PV systems

[JohnD]

Hence, with the grid side neutral earthed and the inverter neutral not earthed

The inverter neutral and the grid neutral are connected together, so it can't be "not earthed"

 

[JohnW2]

If there is a N-E interconnection on both sides of the RCD then most likely the RCD will trip even in the absence of any fault.

Now there's an interesting thought - but then we have westie suggesting that the inverter's N probably always will be earthed, just like a genny!

Going back to the very start of this discussion, (and given that therewill always be a N-E connection on the grid side) it would certainly be a good reason for not having an RCD in the feed from/to the inverter - since, as I've said, I can't for the life of me see how it could serve a useful purpose (other than just to protect the cable from the RCD to the inverter) unless the inverter neutral was connected to earth.

Kind Regards, John

 

[JohnW2]

Hence, with the grid side neutral earthed and the inverter neutral not earthed

The inverter neutral and the grid neutral are connected together, so it can't be "not earthed"

Although I admit that I didn't type it, I obviously meant separately earthed (i.e. at the terminal of the inverter) - thereby providing a path whereby neutral current could get back (from a fault to earth) to the inverter without travelling through the neutral wiring (and any RCDs in the neutral wiring path).

Kind Regards, John

 

[mikeyd]

However, as I said, I think this is only true so long as the grid neutral, but NOT the inverter neutral, are earthed. If both are (separately) earth-referenced, per the comments that started this discussion a few pages back, I think that things change - more in the direction of what I was incorrectly saying before!
Kind Regards, John

I've re-read from the start up until I butted into the thread and I didn't see anything about earthing the inverter neutral. It would, as you know, trip the RCD.

 

[DetlefSchmitz]

I haven't been keeping up with every post - though I plan to.

But has anyone looked at BS7671? In my (rather old) version there is a section on PV, showing an inverter fed RCD and no hint of any earth on N.

This is presumably the font of all wisdom on the subject. I must admit I still don't get it.

 

[JohnW2]

I've re-read from the start up until I butted into the thread and I didn't see anything about earthing the inverter neutral. It would, as you know, trip the RCD.

Indeed, and it's interesting that no-one has thought of (or, at least, mentioned) that until very recently in these 4 pages! It started not as any statement/assertion about earthing the inverter neutral but, rather as a thought/question from me....

Continuing to try to reduce my ignorance concerning this PV stuff ... if I'm now thinking right, presumably the neutral of the inverter output would have to be connected to earth on the inverter side of any RCD for that RCD to serve a useful purpose - otherwise current through the N side of the RCD could not be different from that in the L side (if there were no other possible path back to the inverter's neutral). Is that what is, or would be, done - or am I still thinking totally wrong?!

But then ....

However I am now wondering where the idea that the neutral & earth are not connected together in the inverter? .... Each and every generator that I have come across (either owned by us, hired by us or privately owned and operated) that can operate in parallel with the mains sees either one end (single phase) or the star point (three phase) or the winding connected to earth, so why should an electronic device be different?

Kind Regards, John

 

[JohnW2]

But has anyone looked at BS7671? In my (rather old) version there is a section on PV, showing an inverter fed RCD and no hint of any earth on N. ... This is presumably the font of all wisdom on the subject. I must admit I still don't get it.

As has now been pointed out (although only after 3+ pages!) by a couple of people, if the PV feeds into the house supply on the downstream (final circuits) side of a house RCD, then that RCD would trip if one earthed the inverter neutral when there were any loads.

However, as I've been saying from the very start, an RCD on the feed from/to the inverter can achieve nothing other than protection of the cable (which could well be very short) between that RCD and the inverter unless the inverter's neutral is earthed - which sort-of suggests to me that such an RCD is probably not worth having, even if BS7671 likes the idea!

Kindest Regards, John