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Thread: Generator - link N - E and earth leakage

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    Generator - link N - E and earth leakage

    Hi all
    I'm sure this is right but want confirmation. I have a generator with 4 pole automatic change over. There is an 80 amp 3 phase breaker coming from the generator (in the control panel) before it goes to the change over. I have come from the main switch in the DB (150 amp MCCB) through 100 amp 3 phase breaker (6kA), then to the generator in 35mm 4 core with 25mm CPC. to the change over. I added an E/L next to the 80 breaker in the generator control panel and N-E are linked before the change over (so the E/L operates). Also have the Earth spike coming from the earth point on the generator (2 x 1.5 meter rods end to end, so 3 meters into the ground).

    I have a split neutral bar (as 2 circuits in db through Generator). Main incoming neutral goes to 1st neutral bar from there it goes to generator and is the neutral point for the 2 circuits which are not to be generator supplied. The second neutral is fed from the generator and feeds the bus bar to which all generator supplied items go back to.

    Site guys doesn't like it? Haven't found out why yet but I can't see any thing wrong. Its as per the SANS book (diagrams on back page).

    With the 4 pole change over there is no way 2 N-E links can be connected to board at one time and i have the split neutral bars.

    Anything anyone can see wrong with that. I want to know if i have missed something before the meeting.

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    Diamond Member AndyD's Avatar
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    These generator installs can get a bit tricky depending on what the existing layout is. I'm trying to picture the entire layout in my head, maybe can you attach a sketch of the existing supply and DB layout including the earthing arrangement also the changeover switch and the genny supply.

    Just out of interest what's the Ra of your new rods? I'm assuming the existing earthing arrangement is TN C S, is it PME'd with an existing rod elsewhere on the premises?
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    There is a mini sub which feed a feeder cabinet. The feeder cabinet has a 600amp MCCB as the main switch for the property. From that 3 x 250 amp MCCB feed 3 sub DB's in the 3 buildings. One of the sub DB's is to have a standby generator. The Sub DB in question has 150 amp MCCB as the sub-main switch. From the load side of that MCCB it goes to a 100 amp MCB which then goes to the generator and through the change 100 amp change over and back to a 3 pole 100 amp isolator (labelled as required) before going to the bus bars of the DB supplying the circuits feeding breakers covering various parts of the board. The neutral coming into the board goes to a 250 amp connector block (the type where a 95mm cable goes in and you can connect 2 x 35 and 4 x16 mm etc) and goes out to the generator. When it come back to the DB board it goes straight to the neutral bus bars (separate neutral bar, one the 250 amp connector and the other the neutral bus bar)
    The neutral in the terminal in the generator panel (above the alternator)is linked to the earth of the generator via an earth point in the same terminal box. From there it goes through an 80 amp breaker, through a 80 amp 30 mA earth leakage before going to the change over switch (4 pole automatic type).

    Also on the load side of the 150 amp MCCB sub main switch a 50mm will go to another DB right next to the Generator supplied board. There was a large machine (60 amps per phase) in the generator board which is to be put in a separate board as the generator hasn't got the capacity to run it. They are just interested in keeping the lights and sockets running. The large machine will now be fed from a separate breaker in an adjacent board.

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    Site Caretaker Dave A's Avatar
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    Quote Originally Posted by skatingsparks View Post
    I added an E/L next to the 80 breaker in the generator control panel and N-E are linked before the change over (so the E/L operates). Also have the Earth spike coming from the earth point on the generator (2 x 1.5 meter rods end to end, so 3 meters into the ground).
    Quote Originally Posted by skatingsparks View Post
    The neutral in the terminal in the generator panel (above the alternator)is linked to the earth of the generator via an earth point in the same terminal box. From there it goes through an 80 amp breaker, through a 80 amp 30 mA earth leakage before going to the change over switch (4 pole automatic type).
    One thing you haven't mentioned - Is this main earth point of the generator supply also connected to the earth system of the installation?
    The trouble with opportunity is it normally comes dressed up as work.

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    Quote Originally Posted by Dave A View Post
    One thing you haven't mentioned - Is this main earth point of the generator supply also connected to the earth system of the installation?
    Yup. 25mm Single GRN/YEL run with the SWA cable back to the Generator backed up DB. Also Earth spike installed 2 x 2.5 meters(1 x 1 meter and 1 x 1.5 meter coupled together)

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    All sounds good so far.

    Have you found out why "the site guys" don't like it yet?
    The trouble with opportunity is it normally comes dressed up as work.

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    Quote Originally Posted by Dave A View Post
    All sounds good so far.

    Have you found out why "the site guys" don't like it yet?
    Yup, I beat there quote by quite a lot and got the job. A Master electrician came around gave it the thumbs up as well so all is good.

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