Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 28 replies
  • Subscribers 39 subscribers
  • Views 5288 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

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?

Parents
  • 0

    Hi everyone, it's my first reply since the forum was updated,but have been lurking in the shadows :-)

    The instructions clearly state 

    4.6. Floating earth portable generator use.

    4.6.1. This range of generators adopt a floating earth configuration which means that the Neutral of the alternator is not connected to the Earth of the machine.

    4.6.2. It is therefore IMPORTANT that you ONLY use the generator to supply equipment in the following combinations.

    4.6.2.1. One or more of CLASS II equipment

    4.6.2.2. Only ONE item of Class I equipment

    4.6.2.3. One or more of CLASS II equipment and only ONE item of Class I equipment.  

    That should be enough to convince the purchaser that it is not suitable for its intended use.

    For my own use I would be engineer a N-E link solution, but that would void the warranty, and as others have stated the fuel storage & noise levels make it a poor choice.

  • 0 in reply to WiredScience

    I think in this case the house is seen as a single class 1 item  ;-)

Reply
  • 0 in reply to WiredScience

    I think in this case the house is seen as a single class 1 item  ;-)

Children
  • 0 in reply to mapj1

    Hmmm. I must admit I`d never considered that interpretation Mike. 

  • 0 in reply to mapj1
    mapj1 said:
    I think in this case the house is seen as a single class 1 item  ;-)
    ebee said:
    Hmmm. I must admit I`d never considered that interpretation Mike. 

    Well ... not that far from the mark ... except in this case BS 7430 tells you that you should connect an earth electrode to the MET so the "single class I item" is in fact referenced to terra-firma ... and the MET should also be connected to the neutral of the generator.

    The same sorts of considerations apply to a mobile & transportable unit, but in this case it may be acceptable (if the generator is not touching or otherwise connected to Earth, and no leads will be run outside the unit to power equipment outside) to not use an earth electrode (although this is usually preferred anyway).

    If using the system as a switched alternative to the grid, ESQCR requires isolation of live conductors from the grid, and that the installation as a whole must comply with BS 7671. Additionally, BS 7671:

    (a) prevents duplication of N-E connections in the consumer installation (this may well trip RCDs anyway); and

    (b) has conditions about switching of protective conductor arrangements and timings.

    Hence, a switching mechanism as I described earlier is required.

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines