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-   -   How to calculate the number of lighting poles (https://www.askmehelpdesk.com/showthread.php?t=149470)

  • Nov 7, 2007, 08:44 AM
    paapa94
    How to calculate the number of lighting poles
    Here is the question:

    "How many 120V, two wire, 20 ampere branch circuits are required to supply

    52 parking lot lights, which are rated 500va each and are continuous loads?"


    I am getting ~ 14, but the answer in the book is 18

    Can you help?
  • Nov 8, 2007, 07:31 PM
    caibuadday
    Quote:

    Originally Posted by paapa94
    Here is the question:

    "How many 120V, two wire, 20 ampere branch circuits are required to supply

    52 parking lot lights, which are rated 500va each and are continuous loads?"


    I am getting ~ 14, but the answer in the book is 18

    Can you help?

    Don't you have to derate it ; you get 18
  • Nov 17, 2007, 06:05 AM
    tkrussell
    52 lights at 500 VA=26000 VA / 120 Volts = 216.67 total amps

    A 15 amp circuit with a continuous load must be derated 80%, so the max load allowed on a 15 amp circuit is 12 amps.

    216 / 12 = 18 circuits

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