Service factor

Service factor is a NEMA motor design margin: a multiplier on nameplate horsepower indicating how much continuous overload the motor can tolerate without exceeding insulation temperature limits. Standard NEMA service factors are 1.00 (no margin) and 1.15 (15 percent margin); compressor duty motors commonly run at 1.15.

What it is

A 100 HP motor with a 1.15 service factor can deliver 115 HP continuously at rated voltage and temperature without violating its design envelope. Above SF.HP, motor temperature climbs faster than nameplate, accelerating insulation aging. NEMA MG 1 defines SF and the allowable temperature rise at SF load.

Why it matters

Compressors are routinely sized so that nameplate HP exceeds brake horsepower at rated load. The service factor is the cushion. Reading a CAGI data sheet, the package input kilowatts should be compared against motor SF.HP, not nameplate HP alone, to confirm the motor is not running into its overload reserve continuously.

How it is used in our catalog

Motor nameplate HP and service factor are reported in each compressor entry. CAGI data sheets linked from the rotary screw archive and other class pages confirm package input power and motor sizing.

Common questions

Should I size to nameplate HP or SF.HP?

Nameplate HP for normal operation. SF.HP is a transient cushion, not a continuous rating in practice.

Does a higher service factor mean a better motor?

Not necessarily. A high SF often signals that the manufacturer has used a larger frame than nameplate HP requires. The number to watch is actual brake horsepower at rated conditions.