Single Phase From Three Phase 1

[stripedbass]

I have 240/120 Y 3PH power to a breaker panel. I would like to run a 240 VAC single phase 7-1/2 HP compressor from this panel. Is it correct to say I should be able to draw the power from the 'A' and the 'C' phase to make 240 VAC 1 PH. or will that not work?

thanks,

al

 

[peterb]

You can connect your single phase load to any pair of phases (AB, BC, CA) & get 240V. You should take care to ensure that the loads are reasonably balanced between the phases.

 

[jbartos]

Suggestion: The motor needs certain other conditions to be verified, namely, a size of the upstream transformer; especially, if it is the overhead type, a size of the panel feeder since the motor may draw FLA=40 A and LRA = 240A. Therefore, three phase motors are normally used on the three phase power supplies.

 

[JBUDA54]

Don't forget to provide this 7.5HP, single phase motor with some sort of overload protection. It is wise to use a motor starter for electrical motors. The starter controls the operation of the motor on and off by making or breaking the starter coil. Also the starter should have some sort of overload be it Themal Magnetic or Solid state. The Breaker in your panel is for the Motor Short circuit and ground fault protection and protects the motor feeder. The Motor overloads are there to protect your motor. It is possible to have your motor overheat without the overloads installed.
For Motor Overload Protection reference NEC 430-31
I looked at a Cutler Hammer Enclosed control product guide and a NEMA Freedom Starter Single Phase Magnetic /Non-combination Full Voltage Non-Reversing /Interchangeable Heater OLR / 600VMax 7.5HP 230VAC list cost $467. This may be expense, but to overload the motor and replace it several times could also be expense. It depends on your application. If your application is a very once in a while operation forget about the starter, but if it is a continuous operation and starter is wise. However one burned out motor makes the starter price seem insignificant.