Solar PV mains connection question

wanman

I have a 3.6kW PV system with a Fronius inverter which has been running without problems for the past 7 years. Due to some issues recently I now have concerns it is not correctly connected.

My inverter is connected via its meter and isolating switch to a MCB which is on the RCD section of my consumer unit. This RCD also serves MCBs for three 32A socket circuits and a 16A line to the garage. Just recently I have started getting nuisance trips in the morning with the RCD tripping. These seem to coincide with the time there is sufficient sun for the PV to start generating. I do not believe there is any specific fault on my circuits, just that total usage may trip the 30mA RCD trigger when the PV starts. If I turn off any of the other four circuits there is no trip, and if I wait until the PV is generating I can then switch on the circuit I turned off, which suggests it is just the initial surge combined with all other loads causing the trip.

Reading through various docs on the internet it seems that the PV should not have been connected to the RCD - if it is connected to an RCD it should be on its own and not shared with other circuits. The Fronius manual states that the inverter should not be connected to an RCD, but 'if required by local regs' should be a 100mA one.

So I would like to get this fixed. Ultimately I will look to getting my consumer unit updated but I could do with a quicker solution.

Could I get the PV circuit moved to the other part of my consumer unit, not protected by the RCD?

If I get this done, does it have to be by a MCS registered installer? Or can any certified electrician make the change without invalidating my FIT payments?

chris_n

Any certified electrician can make the changes. The RCD is dealing with earth leakage currents not any initial surge. Having said that it should not share an RCD as nuisance tripping can be an issue with solar inverters.

Ectophile

What's possible depends on how your consumer unit is configured. A simple solution, if it's possible, would be to put the inverter on its own RCBO (a combined RCD and MCB).


Another solution would be a separate mini consumer unit with RCD and MCB. That could even be a 100mA RCD if necessary.


Any qualified electrician should be able to tell you what's most practical.


I previously had problems with an old inverter tripping the RCD on the first sun after a storm. Luckily for me, it was on a separate consumer unit. The new inverter hasn't done that so far.

1961Nick

The simplest way is to swap the position of the solar mcb with one in the non rcb section of the CU.

wanman

Thanks all. Will get an electrician in to move the solar MCB after the Christmas break

1961Nick

wanman wrote: »

Thanks all. Will get an electrician in to move the solar MCB after the Christmas break

It shouldn't take more than 5 minutes so keep an eye out for any sparky working nearby.

Martyn1981

Not a solution to your problem, but just some confirmation about PV issues.

Over the years (got to be neraly 10yrs now) issues of nuisance trips have come up a lot on forums and threads, and they often involve a 30mA, when 100mA is better and typically resolves the issue.

I think these problems tend to surface far more in damp weather conditions too.

mmmmikey

Hi - I'd agree with earlier comments but worth pointing out that if everything has been working fine for 7 years and this is a new problem that does point to either a change somewhere or something starting to fail. So changing the RCD to a 100 mA one of putting the inverter on a separate breaker may solve the nuisance tripping but it doesn't tell you why this has been OK for a long time and isn't now. How old is your wiring and when was it last checked?

joefizz

Slightly unrelated but if everyone has a 'test' button on their consumer unit, I would advise people with PV/batteries to test once a year or so (well everyone really, not just solar owners).


Might be an idea to wait to summer though, it will involve (hopefully) power cut to everything so you might have to reset stuff...


As for the OP, agree with everyone else, get a spark in, they can test all the connections properly and well worth the few quid.

Reed_Richards

My inverter, installed earlier this year, is connected to the wires that run between the electricity meter and the consumer unit. Some sort of tap-in connection is used that looks as if it could be live and highly dangerous - but hopefully is not.

EricMears

Reed_Richards wrote: »

My inverter, installed earlier this year, is connected to the wires that run between the electricity meter and the consumer unit. Some sort of tap-in connection is used that looks as if it could be live and highly dangerous - but hopefully is not.

Hopefully, a 'Henley Block' which if fitted correctly shouldn't be 'dangerous' - but don't try poking a screwdriver into it !