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    guyhood's Avatar
    guyhood Posts: 15, Reputation: 1
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    #1

    Feb 11, 2007, 02:19 PM
    Electrical & lighting
    How many 400 watt Halide Light fixtures should I put on a 20 amp 120 volt circuit. Four?
    Thanks, Guy
    Peter Kwan's Avatar
    Peter Kwan Posts: 26, Reputation: 1
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    #2

    Feb 11, 2007, 06:42 PM
    The 20 AMP breaker usually only rated about 80% of full capacity, therefore, the calculation is:

    20 amp * 120 V * .8 = 1920 Watt

    1920 /400 = 4.8

    You are correct.
    tkrussell's Avatar
    tkrussell Posts: 9,659, Reputation: 725
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    #3

    Feb 12, 2007, 03:38 AM
    Need to be aware that a 400 watt Metal Halide fixture draws more than 400 watts, anywhere from 430 to 480 watts, due to the ballast load. So better to use the rated amperage draw of each fixture to calculate how many fixtures on a circuit.

    With the four you have still fits on a circuit, even at 480 watts each, just be aware of the total load if more are needed.
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