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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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    I agree that petrol seems an unlikely and maybe unwise choice of fuel for an 8 kw generator. Only 30 litres of petrol may lawfully be stored, and 30 litres wont last very long in an 8 kw generator.

    Returning to earthing, I would proceed as follows. Provide at the changeover switch a fixed 32 amp ceeform plug via which the generator may be connected. Bond together all the following, the blue and the green/yellow wires from the generator, the blue and the green/yellow wires into the changeover switch, a green/yellow wire to a local earth rod, and a green/yellow wire to the MET of the existing electrical installation.

    Provide a standard 32 amp ceeform extension lead, with a plug for the generator end and a trailing socket for the connection to the changeover switch.

    Presuming that the stated capacity of the generator is 8 kw short term or intermittent, with the long term capacity being 7 kw or less, then  32 amp connectors will be fine. If however 8 kw can be supplied CONTINUALLY then 63 amp connectors should be used.

    This will ensure that neutral of the generator supply is connected to the general mass of earth and to the CPC. This then resemble a public supply with an earthed neutral.

    I would advise against modifying the internal connections of the generator as that renders it non standard and will void the warranty.

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  • 0

    I agree that petrol seems an unlikely and maybe unwise choice of fuel for an 8 kw generator. Only 30 litres of petrol may lawfully be stored, and 30 litres wont last very long in an 8 kw generator.

    Returning to earthing, I would proceed as follows. Provide at the changeover switch a fixed 32 amp ceeform plug via which the generator may be connected. Bond together all the following, the blue and the green/yellow wires from the generator, the blue and the green/yellow wires into the changeover switch, a green/yellow wire to a local earth rod, and a green/yellow wire to the MET of the existing electrical installation.

    Provide a standard 32 amp ceeform extension lead, with a plug for the generator end and a trailing socket for the connection to the changeover switch.

    Presuming that the stated capacity of the generator is 8 kw short term or intermittent, with the long term capacity being 7 kw or less, then  32 amp connectors will be fine. If however 8 kw can be supplied CONTINUALLY then 63 amp connectors should be used.

    This will ensure that neutral of the generator supply is connected to the general mass of earth and to the CPC. This then resemble a public supply with an earthed neutral.

    I would advise against modifying the internal connections of the generator as that renders it non standard and will void the warranty.

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