RCD Tripping Hell with high load

[Fletch]

Hi all. First time poster here with a hell of a lot less hair than I had 3 weeks ago now! so please be nice, I'll try and explain best I can. I am not a sparky but have some idea of electrics. I also own a multimeter.

Short version. 100A, 30mA RCD trips INTERMITTENTLY on WYLEX 8 fuse board when 'large load' is added (eg ~12A). It's not isolated to 1 MCB as can be cooker or inmersion or Hoover tripping RCD. Does it anytime of day. New immersion heater, new sockets throughout house same problem. Had an electrical safety test pass.

Longer storey.

Bought house in April. Had an electrician change all socket faces and carry out electrical test in doing so he found the RCD on the 'constant live' board (as we have eco 7 board for the storage heaters) had been bypassed. He reconnected it and since then (June) it's been tripping out left right and centre. I've worked out it happens when the load on the circuits is high, e.g. When the cooker AND the immersion is on, or when the heater and Hoover is turned on pulling more than say 10A and this can be across multiple MCBs. But all are ok if on individually. The immersion heater (3KW) is brand spanking new (like installed yesterday new as we were told it could be a leakage there (but we needed a new one anyway ) and the cooker is new ish too . So tripping hell for the last few months not solved by new immersion. Now Over the past 2 nights the RCD has tripped when, the cooker and immersion were on, when the kettle and immersion was on, when the lounger heater and cooker were on and the overnight when the off peak heating kicked in too, (so no hot water in morning) but only on the constant live RCB tripped as though the load of heaters and immersion is too high. There no issues with any low loading appliances such as lighting or phone chargers or plugs. But I'm sat here in bed now the immersion is on happy as Larry with no issues. Als FYI -There is not earth loop throughout the upstairs lighting .

Personal diagnosis:
I've spent days reading about N-E faults but they appear to be on a specific circuit, whereas my RCD Will trip even if the MCB for the last thing to cause the tripping is off... could that still be a N-E fault? I've also been round and unplugged everything (as the sparky did) and plugged things in individually and had no issues (including Hoover and putting just immersion/cooler on) utill putting more than one on.

Other one I've read about is a cummuliative earth leakage, which as the current load on the circuits goes up it exceeds the 30mA RCD value which I think personally is most likely but I don't have any clues on how to test this?!

I've read about broken RCDs too but everyone I've seen/read has said it won't be that.

We've spent a grand on electricians so far and are drastically running out of money, we feel a little as though the guy who did the safety test 'missed' something or didn't investigate properly, but he says it's all fine and can't see anything that would be causing it.

Hellllllllllllp! Is there anything I can do indivually with my trusty multimeter to see if I can work out just WTF is causing it?

I've uploaded a picture of my box setup. You can see that the cooker MCB Is off from last nights requirement for hot water but the immersion will still work with it on just so long as the cooker it's self isn't heating up.

Any help MASSIVELY appreciated.

Cheers

A Balding M

 

[Pete999]

Hi all. First time poster here with a hell of a lot less hair than I had 3 weeks ago now! so please be nice, I'll try and explain best I can. I am not a sparky but have some idea of electrics. I also own a multimeter.

Short version. 100A, 30mA RCD trips INTERMITTENTLY on WYLEX 8 fuse board when 'large load' is added (eg ~12A). It's not isolated to 1 MCB as can be cooker or inmersion or Hoover tripping RCD. Does it anytime of day. New immersion heater, new sockets throughout house same problem. Had an electrical safety test pass.

Longer storey.

Bought house in April. Had an electrician change all socket faces and carry out electrical test in doing so he found the RCD on the 'constant live' board (as we have eco 7 board for the storage heaters) had been bypassed. He reconnected it and since then (June) it's been tripping out left right and centre. I've worked out it happens when the load on the circuits is high, e.g. When the cooker AND the immersion is on, or when the heater and Hoover is turned on pulling more than say 10A and this can be across multiple MCBs. But all are ok if on individually. The immersion heater (3KW) is brand spanking new (like installed yesterday new as we were told it could be a leakage there (but we needed a new one anyway ) and the cooker is new ish too . So tripping hell for the last few months not solved by new immersion. Now Over the past 2 nights the RCD has tripped when, the cooker and immersion were on, when the kettle and immersion was on, when the lounger heater and cooker were on and the overnight when the off peak heating kicked in too, (so no hot water in morning) but only on the constant live RCB tripped as though the load of heaters and immersion is too high. There no issues with any low loading appliances such as lighting or phone chargers or plugs. But I'm sat here in bed now the immersion is on happy as Larry with no issues. Als FYI -There is not earth loop throughout the upstairs lighting .

Personal diagnosis:
I've spent days reading about N-E faults but they appear to be on a specific circuit, whereas my RCD Will trip even if the MCB for the last thing to cause the tripping is off... could that still be a N-E fault? I've also been round and unplugged everything (as the sparky did) and plugged things in individually and had no issues (including Hoover and putting just immersion/cooler on) utill putting more than one on.

Other one I've read about is a cummuliative earth leakage, which as the current load on the circuits goes up it exceeds the 30mA RCD value which I think personally is most likely but I don't have any clues on how to test this?!

I've read about broken RCDs too but everyone I've seen/read has said it won't be that.

We've spent a grand on electricians so far and are drastically running out of money, we feel a little as though the guy who did the safety test 'missed' something or didn't investigate properly, but he says it's all fine and can't see anything that would be causing it.

Hellllllllllllp! Is there anything I can do indivually with my trusty multimeter to see if I can work out just WTF is causing it?

I've uploaded a picture of my box setup. You can see that the cooker MCB Is off from last nights requirement for hot water but the immersion will still work with it on just so long as the cooker it's self isn't heating up.

Any help MASSIVELY appreciated.

Cheers

A Balding M

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When you say there is not an earth loop in the lighting upstairs, do you mean the lighting has no earth wires,( cpcs )?
Did your Electrician explain why the RCD had been bypassed? it seems that whoever bypassed the RCD did so because it was showing the same problems you are experiencing now.
When your Electrician did the "checks" on your installation, did he do any testing with a Multi Function Tester (MFT), and if so were any test results issued to you in the form of EICR? Sorry for all the questions, but with your problems, it's going to be questions, questions until someone can form an opinion as to what the problem may be, one more question, sorry, are there any specific times the RCD trips, for example is it only at night?

 

[Fletch]

When you say there is not an earth loop in the lighting upstairs, do you mean the lighting has no earth wires,( cpcs )?

Yeah the lighting circuits are just 2 core red and black cabling not new 3 core brown blue and green/yellow

 

[Midwest]

Welcome Fletch to the forum. Sorry to hear of your problem. All of those things you mentioned, could be the cause of your problem. Unfortunately for you, you current standard tariff has one RCD protecting all the sockets, cooker etc.

I'm afraid the only way to get to the bottom of this, is to employ a competent electrician to carry out suitable testing to locate the fault(s). Perhaps have an Electrical Installation Condition Report carried out, and even consider having your consumer unit replaced, when the fault has been located.

You are not going to rectify this issue yourself.

 

[Octopus]

There is little or nothing you or your trusty multi meter can do.

You need a local spark to properly test your RCD, test all the circuits INDIVIDUALLY for IR and have an earth leakage clamp meter.

 

[Octopus]

We've spent a grand on electricians so far and are drastically running out of money, we feel a little as though the guy who did the safety test 'missed' something or didn't investigate properly, but he says it's all fine and can't see anything that would be causing it.

Doing what? What certificates have they given you?

 

[Fletch]

I'm afraid the only way to get to the bottom of this, is to employ a competent electrician to carry out suitable testing to locate the fault(s). Perhaps have an Electrical Installation Condition Report carried out, and even consider having your consumer unit replaced, when the fault has been located.

You are not going to rectify this issue yourself.

*crying face* Ok,

Do you Any clues (even ball park figure) on the cost of an electrical installation condition report? 3 bed terrace.

 

[Octopus]

^^ from what you describe a EICR won't help.

Read my post #5 and get that done?

Unless you know the RCD is OK, the IR is OK and you haven't got excessive earth leakage, you won't move forward.....

One other point - it "could" be the incoming supply causing this.

 

[Fletch]

Doing what? What certificates have they given you?

Replaced all socket faces and installed some new sockets. Replaced all light fittings. Carried out electrical safety tests. Replaced earth rod (old one had too higher resistance). Installed earth to the copper piping in house, I have Certs for tests.

 

[Octopus]

^^ OK

So your "grand" has been spent on improvements ........... so its not wasted as such.

If you don't have faith in said spark, ask around locally , but when you call them, I would make sure they have an earth leakage clamp meter they can bring - not all "sparks" have these, and for faults as you describe they are essential.

 

[Pete999]

Hi all. First time poster here with a hell of a lot less hair than I had 3 weeks ago now! so please be nice, I'll try and explain best I can. I am not a sparky but have some idea of electrics. I also own a multimeter.

Short version. 100A, 30mA RCD trips INTERMITTENTLY on WYLEX 8 fuse board when 'large load' is added (eg ~12A). It's not isolated to 1 MCB as can be cooker or inmersion or Hoover tripping RCD. Does it anytime of day. New immersion heater, new sockets throughout house same problem. Had an electrical safety test pass.

Longer storey.

Bought house in April. Had an electrician change all socket faces and carry out electrical test in doing so he found the RCD on the 'constant live' board (as we have eco 7 board for the storage heaters) had been bypassed. He reconnected it and since then (June) it's been tripping out left right and centre. I've worked out it happens when the load on the circuits is high, e.g. When the cooker AND the immersion is on, or when the heater and Hoover is turned on pulling more than say 10A and this can be across multiple MCBs. But all are ok if on individually. The immersion heater (3KW) is brand spanking new (like installed yesterday new as we were told it could be a leakage there (but we needed a new one anyway ) and the cooker is new ish too . So tripping hell for the last few months not solved by new immersion. Now Over the past 2 nights the RCD has tripped when, the cooker and immersion were on, when the kettle and immersion was on, when the lounger heater and cooker were on and the overnight when the off peak heating kicked in too, (so no hot water in morning) but only on the constant live RCB tripped as though the load of heaters and immersion is too high. There no issues with any low loading appliances such as lighting or phone chargers or plugs. But I'm sat here in bed now the immersion is on happy as Larry with no issues. Als FYI -There is not earth loop throughout the upstairs lighting .

Personal diagnosis:
I've spent days reading about N-E faults but they appear to be on a specific circuit, whereas my RCD Will trip even if the MCB for the last thing to cause the tripping is off... could that still be a N-E fault? I've also been round and unplugged everything (as the sparky did) and plugged things in individually and had no issues (including Hoover and putting just immersion/cooler on) utill putting more than one on.

Other one I've read about is a cummuliative earth leakage, which as the current load on the circuits goes up it exceeds the 30mA RCD value which I think personally is most likely but I don't have any clues on how to test this?!

I've read about broken RCDs too but everyone I've seen/read has said it won't be that.

We've spent a grand on electricians so far and are drastically running out of money, we feel a little as though the guy who did the safety test 'missed' something or didn't investigate properly, but he says it's all fine and can't see anything that would be causing it.

Hellllllllllllp! Is there anything I can do indivually with my trusty multimeter to see if I can work out just WTF is causing it?

I've uploaded a picture of my box setup. You can see that the cooker MCB Is off from last nights requirement for hot water but the immersion will still work with it on just so long as the cooker it's self isn't heating up.

Any help MASSIVELY appreciated.

Cheers

A Balding M

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View attachment 38364

Fletch where are you based? as the code you have in your profile comes up all over the place?

 

[Fletch]

^^ OK

So your "grand" has been spent on improvements ........... so its not wasted as such.

If you don't have faith in said spark, ask around locally , but when you call them, I would make sure they have an earth leakage clamp meter they can bring - not all "sparks" have these, and for faults as you describe they are essential.

Magic.. don't work in north Wales do you Murdoch? Haha.

So your consensus is that there's an earth leakage on one of the circuits? Or more than one? If the latter causing a cumulative tripping level leakage?

 

[Fletch]

Fletch where are you based? as the code you have in your profile comes up all over the place?

Ll54 5sd is the postcode.. just south of caernarfon in north Wales.

 

[The Ghost]

Tracking RCD faults is notoriously difficult, personally I am always worried when I get called out for an RCD fault because it can be so many things and somtimes really obscure. The good news is there is a way to test methodically to assess what the problem is it just takes a very logical approach, good test gear and knowing how to use it. You have to measure in different ways the amount of leakage on any part, and all of the installation. As it has been said you need a decent electrician who knows how to do this. Suggest you specifically ask the electrician "Can you track down RCD problem?" You will have to use your nous to divine whether they sound competent or not. I would guess it cannot take more than a day to find the fault, but normally should be quicker.
I might guess that the element is going on your cooker and the symptom is sub clinical so to speak before it becomes full blown cooker circuit blowing. As you say it seems there is cumulative earth leakage identified to cooker and immersion, maybe also other equipment. A ramp test can show how much is leaking from each appliance with a bit of basic maths.

 

[Octopus]

Magic.. don't work in north Wales do you Murdoch? Haha.

So your consensus is that there's an earth leakage on one of the circuits? Or more than one? If the latter causing a cumulative tripping level leakage?

I rarely drive more than 10 miles, let alone 200!

I'm only speculating - and I'm well know for HATING up front RCD's and dual RCD boards.

If and I say if you decide to go for a new fuse board, just remember, one using RCBO's will be more expensive to install, but only individual circuits will trip, so resulting issues down the line will be far easier and cheaper to locate

 

[Midwest]

^^ from what you describe a EICR won't help.
QUOTE]

As you know, I don't do EICR's. But just looking at that CU, with different makes of MCB's, inappropriate circuit identification, missing blanks in other switch gear, I indeed think a check of the remaining installation would obtain some benefit from an EICR. IMO

 

[Octopus]

As you know, I don't do EICR's. But just looking at that CU, with different makes of MCB's, inappropriate circuit identification, missing blanks in other switch gear, I indeed think a check of the remaining installation would obtain some benefit from an EICR. IMO

Not sure I agree ............. a cowboy EICR isn't likely to show anything relating to the issue.

The best thing the OP can do is keep a log of when it trips and what was being used....

 

[Pete999]

Ll54 5sd is the postcode.. just south of caernarfon in north Wales.

Well that rules me out for any practical help, my passport has lapsed.

^^ from what you describe a EICR won't help.

Read my post #5 and get that done?

Unless you know the RCD is OK, the IR is OK and you haven't got excessive earth leakage, you won't move forward.....

One other point - it "could" be the incoming supply causing this.

Hi Murdoch, you mention that an EICR probably wouldn't help, yet in your post#5 you mention IR testing RCD testing and lastly an earth leakage test. The first 2 tests IR nd RCD would be carried out in an EICR, or at least they would if I was doing it.

 

[Midwest]

Not sure I agree ............. a cowboy EICR isn't likely to show anything relating to the issue.

The best thing the OP can do is keep a log of when it trips and what was being used....

Well I go to the foot of my stairs. I've read numerous threads where members advise the complete opposite. I have my views on the costs of EICR's, and as the OP is considering a CU replacement, I'd spend my dosh on that. But you do surprise me Murdoch.

 

[Ian1981]

A ramp test may indicate that the rcd is also a little sensitive
Had one yesterday that tripped at 17mA and kept tripping on a non trip loop impedance test.

 

[static zap]

You have mentioned tripping when things are turned on,but keep a eye out for any tripping when just moving about in house (not turning anything on .)
(Like others have said , need a guy with the right gear)

 

[Octopus]

Well that rules me out for any practical help, my passport has lapsed.

Hi Murdoch, you mention that an EICR probably wouldn't help, yet in your post#5 you mention IR testing RCD testing and lastly an earth leakage test. The first 2 tests IR nd RCD would be carried out in an EICR, or at least they would if I was doing it.

To track down an intermittent tripping RCD, takes much more than a global IR - which is all that is likely with a low cost EICR.

Sure have an EICR BUT the scope of said inspection must be very detailed to make it worth while.

 

[The Ghost]

@SparkyChick to the rescue. I think there are other members as well in Wales that will be able to help. I tend to work on the basis if I don't fix it I don't charge. As I feel charging call-out is a bit of well...unfair really if you don't get somewhere even if it is just working out the fault. Maybe not remedying as the cost or whatever is too much sometimes straight away.

 

[Pete999]

Ll54 5sd is the postcode.. just south of caernarfon in north Wales.

Well that rules me out for any practical help, my passport has lapsed.

^^ from what you describe a EICR won't help.

Read my post #5 and get that done?

Unless you know the RCD is OK, the IR is OK and you haven't got excessive earth leakage, you won't move forward.....

One other point - it "could" be the incoming supply causing this.

Hi Murdoch, you mention that an EICR probably wouldn't help, yet in your post#5 you mention IR testing RCD testing and lastly an earth leakage test. The first 2 tests IR nd RCD would be carried out in an EICR, or at least they would if I was doing it.

To track down an intermittent tripping RCD, takes much more than a global IR - which is all that is likely with a low cost EICR.

Sure have an EICR BUT the scope of said inspection must be very detailed to make it worth while.

To be fair mate thee was never any mention of a global IR test, or cheap EICR, with the OP's problems, I personally think a full on EICR would highlight any problems.

 

[Octopus]

I personally think a full on EICR would highlight any problems.

Not sure I agree....... as I mentioned in a post - it could be the incoming supply!

 

[SparkyChick]

Whilst I like that part of the world for the scenery, an 8-10 hour round trip may make me a little too expensive

 

[Pete999]

Not sure I agree....... as I mentioned in a post - it could be the incoming supply!

OK how exactly

 

[Fletch]

You have mentioned tripping when things are turned on,but keep a eye out for any tripping when just moving about in house (not turning anything on .)
(Like others have said , need a guy with the right gear)

So though I believe myself to be Devine in many ways, I don't beleive I give off an Magnetic field capable of a current inducing nature.. lol..

but I have unfortunately noted that it doesn't actually make a difference where you are in the house when tripping. Mostly we spend time in the dining room, but it trips when the bedroom or lounge or even when I'm outside.

I don't really want to spend on a new CU, as I gather the one I have would be ok unless identified to be faulty?! (How a copper bar can be faulty?!). There have been various additions to the house causing the additional circuits e.g. The stair lift (socket under stairs) 90's the kitchen bathroom extension 80s. And the right hand board is solely for the heating, which has never ever tripped. (Though questionable whether the RCD has been bypassed there) but shouldn't make a difference on the constant board.

 

[Octopus]

OK how exactly

Seen recently

Loose connection on service head

Very poor incoming neutral connection

BOTH caused RCD's to trip.

 

[Fletch]

Whilst I like that part of the world for the scenery, an 8-10 hour round trip may make me a little too expensive

Even if it included free nights stay for however long you need in the scenic areas of snowdonia?!

3 mins from the beach!
10 mins from caernarfon and the base of Snowden!

 

[Richard Burns]

Because you have had electricians working there at least one of them should have tested the RCD to see if it functions properly, even though they may not have done a ramp test as it is not required, this testing should have eliminated the RCD failing as a problem.
Because you have had the 24 hour supply RCD trip when the off peak heating on the off peak supply has come on this means that the fault is reduced to a supply issue or a neutral earth fault because the off peak heating should normally be unable to cause the main board RCD to trip.
If the supply does have a loose connection providing an irregular and highly variable waveform to the main board it is possible but not common for the RCD to be affected by the intermittent effect and trip, this could be initially checked, not by touch!, by observation of the supply tails at the meter and any joints before the meter. If there is a bad loose connection the tails would be getting hot and look darker than normal, possibly signs of flashes if it is dark and a high load is taken. If this is the case then it would need a rapid response to resolve the issue.
If it is a neutral earth fault of high resistance then individual Insulation Resistance
testing of the circuits on the main board should highlight the potential problem, though it would also be critical that the earth was still connected to the earthing system to check for faults to an unexpected earthed part.

The rest of the advice already given above stands.
I would be heading for the NE fault area as a cause based on what you have described.
However only personal inspection and testing would be able to identify it accurately and it may well take a long time. An electrician could also possibly suggest some narrowing down methods if the fault is not clear cut.

 

[Strima]

I would be leaning towards a NE fault. Had one a few years ago where the neutral insulation on a socket outlet had been scored when stripped back on original installation in the 70's. Circuit tested out fine, over 2 Mohms, but when any sort of load was applied the RCD would bang out.

Rather than IR test I ended up doing a continuity check along the RFC to track down the fault, saved me splitting the circuit to narrow down the fault.

 

[telectrix]

as strima. possible N-E fault. shows up when loads applied even to different circuits.

 

[marconi]

Fletch - Could you load up some more images as in (your post #1) which show:

a. to the right of the white MEM box;

b. what is behind the lowered lid of the left hand Wylex CU;

c. the routes of the green/yellow conductors and any bare metal terminals they connect to;

d. the routes of the thick grey conductors.

e. the clamp for the water bond.

f. your intake and meter.

Top left in the white conduit - are they thick round grey conductors or thinner flat ones?

 

[Fletch]

were away from the house now, with the whole thing and a 10 week old we've decided to shift out as it's getting a little over complicated to deal with. So I can do my best to describe but no pictures.

a. to the right of the white MEM box; is a standard 100 am electrical board fuse, one with the "do not touch ownership of welsh electric board, criminal offence" hazard on it.

b. what is behind the lowered lid of the left hand Wylex CU; nothing but wall, as far as I know. Just the feed from the MEM switch into the CUs

c. the routes of the green/yellow conductors and any bare metal terminals they connect to; yes, there's a metal "terminal" rail style thing with about 10 holes and 10 grub screws that then connect to the earth cable that goes out to the new earth rod outside.

d. the routes of the thick grey conductors... by conductors I guess you mean wires? They come in through the wall, into aforementioned 100a welsh board fuse, into the Meter, into MEM Swicth in to CUs

e. the clamp for the water bond. : there are technically 2, on under the sink attached to mains pipe (install during electrical safety test) and one I attached to the piping in the old immersion cupboard this weekend. Though it still tripped before I did that. Both are silvery metal screw clamps.

f. your intake and meter. : The big grey box in the picture is the meter.. the "intake" in gather you mean the mains cable into the property. Comes from next door under guttering round house and in via hole in the door frame in kitchen.

Top left in the white conduit - are they thick round grey conductors or thinner flat ones? That conduit contains all 3 core 2.5mm wires.

Will post pics as soon as I can!

 

[David M]

as strima. possible N-E fault. shows up when loads applied even to different circuits.

This thread reminds me of a RCD intermitting trip fault I attended to a few years back. After an extensive inspection and test of the installation the problem turned out to be an extension lead that was plugged into a socket outlet supplying a bed side alarm clock. The extension lead had been incorrectly wired - N&E reversed. The alarm clock functioned and the earth "leakage" on its own was not sufficient enough to cause the RCD to trip. As soon as a few extra loads where added at the same time, i.e cooker, kettle, immersion, lights... the RCD would trip.

 

[marconi]

Fletch, could you answer these questions please?

1. You state that the 24 hr rcd does not trip when a single large load is turned on eg: immersion heater. Does the rcd remain closed when only the immersion heater is on and its thermostat reaches its set temperature.

2. And is it also so for the heater alone?

3. Does the rcd remain closed when say the oven is first turned on to 220C say and an electric ring is turned on at the same time to low heat setting? Or trip after a few minutes?

4. Does the rcd remain closed when a cold oven is first turned on to 100C and an electric ring is turned on at the same time to the highest setting? Or trip after a few minutes?

5. If you turn on all the rings and oven of the cooker what happens?

6. You state the rcd will trip if the heater is on and the hoover is then turned on. What happens if only the the hoover is turned on and after 20 seconds turned off?

7. What happens if you turn the hoover on and then turn on the heater? And then turn the heater off?

8. If you have a washing machine, tumble dryer or microwave could you un-plug them all and then turn on some items you know usually cause the rcd to trip immediately. Any difference?

9. Do you have an filter socket outlets. Folk sometimes have them as 4 way socket strips and they are marked up as such. If you do unplug it and repeat 8.

10. In general would you say the tripping always occurs when the loading is high and another high amperage load is switched on? Or is 'always' more like 'often'?

OR

11. In general tripping occurs when the loading is high and a high amperage load is switched off by its internal thermostat. Again 'always' or 'often'?

Enough questions for now - I am off for a swim.

(None of these questions replace the requirement for the tests and inspections mentioned in previous posts. But the responses may help understand better what and where the problem is.)

 

[marconi]

Fletch - last from me for today: Please contact your Distribution Network Operator(DNO) which is the company you would call if you had a power cut and ask them if it is possible to convert your home's supply from 'TT' to 'TNCS' and ask how much they charge. Don't commit to doing it just yet - I just want to know if it an option for you.

 

[ringer]

This won't help the OP with his problem, but what worries me is that he says the RCD had been bypassed. It is an RCD mainswitch - how exactly had it been bypassed?!?!?!

 

[Generator]

In all this testing, retesting, checking etc, etc, everyone seems to be assuming that the RCD in question cannot be at fault! Testing it with a 30mA test leakage current does not guarantee it won't spuriously trip when a large load is suddenly switched on.
The easiest way to eliminate that would be to change it! - they aren't that expensive.
If the RCD is faulty at high loads, no amount of other testing will solve it.
Always try the easy things first!