RCCB tripping every 3 hours with 1 hour to re connect

I have a Crabtree RCCB 63 Amp 363/S030 Split Load in a panel with 5 MCB connected. It is quite old as are the circuits connected to it.

It has started tripping at random times. It will not reset immediately but will after and hour or so and then stay live for 3 or 4 hours. It doesn’t seem to trip when the fridge or any other appliance starts.

Has anyone else had this experience or know what is the most likely cause. I  isolating circuits one by one has not identified the cause.

youve got a fault. low insulation resistance. not really something you can find without proper test kit. youd be best contacting a sparky and get them to find it

The fault is likely a N-E issue if isolating individual circuits does not isolate the fault to one circuit.

You need 2 bits of test equipment to find the fault, an RCD tester to make sure it's not a problem with the RCD and an insulation tester to test all the circuits.  These days these functions are built into a multi function tester of MFT.  If you don't have those call an electrician.

It's often worth visually checking any outside light fittings (or any other outdoor equipment for that matter) for water getting in. Otherwise, as above, you need an insulation tester,

David in Stannington said:

I have a Crabtree RCCB 63 Amp 363/S030 Split Load in a panel with 5 MCB connected. It is quite old as are the circuits connected to it.

It has started tripping at random times. It will not reset immediately but will after and hour or so and then stay live for 3 or 4 hours. It doesn’t seem to trip when the fridge or any other appliance starts.

Has anyone else had this experience or know what is the most likely cause. I  isolating circuits one by one has not identified the cause.

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[1]  When it does trip, do you turn ALL of the MCB's off first before trying to reset the RCD?

As often RCD's can trip if you try to re-energise them with multiple circuit loads still connected..

generally best to;  Turn all MCBs OFF, Turn RCD back ON,  then Turn individual MCB's back on one at a time.

[2]  I doubt you have actually isolated any circuits...

Turning individual MCB's off will only remove the power from a circuit it will not fully disconnect that circuit from the RCD...

ALL of the circuit Neutrals and Earths will still be joined together inside the consumer unit ..

To isolate a circuit when investigating RCD faults you need to disconnect Neutral as well as Live..

as the RCD can and will trip with any imbalance to earth from either Live Or Neutral..

i.e. a neutral to earth fault on any single circuit, can and will trip the RCD when power is energised from ANY of the MCB's sharing the same RCD.

[3]  You may have a failing RCD, that is getting oversensitive...    (not that common, but it does happen!)

Various appliances can have natural earth leakage and RCD's should not trip with up to 15mA of leakage..

But they MUST trip if 30mA or greater is detected..

But if they get oversensitive they can cause nuisance tripping at below 15mA.. 

[4]  An electrician with an RCD tester can quickly verify the RCD is operating correctly..

AND with an insulation resistance tester can verify any significant cable deterioration..

From a DIY perspective, other than keeping a written log of every time the tripping occurs,

and any appliances that you know were on when the trip happened..

There isn't that much you can do..

Guinness