Domestic EESS installation topology

Chris Coffin

I have an EESS based on a Victron Multiplus inverter. This has separate AC Input and Output connections so the entire house load is routed via the inverter.

This topology was not covered in either the text or diagrams of the 1st or 2nd editions of the Code of Practice (despite a representative from Victron being on the panel AFAIR). Has this omission now been rectified in the 3rd Edition?

Also, I have installed a changeover switch so I can bypass the inverter for maintenance or if it fails. I am thinking of replacing this with a contactor so if the inverter fails it changes over to grid supply automatically. Is this kind of arrangement compliant with the 3rd Edition?

  • +1

    Hi Chris and thanks for joining the discussion.

    I can only speak generally here as I don't have the full technical information from you but in our experience it is unlikely that most inverters will be adequately rated for "wiring" through as you have set out above, without knowing your exact setup I cant comment much further but I seem to recall that the Multiplus range may max out at 50A. 

    This particular topology needs very careful consideration due to the necessity to keep everything aligned to the overarching requirements of BS7671 and ESQCR 2002 (reg 21) especially in relation to islanding and the necessity to "isolate" from the mains as well as providing a N-E bond / reference when in island mode. 

    In relation to replacing isolator changeover switch with a contactor you would need to use a contactor that was type tested to EN60947-4 and include the isolation symbol on it. 

     Hope that helps steer your interest and thank you for taking part in the EESS Chat !

    Griff Thomas MIET GTEC Training (www.gtec.co.uk)  

  • 0 in reply to Griff Thomas
    Griff Thomas said:
    it is unlikely that most inverters will be adequately rated for "wiring" through

    Most inverters yes, but for other readers the Victron Multiplus range are specifically designed to be used like this, and incorporate neutral bonding and anti-islanding type-approved for UK use. The 50A pass-through rating of the 5kVA unit (which I have) is OK for a small to medium house, and the larger models have pass-through of 100A.

    My point was that the earlier editions of IET's own Code of Practice did not depict this topology so were not much help when I installed it. Hopefully the recording of yesterday's presentation about the 3rd Edition will shed more light once it is posted online.

    Thanks for the pointers regarding the contactor, the one I was planning to use https://www.cef.co.uk/catalogue/products/4327497-63a-modular-contactor-2-no-2-nc-contacts-230v-coil seems to comply.

  • 0 in reply to Chris Coffin

    Hi Chris,

    In relation to the N-E bond as with any other device that switches for safety it must be able to make or break the maximum expected fault current at the point at which it is installed. This is similar to the way in which MCB's have to be rated to 6kA / 10kA etc. 

    This is from the IET CoP 9.4.10 

    it is my experience that an internally provided SMD or similar is unlikely to be capable for fulfilling this requirement and functioning under the local fault current conditions. 

    in relation to the contactor then this is to have the "ISOLATION" symbol alongside the type test as follows:

    Hope this helps

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