Nuisance RCD Tripping - Diagnosis Advice PLEASE

[timhoward]

Ask and you shall receive. Including the world's largest connector block, random upsidedown breakers with bus bar at the top, and holes everywhere. IP00

Wow. That's not just a rats nest, that's dangerous.

It's missing a main switch so there's no single point of isolation, the 6mm carrying the feed to the LH RCD is under-sized for the load and is only protected by the suppliers fuse, the 6mm from the RCD to the bus bar on left is under sized. It also looks like the LH neutral bar is for the right hand circuits. And half the Neutrals for the left hand circuits look to be in a choc block.
In short it's an absolute nightmare, a far cry from a college test rig.

Don't take this the wrong way, but if you haven't yet done much testing I wouldn't make that one your first deep dive testing experience, or your first board change. For context I don't think I've seen one as bad as that this year. I'd be charging a premium to even entertain taking on that!

 

[2nd Life]

Wow. That's not just a rats nest, that's dangerous.

It's missing a main switch so there's no single point of isolation, the 6mm carrying the feed to the LH RCD is under-sized for the load and is only protected by the suppliers fuse, the 6mm from the RCD to the bus bar on left is under sized. It also looks like the LH neutral bar is for the right hand circuits. And half the Neutrals for the left hand circuits look to be in a choc block.
In short it's an absolute nightmare, a far cry from a college test rig.

Don't take this the wrong way, but if you haven't yet done much testing I wouldn't make that one your first deep dive testing experience, or your first board change. For context I don't think I've seen one as bad as that this year. I'd be charging a premium to even entertain taking on that!

I know. Will be getting someone to change the board for me don't worry. There is a isolator between meter and board so at least there's that. Thanks again for all the advice.

 

[littlespark]

whats the top side of the breakers look like?

Does the left rccb power the 7 leftmost breakers, and the right do the other 7?


It could be cumulative earth leakage. Everything tests fine on its own... but every little device has a minute earth leakage... if you've got loads plugged in, it'll all add up. And the 30mA marked on RCD's is just an upper limit. It could trip at 19,20, 21... Thats what the ramp test checks for on an rcd tester.

It appears the right hand rccb has been changed already..... is the problem on this side or the other, older rccb?
(or was that where the mainswitch was?)


Basically.... what im trying to say is, you could spend hours, days, trying to find a fault that wont show up.
By all means, do a the testing.... but if its inconclusive, dont waste time going over and over the same thing

 

[pc1966]

That is quite a "special" CU to be looking at. and is it just camera perspective, or is that the biggest choc block I have ever seen?

 

[2nd Life]

whats the top side of the breakers look like?

Does the left rccb power the 7 leftmost breakers, and the right do the other 7?


It could be cumulative earth leakage. Everything tests fine on its own... but every little device has a minute earth leakage... if you've got loads plugged in, it'll all add up. And the 30mA marked on RCD's is just an upper limit. It could trip at 19,20, 21... Thats what the ramp test checks for on an rcd tester.

It appears the right hand rccb has been changed already..... is the problem on this side or the other, older rccb?
(or was that where the mainswitch was?)


Basically.... what im trying to say is, you could spend hours, days, trying to find a fault that wont show up.
By all means, do a the testing.... but if its inconclusive, dont waste time going over and over the same thing

Hiya. So the left RCCB (the original one by the looks) does the left most 4 circuits (the lighting circuits. And the new one on the right does the other 10, although 2 are redundant so 8 at present. That's the breaker that's tripped like 20 times, although on 1 occasion the other RCCB tripped also. From everything I have read and all the advice people have been kind enough to give. It does look like it will be cumulative earth leakage on those 8 circuits. But I don't understand is why without the introduction of any new appliances after 2 years of no tripping am I now getting it everyday? That doesn't make a lot of sense. Do USB sockets add to leakage as that is the only thing that has changed in that time. I want to do IR testing anyway as if I'm going to get someone to come and change the board. I want to know from my own benefit that the wiring is sound. What I did think was that if it all checks out on the board change goes ahead. Then at least having individual RCBOs will be able to share the leakage and it may just go away on its own? Thanks for having a look at it for me

 

[2nd Life]

That is quite a "special" CU to be looking at. and is it just camera perspective, or is that the biggest choc block I have ever seen?

Special is one word. And yes that is not a trick of the camera. That is the biggest connective block I have ever seen with two 10 mil bonding cable stuffed into it

 

[timhoward]

I want to do IR testing anyway as if I'm going to get someone to come and change the board.

I'd start with a 30ma ramp test plugged into a sockets circuit.
Then I'd turn everything off (at the service isolator not pictured), perform safe isolation check, and do a global IR test (Live and Neutral together tested to CPC bar) of each side of the board. This can be done with no disassembly if you have the right test leads, or minimal disassembly if you don't.

 

[2nd Life]

I'd start with a 30ma ramp test plugged into a sockets circuit.
Then I'd turn everything off (at the service isolator not pictured), perform safe isolation check, and do a global IR test (Live and Neutral together tested to CPC bar) of each side of the board. This can be done with no disassembly if you have the right test leads, or minimal disassembly if you don't.

Thanks again Tim. I'll do that. Incidentally here's a pic of the whole thing. We have a 30 amp Aga running off its own CU with a 32 amp MCB and isolator running off a Henley block, and I actually only tried to turn it back on for winter this morning and what do you know tripped the sockets RCD immediately. The mini CU has it's earth linked into the MET in the main box so doesn't surprise me

 

[timhoward]

A rather pertinent detail - have you noticed an earth rod anywhere?
At the moment I don't see how that lot is earthed and how fault protection for the Aga is going to work.

 

[pc1966]

The more we look, the more concerns we have

@timhoward has spotted the very important question of means of earthing, if it is a TT system or some other connection to the supply earth is in use but not visible (and possibly not acceptable, such as service pipe bonding).

There are a lot of circuits, and the Aga on a separate CU interacting with the main CU is troubling. Is this a big house, i.e. how many of those circuits are in use and necessary?

It might be a bit beyond you just now, but it really looks like a case for biting the bullet and replacing the main CU with a new all RCBO board and bringing the Aga in to that, as for the rest of the circuits. But before considering that in any detail, you need to establish the means of earthing and to do your basic checks on polarity, IR, Zs/Ra, and identifying the circuits in-use and seeing what is needing done ASAP and what can be part of a planned out change.

 

[pc1966]

Do USB sockets add to leakage as that is the only thing that has changed in that time.

Probably, but they are unlikely to be a big change as they ought to be sub-mA levels.

I want to do IR testing anyway as if I'm going to get someone to come and change the board. I want to know from my own benefit that the wiring is sound. What I did think was that if it all checks out on the board change goes ahead.

It might be worth seeing if anyone on this forum is nearby and willing to help you with the CU change. As you are learning to be a spark it would be good if you could be involved in that process but not all folks are happy to get involved that way.

Then at least having individual RCBOs will be able to share the leakage and it may just go away on its own?

If there is no fault beyond poor design / feature creep over time then that would (a) solve the problem of accumulated leakage, and (b) help pinpoint any future faults and reduce the impact they have until a fix can be done. But if you can safely do IR testing, etc, you can help pinpoint what is happening now.

 

[2nd Life]

I'd start with a 30ma ramp test plugged into a sockets circuit.
Then I'd turn everything off (at the service isolator not pictured), perform safe isolation check, and do a global IR test (Live and Neutral together tested to CPC bar) of each side of the board. This can be done with no disassembly if you have the right test leads, or minimal disassembly if you don't.

So bizarrely the ramp test at the socket did not trip the RCD, just get a reading of greater than 33mA where the tester I assume stopped. I tried the speed test too and same result. No trip. For an RCD that seems on the verve of tripping constantly not sure what to make of that. Could be the tester at fault?

 

[2nd Life]

A rather pertinent detail - have you noticed an earth rod anywhere?
At the moment I don't see how that lot is earthed and how fault protection for the Aga is going to work.

Yes. It's on a TT system (also terrible) I'll stick a pick in of the "electrode" but I have ZE it and I'm getting 165 ohms so well within the max miraculously

 

[timhoward]

Yes. It's on a TT system (also terrible) I'll stick a pick in of the "electrode" but I have ZE it and I'm getting 165 ohms so well within the max miraculously

Issue one is the Aga CU. That has a normal main switch (not RCD) and an MCB. So a live-earth fault would not trip the MCB as less that 2 amps of fault current would flow. It would stay on waiting for someone to touch it and that someone would become the path to earth.

So bizarrely the ramp test at the socket did not trip the RCD, just get a reading of greater than 33mA where the tester I assume stopped. I tried the speed test too and same result. No trip. For an RCD that seems on the verve of tripping constantly not sure what to make of that. Could be the tester at fault?

Does the test button on the RCD itself work?
If not, then this all becomes even more serious as things won't turn off under fault conditions.

Which make/model MFT is it? It could be a faulty RCD, faulty tester, or the tester being blinded by DC earth leakage.

 

[2nd Life]

Issue one is the Aga CU. That has a normal main switch (not RCD) and an MCB. So a live-earth fault would not trip the MCB as less that 2 amps of fault current would flow. It would stay on waiting for someone to touch it and that someone would become the path to earth.


Does the test button on the RCD itself work?
If not, then this all becomes even more serious as things won't turn off under fault conditions.

Which make/model MFT is it? It could be a faulty RCD, faulty tester, or the tester being blinded by DC earth leakage.

Test button works on the RCD in question it looks to be a newer one, but not on the other one after investigation.

It's a Di Log 9110 and had a calibration sticker that ran out in July. Got it for good money so planned to spend the savings on calibration but not as yet.