Motor calculation problem.

[ramihamdan]

A three-phase motor draws 45 amps at 240v. How much does the same motor draw at 480v three phase? What would be an equation for this theory problem.

 

[LarryFine]

As a purely linear (resistive) load, if you double the voltage, the resultant current also doubles.

This statement presumes you are not modifying or replacing the load to suit the new voltage.

 

[ptonsparky]

Look at the NEC tables for motor FLA and see what you can figure out. The label on a three phase motor should point you in the right direction as well

 

[garbo]

A dual voltage motor such as the motor drawing 45 amps @240 volts is connected to two sets of winding between phases and in the lower voltage ( 240 volts ) are in parallel so each coil draws 22.5 amps. At the higher voltage ( 480 ) the two windings are in series therefore each winding draws 22.5 amps. So that motor would draw 22.5 amps at 480 volts and the same amount of power on either voltage. Typical plain Jane 9 lead NEMA frame motors have 6 windings with the one lead of three windings internally connected together.

 

[infinity]

Like garbo said just divide by 2. Double the voltage 1/2 the current.

 

[LarryFine]

Like garbo said just divide by 2. Double the voltage 1/2 the current.

Mathematically, or if you modify the load for the new voltage, yes.

As I said the last time this was asked, the OP said "the same motor."

 

[infinity]

Mathematically, or if you modify the load for the new voltage, yes.

As I said the last time this was asked, the OP said "the same motor."

Yes I'm stating the obvious that the motor was designed for dual voltage operation otherwise a 240 motor at 480 volts wouldn't run too long.

 

[texie]

And since the motor will only draw half the current it will cost only half as much to run.
Ok, just kidding.