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RCBO Tripping

Hi All,

A long post, but trying to tell the whole story!!

I have a nuisance problem of 1x particular RCBO (30ma) tripping on grid failure. The following is a description of my system:

MP2 48/5000, 48v 240ah Victron AGM Batteries, AC Coupled Enphase S270 micros (10x Panels) @ 3.16kw Panels and an ET112 on the Enphase AC.

The MP2 is configured only on AC-1 out to run as a UPS for selected circuits and therefore when we use battery power in the evening it only powers the following circuits:

2x Aircons, 1x Lights, 1x power.

The rest of the house runs off the grid or not during grid outage.

This has generally worked really well as we only use max 85% SOC including a/c for heating or cooling for a few hours in the evening and solar charges the batteries the next day.

The nuisance RCBO tripping is when we do have a grid outage the power circuit most (all) of the time will trip. This circuit powers the fridge, TV (Plasma) and computer(s), modem, phones and electric start for instantaneous gas hot water.

I’ve had the electrician check all the powerpoints and powerbars for earth leakage as well a mega testing – all clear.

When it trips, resetting the breaker and all is well again, when power comes back on no problem.

If I turn off the Enphase mainswitch the RCBO power does not trip and the thinking is that the build of earth leakage with the tv and computers as well as the earth leakage of the micros (Enphase says .5 to 1ma per micro – 5 to 10ma) could be enough to trigger the CB. Another possible issue is that the normal voltage whilst on grid with solar on is around 245+ VAC and when the grid fails and the MP2 comes on at 230VAC.

The fridge and water heater by themselves don’t seem to cause the RCBO to trip.

This a big ask – has anyone got any idea on why and how to fix it.

Cheers and thanks for any help - Paul

Multiplus-IIAC PV Couplingenphase
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rotevery avatar image rotevery commented ·

I think you should use an earth leakage current meter to measure your normal earth leakage current. Please share the measured value. It may be too close to 30mA. You know the 30mA RCD (RCBO) does not necessarily trip at exactly 30mA but somewhere between 20mA and 30mA. If earth leakage is too close to RCD set point, then the solution would be to separate the circuit into different RCBOs as has been mentioned below by @Guy Stewart.

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Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Am I understanding that the Enphase AC and the loads are running through the same RCBO?

Can you put the Enphase AC circuit on it's own RCBO, seperate to the power circuits?

So add another RCBO to the system, one for loads, the other for the Enphase AC? Or separating out the loads so they aren't all on the same RCBO, such eg AC and power points on seperate RCBO circuits.

It may be a cumulative thing from numerous small sources of leakage that are 'spiked' when the grid outage occurs. At that point of outage, the MP-II also does it's relay checks and will introduce it's own small, additional earth leakage, taking you over the tipping point.

Could also try replacing the RCBO you have, perhaps with another brand and you might get one a little less touchy.

It is also important to check that the RCD is bi-directional because the use of a directional (polarised) RCD could result in nuisance tripping.

Lastly, I know it's too late now but Enphase IQ7 microinverters are double insulated, with no earth connection. This means that there is no possible path to earth within the microinverter, eliminating the risk of nuisance tripping.

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bassman avatar image bassman commented ·

Hi Guy, Thanks for quick response. No, the Enphase is on its own circuit, I don't know it has an RCBO but I'll check. I know Enphase (in Nov 2018, released a document that allows for a Bi-directional RCBO - I'll check) We've tried another RCBO, at first we thought it did the job, but no!

It's funny, the 7.1kw a/c has absolutely no problem. But I'll speak with our sparky re the bi-directional issue.

Cheers - Paul

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bassman answered ·

@Guy Stewart

Hi Guy, Would it be possible to program an assistant to do the following:-

Upon grid failure, immediately frequency shift up to to turn off micro inverters instantly. Once micro's are turned off frequency returned to normal.

My thinking is that this would take the micros out off the cause of RCBO tripping and would allow the micros to come back online in sync with the MP2.

At the moment, the system is set up with relays to control the micro's based on battery charge - 100% SOC = micro's off, 95% SOC = micro's on.

The current setup might be causing the RCBO to trip because the micro's may be causing a spike or surge. As I posted before, turning the micro's off, turn the grid of at main switch - no problem, turn the micro's back on no problem, turn the grid back on - no problem.

What do you think?

Cheers - Paul

ps: I'm also discussing this with my installer and electrician.

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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ commented ·

Perhaps you could put the micros on AC2 out, and have some assistant programming do something to stagger the issue?

I’d first seperate the load circuits onto different RCBO’s and see if that took care of it. Easier if it works.

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