Motors

[A/A Fuel GTX]

Are 3 phase and polyphase motors the same thing? Also, how do I determine if a motor is a wound rotor or squirrel cage? I'm trying to size the OCPD on a 3 phase, 5HP, 230V motor. I'm assuming at this point I can go 250% from the values on table 430.250. Thanks

 

[tom baker]

Re: Motors

Are 3 phase and polyphase motors the same thing?
I was going to say yes, lets see on this.
Also, how do I determine if a motor is a wound rotor or squirrel cage?
A wound rotor motor is not a common motor, it would have slip rings.
If the motor name plate states Design B then its a three phase, squirrel cage

 

[BKearney]

Polyphase = 2 or more phases

But I wont say yes to your question, because in my mind a single phase PSC (permanent split capacitor) motor could also, by some, be considered a polyphase motor because the cap in essence creates a second phase within the PSC motor...

But, in general, I would think when you hear the term "polyphase" it is referencing 3-phase...

 

[69boss302]

I am embarrassed, at first I would of agreed right away with the other posts, however, I actually looked this up. Out of the American Electricians Handbook 10th edition 7-144 "General construction of polyphase motors. Polyphase induction motors have two windings, one on the stationary part of the machine, or stator, and one mounted on the revolving part, or rotor."

The squirrel cage rotor is considered a winding on the rotor.

Rotor winding is either squirrel cage or wound rotor.

Out of the Electric Motor Repair book (Commonly referred to as the Rosenburg) second edition. "Polyphase motors are a-c motors that are designed for either three-phase or two-phase operation. The two types are alike in construction, but the internal connections of the coils are different."

Wound rotor motors have slip rings, usually used when looking for some kind of speed control. (Before the time of VFD's) (Very limited speed control but some)