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Over load relay

    • 43 posts
    December 21, 2019 12:45 PM PST

    Does it make sense to use over load relay on non motor feeder?

    • 72 posts
    December 21, 2019 12:57 PM PST

    The purpose of an overload relay is to change the state of a control most applications are in control circuits. Please note that the overload relay is not same as an over current protection device.


    This post was edited by Reynaldo Danilo at December 21, 2019 12:59 PM PST
    • 103 posts
    December 22, 2019 2:17 PM PST

    Overload protection for motors is not considered overcurrent protection for a feeder or a branch circuit & would not be code compliant.

    Overload protection for a motor would be applied on the motor end of the feeder, where it would provide protection for the motor. An overcurrent device would be applied at the opposite end & provide protection for the feeder conductors.

    • 75 posts
    January 5, 2020 12:44 PM PST

    Following Reynaldo's and Steve's posts:

    A over load is considered a Thermal Device.  If you are under the NEC, Article 240.9 appies:

    240.9  Thermal Devices.   Thermal relays and other devices not designed to open short circuits or ground faults shall not be used for the protection of conductors against overcurrent due to short circuits or ground faults, but the use  of such devices shall be permitted to protect motor branch-circuit conductors from overload if protected in accordance with 430.40.

    So, only in a motor branch circuit.

    Now, that being said, I have had some pretty bright, knowledgeable sorts tell me that a motor starter bucket in an MCC, containing a CB, contactor, overload, can be used to feed a non-motor load.  One just has to set the overload high enough the CB trips first on a short circuit.  And, of course, pick the right CB rating.

     

    Two issues with that I have run into:

    1.  ninety-nine (point) nine percent of all the motor starter buckets that I deal with are a listed combination starter with a mag-only CB.  So that is not going to work with a non-motor load.

    So, one picks a bucket with a TM CB.  And installs the highest possible overload

    2. I'm curious - how do you know the CB will trip before the overload?

    My choice is to get the right bucket - TM CB and a contactor, no overload.


    This post was edited by Carl Coulter at January 5, 2020 12:44 PM PST