calculating wire size for motor load

[garylr]

I'm in the process of sizing power cords for our motor operated equipment. I have calculated voltage drops and have calculated my cord AWG using a Voltage drop rule of 5%of the source voltage. My co-worker has requested I calculate voltage drop using Locked-rotor amps as well as FLA for the motor.

Is there any justification to calculating wire size with Locked rotor amps?? My co-worker said he wants to make sure the motor will start. This does not make sense to me? AS long as the motor is supplied with votage within 10% of nameplate rating.

 

[charlie b]

Re: calculating wire size for motor load

You certainly could use LRA. But there is no reason to do so. It would be overkill, and overly expensive.

 

[bphgravity]

Re: calculating wire size for motor load

Locked-rotor currents would be more of a concern when sizing the ground-fault / short-circuit protection devices rather than sizing the supply conductors. I would think the 5% total drop you have already worked in will be sufficient for both the starting and running of the motor.