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]

Actually thinking a bit more - if there is a N-E fault downstream of the 30mA RCBO it should also trip as it would see the imbalance as well. That assumes the trip speeds are selective, is the 100mA one a delay RCCB (i.e. "type S" for selective)?

 

[Jackster]

Actually thinking a bit more - if there is a N-E fault downstream of the 30mA RCBO it should also trip as it would see the imbalance as well. That assumes the trip speeds are selective, is the 100mA one a delay RCCB (i.e. "type S" for selective)?

I guess we shall find out when my "incompetent" --- gets a multi-function tester on Monday

 

[timhoward]

I guess we shall find out when my "incompetent" --- gets a multi-function tester on Monday

Don’t take it personally! We have to assume that unknown people can’t test safely. In colleges testing is taught after installation and after experience has been built up with how things are typically wired.
And electrical testing can be a dangerous business and doesn’t always give clear answers - there are regular questions on here from qualified sparks about interpreting results. Some tests are dead and some are live and it’s very easy to make a mistake.
We just care about safety.

 

[Jackster]

Well, I am still alive.

So I managed to find my clamp meter and it is showing 0.15A to 0.5A on the 20A setting depending on if I clamp near the RCBO or the main tails where the 4mm cable is accessible.
Don't think one can trust it... Ideally need something that measures in the 2A range. Will be worth it in my electronics lab so I will grab one tomorrow.


Got my hands on the multifunction tester. A pretty good bit of kit to have a play with. Found a fault on an old extension cord (not been used in years) so that has gone in the bin so already paying itself off.

I did the RCD tests on both AC/AC+DC settings. The 30mA RCBO for the sockets was fine as was tripping within spec.
The 100mA RCCB tripped at a max of 105mA on AC and at 450mA on AC+DC. Not 100% sure about those results.


I did an IR test on the board between N+E and L+E * 3. All fine.

Having been messing around with all the plugs and sockets (mostly extension cables in the office area), I have reduced the apparently N to E leakage down from the average reading on the socket circuit of 0.4-0.5A to 0.1-0.2A.
Put a few new 8 way extensions in while I was down under the desks which might have helped?

I did do an IR test on all the existing multi-way extension cables and all were fine on 500v.

The RCCB has yet to trip under normal conditions but as soon as I put a load on my benchtop AC to DC power supply, it trips.
Could be a fault with that bit of kit but that kit is not normally plugged in. I tested it at home and the RCD did not trip there.

 

[pc1966]

Well, I am still alive.

A good start to the day!

So I managed to find my clamp meter and it is showing 0.15A to 0.5A on the 20A setting depending on if I clamp near the RCBO or the main tails where the 4mm cable is accessible.
Don't think one can trust it... Ideally need something that measures in the 2A range. Will be worth it in my electronics lab so I will grab one tomorrow.

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.

Got my hands on the multifunction tester. A pretty good bit of kit to have a play with. Found a fault on an old extension cord (not been used in years) so that has gone in the bin so already paying itself off.

I did the RCD tests on both AC/AC+DC settings. The 30mA RCBO for the sockets was fine as was tripping within spec.

Good to hear.

The 100mA RCCB tripped at a max of 105mA on AC and at 450mA on AC+DC. Not 100% sure about those results.

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 did an IR test on the board between N+E and L+E * 3. All fine.

Having been messing around with all the plugs and sockets (mostly extension cables in the office area), I have reduced the apparently N to E leakage down from the average reading on the socket circuit of 0.4-0.5A to 0.1-0.2A.
Put a few new 8 way extensions in while I was down under the desks which might have helped?

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 did do an IR test on all the existing multi-way extension cables and all were fine on 500v.

OK.

The RCCB has yet to trip under normal conditions but as soon as I put a load on my benchtop AC to DC power supply, it trips.
Could be a fault with that bit of kit but that kit is not normally plugged in. I tested it at home and the RCD did not trip there.

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.

 

[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.