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Solar PV into load side of RCD

lyledunn

At Section 8.8 in the COP for Grid connected Solar PV systems it clearly indicates that the inverter should not be connected to the load side of any RCD that is shared with other circuits. The note explains the reasons without elaboration.

I am trying to understand how an inverter would continue to supply the fault after the RCD has operated. Is it not a separated circuit at the loss of supply?

 

Parents
  • 0

    Just visited a home where the solar system is sharing an RCD with 5 or 6 other circuits. Wondering if others would consider this a C2 or C3. 
    In this case I don't think the solar system supported island mode. Wondering if the potential delay in supply disconnection when there is a fault and also potential blinding of the RCD by excess leakage should be considered as a C3 or C2. It comes down to how big is the risk of this happening in real life and personally I just don't know. 

    I am thinking along the lines that the most significant risk is that the inverter will take time to shut down once the RCD trips for a fault, therefore if the fault is someone touching a live wire it will take longer than the allowed 300mS for the supply to be disconnected.
    I thought solar systems shared a common earth with the main supply, including a TT rod when island mode supported, with the main earth disconnected when in island mode. Therefore don't quite understand the discussion about loss of reference earth.

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  • 0

    Just visited a home where the solar system is sharing an RCD with 5 or 6 other circuits. Wondering if others would consider this a C2 or C3. 
    In this case I don't think the solar system supported island mode. Wondering if the potential delay in supply disconnection when there is a fault and also potential blinding of the RCD by excess leakage should be considered as a C3 or C2. It comes down to how big is the risk of this happening in real life and personally I just don't know. 

    I am thinking along the lines that the most significant risk is that the inverter will take time to shut down once the RCD trips for a fault, therefore if the fault is someone touching a live wire it will take longer than the allowed 300mS for the supply to be disconnected.
    I thought solar systems shared a common earth with the main supply, including a TT rod when island mode supported, with the main earth disconnected when in island mode. Therefore don't quite understand the discussion about loss of reference earth.

Children
  • 0 in reply to Alan B
    Alan B said:
    Just visited a home where the solar system is sharing an RCD with 5 or 6 other circuits. Wondering if others would consider this a C2 or C3

    BS7671 regulation 134.1.1

  • 0 in reply to Alan B

    The earth reference is mentioned as far as fault currents goes relating to the location of a neutral earth bond - in effect if the inverter keeps going, but the NE path to earth is broken, how do you get a shock ? Its a bit like the transformer isolated shaver socket, in the sense you can toucvh either pin and be earthed yourself and not get a shock. 

    If it cannot run as an island, then it is OK to rely solely on the DNO earth, as when the DNO supply has gone the inverter stops. The trip time thing is a more tricky one, and  I dont have an answer to that  without knowing a lot more about the behaviour of the specific kit. clearly its not ideal, but if it is potentially as dangerous as no RCD or not ?

    Mike

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