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Service factor (SF) accounts for operating conditions beyond rated values. Use 1.0 for ideal conditions, 1.15 for moderate ambient or occasional overloads, 1.25 for harsh environments, and 1.5 for severe duty with frequent starts or high-inertia loads.

Constant torque loads (conveyors, positive displacement pumps) require the same torque regardless of speed — power is proportional to speed. Variable torque loads (centrifugal fans/pumps) have torque proportional to speed² and power proportional to speed³ — they need much less power at reduced speed.

Motors are only made in standard sizes. You must always select the next standard size up. Additionally, slight oversizing (10-15%) provides thermal headroom, compensates for voltage variations, and extends bearing life.

Use a VFD when: (1) variable speed is needed, (2) soft starting is required, (3) energy savings on variable torque loads are important, (4) the power supply cannot handle DOL starting current. VFDs also reduce mechanical stress on couplings and driven equipment.