Recommended electric motor feeds

For sure below one hp. If the motor is loaded and running constantly then 3 phase for sure. If less than 50% loaded or running then below 5 hp use single phase. My thoughts only.

If given a choice I always go for 3 phase and the highest voltage normally available (480 in the states). You won't have the starting caps to deal with or replace and the motor will run more efficiently and cooler at the higher voltage........have a great holiday, Ross

In a "perfect world" I would agree. BUT good protection for a single phase motor is a LOT cheaper than good protection for a single phase motor.

Moreover, a 2 or 3 wire switch is a LOT more expensive than a 1 wire switch.

Given all this, I would GUESS that the breakeven point is at around the 2hp level.

Just my opinion.

Sounds like good advice John....I wrote equipment specs at one time and that was just my rule of thumb...I know there are a bunch of folks out there much more educated on this subject than I.....have a great holiday season!...Ross

Another consideration might be distance. How far will the motor be from the utility's transformer? Voltage drop is a lot less for three phase than single phase. I don't know if there is a rule of thumb for this.

Dean

It is hard to find a single phase motor over 5hp. Residential single phase air conditioning stops at 5 hp....if you need more than that they usually install multiple units.

If you have many motors over 100hp you are probably going to want a 480 volt service.

You can get an idea looking at the amperage tables for motors in the NEC.

Sincerely,

Donald L. Phillips, Jr., P.E. Worthington Engineering, Inc.

snipped-for-privacy@worthingtonNSengineering.com (remove NS to use the address)