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Solax PV invertor on shared 30mA type A RCD

Lee B

Good afternoon,

I require some guidance on the subject of a SOLAX PV invertor being installed on a shared type A RCD. We have a contractor who claims there is differing industry guidance on this subject but they have providied any supporting evidence to suggest this is the case. 

The contractor sent me the following from the manual - 

I gave them the guidance from the COP Grid connected solar PV systems page 90 - Solar PV systems shall not be installed to the load side of any RCD that is shared with other circuits (for example, where the RCD is feeding a number of circuit breakers / circuits)

I gave them the scenario that if one of the shared ciruits tripped the RCD under fault conditions, would the invertor carry on feeding the fault or disconnect within 300ms as per the 30mA shared RCD.

Any help on shedding light on the above matter is greatly appreciated.

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    I gave them the scenario that if one of the shared ciruits tripped the RCD under fault conditions, would the invertor carry on feeding the fault or disconnect within 300ms as per the 30mA shared RCD.

    Provided the RCD is a double pole device (i.e. opens N as well as L, unlike some RCBOs) - it should trip OK, and as you say the inverter may continue to supply a voltage into the "disconnected" circuits ... however as N to the supply has been opened the whole lot now becomes disconnected from Earth - akin to a separated circuit, so the risk of shock (from an exposed live conductor to Earth) is in theory eliminated.

    In practice the inverter may or may not provide suitable isolation from Earth to maintain suitable separation (esp. if it's transformerless and the d.c. side is earthed) - so the theory doesn't always work ... which is probably what's driving the advise for separate devices for additional protection.

       - Andy.

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    I gave them the scenario that if one of the shared ciruits tripped the RCD under fault conditions, would the invertor carry on feeding the fault or disconnect within 300ms as per the 30mA shared RCD.

    Provided the RCD is a double pole device (i.e. opens N as well as L, unlike some RCBOs) - it should trip OK, and as you say the inverter may continue to supply a voltage into the "disconnected" circuits ... however as N to the supply has been opened the whole lot now becomes disconnected from Earth - akin to a separated circuit, so the risk of shock (from an exposed live conductor to Earth) is in theory eliminated.

    In practice the inverter may or may not provide suitable isolation from Earth to maintain suitable separation (esp. if it's transformerless and the d.c. side is earthed) - so the theory doesn't always work ... which is probably what's driving the advise for separate devices for additional protection.

       - Andy.

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