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 ..