RCD trip times in islanding mode.
I have brought this to the attention of the technical team but I am curious to anyone else's opinion.
As far as I'm aware Sunsynk say that the Inverter needs to have RCD protection on the feed.
Also the essentials consumer unit needs to have RCD protection.
Now, when the system is running as normal, grid supply is up and battery is charged, if you carry out an
RCD trip test on the essentials load circuit, it can trip the inverter feed RCD first.
The issue I see here is that if there was a fault during normal operation on the essentials circuit it could
potentially trip the inverter RCD, putting it into islanding mode re supplying power to the faulty circuit.
You would then have to wait for the essentials RCD to trip to finally disconnect the faulty circuit.
This could theoretically double the time it takes for the faulty circuit to be disconnect from power, which could mean it
Fails to disconnect in the permitted times laid out in BS 7671.
My initial thought is to not supply the inverter with an RCD, the cables in my set up are run in
trunking and so don't need it. However Sunsynk tech say that it needs RCD protection, like wise
any systems fed with cables that require RCD protection would have the same issue.
Hi thanks for the reply.
Just to be clear this isn't a fault with the inverter. This will be the case for every inverter that is fitted with RCD protection that has an essentials load board that also has RCD protection. When you carry out RCD testing with a tester on the essentials load it can trip the inverters RCD first.
This is the same as having a main consumer unit with RCD protection feeding a submain and the submain also having RCD protection. Quite often what you will find it the main RCD will trip first. Sometimes both trip and sometimes the submain will trip.
Now that isn't normally an issue as the faulty circuit is disconnected, how ever you would normally try and feed that submain in SWA so it could be fed on an MCB to avoid nuisance tripping.
The issues here is that the essentials load becomes live again. So the trip time could potentially double resulting in a failed test result and potential danger for the person in contact with that faulty circuit.
This issue relates to the British Wiring Regs. The earlier comment mentioning trip times at 200ms, that is only at 1x fault current. We have to rest at 5x as well. That means 40ms. Doubling the time it takes to trip could easily lead to more than that 40ms.
Again this isn't an inverter fault or a earth system issue.