Incorporating COTS motorized equipment into other controls.

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david.mullins

david.mullins

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Location
Santa Barbara, CA, USA
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Electrical Engineer
Sr. Mechanical engineer is proposing we use off the shelf fans and air compressors in a large material handling system. Our control cabinet will turn them on and off with relays. At what point do I have to include overcurrent, overload, and disconnects for the motor in each one?

If I cut off the plug and run the cord into my cabinet?
If I provide an outlet on my cabinet and plug it in?
 
ALL motors are required to have short circuit and overload protection, and a disconnecting means.

Many small motors (especially 120 V single phase motors) have the overload protection built into the motor, so no further overload protection is required.

Short circuit protection can often be supplied by the branch circuit small motors are supplied by, and the BC disconnecting means can often be the motor disconnecting means.

Personally, I would not be cutting the cords. That might be a violation of 400.10. I would be inclined to install a receptacle near where each motor is physically located and run power through the control relay to that outlet. Then the receptacle can serve as a disconnecting means.
 
Thank you. I was also thinking that if it came with a 120 or 240 V plug then it must have overload built in, right?

Problem with receptacles, in this case is that it goes on the back of a ship and could see 2' to 3' submersion in salt water! I'll look up 400.10 when I get back to work, Monday.
 
Most of the time, it's operated on land in our yard for development and testing. When at sea, we follow IEEE 45 but:
  1. It's mostly the same as the NEC for these things.
  2. Mike doesn't have an IEEE 45 forum. :confused:
 
Motors under I believe 1 hp continuous duty may not need overload protection but just OCPD short etc protection according to nec
 
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