Main circuit breaker wont switch on

[kitchy]

All the MCB's are in the off position. When I flick the master circuit breaker switch it clicks as if going on but flicks itself back down to the off position.
This all worked fine about a week ago and the only thing that has changed is my plasterer has done some work. But surely that can't affect it as all the circuits are in the off position.

Please help me solve this riddle.

Thank you

Graham

 

[Adam_151]

You have a neutral to earth problem, switching the overcurrent breakers off doesn't really help as they only break the phase (although in quite a few cases having no load on the system eases things)

If you feel competant, you can try narrowing down the fault by (with the mcbs off) dropping the neutrals for each circuit in turn out of the bar and seeing if your RCD will reset, concentrate on circuits that are present in the room that had plastering work done.

If not, you'll have to get an electrician out and he'll conduct insulation resistance tests on the circuits (you can help him by unplugging everything before he comes)

The actual fault is likely to be a cable nicked by the plastering trowel or water and plaster inside an electricial accessory

 

[JohnD]

I think
...you mean the RCD
...you have a neutral/earth fault which the MCB will not isolate as it only breaks the phase conductor.

If it is really connected with the plasterer, then perhaps he nicked a cable with his steel trowel; or perhaps he got water inside a fitting; or perhaps a switch or socket was taken of the wall to plaster round and damaged or reconnected wrongly.

You can however try unplugging all appliances; and turning off the cooker switch and the immersion heater switch; and the switches for all appliances that do not have plugs. Quite often the fault is in a heating element or in an appliance containing water.

To trace the faulty circuit, either you or an electrician is going to have to rummage about inside the consumer unit. Are you confident to do this? If not ask around friends and neighbours for a recommended local electrician. Even when you have found the faulty circuit it can be difficult to track down where the fault is without skill and instruments.

edited: bah Adam_151

 

[sm1thson]

How many electrical items (sockets / switches etc) did the plasterer go near, if its not many then you could open them up (with power off –but that goes without saying as you have no choice) and check that when they’ve been screwed back down its not screwed through the neutral. –this might easier than opening the consumer unit, although if you cant see any problems then you will need to open the cu to do as above to work out which circuit is having problems.

 

[kitchy]

Thanks for these suggestions. That appears to be what it must be.

I have the confidence to drop the neutrals in turn, but I have a further question about the possible result.

Let's say it is as you say, and let's say the plasterer got water in somewhere, or nicked a nuetral etc. If I locate it the circuit it belongs to is it possible that once the plaster dries out the problem will rectify itself? I ask this before going ahead and stripping out/re-doing etc. The pasterer only finished yesterday and everything is still drying.

If this is a possibility is it worth waiting a few days before going through the tests etc?

I should say at this point that there are only cables installed, ie, nothing is connected to the light circuit except the main fittings (no bulbs etc), plus the cooker cable has not been connected to anything yet. The flat is still in a state of renovation.

Graham

 

[securespark]

Have you found out which circuit it is on yet?

You really need to pinpoint the problem before you can make a decision on what to do.

 

[sm1thson]

i would say test and find out now. “problems that go away by themselves come back by themselves”. ie once the plaster dries it is probable that the fault current will reduce such that its no longer tripping the RCD, however there will probably still be some fault current meaning that a slight leakage on something else (which is acceptable for heaters and PC’s) will trip the RCD. To solve the problem then will be harder as it will be less evident and you will more likely need a sparky with an insulation tester. Find it now it could save hassle later, you really don’t want to wait till you’ve finished decorating for the problem to come back!!

 

[kitchy]

Thank you.
Basically the cooker cable had been wound up and squeezed inside the socket box. The earth and the neutral were touching at the end of the cut wire.

Thank you so much for solving this.

Graham

 

[Tim 77]

Thank you.
Basically the cooker cable had been wound up and squeezed inside the socket box. The earth and the neutral were touching at the end of the cut wire.

Thank you so much for solving this.

Graham

I take it the cooker cable wasn't on any conectors at the cooker end and still fully connected at the board?