RCD trips in AIO off-grid mode

General Everything Else
1

I’ve noticed that when forcing the AIO to run in off-grid mode, it trips one of the 2 RCDs in the main consumer unit.

After some trial and error, I’ve narrowed it down to one specific MCB (kitchen sockets) and specifically 3 fused spurs (any one of these being on causes the RCD to trip, but if I turn them off, I can reset the RCD).

  1. Dishwasher
  2. Washing machine
  3. Gas boiler

We had not one but two earth rods installed as part of the AIO + solar install. All is well when the house is running exclusively on solar or battery (and when grid is up, i.e., not in off-grid mode).

From reading up on other similar-ish issues elsewhere, this is likely to be some sort of earth leakage issue as a result of the earth rods installed for the AIO/solar, but just wanted to see if anyone else had a similar view?

It feels like it must be related as the issue only occurs in off-grid mode, so I assume the solar installer should be able to resolve this somehow?

2

100% get your installer back… I had a similar issue with an RCD tripping and it just turned out to be a faulty RCD, the tolerances in these can vary.

But a sparky is the only way to confirm

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3

There was a discussion about the way the AIO supplies voltage to the house in off grid mode. Evidently the AIO supplies 120 - 0 - 120 volts split phase instead of 0 - 240 volts and this can trip some RCD’s.

4

Hmmm, interesting…I’m wondering if moving the affected circuit to a separate sub-consumer unit might work, but using RCBO instead of RCD?

But admittedly I have no clue what I’m talking about so this might solve nothing…

5

I think that was found to be incorrect. And it is an IT earth method instead.

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6

A good video came out on this topic here: https://youtu.be/huN6yNxmjz0?si=yL0oEyL6Z5bxocy3

Spoke to Mark and he suggested checking the AIO neutral earth bond, as it’s not activated by default and can cause downstream RCD tripping, so I’ll pass this onto my own installer and get them to investigate further…

I had a spare C Curve MCB so I tried changing to that (from B Curve), but as expected, it didn’t resolve anything (didn’t think it would, but it was a quick experiment to be sure!).

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