Increased earth leakage on installs with Solar PV

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Walter Leach

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I don't install PV myself but I now have two customers where I have done work and installed split load CU's (2 * 30mA RCDs) as part of the work who have since had Solar PV installed and they are now experiencing increased nuisance tripping since the PV was installed (all anecdotal so far). I have had a quick look at one site and where my x1 RCD ramp trip tests were tripping at 24.0mA with the solar PV connected they now trip at 18/19mA which implies the inverter is creating about 5-6mA earth leakage. If I isolate the PV the trip test reverts back to 24mA. Customer has had their PV installer out to look at it and he said his side is all OK and suggested customer moves some sockets to the other RCD but that would put all sockets on one RCD rather than across two. I plan to get a meter and measure the actual current in the earth to follow this up but is this typical?

 
Many inverters are transformerless, so any leakage in the dc cabling will contribute to leakage on the mains.

but the more worrying thing from your post, is by implication, the Solar PV installer has fed the inverter input to an MCB sharing one of your RCD's.

This is plainly WRONG as has been discussed here many times, because in the event of an RCD trip, the inverter can continue feeding power for up to 5 seconds, so your RCD will not have provided isolation (within the specified times)

If that is the case, get the solar PV installer back to correct it, and either feed in via it's own rcbo or via a seperate mini CU.

 
+2 new small db for pv only unless there's space to put it on the main switch side

 
DON`T use an RCBo - you`re "back-feeding" it, which they seriously don`t like!!!

Stand alone board, labelled "for PV generator use only".

As the guys have said, lumping the PV onto a "spare way" in a DB is non-compliant, and affects the integrity of the existing installation.

 
I made it clear to the maint company im subbing too i will EDN any install backfeeding into a rcd split and if they dont like it they can get someone else in, found one in a small shop friday they now have to get the installers back made my day.

 
Hmm seems I need to get my installer back too! He really seemed to know what he was doing electrics wise as well. Been in the contracting business for 20 years including several in solar.

He put an MCB in a spare way, on the split RCD. Then when the RCD kept nuisance tripping he offered a replacement RCCB! Crabtree as well, not a cheap option.

Seems he'd have saved money by putting a small board in. :(

 
I would like to think that they are going to work on levels that they are probably most familiar with. And with the available inverters being transformer less, I think that the choices you make with the cables would also say much about how they are going to contribute with the mains.

And hopefully there will be more things that would let them work just right.

 
DON`T use an RCBo - you`re "back-feeding" it, which they seriously don`t like!!!Stand alone board, labelled "for PV generator use only".

As the guys have said, lumping the PV onto a "spare way" in a DB is non-compliant, and affects the integrity of the existing installation.
Thinking about this, you ALSO have to be careful that the RCD used in the stand alone board CAN be back fed.

I know for instance Contactum RCD's will self destruct in spectacular fashion if back fed.

I forsee the need for someone to do some testing and publish a concise list of which RCD's can be back fed and which can't.

Better still an updated BS standard is needed that specifies an RCD must be capable of being back fed. Then we can buy one compliant with that new standard.

 

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