RCD Tripping MCB's on Circuit OK

[dksanders]

Can't believe some of the responses I've read to this.

The MCBs aren't tripping because it's an earth leakage fault not a current overload fault.
The fault isn't definitively a N-E RI fault but could still be a L-E RI fault.
The ONLY way to find out is to use an insulation resistance tester on each of the circuits to find the one with low IR, then remove all connected devices from that circuit (you may have double pole sockets but how can you be certain they are all DP sockets?, one may have been replaced/fitted with SP).
Do a continuity test between live and neutral to prove all devices are disconnected.
Then test the circuit again, if you've still got a low IR the fault is in the fixed wiring/accessories. If the IR reading is OK then it was one of the connected devices. Use the IR tester on each to find out which one.

 

[Pete999]

Can't believe some of the responses I've read to this.

The MCBs aren't tripping because it's an earth leakage fault not a current overload fault.
The fault isn't definitively a N-E RI fault but could still be a L-E RI fault.
The ONLY way to find out is to use an insulation resistance tester on each of the circuits to find the one with low IR, then remove all connected devices from that circuit (you may have double pole sockets but how can you be certain they are all DP sockets?, one may have been replaced/fitted with SP).
Do a continuity test between live and neutral to prove all devices are disconnected.
Then test the circuit again, if you've still got a low IR the fault is in the fixed wiring/accessories. If the IR reading is OK then it was one of the connected devices. Use the IR tester on each to find out which one.

Right RI fault?

 

[Octopus]

Can't believe some of the responses I've read to this.

It could simply be accumulated earth leakage from a variety of sources of equipment on the circuit(s) - you will not find this out simply by doing IR tests.......... you need a clamp meter..................................

Seen this on a number of occasions.........

 

[Pete999]

It could simply be accumulated earth leakage from a variety of sources of equipment on the circuit(s) - you will not find this out simply by doing IR tests.......... you need a clamp meter..................................

Seen this on a number of occasions.........

Preferably one that reads miliamps

 

[NDG Elecs]

I'm with Tel on this. New builds are generally built like an Ikea wardrobe, no solid backbone, no integrity, just done to the lowest common denominator. The fact that we as a society have taken generations to master all aspects of building, and then accepted the carp that is produced is woeful. Yes, economics (and greed) play a part, but the standards we currently accept are sad.

So, get it knocked down and build a proper house!! Or move....

Re the OP; Murdochs suggestions sound a good plan to me.

 

[DDD]

Unfortunately, the lottery numbers haven't come through yet so moving will have to wait until this weeks Euromillions draw.

In the mean time - Ok here it goes, I'll wait for the onslaught. "Would it help (if room in the CU) to replace the MCB's with RCBO's, to determine the circuit that may be causing the issue".

 

[Wilko]

Shouldn't be necessary. Apart from the cost, the risk is a second fault may be introduced doing the change. I prefer to fix known faults first