PV Panel Earthing

[Barney12]

Quick question:

I'm just planning my cable runs for the PV array. Our panels are in the plastic GSE trays. Does that negate the need to earth bond the panel frames?

If no, what size earth cable should I allow for (2 arrays of 500w and 1 array of 1500w)?

I would ask my spark but he never answers his flippin phone! Grrrr!

[Jeremy Harris]

Yes, it does.  There's nowhere to make an earth connection to, as everything is insulated.  Ours just has four wires coming down from the roof to the inverter, run inside 25mm flexible conduit, for the two strings of panels.

[Barney12]

3 minutes ago, JSHarris said:

Yes, it does.  There's nowhere to make an earth connection to, as everything is insulated.  Ours just has four wires coming down from the roof to the inverter, run inside 25mm flexible conduit, for the two strings of panels.

I thought that must be the case. Especially as the metal frame effectively is not connected to anything.

[Jeremy Harris]

On our panels there is no means of connecting an earthing lead to the panels, as they are, in effect, double-insulated, by the glass and EVA encapsulant holding the cells.  The terminal box is on the underside of the insulated part of the panel, too.

I think the only reason for needing to earth bond roof mounting frames is because there are cables tied or dangling over them, plus, possibly, the need to keep the frames at earth potential just to stop any build up of static or very tiny leakage current charge.  The main risk is probably from damage to a cable tied to a frame causing it to short to it and make the whole frame sit at some high DC voltage.  Also no insulator is 100%, so if the metal mounting frames were not earthed then there is a slight chance, given the large size of most mounting frames, that they could hold enough charge to give someone a slight jolt.  It would only be tiny, a bit like the static shock you sometimes get when touching a door handle after walking over a carpet, but could, possibly, be enough to be a risk to anyone working on the roof, in terms of causing them to lose hold.

With no metal frame work on the roof, just plastic mounts, the problem isn't there.  The small alloy frames around the edge of the panels are anodised (so insulated to a fair degree) and don't come into contact with any of the cables, as they run out underneath the centre of the plastic frames.

[SteamyTea]

There is usually something in the inverter spec about not earthing too.

Should it be earthed or bonded?

[Barney12]

10 minutes ago, SteamyTea said:

There is usually something in the inverter spec about not earthing too.

Should it be earthed or bonded?

The inverters suggest no requirement for earthing due to an integrated ground.

I'm not sure how bonding could be relevant/needed in this scenario?

[Jeremy Harris]

41 minutes ago, Barney12 said:

The inverters suggest no requirement for earthing due to an integrated ground.

I'm not sure how bonding could be relevant/needed in this scenario?

I'm pretty sure the bonding requirement is as above, it really only applies when you have a large metal frame on the roof, and the idea is to ensure that everything sits at the same potential, to minimise the risk of shock.  It's a bit like bonding the pipework in a house.  Our current house has an MDPE water main, with a earth bonding wire connected to the stop cock just above it.  There are similar bonding wires connecting the hot and cold pipes together all over the place (it's all copper).  The idea was to keep all the metalwork that anyone can touch at the same potential, so you can't, for example, have the hot tap sitting at mains voltage (due to a fault) and the cold tap at earth potential - such a fault would cause enough current to flow to blow the fuse.

With the advent of mandatory RCDs and plastic pipe fittings the need for bonding has pretty much gone for most situations, although there are still one or two places where it's needed, IIRC.