RCD / RCCB Continuous Tripping

[ODS]

This morning the main RCCB unit in my house tripped out and would not reset. I switched off each MCB in turn and found the 'sockets' circuit caused the problem.
I went round every socket in turn and switched off and tried the RCCB each time. It would not reset until the last socket was switched off.
Thinking I had found the fault on the last socket, I switched one socket back on and the RCCB tripped immediately.
I then tried other appliances individually. Some tripped the RCCB immediately, other came live but then tripped the circuit when a load came on line. With further experimentation, the fault is consistent across different circuits with the same pattern every time.
For example, the cooker comes on and shows the clock, but the RCCB trips if I tun on the oven. The microwave switches on, but trips if it is started. Low drain items seem to be no problem - the broadband router has not tripped the RCCB, hence the internet connection. Even the TV can work, but normally it trips the RCCB as well.
I get the same fault pattern on each protected circuit even if all others are switched off to try and isolate the fault.
I do not know how to test the RCCB, but cannot see any other possible causes than this unit being faulty. I have checked the tightness of all terminals in the consumer unit and they are OK.
Any ideas how to fault find / solve this problem would be appreciated.

 

[Spark123]

It sounds like a combination of a N-E short on a TN-CS system on an RCD protected circuit. Have you had any work carried out recently? Disturbed anything? The best way to find this would be with an insulation resistance meter, this may mean phoning out an electrician.

 

[ODS]

No work at all, which is what is confusing me. I was outside this morning and came in to find the power tripped. Our 4 year old was in the house and he does like plugging things in, but I have switched everything off and the problem is not related to any specific circuit.

 

[Spark123]

Just switched off? Try unplugging everything and see if this helps. Some sockets are only single pole switches which do not isolate the neutral.

 

[ODS]

What am I testing for? If I unplug everything, I already know that the circuit will remain live with no load. Should I unplug all then try and switch one appliance on in different sockets?

Update. Everything is now unplugged. I plugged in the laptop power supply, which previously tripped the RCCB, but now works OK. Will try and add appliances 1 at a time!

 

[Spark123]

Try unplugging everything first, then plug in an item such as a table lamp (double insulated, has no earth).

 

[ODS]

I tried a few sockets with a lamp, halogen type, which I checked had no earth.
The lamp is OK, but not in one socket when it trips the rccb.
I tried in socket in the kitchen and it was OK, then remoived and plugged in the kettle to the same socket. Tripped immediately.

 

[Spark123]

Have you got absolutely everything unplugged? What else is on the RCD side of your consumer unit, or is it there only 1 RCD protecting the whole house?

 

[ODS]

The RCD does the whole house.

 

[ODS]

There are 4 MCB's
1 for sockets
1 for kitchen
2 for 2 shower units

I can't physically unplug the cooker or the shower units.

Heating is also hard wired to a switch on onme of these circuits, oil boiler not electric heating.

 

[Spark123]

Both the showers and the boiler will hopefully have isolation switches. If you turn these off does it clear the problem? Failing this the fault is sounding like it is with the fixed installation wiring and you can probably do with an electrician with a tester to sort it out.

 

[ODS]

Yes, showers and heat isolated. I will sort out to get someone to check it properly - typical to happen on a bank holiday weekend, will have to suffer until Tuesday. Thanks for the help.

 

[viewer]

ODS, if it tripped in one socket only, it rather suggests it is worth taking the front off that socket (after turning off all power - you know the circuit is a problem). Anything touching, loose, uncovered?[/b]

 

[ODS]

I found that the 'sockets' MCB had 6 live wires in it. I removed them and traced the neutrals and then worked out which neutral is the problem. At least I have some sockets reconnected now and the other circuits can wait for someone qualified to look at them.

Looks like a new consumer unit - there is not enough space for MCB's to segregate the various socket ring mains at the moment.