Disconnection time with a PV sytem installed.

Dave1982 · Oct 10, 2011

Hello all.

Could any experienced sparkies please please explain to me how RCD tripping times can be adhered to when a PV sytem is integrated into a domestic consumer unit if the inverter takes up to 5 seconds to isolate the AC outputwhich it feed to the domestic supply at the consumer unit. Fed into the buzzbar through the required MCB. Surely safety is compromised. Or am I missing something. I have just completed my first day of a PV course and am a bit confused. after browsing the spec for a SunnyBoy inverter.

Any help appreciated.

Many thanks

BruceB · Oct 10, 2011

It should not be sharing an rcd with other circuits.

The proposed V3 of the DTI guide makes it clearer:
"The final connection into a distribution board that contains one or more circuits protected by an RCD, shall be made in such a way that the outgoing circuit for the PV system is not connected into the outgoing side of an RCD installed for the protection of other circuits (ie in a split board – connected into the part not protected by the RCD) ."

Regards
Bruce

peanutty · Oct 10, 2011

hi, i'm new to the solar systems myself but don't they cut out straight away if power from supply i.e. mcb/rcd trips? as i thought they had to take a tiny amount of current to operate making a closed circuit. if no supply power to invertor doesn't the circuit become open inside invertor. think that makes some sense?!?!?

BruceB · Oct 10, 2011

The G83 spec is cut out within 0.5 second of loss of mains, or 5 seconds if the inverter can withstand energisation with an 180 degree out of phase exitation voltage.

Have a look at some inverter G83 test sheets and you will see the test results.

Regards
Bruce

dougalthedog · Oct 12, 2011

Hi,

I have carried out some tests on this - in my experience disconnection times are still met but increased. However, as the inverter is "allowed" up to 5 seconds to shut down, there is no guarantee that disconnect times will be met under all circumstances (e.g. if the power supplied is close to the instantaneous load). In my opinion this is a big grey area which should have been dealt with clearly before now as safety could be compromised. Best practice is probably to fit a seperate consumer unit or protect with RCBO.