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Thread: Commercial Load Calculations

  1. #1
    Join Date
    Feb 2005

    Commercial Load Calculations

    I have a worksheet that takes me through 8 steps of doing a load calculation for a commercial building, with the code references for each step including the specific tables (and then references for sizing the neutral and ground).

    This sheet is about 12 years old or more and all of the code tables and code references have changed, so the sheet is no longer relevant. I was asked to do a load analysis as a favor for my church and can't seem to find the necessary resources for doing this. It was second nature 16 years ago when I worked as a journeyman, but I have changed industries and have forgotten the steps.

    If anyone can email me a worksheet that would assist me I would be eternally grateful, they need me to do this by the end of the day tomorrow. Thank you!

  2. #2
    Join Date
    Feb 2003

    Re: Commercial Load Calculations

    This is not an all-inclusive procedure for sizing a service to a non-dwelling occupancy. Please reference Article 220 for exact code specifications.

    STEP 1 Use Table 220.3(A) (2005-220.12) and multiply lighting load va to total square footage. Feeder conductor at 125% for continuous load.

    STEP 2 Demand load for motel, hospital, warehouse. (Table 220.11) (2005-220.42) All others at 100%.

    STEP 3 Compare heat with A/C. Omit smaller. (220.21) (2005-220.60)

    STEP 4 Heavy-duty lampholders at 600va each. (220.3(B)(5)) (2005-220.14(E))
    Other outlets at 180va each. (220.3(B)(11)) (2005-220.14(I))
    Multioutlet assemblies each 5-foot at 180va each. (220.3(B)(8)) (2005-220.14(H))
    Show window lighting each linear foot at 200va each. (220.3(B)(7) (2005-220.14(G))

    STEP 5 Demand for receptacle loads over 10kva. (220.13) (2005-220.44)

    STEP 6 Demand for kitchen equipment. (Table 220.20) (2005-220.56)

    STEP 7 Largest motor increased by 25%. (220.14) (2005-220.50)

    STEP 8 Size the service by dividing the total va by the applied voltage. Use Table 250.66 to size grounding conductor. (It cannot be smaller than the neutral)
    Bryan P. Holland, MCP
    NEMA - Codes & Standards

  3. #3
    Join Date
    Nov 2004
    Las Cruces N.M.

    Re: Commercial Load Calculations

    I have a worksheet that I have used to teach load calcs with. You can use it for reference if you choose. Send me your e-mail adress in a personal message, and I'll send it to you.
    Jim T

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