused this

 

[ericmark]

Cheers
The problem is any of the small MCBs will trip the main RCD if there is any current running on their circuit.
Tried one at a time, as soon as any current flows, the main RCD trips. Wondering if the main RCD is screwed.

Does sound like a neutral fault, the MCB in the consumer unit does not switch neutral off, so unplug and switch everything off at socket or FCU, I would guess likely water heater fault so insure that is switched off.

 

[Giblets46]

Hi, thanks for the advice, ended up calling out a sparky.
Seemed equally flummoxed at first. So after investigation he essentially found two faults, one on a coffee machine (as suspected, although it was still tripping after it was unplugged), the other on the lighting circuit, apparently the patio lights had been added to the circuit later (we moved in two years ago, and they were installed by the previous owner) and there is a fault somewhere in the wiring.he simply disconnected the wiring.