Traditional Speed Torque Curves

Capacitor Start/Induction Run

A single phase general purpose design, with an electrolytic capacitor in series with the start winding, offering maximum starting torque per ampere. A centrifugal switch removes the auxiliary winding and capacitor when the motor approaches full load speed. The design is a heavy-duty unit which has approximately 300% (of full load) starting torque. Common applications include compressors, pumps, conveyors and other “hard-to-start” applications.

Permanent Split Capacitor (PSC)

This design has an auxiliary winding with a “run” capacitor, but unlike the capacitor start/induction run  motor,  the  capacitor  and  auxiliary  winding remain  in  the circuit  under  running  conditions.(There is no centrifugal switch on this type motor.) A  permanent  split  capacitor  design  has  low starting torque and low starting current. They are generally used on direct-drive fans and blowers. They  can  also  be designed  for  higher  starting torque and intermittent applications, where rapid reversing is desired.

Three Phase or Polyphase

General purpose three phase motors have different electrical design classifications as defined by NEMA®. NEMA Design A and B motors are of normal starting torque with normal starting current.  NEMA Design C motors have higher starting torque with normal starting current. All three types have slip of less than 5%. (“Slip”  being a term which expresses, as a percentage, the difference between synchronous motor speed and full load motor speed, for example, 1800rpm synchronous versus a full  load speed of 1740 rpm.

NEMA’s Design B and C standards are minimum performance standards. In practice, some manufacturers (including Regal Rexnord) build small integral HP Design B motors with locked rotor and breakdown torque levels equaling NEMA Design C standards.

NEMA T frame motors 1 through 200 HP covered by EP Act (identified with a “G” catalog prefix) are labeled Design B, exceed NEMA Design B performance levels, and have efficiencies equal to EP Act mandated levels. EP Act exempt three phase, base-mounted motors are labeled Design C and have performance characteristics meeting NEMA’s Design C standards, with standard motor efficiencies. Motors 250 HP and larger are exempt from EP Act legislation.

Permanent Magnet DC

This  design  has  linear  speed/torque characteristics over the entire speed range. SCR rated motor features include high starting torque for heavy load applications and dynamic braking, variable speed and reversing capabilities. Designs are also available for use on generated low voltage DC power or remote applications requiring battery power.