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Thread: Elevator Overcurrent Sizing

  1. #1
    Join Date
    May 2003
    Posts
    20

    Elevator Overcurrent Sizing

    I am doing a design for a building that is to have an elevator in it. The elevator manufacturer gave me two amp values for the elevator (which is 208 3 phase): 121 Amps running current, and 278 Amps starting current. I asked the rep if the overcurrent device, conductors, et al had to be sized for the running or starting amps, he said starting. This does not seem to agree with NEC, and it is a big difference in equipment cost. Can anyone clear this up for me?

  2. #2

    Re: Elevator Overcurrent Sizing

    Table 430.52 of NEC says that OCD for inverse time delay breakercan be sized to 250% of motor nameplate. 121 amps x250%= 302.5. This means that a 300 amp breaker would satisfy the start amps AND fit within NEC requirements. Kep in mind that elevators typically require a shunt trip style breaker controlled by a heat detector in the machine room. Check with your local AHJ for specific requirements.

  3. #3
    Join Date
    May 2003
    Posts
    20

    Re: Elevator Overcurrent Sizing

    I appreciate the response. I know that I can do it this way and satisfy both NEC and the installer, however, does the NEC require that I do it this way by sizing for the starting current?

  4. #4

    Re: Elevator Overcurrent Sizing

    (B) All Motors. The motor branch-circuit short-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor.(NEC 430-52b)
    Yes, your eqipment does have to be sized to carry the starting current. You could, with most motors, use a 175% sized fusible disconnect switch and fusses. The shunting issue is what makes me go to the breaker for elevator circuits.

  5. #5
    Join Date
    May 2003
    Posts
    20

    Re: Elevator Overcurrent Sizing

    Ok, I understand. Thanks.

  6. #6
    Join Date
    Feb 2003
    Location
    Massachusetts
    Posts
    49,054

    Re: Elevator Overcurrent Sizing

    darren71

    Do not forget that even with a 300 amp breaker your feeder conductors can be sized by the running load per the tables in 430. (430.6(A)

    So you could use (approximately) 1/0 AWG to cover your 121 amp running load and still land these on the 300 amp breaker.

    Breakers for motors are not overload protection, just short circuit and groundfault protection.

    Bob

  7. #7
    Join Date
    Mar 2003
    Location
    Pennsylvania
    Posts
    1

    Re: Elevator Overcurrent Sizing

    Look at example D9 or D10 in annex D of the 2002 NEC it might help you out it gives code references I fine these examples to be invaluable training aids.

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