Earthing PV rails

[Sidecar Man]

Just started doing my solar array. I'm 2391 trained but never done any solar before
Wanted to know do I need to earth my PV rails. I'm using a Solar edge inverter. If so is it 10mm back to board. Thanks.
Also is it worth putting Rcd and M C B straight off AC side of inverter

 

[Deleted member 26818]

When I was at College, we were asked to draw Earth fault paths.
I wonder what the Earth fault path for a d.c. panel would be?
As for an RCD, you really should be reading the inverter manual.

 

[Sidecar Man]

Yeah inverter manual doesn't say anything but with the cable been less than 50mm from the surface of the wall I thought it would be necessary or advisable.
Thanks Phil.

 

[Deleted member 26818]

If the AV supply cable is concealed in a wall, then yes it could well require RCD protection, at each end of the cable.
The inverter manual should really be telling you if and what type of RCD is required.

 

[bill01803]

Remember the rcd should not be shared with other circuits

 

[Gavin A]

MCS standard says no, IET guide says yes to earthing rails.

MCS hasn't adopted IET guide despite the lead authors also being members of the MCS technical steering group who wrote most of the MCS guide.

So officially the answer is depends which guide you want to follow.

We don't for multiple reasons, and probably 95% of all installations in this country also haven't.

 

[davesparks]

Yeah inverter manual doesn't say anything but with the cable been less than 50mm from the surface of the wall I thought it would be necessary or advisable.
Thanks Phil.

There is a source of supply at both ends of the cable, so you'd need the RCD to disconnect both ends of the cable simultaneously. As far as I know this isn't possible so you need to consider an alternative means of protection for the buried cable.

 

[Deleted member 26818]

Not aware of any requirement for the two RCDs to operate simultaneously?
My understanding, is that they just have to operate within the times specified in BS7671.
As for earthing the rails, not sure why anyone would want to, or what would be the intention for doing so?
Traditionally, where there are two sources of supply, any earthing is kept separate. This is primarily to keep Earth faults from one supply separate from the other.
With d.c. systems, unless either a positive or negative grounding system is in use, earthing is not possible.
Earthing the rails to the a.c. supply would just mean the rails would become live in the event of an earth fault occurring on the a.c. side.

 

[davesparks]

Not aware of any requirement for the two RCDs to operate simultaneously?
My understanding, is that they just have to operate within the times specified in BS7671.
.

I didn't say two rcds, I said one RCD disconnecting both sources of supply simultaneously. The regs require protective devices to be fitted at the end of the circuit where the relevant earthing system is, ie at the DNO supply end, not the inverter end of the cable.
There is no specified disconnection time in the regs, only a tripping current and touch voltage.

 

[Deleted member 26818]

Not aware of any requirement for both sources of supply to be disconnected simultaneously.
As far as I am aware BS7671 requires an operating time for RCDs (used to provide additional protection), not exceeding 40 ms at a residual current of 5 X I delta n.

 

[Gavin A]

no need for a second RCD as the first at the supply end will disconnect the return paths connection to earth, leaving a circuit that's protected by being a separated circuit. As long as the neutral and earth aren't bonded at the inverter, which they shouldn't be.