PV Array trips RCD's

[Lastminuteandy]

Hi, anyone got any advice re this problem that I can't solve....
I have 2 PV arrays installed, a 4.2Kw and a 5.0Kw. The electricity supplier here made me install them on 2 seperate single phase supplies. My house now runs on 2 seperate supplies, half on one supply and the other half on the other.

My house is 80m from the main road so the electricity meters are at the roadside and then two 35mm2 cables run up to the house.

At the road end each supply has a seperate board with a 50amp mcb and a 300ma RCD. At the house end each supply has its own board with 30ma RCD's.

The PV arrays are connected into the house end of the 35mm2 cables, without going through any of the house boards. Each array has its own mcb and 30ma RCD on its feed out to the cable.

The problem is that overnight I keep getting random trips of the 300maRCD's at the road side. I think it happens when it gets light and the panels start to generate. It happens about every 3 or 4 days and is not the same RCD each time. Is this something to do with reverse flow?

Any one got any ideas as to what is going on?

 

[Mork]

Make sure the 300m/A rcd is correct type, I think you need a type A and not a type AC, you may have to do some research, to find the right one for your application.

 

[SibertSolar]

No other RCDs trip than the roadside 300mA units?

 

[Gavin A]

that's bizzare, it shouldn't be tripping out a 300mA RCD.

what inverters and panels do you have, and what roof construction is it?

The issue will be something to do with capacitance, which occurs most in damp conditions on TL inverters, but it really shouldn't be tripping out a 300mA RCD - for reference, we install most of our 3.7kW limited TL inverters on 30mA RCDs on dedicated circuits and have never had a tripping issue other than in the event of a grid fault. Manufacturers recommend 100mA, so 300mA per inverter should be more than adequate.

unless of course you've already for some significant earth leakage going on. Do you have any other circuits not on the 30mA RCDs in the house that could be responsible for live neutral imbalances on both sides? maybe a rogue shared neutral / neutral > shared earth fault > neutral on something like a heating circuit that also comes on at that sort of time? Maybe try switching the solar off over night and see if it happens without it just to be sure?

 

[Lastminuteandy]

No other RCDs trip than the roadside 300mA units?

Nope, just the road side ones and usually just one or the other. Only once have both tripped.

 

[Lastminuteandy]

Hi, thank you for that. I have Sunny inverters a 4kw and a 5kw. The only other load I could think was a 1kw dehumifier (because we have building work going on), but I turned this off and the tripping still happens.

I have been starting to wonder whether the problem is to do with the earth. Earthing is by a two 2.5m copper rods driven into the ground vertically. One is next to the meters, th eother inside the house at the other end of the 35mm2 cable. Both supplies share th esame earth as the 35mms cable is actually a 4core 35mm2 swa.

 

[Lastminuteandy]

I have been 'googleing' and still can't find the answer. However, the Americans seem to get quite concered with revers feed and make sure that they have RCD's that are reverse flow compatible. Has anyone come across this?

 

[Earthstore]

If it was your PV then it would trip your 30ma RCD's first, I feel you may be looking in the wrong area.

 

[SibertSolar]

Agreed

 

[Gavin A]

Hi, thank you for that. I have Sunny inverters a 4kw and a 5kw. The only other load I could think was a 1kw dehumifier (because we have building work going on), but I turned this off and the tripping still happens.

I have been starting to wonder whether the problem is to do with the earth. Earthing is by a two 2.5m copper rods driven into the ground vertically. One is next to the meters, th eother inside the house at the other end of the 35mm2 cable. Both supplies share th esame earth as the 35mms cable is actually a 4core 35mm2 swa.

sounds like it could also be inductance in the cable?

What loads are you running overnight? Any electric heating, storage heaters or other big loads?

 

[sedgy34]

Im assuming This problem is since the Pv arrays being installed

 

[Toonlad]

Im trying to understand what is shared. You have a 4c 35mm swa .. you say it is earthed either end. Is that through the steel armour also

 

[Lastminuteandy]

sounds like it could also be inductance in the cable?

What loads are you running overnight? Any electric heating, storage heaters or other big loads?

The only overnight load has been few led lights and a couple of flourescents.

- - - Updated - - -

Im assuming This problem is since the Pv arrays being installed

Yes, but the cable and twin supplies was installed at the same time.

 

[Lastminuteandy]

Im trying to understand what is shared. You have a 4c 35mm swa .. you say it is earthed either end. Is that through the steel armour also

Yes. 4 core swa, with the armour connected to the earth pits at either end.

 

[Earthstore]

Question to others, would the RCD trip if the inbalance was on the incoming?

 

[Gavin A]

Yes. 4 core swa, with the armour connected to the earth pits at either end.

right, RCD located on a board at the end of the road... I'm plumping for incorrect IP rating, resulting in condensation on cold damp nights that's tripping the RCDs.

and if it turns out I guessed that right, I'll be erm quietly impressed with myself, but it's a bit of a longshot.

 

[BruceB]

As a starter for 10 I would get an electrician to test each of the rcds to make sure that they are tripping at the correct value.

I would also consider making the rcds at the entrance type S (time delayed) rcds so that you have proper discrimination between the house rcds and the road entrance rcds.

It sounds like you might have a couple of TT systems run in parallel which is inviting trouble from faults in one installation causing trips in another.

I hope your electrician and the DNO had a really good reason for bringing in 2 separate single phase supplies and metering it at the roadside. It strikes me you would have been better just bringing in a 3 phase supply to the house and metering it there. At the moment on cold winter days and nights you will be paying for the electricity that is heating the ground between your entrance and the house, which adds up over say 20 years.