Strange RCD tripping problem

[Mjbarnard]

Marconi,

Have tried your steps. Unplugged dishwasher.

To complicate things even further in the middle of the night RCD tripped again. This time it could not be reset unless mcb for A?C 3,4,5 was switched off. This is the first time this circuit has been a problem. So this has altered the steps:

Turn off MCB for a/c 1 and 2 and DP switch for DW.

1. then see if with the DW circuit on at the labelled DP switch the RCD trips when you turn on the MCB for a/cs 1 and 2?

Turn off MCB for a/c 1 and 2 and DP switch for DW.

2. now turn on MCB for a/cs 1 and 2 and then turn on DW DP switch.

Turn off MCB for a/c 1 and 2 and DP switch for DW.

3. Turn on MCB for a/c 1 and 2 and leave DP switch for DW off for several hours.

What does RCD do for 1, 2 and 3?

Washing machine unplugged. BOTH mcb's off

1. RCD trips if either mcb is turned on, when other one on.

2. MCB a/c 1,2 on, turn on DW DP. RCD trips if other a/c mcb on. Doesnt trip if other mcb off.

3. In process of 3. For about a couple of hours now, no RCD trip but only if mcb 3,4,5 is off. Otherwise trips immediately.

I get that this now makes it even more complicated. Cant seem to get an electrician for a 2-3 weeks.

 

[Octopus]

I would suggest you switch all the AC units off ...

Then see what happens

Can you post a picture of the CU?

 

[Devonchris]

As this has been happening since the A.C. units were fitted, then this has to be the main suspect. What heating did you have before? How was it wired? Has some of the fixed wiring been used for the AC controls? Or are there time switches or thermostats still in situ?

 

[DPG]

Be interesting to get a sensitive clamp meter on each of the aircon cpcs to check leakage. Maybe they need to be on separate RCBOs.

 

[Pete999]

Borrowed Neutral maybe??? did the A/C guys leave you any testing results or did they just install switch on an then leave.?

I posted this yesterday and since many people have tried to help, but for some reason you haven't answered what I consider a relevant question, so did the A/C installers do any electrical testing, if so did they leave you any paperwork, certificates of any sort? from what has transpired since I doubt it, but it would be useful to confirm. If the answer is no, then the first step would be to carry out a full set of electrical tests.

 

[elsparko]

if everything was working fine prior to the air con install then what would occams razor tell us?

 

[elsparko]

could just sell the house and move on?

 

[Wilko]

Hi - the AC compressor units, do they have a local isolation switch next to them? Hopefully they do, if so perhaps try the tests with air con MCB on but the units isolated locally. Isolation switch may look like this ...

 

[lurch]

Had similar last year. Erroneous tripping of rcd. No obvious low readings on insulation resistance testing of circuits. Could not narrow down to a specific circuit and no new installs to point the finger at unlike the aircon units. Moved kitchen ring main away from rcd and put it on rcbo and all was ok. My summary was that combined earth leakage of all the kitchen appliances plus that of the downstairs socket took the earth leakage over the edge in certain scenarios.

 

[Octopus]

^^ do you have a clamp meter?

This is another reason I only fit rcbo boards ..

 

[Toneyz]

You are correct, but I think @Pete999 is on the case.

I would have thought that this would have been ruled out by now.

 

[Mjbarnard]

Thanks for suggestions. Am in the hospital today so haven't been able to do much more observations.

Murdoch (msg 42) not sure what you mean by "off", but all the internal units have been off for months, and tripping occurs frequently when they are not on.

Devon Chris (43) A/C circuits new and completely separate to everything else. HEating is via conventional boiler, underfloor heating radiators, thermostats, controllers etc. Only control for A/C are the buttons on the units and the remotes.

DPG (44) happy to install rcbo's if that's a solution. In fact discussed with previous electrician possibility of swapping whole CU to rcbo's.

Peter999 (45) as I recall original install only provided statement saying it had been checked and commissioned satisfactorily. Don't recall any technical data. I will recheck. When A/C engineers returned to investigate they left a document stating fault lay with dishwasher circuit.

Elsparko (46) I have been pointing this out to A/C company all along, but they don't appear interested.

Wilko (48) interesting point. There are local external isolation switches like your picture. Now I haven't tested recently but on one of the first occasions red tripped , I was away and my wife rang to say she couldn't reset the tripped rcd. I advised her to isolate using the external switch, and she confirmed she could then reset the rcd. I told the A/C company this in no uncertain terms and even provided their engineer with a written summary including this, but they didn't seem to think it mattered.

Lurch (49) obviously will get professional advice but happy to change some/any/all mcbs to rcbos if that provides a solution.

Murdoch (50) I don't know what a clamp meter is, but I would expect an electrician to have or obtain whatever is necessary?

Thanks again.

 

[Pete999]

Thanks for suggestions. Am in the hospital today so haven't been able to do much more observations.

Murdoch (msg 42) not sure what you mean by "off", but all the internal units have been off for months, and tripping occurs frequently when they are not on.

Devon Chris (43) A/C circuits new and completely separate to everything else. HEating is via conventional boiler, underfloor heating radiators, thermostats, controllers etc. Only control for A/C are the buttons on the units and the remotes.

DPG (44) happy to install rcbo's if that's a solution. In fact discussed with previous electrician possibility of swapping whole CU to rcbo's.

Peter999 (45) as I recall original install only provided statement saying it had been checked and commissioned satisfactorily. Don't recall any technical data. I will recheck. When A/C engineers returned to investigate they left a document stating fault lay with dishwasher circuit.

Elsparko (46) I have been pointing this out to A/C company all along, but they don't appear interested.

Wilko (48) interesting point. There are local external isolation switches like your picture. Now I haven't tested recently but on one of the first occasions red tripped , I was away and my wife rang to say she couldn't reset the tripped rcd. I advised her to isolate using the external switch, and she confirmed she could then reset the rcd. I told the A/C company this in no uncertain terms and even provided their engineer with a written summary including this, but they didn't seem to think it mattered.

Lurch (49) obviously will get professional advice but happy to change some/any/all mcbs to rcbos if that provides a solution.

Murdoch (50) I don't know what a clamp meter is, but I would expect an electrician to have or obtain whatever is necessary?

Thanks again.

So in layman's terms "a whitewash"

 

[Octopus]

Murdoch (msg 42) not sure what you mean by "off", but all the internal units have been off for months, and tripping occurs frequently when they are not on.

Murdoch (50) I don't know what a clamp meter is, but I would expect an electrician to have or obtain whatever is necessary?

Thanks again.

42 - thats very interesting so it rules the internal units "out" of the problem - but not the cabling installed for them.

50 - not all sparks have them, but I find them, in cases such as yours essential - so ask when you're trying to find a new spark - if they say "I don't need one" don't let them on site.

 

[Toneyz]

IMO there is an accumulation of leakage currents, insulation test maybe won't show until appliances/A C units powered up a leakage test would be a start.The neutral being on the wrong RCD side should have been ruled out ages ago.Swopping a few circuits around between both the RCD's may even the leakage current out between RCD's but as time goes on the leakage may get worse from the appliances with age I think Tel was right in his first post and the one regarding your electrician. Installing a new consumer unit with RCBO's or buying replacement internal parts to have a
main switch some high leakage circuits on RCBO's and a RCD protecting other circuits with MCB's or if costs permit all RCBOs another thing to consider is you have no more spare ways.

 

[Mjbarnard]

Ta - electrician previously supplied quote for swapping all mobs to rcbo's as one of the options. Not sure why we didn't do it - I think he wasn't certain it would solve it.

 

[Wilko]

Hi - if I understand your post #52 correctly all your problems stop if you isolate the air con units - or ?

 

[Mjbarnard]

Yes if I isolate the air con external units or turn the air con mcb's off OR leave the air con on and isolate the dishwasher (irrespective of whether it is plugged in or not).

 

[DPG]

A check on earth leakage is the way to go. You're going to be guessing otherwise. Check leakage on each air con unit.

Took me 10 minutes to type this as I have been drinking since 6pm. Bear with me if I don't make much sense.

 

[Wilko]

A check on earth leakage is the way to go. You're going to be guessing otherwise. Check leakage on each air con unit.

Took me 10 minutes to type this as I have been drinking since 6pm. Bear with me if I don't make much sense.

10 minutes ? I had to wait till morning