Small Comercial/Industrial Moters

[kaival]

I have always wondered why small induction motors have ratings up to 6/7 HP yet are still the same size as 2/3 HP motors except having an extra start capacitor(commonly seen on compressors). Industrial motors are twice as big for the same HP. Do they use the same rating system? Is torque a function of size to some deqree?

 

[JoeA]

Many small commercial motors bypass the standard NEMA rating and use momentary peak available HP for the advertised rating. Look at the "Cheap" compressors available from companies such as Harbor Freight that sell 6.5HP compressors for $400. A good industrial motor alone is close to that. If you compare the air output to a 5HP industrial compressor the cheating is immediately evident. Just taking advantage of the gullible public!