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Thread: Standby Generator

  1. #1
    Join Date
    Aug 2015
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    3

    Default Standby Generator

    I have inherited a surplus military generator that puts out 60KW 240V 3 Phase power. I had a manual transfer switch installed when my house was wired and wish to see about hooking up this generator. What are the do's and don'ts of connecting to two legs of 3 phase power for 240V house current?

  2. #2
    Join Date
    Feb 2012
    Location
    Lala land, OH
    Posts
    244

    Default

    Dont....until you know it's going to work.

    First, being military surplus... is it 60hz? Double check, some military stuff is 400hz.. Fast way to ruin electronics.

    What is the 3 phase config? (delta/wye) Is there a neutral?

    Your house is split single phase (NOT 2 phase) and it is not directly compatible with 3 phase. You may need a phase converter (big transformer) to make it work or work with the full capacity of the generator. A big one will be expensive.
    Last edited by Mr T; 08-28-2015 at 06:35 PM.

  3. #3
    Join Date
    Aug 2015
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    Default

    I know the generator is 60hz. Is there a way to determine 3 phase config and if it has a neutral?

  4. #4
    Join Date
    Feb 2012
    Location
    Kent, WA
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    243

    Default

    What type of output does it have -- normal receptacles, a cable whip, terminal blocks, ...? You need to see if there are 3 or 4 wires (plus maybe a 5th for ground). Once you find the output, you need to run the generator and measure the voltage between all the terminals. This would be suitable for household use, but some of the things that use 240V would be slower to work (e.g. water heaters, electric ranges), and things with motors may or may not work (e.g. if an air conditioner says 208/240V, it will work. If it says 230V, it most may not work or could be intermittent).

    A wye generator will have 4 terminals and be 208V phase to phase (3 pairs of wire will have this value -- AB, BC, CA) and 120V phase to neutral (again 3 pairs will have this AN, BN, CN).

    A delta generator will have at least 3 terminals and be 240V phase to phase (AB, BC, CA). They are usually corner grounded and have no neutral. This won't work for you except for pure 240V loads like baseboard heating and water heaters and even then it is problematic because of grounding (it is 240V to ground instead of 120V). You'd need a transformer to make it suitable for household use.

    If there is a 4th neutral terminal, it may be suitable for residential purposes and you'll get 120V from 2 phases to neutral (e.g. AN, BN) and 208V from the 3rd phase to neutral (CN). In a jurisdiction under the NEC (which the military is not), that phase C would be called the high leg and be colored orange. You then just connect A, B, and N to your house and not use the high leg.

    Inheriting this generator may be more trouble than it is worth.
    Mark
    Kent, WA

  5. #5
    Join Date
    Aug 2015
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    Thanks Mark for all your information. It has 4 four terminal blocks (with one marked neutral) and is configured in "wye". You have been most helpful! Bob

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