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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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    It might be worth having a careful look at the way the changeover between 115 & 230 is done on the Gen. I've seen these windings tapped in such a way that its not possible to modify the set such the NE bond is at one end of the winding in 230V mode but yet correctly at the 55-0-55 tap when in 110V mode - I've had to completely disable the 110V option to make this work.

    As others have said, without connecting the 'earth' to one end of the winding, there will be no path for an earth fault current to take & hence an RCD or MCB will not operate in the event of such a fault. Indeed with such a small genset, its doubtful it will be able to deliver enough current to operate anything bigger than about a 10A MCB in the instantaneous region - more likely that either the prime mover will stall or the voltage will collapse.

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    It might be worth having a careful look at the way the changeover between 115 & 230 is done on the Gen. I've seen these windings tapped in such a way that its not possible to modify the set such the NE bond is at one end of the winding in 230V mode but yet correctly at the 55-0-55 tap when in 110V mode - I've had to completely disable the 110V option to make this work.

    As others have said, without connecting the 'earth' to one end of the winding, there will be no path for an earth fault current to take & hence an RCD or MCB will not operate in the event of such a fault. Indeed with such a small genset, its doubtful it will be able to deliver enough current to operate anything bigger than about a 10A MCB in the instantaneous region - more likely that either the prime mover will stall or the voltage will collapse.

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