UK 100mA RCCB keeps tripping with certain items connected.

[Jackster]

Hi all

I am in an industrial unit and the 100mA RCCB keeps tripping.
They use it as the main switch inside of the unit's distribution board. The mainboard that feeds all the units has an MCB in it.

The RCCB keeps tripping when I plug-in AC to DC transformer loads such as laptops, speakers, monitors etc.
The 30mA RCBO that does the sockets (and my lights in my office) does not trip.
And I don't have all of these devices plugged in at the same time. Right now my laptop is plugged in with the other office equipment, but my monitors and speakers are not. If I plug those in, it trips. If I put any load on my constant current/voltage DC power supply, it trips. Talking less than 1w and it trips.

I have already replaced it with another RCCB of the same make and model just to see if the old one is faulty but it does the same thing.
When I swapped the RCCB over, it tripped as soon as I connected it back up to the board. The MCB was off, though it was only a 3 pole...

It also trips randomly when everything has been fine for hours. Not much if anything connected and it will just trip.
Every night it trips.

Any ideas on what I can do? What tests can I do?
I am thinking it is a natural leaking to earth somewhere? I should check between ground and neutral on the incoming supply and within my unit?

Thanks
Jack

(yes I am aware that I should get an electrical in, the site electrician was meant to be on site last week but never showed and I will be getting my personal electrical in next week or so when they can book me in)

 

[pc1966]

If you plug in a big load there, say a heater, then switch the heater on without physically disturbing the socket, is it OK?

Trying to work out if some odd neutral path or similar. I'm guessing you have IR tested that circuit to rule out N-E permanent fault?

 

[Jackster]

OK.

Did you test the heater's whole circuit (i.e. IR it at the CU) or just disconnected the heater to check it alone? Might be nasty cable fault developing otherwise.

I did an IR test on it up to 500v and there was no fault. I did it while it was warm also.

Have you opened that socket to inspect it? Or try a new one?

It might be the actual act of inserting the plug is causing a fault, maybe N-E so no bang but enough to trip the RCCB.

I will test but it tripped on other sockets too. That socket is only 6 months old.

If you plug in a big load there, say a heater, then switch the heater on without physically disturbing the socket, is it OK?

Trying to work out if some odd neutral path or similar. I'm guessing you have IR tested that circuit to rule out N-E permanent fault?

Will try that. I have IR tested the socket circuit and no issues.


Hopefully, the electrician can work it out tomorrow.

 

[pc1966]

I did an IR test on it up to 500v and there was no fault. I did it while it was warm also.

OK.

I will test but it tripped on other sockets too. That socket is only 6 months old.

Have you PAT tested what you are plugging in? Maybe faulty plug/adaptor and strain/movement is causing it to N-E short?

I am still puzzled by why the 30mA RCBO is not tripping in that case though.

Will try that. I have IR tested the socket circuit and no issues.

Hopefully, the electrician can work it out tomorrow.

Hopefully!

 

[nicebutdim]

That's a very high leakage. Is that meter accurate down to low mA figures?

If it's the one from CPC, linked by @pc1966, I can confirm that they're fairly accurate - on a par with other more expensive testers.

 

[Jackster]

So I am hearing this second hand as I was not here, but the spark looked at the DB and the unit's plumed in circuits and they are all okay.
He has stated that I "need to get my equipment PAC tested" and "my equipment is tripping the breaker".

 

[DPG]

So I am hearing this second hand as I was not here, but the spark looked at the DB and the unit's plumed in circuits and they are all okay.
He has stated that I "need to get my equipment PAC tested" and "my equipment is tripping the breaker".

He would have said 'PAT tested'. Which is what you were going to do back in post #21. Seems like a good thing to get done.

 

[pc1966]

Am I doing this right? This result expected?

Looks right method, results are bizarre!

The 1mA on the CPC would be reasonable for a floating bit of kit and some filter capacitance.

The 39mA for the L-N difference is difficult to explain and ought to be triggering the RCBO that feeds it.

What is attached to the cable you are testing, has it any external cables such as network or RS232, etc, or is in contact with building metalwork, machines being controlled, etc?

I am still going through all the kit in the office doing IR, earth to case and polarity check. No issues so far.

If you IR test that kit you clamped (above) what do you get?

And when doing the IR test try having the CPC/earth also linked to the supply earth at the time.

Edit to add: Have you used your MTF to ramp-test the RCBO from that socket that you are getting 39mA and no trip from?

 

[Jackster]

Looks right method, results are bizarre!

The 1mA on the CPC would be reasonable for a floating bit of kit and some filter capacitance.

The 39mA for the L-N difference is difficult to explain and ought to be triggering the RCBO that feeds it.

What is attached to the cable you are testing, has it any external cables such as network or RS232, etc, or is in contact with building metalwork, machines being controlled, etc?

If you IR test that kit you clamped (above) what do you get?

And when doing the IR test try having the CPC/earth also linked to the supply earth at the time.

Edit to add: Have you used your MTF to ramp-test the RCBO from that socket that you are getting 39mA and no trip from?

Thought I was not losing it...

That kit is a small 2kW space heater. The RCBO never trips unless I use the Megga's RCD test function or the button on the RCBO.
It is a full plastic housing space heater and the RCCB trips with or without it.

IR tested it and it is fine when powered off. Obviously if I IR L+N, when powered on it, is a resistive short.

Ramp testing using that socket, 21mA


Going to leave things for now and see if it trips again. It was fine yesterday after tripping a few times when I plugged in my computer equipment. It is all still connected but is not tripping. I do have a 5kW 3ph load cycling on and off though so not sure if that is helping prevent it from tripping?

 

[pc1966]

Have you tired taping the L & N on your test plug/socket together and checking the L-N clamped current again?

Have you tried clamping the whole 3-core cable?

Usually the fact both conductors are through the clamp is enough, but you can see some imbalance if they are quite different paths.

 

[Jackster]

PAT guy came over and tested everything. All passed. Even my work passed.

 

[Jackster]

Site electricians came today and swapped the RCCB for an isolator.

Problem solved!

 

[westward10]

@Jackster what you have done may well have compromised the safety of the installation but if an electrician carried out this 'remedy' then I would assume they feel otherwise and this may be the case. On that note this thread is closed.