Help needed to diagnose MCB/RCD tripping

[stargazer30]

Hi everyone,

I'm new here, this is my first post

I have a really annoying problem and I'm about to give up an call an electrician. The downstairs MCB keeping tripping and with it the RCD goes and knocks all the power off. Its been happening for about a week on and off. It might go a couple of days no issue then when it trips I can turn it straight back on and within 5 to 30mins it trips again. Last night it went off about 5 times from 10pm till 4am!

Now I've pretty much ruled out an appliance problem. Last night I had everything unplugged downstairs (all kitchen appliances) with the exception of the modem/phone/TV and it still tripped out.

Any idea's what it could be? I don't fancy ripping all the downstairs wiring out looking for a needle in a haystack (or twin & earth)

[Rant]The other question I have is why does my RCD nearly always trip when a MCB goes. Its done this ever since it got installed 5 years ago. I think I've only ever seen an MCBs trip once without the RCD going. Really annoying as the whole idea of having separate MCBs is the unaffected circuit stays on![/Rant]

Thanks for any help

David

 

[1john]

If you didnt want to effect other circuits you should have had RCBO's installed on each circuit, they would truly be independant then.

Have you disconnected the boiler?
Have you unplugged things by removing the plug from the socket or just switched the socket off?
Are you 100% certain that you haven't missed anything?

 

[stargazer30]

If you didnt want to effect other circuits you should have had RCBO's installed on each circuit, they would truly be independant then.

Have you disconnected the boiler?
Have you unplugged things by removing the plug from the socket or just switched the socket off?
Are you 100% certain that you haven't missed anything?

Thanks for the quick reply,

The boiler was connected until last night when I got well sick of it and unplugged everything including the boiler, tripped after that as well.
I am aware earth faults/RCDs can trip when the power is off so I did literally unplug everything, except the TV unit appliances, phone, modem, xbox, tv nothing major on that socket.

 

[chappers]

well then try unplugging the other things that you left plugged in and see if it still happens.

 

[stargazer30]

Well its fixed, but I had to give up and call an electrician in so I'm £250 lighter today

It turned out to be a combo of;

1. a faulty cable between one of the sockets and the board, the insulation had broken down or was crushed somewhere under the floor.

2. The RCD was knackered and needed replacing.

Whilst checking everything he also found the downstairs ring wasn't a ring at all so the 32amp MCB I had in wasn't safe either and had to be replaced with a 20amp one. Looks like the former owners when they knocked out an internal wall must have broken the ring somehow.

 

[Electrifying]

How long was he there?

 

[kai]

I used to get spurious tripping by leaving the Sky box and/or DVD player on standby for long periods, Once I got in the habit of turing them off properly at the wall when I finished with them, the problems went away overnight!

 

[ColinJacobson]

Well its fixed, but I had to give up and call an electrician in so I'm £250 lighter today

It turned out to be a combo of;

1. a faulty cable between one of the sockets and the board, the insulation had broken down or was crushed somewhere under the floor.

2. The RCD was knackered and needed replacing.

How do you check if an RCD is "knackered"?

 

[PrenticeBoyofDerry]

How do you check if an RCD is "knackered"?

Two ways the test trip button on the RCD and also, with the help of special RCD test equipment, you can test and measure tripping times.

 

[JohnD]

Depends what you mean by knackered. If you mean it will not reset even when the fault has been cleared, the easiest way to find out if this is the case is to turn off the main switch. With no power supply, there can be no current passing through the RCD, therefore no current imbalance, therefore if it will not reset it is faulty.

You have to be careful of people assuming an RCD is faulty when it will not reset because they are under the incorrect impression that there is no fault.

 

[ban-all-sheds]

How do you check if an RCD is "knackered"?

Take it out of the CU.

Place it on a firm, hard, flat surface.

Strike it with several strong blows with a club hammer.

If it breaks into lots of small pieces it's knackered.