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    alpha1955's Avatar
    alpha1955 Posts: 2, Reputation: 1
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    #1

    Sep 24, 2013, 07:11 PM
    Connecting a three phase emergency generator to a transfer switch
    Is it required to connect the neutral from the emergency generator to the neutral at the transfer switch.
    hfcarson's Avatar
    hfcarson Posts: 1,003, Reputation: 49
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    #2

    Sep 25, 2013, 04:30 AM
    ... "Required?" what if the load does not have a neutral?
    Typically yes, if the service has a neutral it needs to be connected through the transfer... Could the question be more specific?
    sinnadurai's Avatar
    sinnadurai Posts: 127, Reputation: 2
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    #3

    Sep 25, 2013, 10:41 PM
    Consider the earthing system of the installation(TT,TN-S,TNC-S etc)
    alpha1955's Avatar
    alpha1955 Posts: 2, Reputation: 1
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    #4

    Sep 26, 2013, 08:37 PM
    Quote Originally Posted by hfcarson View Post
    ..."Required?" what if the load does not have a neutral?
    Typically yes, if the service has a neutral it needs to be connected through the transfer...Could the question be more specific?
    The normal source provided by the utility company is a 3 phase 4 wire 240 volts, and its neutral is grounded at the normal source main disconnect. The transfer switch has an isolated neutral connection lug and the grounded neutral from the normal source service disconnect is wired to this lug. The emergency source (generator power) neutral is connected to the isolated neutral lug at the transfer switch, but there is no bonding connection from the isolated neutral lug to the transfer switch metal enclosure.
    I have several questions; do I need to bond the transfer switch metal enclosure to the isolated neutral lug? It is required to ground the chassis of the generator to a ground rod at the generator site or the neutral from the generator to the transfer switch isolated neutral ground is enough for grounding the generator chassis.

    Thanks for your help
    hfcarson's Avatar
    hfcarson Posts: 1,003, Reputation: 49
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    #5

    Sep 30, 2013, 04:14 AM
    In most cases the neutral of a service is only "grounded" or bonded to ground "once". There are a few reasons this "bond" should only happen one time. So unless the generator is a separately derived system, there should only be "one" bond. In this case the generator neutral and ground "should not" be bonded.

    If the generator is set up as a separately derived system, then you would bond neutral to ground and establish a grounding electrode system. The rules for this in detail are found in the electrical code articles 700, 701, 702 and 705 among others.
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