UK 100mA RCCB keeps tripping with certain items connected.

[Jackster]

Something like this is needed:
https://cpc.farnell.com/multicomp-pro/mp780050/mini-leakage-current-tester/dp/IN08364
Also you need to get the L and matching N in to the clamp to see the residual. I would strongly advise against moving cables in an energised DB! Try and get anything to measure in-place and accessible with all power off.

Ah nice find. The one I was looking at was £5 more and not as accurate.

I am doing the L + N matching pair for the sockets and the DB. Both are accessible without moving the cables.

If it is type AC and tested on a type A waveform with DC component then it can be desensitised.

If 100mA rating it ought to trip between 50-100mA. You need to have all loads off so you are just testing it alone, and not having system currents also present.

I will test again on Wednesday when I am back at the unit. Or tomorrow night.

Those are massive currents! Is that measured with L&N in the clamp, or are you (incorrectly) clamping the CPC? If so then any metalwork anything is in contact with could be causing odd currents to circulate.

I am clamping the Live and Nutrual 4mm singles coming out of the RCBO. It ranged from 0.2A to 0.7A but it really came down to how I was holding the clamp meter on the cables and at what angle. That is why I don't believe my 20A clamp meter. Will wait for the one from CPC to arrive.

Have you IR tested the power supply? I.e. the sort of basic PAT testing part (along with CPC bond resistance, etc)

Are you sure the power supply is going in to the RCBO's supply? There is something inconsistent with being able to trip the 100mA incomer and not trip the 30mA socket feed, unless the installation happens to be sitting only a few mA leackage below the trip point normally.

I tested N+E and L+E on that power supply up to 500v. No issues. Will look into the PAT procedure and get back to you on that.


There are only 3 circuits on the DB. Sockets, Door and Lights. I can follow the 4mm singles from the sockets up into the RCBO.
This is the reason why I am struggling to get my head around it all.

 

[pc1966]

There are only 3 circuits on the DB. Sockets, Door and Lights. I can follow the 4mm singles from the sockets up into the RCBO.
This is the reason why I am struggling to get my head around it all.

Check the general leakage to see if it is close to the 100mA RCCB's trip threshold.

Check that the 100mA RCCB is a delay type (S), otherwise a very short spike might just trip it before the 30mA one goes.

 

[Jackster]

Check the general leakage to see if it is close to the 100mA RCCB's trip threshold.

Check that the 100mA RCCB is a delay type (S), otherwise a very short spike might just trip it before the 30mA one goes.

It has an S on the front off it.

When I checked using my crappy clamp meter, it said nearly 1 amp...

I did test the meter and it was saying I was drawing 11A during normal use of the office.
That is a 1700w blower heater, 800w (max) IR panel, 2 monitors, laptop, printer, 160w of LED tubes and a little bit of networking gear.. So somewhat accurate there.

Just noticed the power has gone out at the unit. Either the internet has gone (doubt it) it the power tripped.

 

[Jackster]

The half-decent leakage current tester arrived today and it is very good. Very nice build quality for the price.

So I tested a load of stuff and my space heater, is leaking around 60ma. My LED lights/printer/network/IR heater circuit is leaking around 30ma.

Without these two circuits, my leakage is down in the 3-5mA range.
With these circuits, it is in the 100-125mA range for the whole DB.

So I guess we have found the issue. As to why the RCCB trips and not the RCBO, no idea.
The RCBO is 30mA and the RCCB is 100mA.
I tested the RCBO and it trips fine on the Megga multifunction tester. The RCCB trips at 110mA.

I have done an IR test on the space heater and it is fine up to 500V.
Think I will retire that anyway as it is on recall apparently...

Will go through the other circuit at a later date to see what in that is causing the 30mA leakage.

 

[DPG]

The half-decent leakage current tester arrived today and it is very good. Very nice build quality for the price.

So I tested a load of stuff and my space heater, is leaking around 60ma. My LED lights/printer/network/IR heater circuit is leaking around 30ma.

Without these two circuits, my leakage is down in the 3-5mA range.
With these circuits, it is in the 100-125mA range for the whole DB.

So I guess we have found the issue. As to why the RCCB trips and not the RCBO, no idea.
The RCBO is 30mA and the RCCB is 100mA.
I tested the RCBO and it trips fine on the Megga multifunction tester. The RCCB trips at 110mA.

I have done an IR test on the space heater and it is fine up to 500V.
Think I will retire that anyway as it is on recall apparently...

Will go through the other circuit at a later date to see what in that is causing the 30mA leakage.

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

 

[pc1966]

It is odd to see 100mA leak and no DC effect, unless there is some largish capacitor in there! Or maybe something odd happens when it gets hot. Either way, that is a rather sick heater!

As you are running close to the up-front RCCB's threshold the trips make perfect sense. Without the heater can you now plug in stuff, etc, and all is happy?

 

[Jackster]

It is odd to see 100mA leak and no DC effect, unless there is some largish capacitor in there! Or maybe something odd happens when it gets hot. Either way, that is a rather sick heater!

As you are running close to the up-front RCCB's threshold the trips make perfect sense. Without the heater can you now plug in stuff, etc, and all is happy?

I will remove the heater from the circuit when I leave and see if it trips overnight. I have removed all the plugs from the sockets before and have had it trip so I don't know if this is the only issue here.

 

[pc1966]

I will remove the heater from the circuit when I leave and see if it trips overnight. I have removed all the plugs from the sockets before and have had it trip so I don't know if this is the only issue here.

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.

 

[Jackster]

It just tripped again. I removed the heater and it still trips. My lights/printer/IR heater (turned off) and network circuit is fine. <5mA leak.

But as soon as I plug in my office equipment (Laptop, speakers, monitors, phone etc) and it trips. These were only adding 5mA earlier.

https://drive.google.com/file/d/1KQiSVuwgiJi9dorh8_jdm3vHrAHscI0G/view?usp=sharing

(should be able to view shortly without downloading)

Literally just as I am about to post this, the site spark at door.
He will be around tomorrow to see what's up.

 

[pc1966]

But as soon as I plug in my office equipment (Laptop, speakers, monitors, phone etc) and it trips. These were only adding 5mA earlier.

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.

 

[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.