Power and Efficiency
Brake horsepower is the input power required at the compressor input shaft for a specific speed, capacity, and pressure condition.
Motor horsepower is the nominal rating of the prime mover.
The service factor is the additional power built into an electric motor above its nominal rating - expressed as percent. Within the service factor, the brake horsepower driving an air compressor can be higher than the motor's nominal horsepower.
The power efficiency of a compressor is the ratio of the air delivered by the compressor and its input electrical requirements.
Efficiency usually is expressed as brake horsepower per 100 cfm of delivered air.