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Thread: Load Calculations for Existing Panelboard

  1. #1
    Join Date
    Sep 2003
    Boulder Colorado

    Load Calculations for Existing Panelboard

    Can someone advise me on Article 220.60. I have 4 Dock doors & 4 Dock Ramp levelers on separate circuits. 2 are used for 5 minute intervals about 3 times each day. The one at shipping & one at receiving. Can I use 220.60 in calculating the load for an existing Panelboard. To get a permit for a 20 amp circuit the authority wants a load calculation for the Panelboard. Can I use 1 of the opener & ramp or do I have to use all 8 circuits in my calculation? Thanks Ron

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  2. #2
    Join Date
    Dec 2008
    In my opinion, if all 8 branches supply motors then art.220.50 it is more suitable.

  3. #3
    Join Date
    Feb 2003
    Seattle, WA
    First step: Count all 8, including the largest at 125%. Then add the rest of the loads on the panel. Is there enough remaining spare capacity to handle one more 20 amp circuit? If so, submit it that way, and call it good.

    Second step: If the above process yields a calculated load higher than the rating of the panel, then you need to make some assumptions. If a motor runs for only 15 minutes a day, then I believe you can make a case for non-coincident loading with other motors.
    Charles E. Beck, P.E., Seattle
    Comments based on 2017 NEC unless otherwise noted.

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