32 minutes ago, plonkster said:

I actually have an insulation tester now. And I've learned that 99% of the time, an RCD trip is because you have an insulation problem somewhere. It's been a bit of a quest of mine to understand the remaining 1%

500V is generally enough, put it on that suspect circuit and tell us the reading.

edit: test both garage door open and closed. and stalled in between if you can.

Edited August 13, 20206 yr by phil.g00

17 minutes ago, phil.g00 said:

500V is generally enough, put it on that suspect circuit and tell us the reading.

edit: test both garage door open and closed. and stalled in between if you can.

I moved house in the mean time. And the opener itself also broke and got replaced. I kept the guts of the unit specifically to test it in more depth later. When I find time 🙂

Edit: for interest sake. It's an ET DC Blue. The entire thing is low voltage (24V battery, motor, etc), with a really decent old-school power supply in the back (toroidal transformer, etc). It needs an earth because it has exposed metal parts. For whatever reason, they decided to also put the little triad of MOVs on a board next to the fuse...

Edited August 13, 20206 yr by plonkster

@plonkster,If I am looking right it appears as if that entire PCB is removeable/disconnectable, This will lend itself to testing it and the rest of it discretely.

Go on, test it, it'll take longer to reply to this post.

2 hours ago, phil.g00 said:

Go on, test it, it'll take longer to reply to this post.

Right. So I suppose you were right and I was wrong. Mostly. The leakage is indeed very low. I faked a neutral earth bond, and rapidly connected/disconnected it, and it does increase the leakage, as much as 4-fold, but still only about 40nA... maybe, I doubt the clamp meter is terribly accurate that low down. The clamp meter samples 30 times a second so I figured even if the transient is much higher, the duration is going to be so short I doubt it is worth it to set up the scope.

Still, I saw what I saw at the time. Somehow, this unholy gathering of filters and arresters worked together to make my life difficult.

I still have the EMI filter from another part of the house. Somewhere. This one actually makes a small spark when you rapidly connect and disconnect the TN bond. Not enough on its own to trip an RCD (already tested), but possibly enough to bother setting up the scope for. This thing:

On 2020/08/12 at 2:56 PM, plonkster said:

I have a 13mA standing leakage...

I think this standing leakage is pretty normal in most installations, I did the same test a few months back in my house and measured 15.4mA with all my CB’s turned on, for every circuit breaker I switched off it dropped about 1.5mA. I think each circuit going where ever in the house has it’s own little capacitance that adds up giving the total of 15.4mA. 

I done this test due to nuisance tripping sometimes the earth leakage tripped when my ATS switched back to grid. I than installed a better quality earth leakage (ABB) and problem disappeared. 

On 2020/08/12 at 2:56 PM, plonkster said:

I have a 13mA standing leakage...

I think this standing leakage is pretty normal in most installations, I did the same test a few months back in my house and measured 15.4mA with all my CB’s turned on, for every circuit breaker I switched off it dropped about 1.5mA. I think each circuit going where ever in the house has it’s own little capacitance that adds up giving the total of 15.4mA. 

I done this test due to nuisance tripping sometimes the earth leakage tripped when my ATS switched back to grid. I than installed a better quality earth leakage (ABB) and problem disappeared. 

1 hour ago, Gerrie said:

I think this standing leakage is pretty normal in most installations, I did the same test a few months back in my house and measured 15.4mA with all my CB’s turned on, for every circuit breaker I switched off it dropped about 1.5mA. I think each circuit going where ever in the house has it’s own little capacitance that adds up giving the total of 15.4mA. 

Yup. And somewhere between 15mA and 20mA you start to get nuisance tripping. Then you have to split the circuits and install two RCDs.

There is also leakage on the neutral side, because often there are surge arrestors/filters between earth and neutral too. Since earth and neutral is bonded, there is almost no leakage here... until the bonding relay in the inverter opens (to do the relay test). It is quite a bit harder to find these little leakers... cause opening the breaker does not interrupt the neutral.

so, I've installed a new main switch with overload protection and a new RCD, after the main switch, and connected the inverter grid input from before the RCD and have been running the inverter load for a few days and all seems good now with no more grid side RCD trips.
Thank you all for the tips etc...
For those new to reading this post, here is my new basic wiring diagram...

3 hours ago, RhysMcW said:

For those new to reading this post, here is my new basic wiring diagram...

That's good. In my own setup I put the changeover before the earth leakage breakers, so that the earth leakage on the output of the inverter is always used for the backup loads.

The way you have it wired here (though perfectly fine and safe) means that your output loads are moved to the other RCD when bypassed. Which is fine, but I like to keep them split especially since standing leakage currents for the whole house, when using modern appliances, can be quite high already.

4 minutes ago, plonkster said:

The way you have it wired here (though perfectly fine and safe) means that your output loads are moved to the other RCD when bypassed. Which is fine, but I like to keep them split especially since standing leakage currents for the whole house, when using modern appliances, can be quite high already.

@plonkster, good point there. I originally had the load RCD after the changeover but thought the second RCD in series with the grid RCD was causing/adding to the grid side RCD trips so rewired the output RCD to be before the changeover, thereby only having the one RCD in play at any time.
I understand what you're saying about the standing leakage currents so may move the output RCD back to be after the changeover, although I thought the first RCD in the series would typically detect the total leakage anyway, but the "more sensitive" RCD would end up tripping...

6 hours ago, RhysMcW said:

the first RCD in the series would typically detect the total leakage anyway, but the "more sensitive" RCD would end up tripping...

Correct, that is what happens. Ideally one should have just one RCD in "series". In cases where you must have two, the upstream one will have a slightly higher leakage current specification, to ensure that the closest one trips first. If you do this, then of course the upstream one cannot feed plugs directly. Plugs must always have a 30mA RCD.

In my experience, a good deliberate leakage (eg RCD tester) will trip both RCDs, but nuisance tripping will trip the more sensitive one first.