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Petrol Generators and Earthing

sparkiemike

A customer has asked me to install a change-over switch for a 8kW petrol generator to his house consumer unit to be used in the event of power loss from the grid.

The user manual for the generator states that it is a "floating earth configuration which means that the Neutral of the alternator is not connected to the Earth of the machine". It then mentions that you can only use 1 type of class 1 equipment or more than 1 type of class 2 equipment etc.

The generator has 2x 115V 16A CEE yellow output and 1x 230 230V 32A blue output. The generator has "overload protection which will cut off power if it exceeds the maximum energy capacity" but NO RCD.

When the generator runs I get 90V between Earth and the Neutral pins and 90V between Earth and the Line pins, this would suggest that the protective earth (centre)-tapped to the winding.

The earth pins of the CEE form sockets generator are connected to the frame and a ground stud/pin. The user manual states that BS 7971:2008 requires the frame to "be properly connected to an approved earth ground".

1. I can't see what function any earthing would provide as the N and E are not connected, if they were connected it would result in catastrophic failure of the machine. Is this correct?

2. Secondly I am correct in thinking that this generator is not suitable for connecting to a house, and he would be better off getting a new machine with correct type earthing arrangement, or are there alternative ways of connecting this generator safely?

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  • 0

    Normally you can earth the neutral of such a genset (and should if you want to use it to run an installation where the ADS relies on an NE bond) , but you should perhaps try to do so via a limiting resistance first to check that nothing untoward happens.

    Do you have a web link to the genset datasheet?

    Note that without an interconnection between windings and CPC, then RCDs will not work, and single pole MCBs and fuses will not be in the right pole, or more correctly without a clear neutral, there is no clear live either.

    Be aware that you will need to provide an NE bond and an electrode, as during an external mains fault you cannot rely on the mains for earthing - the cable be be disconnected in the street for example, and then be aware that in areas cvered by the ecsqr, that NE bond has to be on the other side of a double pole switch to the one from the DNO.

    Mike

  • 0 in reply to mapj1
    mapj1 said:

    Do you have a web link to the genset datasheet?

    Data sheet 

    User Manual 

Reply Children
  • 0 in reply to sparkiemike

    Hmm not the most useful documentation is it. I'd try grounding the neutral via a modest resistance - in the old days I;d have said a light bulb, now in the world of the LED  it probably has to be a small appliance like a fan or a heater, to see if the neutral shifts to 0V and the live goes up as you'd expect.

    M

  • 0 in reply to sparkiemike

    I know that it doesn't help, but customer seems to have bought something which is totally unsuitable for it's intended purpose.

    "Fuel should be emptied before storage for 30 days or longer." As I said!

    96 dB - you wouldn't want that under your kitchen window for very long.

    Perhaps in this situation the best response is to walk away?

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