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Thread: Sizing of Wireway & size of conductors in wireway

  1. #1
    Join Date
    Jun 2014
    United States

    Sizing of Wireway & size of conductors in wireway

    Three 100A 120/208v, 48P MLO panelboards to be fed from one 75kVA transformer. 48P with all 1P/20A CB. Branch circuits from these panelboards will go out of a pre-cast windows of size 40”W x 20”H. We have 3 other high voltage 18P panelboards for lighting and mechanical equipment, these branch circuits to use the same shear opening.

    Utilize existing shear wall opening to route branch conduits out to the space. No new opening allowed.
    Coordinate with mechanical contractor for location of exhaust duct size 12”x14”.
    All circuitry shall be installed in EMT. Conductors, no. 10 AWG and smaller, solid copper.
    All multiple circuit homeruns shall be provided with #10 AWG neutral Conductors. Contractor shall comply with wiring requirements of New York City Electrical code, table 310.15(b)(2)(a) for adjustment factors associated with more than three current carrying conductors in a raceway.
    Utilize #10 AWG, Solid conductors, for all homeruns containing 4 or more current carrying Conductors.
    Contractor shall limit maximum current carrying conductors to 9 per conduit. Neutral conductors utilized in 120v single phase circuits and shared between two (2) 120v, single phase circuits are defined as current carrying.

    When asked to relax the 9 CCC rule to 12 CCC, we were told to de-rate #10 to #8.

    Main concern is branch home-runs out of the shear opening for the (3) 48P panelboards.

    Option #1
    Run one 12”x6” wireway for all 3 panelboards combined with approx. 312 #8 Cu THHN. All 3 panelboards are fed from the same source, so no partition required.

    Option #2
    Run one 6”x6” wireway for Each of the panelboards with 104 #8 Cu THHN (48H + 48N + G) in each wireway

    Option #3 (last resort)
    We can run about 12 conduits per 120/208 panelboards (4+4 +G), total (36) 1” conduits. (1” over 3/4" due to use of #10 solid conductors).

    My questions are for each of the options #1 & #2

    1. Is this allowed per code?
    2. Do I need to de-rate? If yes, how much?
    3. How to apply 310.15(b)(2)(a) for adjustment factors?

    Thank you All.

  2. #2
    Join Date
    Jul 2003
    New Jersey
    Options 1 and 2 may not work if you have multiple receptacles on any circuits since your #8 conductors are too small after derating for more than 30 CCC's in a wireway. {55 amps * 35% = 19.25 amps}

    Option #3 is OK.

    IMO #10 solid conductors in raceways are just plain stupid.


    All responses based on the 2014 NEC unless otherwise noted

  3. #3
    Join Date
    Jun 2014
    United States
    Thanks infinity.

    Sent from my Nexus 6P using Tapatalk

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