We are currently installing solar pv systems, and have had a third party at one of our installs carrying out an EICR. They have flagged a C2 for the RCBO we have used only being single pole.
In section 712 of BS7671 ‘Special Locations – Solar PV’ we cannot see a regulation that states that a double pole RCD is required. Any advice on this matter would be greatly appreciated.
Quite. Actually I'd not hold my breath for that 4KW array to do a fat lot with a 13A fuse either unless it is very sunny or there is a DC battery to help it along a bit.
Now for an L-N fault or overload, the inverter output collapses until the load is reduced to a level it can sustain - and no harm will come to the wiring, but everything will 'brown out' or 'black out' until the fault or extra load is removed.
However if this extra current is due to the sort of fault to earth that might actually also shock or even electrocute someone, we would appreciate a rather more prompt disconnection. Enter the RCD stage left to save the day.
M.
Inverters in general should not be supplied from RCD protected circuits, as most RCDs and RCBOs are not bi directional, and therefore are not suitable for solar or battery installations. and as for double pole isolation this is the best I can come up with Because most systems use the 1 amp fuse/detection breaker between the array negative and safety ground. it turns a ground referenced system into floating power system--Which does need two pole breakers for safety
Because most systems use the 1 amp fuse/detection breaker between the array negative and safety ground. it turns a ground referenced system into floating power system
Point of order: Most PV installations in the UK are floating on the DC side by design and rely on double insulation for protection against fault plus insulation monitoring, with DC fuses where required for overload protection (in case of reverse current). Other countries' practices may vary, particularly when dealing with older installations. There are some which are functionally earthed (C21e tiles come to mind; from distant memory), which depending on the manufacturers instructions (and it does vary for technical reasons) could be earthed via + or -. For safety this will either have a resistor to limit fault current, or an OCPD (fuse/MCB) to interrupt fault current; in the latter case said device must be monitored and raise an earth fault alarm if it operates.
Inverters in general should not be supplied from RCD protected circuits
I don't disagree, albeit mainly coming from the angle of leakage currents causing maloperation or blinding of RCDs. But yes if an RCD (or other earth fault leakage device, including MCCBs with LSIG etc) is present upstream compatibility in all regards should be properly checked.
My enquiry to the manufacturer of my particular device has yielded an interesting reply - while they confirm it is not bi-directional, they suggest that as it's still working after several years of service (I've just run a full set of RCD tests to confirm that), they don't see any immediate safety issue - so basically no need to worry about it - but if I wanted to upgrade to meet current regs they'd recommend their two-module version.
Which sort of leaves me wondering what the problem really is?
(I'm reminded of my enquiries to a combi boiler manufacturer about converting the system to open-vented - they initially said no - when I asked why, the answer wasn't any particular technical limitation, just that they hadn't specifically tested it in that situation so were unwilling to guarantee that it would ... in practice it was of course fine. I might be being unfair though.).
- Andy.
How often has the RCD ever tripped, and in what direction was power flowing when it did ? I'd not expect any damage under any conditions until it tries to trip. Have you tested it trips OK on the tester both ways round,.
You may be right and it is just an example of stickerism and a lack of understanding by the makers of their own product,
Mike.
As I think that Mike implies, that can perfectly simply be explained by no fault having occurred!
Inverters in general should not be supplied from RCD protected circuitsI don't disagree, albeit mainly coming from the angle of leakage currents causing maloperation or blinding of RCDs. But yes if an RCD (or other earth fault leakage device, including MCCBs with LSIG etc) is present upstream compatibility in all regards should be properly checked.
"In general" isn't always the case ... we can't forget TT systems "in general", but also I've seen an inverter arrangement actually supplied with 30 mA RCDs for the installation.
How often has the RCD ever tripped, and in what direction was power flowing when it did ? I'd not expect any damage under any conditions until it tries to trip. Have you tested it trips OK on the tester both ways round
Many times, but only by T button or RCD tester - and almost certainly only when the PV wasn't generating (I wouldn't want to miss out on some of my home grown!). I may well have an experiment, but after I've swapped it for a two module one, so it won't be a disaster if I do fry it. Possibly a saving grace is that the PV system will shut down automatically on loss of main (after a few seconds) so that might limit the potential for burn out too. The 3rd contact in the test circuit also eliminates some failure modes.
- Andy.
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