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Generator earthing....Again!

gibb01

Hi All,

We've just installed a 400A manual changeover switch for a client that requires a backup generator (Not permanently installed - as It's being supplied by a generator hire company as and when there are power outages) It's a semi rural location and they seem to get power cuts several times a year.

The generator company aren't being particularly forthcoming with information regarding the sets they will be supplying (Other than saying they all have in built earth fault Leakage protection) 

The existing supply is TNCS & I know we can't rely on the DNO earthing during a power cut. With this in mind and little more information to go on from the generator company,  Should we be installing a Rod(s) and just ensuring we have a resistance lower than 20 Ohms.  Is there anything else I need to consider, Obviously my concern is ensuring that any existing protective devices will still operate under fault conditions whilst supplied by the generator.

Given that  411.4.2 now recommends an electrode at the point of supply, I assume we have no real issue with a combined  TT / TNCS arrangement!

All thoughts are more than welcome,

Thanks,

Tim

  • 0 in reply to grahamro

    seems to depend on who you speak to nowadays on the helpline.

    Rest assured, you can easily get multiple, often contradictory, opinions from here too!

       - Andy.

  • 0 in reply to grahamro
    grahamro said:
    Many thanks. That's not quite the information I received via the NICEIC. It unfortunately seems to depend on who you speak to nowadays on the helpline.

    I can confirm ESQCR reference made to by Andy, also see Regulation 21 of ESQCR, which mandates BS 7671 when you have a generator that can provide a switched alternative supply to the grid, and also mandates that the switching arrangement does not permit the standby generator to operate in parallel with the grid (unless, as identified in G99, the generator is suitable for operation as a grid-connected generator too ... this is possible with some inverter output generating sets, where the inverter is type-tested for G98/G99 operation).

  • 0 in reply to gkenyon

    This is a standby generator for a village hall in the wake of Storm Arwen.It'll only be used when the DNO supply goes down.
    Ironically during said Storm Arwen when the rest of us in the area were without for 4 and 5 days that particular hall wasn't affected by power cuts at all!!

  • 0 in reply to grahamro
    grahamro said:
    This is a standby generator for a village hall in the wake of Storm Arwen.It'll only be used when the DNO supply goes down.

    One of the reasons for the ESQCR requirement that the generator has to be switched, so it can't operate in parallel with the grid, is to help protect those working on distribution network cables from "back-feed".

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