keeps tripping

[RF Lighting]

That sounds like a short between live and earth then

That is the only fault which will trip both devices.

 

[whyme!]

Why would it just do that then?

 

[Spark123]

An MCB trips on overcurrent i.e. there is too much load being taken - this could be caused by a fault or too much equipment being connected.
As it trips with everything turned off then it indicates a fault is present. Best bet is to have an electrician do an insulation resistance test - this should indicate wether or not the cable insulation is sound.

 

[whyme!]

Anything i can do with a multi meter? Could it be a faulty MCB?

 

[Spark123]

I wouldn't rule out a faulty MCB, however the likelyhood of it is small. You can try and fault find with a multimeter however unless it is a copper to copper fault it will not show up the same results as a "Megger" insulation resistance tester which introduces 500V into the circuit to see if there is a problem with the insulation.

 

[RF Lighting]

I know this sounds a bit vague, but it could be caused by anything from an overheated socket to damage by vermin.

Are you certain everything is unplugged and or switched off? Fridge freezer, washer, dryer, dishwasher, cooker extractor hood, cooker / oven / hob, kettle, toaster, microwave, boiler, waste disposal, fan, heater, tin opener, blender, toastie machine, george formby grill, TV, phone charger, wireless doorbell....

 

[whyme!]

ok, thanks for your help guys.

 

[whyme!]

Just a thought. Could it be an actual socket earting out, causing the problem? Faulty socket kind of thing.

 

[Spark123]

Yep, it could be a faulty socket, it could be the wires behind a socket, it could be water, it could be a nail across the wires which has remained dormant for years but has suddenly shorted out to name a few ideas.

 

[whyme!]

Is there a way of telling which socket is the first in the ring and the last?

 

[RF Lighting]

Just a thought. Could it be an actual socket earting out, causing the problem? Faulty socket kind of thing.

It's possible, but unusual if none of the sockets have been disturbed recently.

An over heated connection can cause the insulation to melt off which can cause a short.

It can't do any harm to have a look at the sockets. Make sure the power is off before you start, as there may be damaged insulation or loose wires at one of the sockets.

You haven't been doing any DIY, or hanging pictures, banging in nails or screws or anything like that.

To give you an idea of how difficult somthing like this can be to find, It may be a cable which has become crushed due to walking on a slightly loose floorboard. Unfortunatly, at this stage it really could be anything.

The normal fault finding procedure would be to split the ring in half and test each half individually for insulation resistance and continuity, and then split the faulty half in half again until you are left with only one socket or peice of cable.

Unfortunatly, even with the proper test equipment this could be very hard to find.

Is there a way of telling which socket is the first in the ring and the last?

It is often the two closest to the consumer unit, but not forced to be.
It just depends on which was the easiest two to run the cables to at the time the circuit was wired.

 

[whyme!]

It is all newish wiring done on my new extension. Ive got the guy coming out to look at it whoinstalled it. Kitchen units have been fitted some 4 months ago, but i was very carefull as to where they were screwed in.
When it first tripped this morning reseting it got it working for 5 minutes, when it tripped that time it won't now rest at all.
I have looked at the cables behind the plugs and all seem fine. The screws holding the units i have done a resistance check between the screws and the earth/live and neutral of the sockets and they all show as open circuit. I'm praying its a faulty trip switch MCB

 

[RF Lighting]

Here's an easy test for MCBs.

Does the MCB hold in with the main switch turned off?

 

[whyme!]

Here's an easy test for MCBs.

Does the MCB hold in with the main switch turned off?

Do you mean, when the main rcd is off, does the mcb switch on and stay on?If it does or does not, what will that tell me?

 

[Spark123]

It will tell you if there is a fault with the MCB as opposed to the circuit as no current will flow through it to trip it when the main switch is off.