Photovoltaics

Bsharp · Dec 29, 2019

good morning all, I’m looking for a little advice regarding an existing PV install, I’ve just waited a property where a PV install exists (working no problems) my question is on the correct connection to consumer unit, the PV is connected as was with a 2.5T+E from inverter you consumer unit via DC iso and 2 x AC (one local to inverter and one at consumer unit end)
Stupidly I have disconnected the 1 way RCD protected consumer unit which fed the PV power to the main consumer unit and not taken a great deal of notice of the connections durrrrr!!!
My question is on the reconnections. This is probably going to sound simple to those who deal with this every day but I I’ve started to over think things and hit a mind blank. Could anybody post a simple diagram of the “correct” connections from AC iso through 1 way board to main board? Basically which side of RCD should PV go to before feeding my 16amp MCB in main board.
Thanks for any assistance, as I said I’ve over thought this for sure.

littlespark · Dec 29, 2019

I think you just treat the inverter as a normal load. Ie, supply to the supply side of rcd, inverter on load side.
I see the confusion.... the PV is a supply, so shouldn’t it be the other way??

All I know is my own installation, where the pv is connected through an mcb in my main split rcd board. Which is on the load side of the main rcd.

The cables are hidden in trunking, but I believe it goes...
MCB - export meter - Iso at board
Then up to the attic to another iso - invertor - DC iso - panels.

oh, my install is done in 4.0mm T&E

Wilko · Dec 29, 2019

Hi - I stand to be corrected (as always

) but if the PV inverter is connected to the CU busbar via an mcb then it may power the CU final circuits even if the additional protection RCD in the CU trips. This timeout in the inverter is supposed to be 500ms or less but as far as I know no one ever tests this (?) ... unlike the RCD trip times which we confirm each time we touch a circuit. If the RCD trips to provide protection to a Person who has got hold of L then I think the risk is ADS will not work as quickly as intended.

marconi · Dec 30, 2019

Regarding the RCD(PV) - in the single way enclosure near the main CU - between the load terminals of the 16A mcb in the main CU and the inverter's mains output terminals - you connect the supply side of the RCD(PV) to the load side of the 16A mcb and the load side of the RCD(PV) to the inverter.

Just check the inverter has galvanic isolation between the ac and dc sides as provided by a transformer - in which case a type AC RCD will be fine for RCD(PV) and the mains secondary winding must not be earthed. Without galvanic isolation a different type of RCD is required for RCD(PV) capable of detecting dc components in a fault current.

Here is a nice reference:

https://www.----------------------------/media/1202/best-practice-guide-3.pdf

Look at Fig 1A, and pages 11-13.
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PS: Double pole RCD(PV)