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Thread: Elevator Breaker Size

  1. #1
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    Feb 2010
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    Elevator Breaker Size

    Hello Everyone,

    Im sizing a breaker for a 20HP elevator motor (208Y-3) I have a chart with the elevator electrical specifications, with the following info:

    Rated AC amps: 65.1 amps
    Solid State, min-max : 130-293 amps

    Motor AC amps: 91 amps
    Control Amps: 4 amps

    So basically my total amps is 95 amps, would I be OK to put this on say 150A breaker? What scares me is the solid state amps. Any opinions would be helpful, thanks.

  2. #2
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    Feb 2010
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    No replies yet :-(

    Im looking at 430.52 A & B, I suppose im having a hard time interpreting it. It says I can size the breaker at 150% - 300% of the motor FLC.

    So assuming my FLC is 95 amps, that would equate to 150A breaker through a 300A breaker. Pretty large jump there..

  3. #3
    Join Date
    May 2007
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    Westminster, MD
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    ...alright NP, I'll chime in.
    Cable size: I'd go 140% of the 430.250 table fla of 59.4 =
    83 amps: #3 or #4 depending on the length. (I say #4 because of their 91 amp max ac rating)
    It looks like - from the numbers you're showing - that it could run into a high service factor, such that 125% wouldn't get it.
    As far as 430.52, max rating - as you've stated you can go to 300%. Your overloads will protect the cable at its ampacity, so this is just for GF/SC protection.
    The issue will be whether or not the motor can start under the curve of this breaker. I'd suggest that if the panel can fit the larger breaker, go with the largest one that meets 430.52. The namplate info suggests 293 amps inrush, which your 150 amp thermal mag breaker may or may not tolerate for the duration of the motor start. I don't think elevator motors have signiifcant inrush, so the 150 may work, but you'd have to plot it against the elevator controller's Motor Circuit protector or breaker.
    I suggest going to the NEC max though to permit the elevator controller to act first.
    John M
    Last edited by mayanees; 05-27-10 at 01:06 PM.

  4. #4
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    Thanks for the reply :-)

    I think I will go to a 200A thermal magnetic breaker and feed a non-fused disconnect in the elevator machine room to power the elevator alone. I know I can go to a 300 A breaker but the wire size will make the run more expensive. SOund OK?

  5. #5
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    NP,

    The elevator motor overloads will provide ampacity protection for the cable.
    I believe it's an assembly that's treated as a single motor, so you can just run the required ampacity at 91 amps, treating the main cb as short circuit/gf protection, which lets you get to the 300% level.

    Remember that an unfused disconnect switch is only good for 10 kAIC, so you should make sure that requirement is met.



    John M

  6. #6
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    Quote Originally Posted by Npstewart View Post
    Thanks for the reply :-)

    I think I will go to a 200A thermal magnetic breaker and feed a non-fused disconnect in the elevator machine room to power the elevator alone. I know I can go to a 300 A breaker but the wire size will make the run more expensive. SOund OK?
    I think you'd be limited to a 175A circuit breaker. It appears to me that the 20HP motor has a FLC of 65.1Amps, and I guess that the "Motor AC Amps" is the FLC of the motor multiplied by 140% as defined in Table 430.22(E) for an Intermittent duty elevator using a continuous rated motor (65.1Ax1.4=91.1A.)

    The elevator branch circuit OCPD device (per 620.61(D)) would be sized per Article 430, Part IV. Per 430.53(B), for a motor and additional load, the OCPD would be selected using table 430.52, which allows a max breaker size of 250% (not 300%) which can be upsized to the next higher standard ampere rating.

    65.1Ampsx250%=162.75Amps, for which 175A would be the next higher standard size. So you should have conductors with a min. ampacity of 95A (91 for the motor plus 4 for the controller) and a max c/b of 175A.

    I'm not sure what the "solid state amps" would be, but my initial impression was that it would be volts. It seems to be close to 208V +/- 40%.

  7. #7
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    David, I think you finally made sense of that section for me. That entire section is a mess in my opinion. I really don't like having a conductor rated for 91 amps protected by a 175A breaker! But I know in cases such as this it is permitted. Given your interpretation I will go with 175A breaker, and most likely a #2/0 to match the over current protection of 175 amps. If anyone asks I will say its for voltage drop :-)

  8. #8
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    Quote Originally Posted by Npstewart View Post
    Thanks for the reply :-)

    I think I will go to a 200A thermal magnetic breaker and feed a non-fused disconnect in the elevator machine room to power the elevator alone. I know I can go to a 300 A breaker but the wire size will make the run more expensive. SOund OK?
    Npstewart,

    Don't you have the "Elevator Machine Room" electrical lay out ? It will tell you exactally

    what 'they' want, and where they want it located. Lately they have been specing out a

    combo 'shunt trip / disconnect / assecessory package ' unit.
    Frank Arizona,USA

  9. #9
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    Feb 2010
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    No, I only have a spec package, but no machine room layout :-(

    That's a good point though, I have a contact at the elevator company (thysen krupt)

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