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Fixed diesel generator earthing

D4G
Hi folks, i'm after your knowledge again!


I have a 184KW diesel generator which is to supply a test bay for testing machines to big for the building supply.  The generated supply will not be used/connected to the building supply.

Would the earthing arrangements be as TT with a rod at the generator connected to the neutral/star connection?


Thanks in advance ?
  • 0
    It would usually have it's own rod connected to the star point & PE to the building - making it TN-S.

       - Andy.
  • 0
    Yes. BS 7430 says an electrode with an earth resistance of 20 ohms or less.


    Make sure the star point neutral is connected to the frame and the earth electrode.
  • 0
    Thanks for the speedy replies gents.


    Its an old unit with MCCB in the main panel, does this need to be RCD protected or is RCD protection at the switch gear in the test bay fine?
  • Former Community Member
    0 Former Community Member
    D4G:

    Hi folks, i'm after your knowledge again!


    I have a 184KW diesel generator which is to supply a test bay for testing machines to big for the building supply.  The generated supply will not be used/connected to the building supply.

    Would the earthing arrangements be as TT with a rod at the generator connected to the neutral/star connection?


    Thanks in advance ?


    Hi, do you have a link to the generator manufacturers instructions available?


  • Former Community Member
    0 Former Community Member
    Photographs/ descriptions of the test bed area, type of equipment being tested, generator position,  etc may also help?
  • 0
    At the generator I would connect together all the following

    Alternator star point.

    Frame or enclosure of the machine.

    One or more local earth rods.

    Outgoing neutral conductor to load.

    Outgoing earth conductor to load.

    Any nearby building metalwork or pipes etc.

    A suitable bonding conductor to the MET of the existing installation. (Unless the existing DNO supplied installation is so distant as to render this irrelevant)


    The supply from the generator to the load will therefore be 5 wire, with a seperate neutral and earth, so as to resemble a public supply of type TN-S.
  • 0
    Not to hand, I am looking into this though...
  • 0
    Equipment being tested is generally screw compressors,

    Test area is just a section of an industrial unit, so inside on a concrete floor, Brick walls so no exposed metalwork, water supply is non conductive.

    Generator is outside the other side of the wall...
  • 0
    broadgage:

    At the generator I would connect together all the following

    Alternator star point.

    Frame or enclosure of the machine.

    One or more local earth rods.

    Outgoing neutral conductor to load.

    Outgoing earth conductor to load.

    Any nearby building metalwork or pipes etc.

    A suitable bonding conductor to the MET of the existing installation. (Unless the existing DNO supplied installation is so distant as to render this irrelevant)


    The supply from the generator to the load will therefore be 5 wire, with a seperate neutral and earth, so as to resemble a public supply of type TN-S.


    Thanks, this is along the lines of what I was thinking.

    I was unsure about connection to the MET as I thought I read somewhere not to do this? There again if I bond to anything which is bonded to the MET then thats pretty much the same thing!

    RCDs??


  • 0
    The genset should be able to operate its own ADS in a suitably safe time against credible failure modes - if the non RCD cables are armoured, and the armour is properly earthed, then you probably will not need to add an RCD, at least for anything that can be considered to work like a sub-main - the idea is that any damage to the cable connects to the earthed armour first.

    At the load end, it rather depends how it is being used. Test rig sounds like cables get connected and disconnected fairly often so  a faulty connection, or a missing earth, or indeed just a defective unit under test, may be more likely than in a normal fixed installation. Clearly if you are supplying sockets and or  portable kit as well, then these need RCD cover, but that maybe just for a smaller sub section of the system.

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