UK Unusual Tripping RCB

[Dobbies]

Hi,
As a farmer I use an electronic fencer to keep animals contained in my field. The one I use simply plugs into a 230 volt supply and the two output cables connect to earth and fence consecutively. It’s been working fine for the last 12 months until yesterday when it tripped an RCB.

There are three RCB’s in the circuit, the first is the mains supply in the house. The house supplies the workshop (2nd RCB), and the workshop supplies the barn (3rd RCB) where the fencer is connected, dry and free of damp. Being puzzled why it tripped the middle RCB and not the first or third, I connected it directly into the house ring main where it works perfectly. I then took it to a neighbour’s house and it also works perfectly, but returning to the barn the same middle RCB tripped.

Could it be an over sensitive or faulty RCB?

Any ideas would be greatly appreciated.

 

[SJD]

I'm guessing the photo shows the RCD that tripped - in the workshop - which is rated at 30mA trip current? Do the other RCDs have the same trip current - e.g. the one in the house could be larger, e.g. 100mA? And your neighbours' house RCD? Post photos if you are not sure.

It is possible the fencer is faulty, is it also possible there are other issues at the workshop board (earth leakage on other circuits) contributing to tripping.

Generally it is not a good idea to have RCDs of the same value trip current in series, it can be somewhat random as to which trips.

NB: There should not be a half-module opening between the RCD and the first circuit breaker MCB in the photo you posted, looks like a half-module blank has fallen out. Plus there are 3 different brands of RCD/MCB, which is not recommended.

 

[James]

Most likely is a corroded or poor joint somewhere on the circuit. Possibly a wet joint that is passing current from N to Earth.

 

[littlespark]

Although all 3 rcd’s may be rated at 30mA, they may trip slightly under that. The middle one could be the most sensitive of the 3.
Repeating what others have suggested, it could be a combination of things and the fence is just tipping it over.

Have you checked the rcd’s with their test buttons? If they don’t work it may be faulty and one may never trip with a fault.
Be aware that pushing one button may trip the rcd up stream