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Thread: Motor Overload Protection

  1. #1

    Motor Overload Protection

    Some times I see other electrical devices being feed off the motor/overload terminals of a motor starter. NEC article 430 only addresses overload usage with motors.

    I have not come across any manufacture specifications that says it is permissible to size overloads with other electrical devices or controls. It has always been my understanding overload protection on a starter is for individual motor protection.

    Are some doing this because the informational materials don’t actually say nothing else can be connected to the overloads with the motor? Also what is UL and OSHA impact on this?

  2. #2
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    overload taps

    Quote Originally Posted by Wire_nutz View Post
    Some times I see other electrical devices being feed off the motor/overload terminals of a motor starter. NEC article 430 only addresses overload usage with motors.

    I have not come across any manufacture specifications that says it is permissible to size overloads with other electrical devices or controls. It has always been my understanding overload protection on a starter is for individual motor protection.

    Are some doing this because the informational materials don’t actually say nothing else can be connected to the overloads with the motor? Also what is UL and OSHA impact on this?
    In my old water utility job we would only tap above the overload to supply power to a relay or other small current device. This was only done if that device( by means of other detection) would stop during a motor overload. IE: chemical pumps tied into a well motor starter. It was a rule passed down from the board of health. I don't know if our situtation originated from NEC or OSHA.

  3. #3
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    Poor practice?

    If you add non-motor related devices below the overload then 430 part III doesn't let you increase the size of the overload for them. 430 part III calculations limit the overload size to that required by the motor circuits.
    A rose by any other name is tax deductible [1978 Wayne Wilcox]
    People who read too many books get quirky. [2000 John Taylor Gatto]

  4. #4

    Moderators please feel free to offer your input.

    I am not getting much help here. Moderators please feel free to offer your input.


    The NEC doesn’t say no other loads other than a motor may be connected to the motor terminals of a starter with a motor. The NEC does not say other devices shall not be connected on the ‘T’ terminals of a motor starter with a motor.

    Motor starter manufacture starter specifications only mention motors connected to a motor starter with overloads.

    Since the NEC does not say shall not, and the manufacture literature does not say you can not have other devices on the motor terminals with overload protection. Does this make it OK? Apparently people are doing it?

  5. #5
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    I am not aware of anything in the NEC that specifically prohibits connecting other loads to the load side of a motor starter after the motor overloads.

    The biggest problem will be that the motor overloads must be sized at no more than 115% or 125% of the motors nameplate rating. This would make any load added after the motor overloads to either be very small or cause the motor overloads to trip. (Check out Part III of Article 430 for motor overload protection)

    Chris

  6. #6
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    Everything depends on the overcurrent device protecting the motor starter, the overloads have nothing to do with it. The protective device must meet and be sized under the requirements of Article 240.

    Table 240.4(G) grants an exception for motor circuits, not for motor starter overload relays. If the conductors do not feed motors article 430 is not applicable per 430.1.
    Just because you can, doesn't mean you should.

  7. #7

    Design Intension

    Does the NEC require overload protection for motors? The specific size of the overload to be used is based on the current draw of the motor. By adding another electrical device on the same terminals as the motor would interfere with the sizing of the overload.

    Combination motor starters are intended for a motor load and controls. The manufactures of the starters provide auxiliary contacts and control relays for the use of other electrical devices and are not connected to the motor over load terminals.

    Normally most electricians use and wire a motor starter as intended by the manufacture. Is there any documentation by UL or OSHA or some other standard that a piece of electrical equipment must be used as it attended or designed for?

  8. #8
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    Your making a big deal over nothing. As long as the overload is sized according to the nec who cares. It then becomes a design issue which the nec doesnt cover most of the time. If these people want to take a chance on nuisance overload tripping then let them.
    To answer your question, I to not know of anything that would say you could not do this.

  9. #9
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    Quote Originally Posted by Wire_nutz View Post
    Does the NEC require overload protection for motors?
    Yes, check out Part III of Article 430

    The specific size of the overload to be used is based on the current draw of the motor.
    Correct

    By adding another electrical device on the same terminals as the motor would interfere with the sizing of the overload.
    The NEC would require that the overload for the motor be sized off the motor nameplate FLC rating and you would not be permitted to increase the overload size for additional loads.

    Combination motor starters are intended for a motor load and controls. The manufactures of the starters provide auxiliary contacts and control relays for the use of other electrical devices and are not connected to the motor over load terminals.

    Normally most electricians use and wire a motor starter as intended by the manufacture. Is there any documentation by UL or OSHA or some other standard that a piece of electrical equipment must be used as it attended or designed for?
    110.3(B) requires us to follow the installation instructions for a listed piece of equipment.

    Chris

  10. #10
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    Quote Originally Posted by Wire_nutz View Post
    Normally most electricians use and wire a motor starter as intended by the manufacture. Is there any documentation by UL or OSHA or some other standard that a piece of electrical equipment must be used as it attended or designed for?
    Normally? I am not sure you can speak for what most electricians do.

    Quote Originally Posted by raider1 View Post
    110.3(B) requires us to follow the installation instructions for a listed piece of equipment.
    I agree but will be very surprised if there is anything in the listing that prohibits other loads.

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