Strange RCD tripping problem

[The Ghost]

I suppose like distance diagnosis/prognosis of electricals/bodies there needs to be schematics and info nothing like being on site. I don't suppose the electrician would care to join us and give further info like his tests or bonding situation etc. etc.???

 

[Mjbarnard]

Thanks. The downstairs ring mains which supplies the dishwasher is also on the same RCD. I asked the electrician if the air con neutral was correct and he came and rechecked - and said it was.

 

[telectrix]

so. that does lend itself towards accumulative leakage, as i said before.

 

[ruston]

I suppose like distance diagnosis/prognosis of electricals/bodies there needs to be schematics and info nothing like being on site. I don't suppose the electrician would care to join us and give further info like his tests or bonding situation etc. etc.???

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

 

[ruston]

so. that does lend itself towards accumulative leakage, as i said before.

If he is correct that is. His track form is not great.

 

[telectrix]

If he is correct that is. His track form is not great.

please expand on that.

 

[Wilko]

In my humble opinion, if the AC guys had fitted rcbo for their new circuits this problem perhaps would not have occurred or would be obviously AC related. Agree with Various about leakage and possible mixed Ns.

 

[ruston]

@Telectix .
If the electrician is correct that they are in the correct respective breakers and neutral bars.

 

[telectrix]

@Telectix .
If the electrician is correct that they are in the correct respective breakers and neutral bars.

i see .

 

[DPG]

Tel, I think Ruston was meaning that it is difficult to give a good diagnosis if basing it on the findings of the OP's spark, who's track record hasn't been 100% so far. Don't think he was aiming it at you.

 

[ruston]

@DPG AND @telectrix I was yes , I can see I abbreviated that too much.
I think Tel is correct if the breakers are wired correctly . The reference to the grid switch could be an influence too.
You have to be there for one like this.

 

[Mjbarnard]

Thank you all for the courtesy of your replies and for sharing your expertise.

I never expected a 'remote diagnosis' but the information has been interesting and useful.

I do not think there is anything to be gained by commenting in public on my electrician but I note the opinions. Suffice to say we will be moving on, but he has performed several installations for us which have worked satisfactorily.

While I realise it will not correct any fault, I will probably take the opportunity for the next electrician to fault find but also convert the CU to RCBO's - at least it will make any future faults less intrusive. I have some neighbour's recommendations but would you recommend placing a post on the Find An Electrician forum?

 

[marconi]

In your initial description you wrote 'the mcb' which I highlighted in my post #16. It appears to me from looking at an enlarged image on my CPU screen of your consumer unit, there are two MCBs on the far right which between them supply the 5 split system units. The left of the two feeding a/c systems 3, 4 and 5 and the right of the two a/c systems 1 and 2. Is this correct?

(And I understand from what you wrote you have 5 split systems where each split system comprises of an internal unit(IU) and two external units(EU). Or, do you have 5 internal units and two external units, 3 IUs working with one EU and the other 2 IUs paired with the other EU - to create 2 multi-split a/c systems?).

And I understood that only one of these MCB protected a/c circuits was causing RCD trip problems when interacting with the DW and/or its circuit. I assumed, perhaps wrongly, that the offending mcb was the far right one since it was off.

My post #16 seeks to clarify if the powered up/down state of one of your home's split a/c systems has any effect on whether the other (which I called the offending one) causes the RCD to trip if the DW is not isolated.

Could you also tell me the model number of your EUs and whether they are described as 'inverters'.

 

[telectrix]

your present electrician may be a good spark, but fault finding is something that can be difficult for even the most experienced. i know , being biassed towards repairs and faults. some can be baffling to say the least. example is i've had several RCDs fail to trip, even on the test button. each case has been a Neutral fault that has taken up to a few hours to solve, still tink a ramp test and a trace of leakage on both the a/c and appliances is the way to solve your problem.

 

[Mjbarnard]

Marconi - thanks.

There are two mcb's on the far right. The left is 3,4,5 and the right is 1,2. (it is the 1,2 which seems to cause a problem).

there are 5 internal units. THe 3 bedrooms go to one external unit, the kitchen/family room and the living room go to the (slightly larger) external unit.

The circuit which appears to cause the problem is the end MCB supplying 1,2 (kitchen & living room). You are correct that is why we keep it off.

THe powered up/down state has no effect. It occurs when they are not on, and frequently has occurred in the middle of the night when also no other appliances are on.

The units are the Mitsubishi Zen R410A inverters. The two external units are slightly different (detailed calcs showed units 1,2 needed larger units). I will get the exact model details shortly.

 

[Mjbarnard]

Marconi - from the A/C contract:

To supply, install and commission a comfort cooling system at the agreed location.

We have specifically selected Mitsubishi Electric equipment for this installation. Mitsubishi Electric are widely recognised as leading manufacturers of air conditioning equipment and offer exceptionally high quality engineering coupled with, what experience has taught us, maximum reliability and longevity.

The Inverter driven system offers both cooling and heating functions.

System Specification

Kitchen/Family Room & Media Room (Multi-split system)

1 X 5.0kW Zen Wall Mounted System

1 X 3.5kW Zen Wall Mounted System

Olivia, Francesca & Master Bedrooms (Multi-split system)

3 X 2.5kW Zen Wall Mounted Systems

 

[Sparkie30]

@Op

Tel is righ about earth leakage. Should have used a clamp meter and narrow it down.

Has he ever tried swaping that ac unit mcb which is off with one of the mcbs from another rcd?

 

[marconi]

Are you able to unplug the dishwasher easily? If you can could you do that and then:

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?

Take care to be around lest you have fridges and freezers supplied by the RCD.

 

[Mjbarnard]

Marconi - it's a new miele dishwasher and it's only 4 screws to pull it out. Will be able to do without much difficulty.

I will try as you suggest - will report back and be interested in the results.

Booking a new electrician.

Sparkie - one of the troubleshooting steps previously was to replace the MCB with a new one. It made no difference.

 

[elsparko]

rip it all out and start again