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Thread: Machinery electrical hookups

  1. #16
    Join Date
    Nov 2003
    Location
    Central North Carolina
    Posts
    1,830
    On larger plugs with arc shields we drilled a hole in the edge of the arc shield for a padlock to lock them out. Some of the smaller twist locks have a small hole in the ground pin that we enlarged to be able to use a small padlock through it. In either case, the padlock prevents the plug from being inserted. Add the lockout tag and it complies. If the disconnected plug on smaller equipment is in full view by the person servicing the equipment a lockout is not required. Unplug the machine and tape the plug to the machine cabinet in full view and you have complied. If the machine will be left unmanned for any time, it's best to lock the machine off with a lockable container for the plug, unless a lock can be applied to the plug as above.

    Charley

  2. #17
    Join Date
    Jul 2005
    Location
    Eastern Iowa
    Posts
    751
    Quote Originally Posted by Rollie Meyers View Post
    A plug/receptacle used for a disconnect is required to be rated for the HP of the equipment, for motors above 3 HP, they are super expensive making a safety switch pretty economical in comparison, pretty much of all the cord & plug connected single phase 5 HP equipment does not meet code. 430.109(F)
    NEC wrt motors is an entirely different animal. You must account for ground fault protection, short circuit protection, and over-current protection. All at the same time.
    .... AND make sure that the over-current protection allows the motor to start .... at maybe six times its running amps.
    Each part has its own table to determine conductor size and circuit breaker or fuse size, and sometimes it can lead to weird pairings... a 14g wire on a 30 amp breaker, for instance.
    Comments made here are my own and, according to my children, do not reflect the opinions of any other person... anywhere, anytime.

  3. #18
    Join Date
    Jul 2005
    Location
    Eastern Iowa
    Posts
    751
    Quote Originally Posted by Charles Lent View Post
    On larger plugs with arc shields we drilled a hole in the edge of the arc shield for a padlock to lock them out. Some of the smaller twist locks have a small hole in the ground pin that we enlarged to be able to use a small padlock through it. In either case, the padlock prevents the plug from being inserted. Add the lockout tag and it complies. If the disconnected plug on smaller equipment is in full view by the person servicing the equipment a lockout is not required. Unplug the machine and tape the plug to the machine cabinet in full view and you have complied. If the machine will be left unmanned for any time, it's best to lock the machine off with a lockable container for the plug, unless a lock can be applied to the plug as above.

    Charley
    The lockout is good, but it is that arc shield that gives the plug it's hp rating. A disconnect must be able to safely interrupt power from the motor. Motors are just generators backwards. A spinning motor can sustain an arc when disconnected. so, arc shields, enclosed pin and sleeve, spring disconnect, whatever to contain/control the arc.

    Edit: as Rollie said, switch is easier
    Last edited by Charlie Velasquez; 09-19-2020 at 8:50 PM.
    Comments made here are my own and, according to my children, do not reflect the opinions of any other person... anywhere, anytime.

  4. #19
    Quote Originally Posted by Charlie Velasquez View Post
    NEC wrt motors is an entirely different animal. You must account for ground fault protection, short circuit protection, and over-current protection. All at the same time.
    .... AND make sure that the over-current protection allows the motor to start .... at maybe six times its running amps.
    Each part has its own table to determine conductor size and circuit breaker or fuse size, and sometimes it can lead to weird pairings... a 14g wire on a 30 amp breaker, for instance.
    But you do not get to use those "weird" pairing with a receptacle, it would need to be hardwired.

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