Matching the Induction Motor Rating to the Driven Load Power

It is of utmost importance that an induction motor selected for a particular application to have sufficient power and torque to be able to function properly and efficiently. Starting high inertia loads (i.e. conveyors) require a high starting torque motor where a normal torque motor may fail to start or accelerate.

Table 1 provides a rule of thumb for the relationship of the driven load power to the motor rating.

Table 1 Margin of motor rating above the machine rating [1]
Driven Load Power (kW) Margin multiplier (per-unit)
Up to 15 1.25
16 to 55 1.15
56 and above 1.10

Belt-driven loads require higher margin factor than for direct coupled driven machines due to the lower transmission efficiency of belt drives. It is also advisable to obtain advice from the manufacturers of both the driven machine and the motor.

1. Handbook of Electrical Engineering: For Practitioners in the Oil, Gas and Petrochemical Industry
Alan L. Sheldrake
ISBN: 0-471-49631-6

A Filipino Engineer, Registered Professional Engineer of Queensland (RPEQ) - Australia and Professional Electrical Engineer (PEE) - Philippines with extensive experience in concept select, front-end engineering, HV & LV detail design, construction and commissioning of Hazardous and Non-Hazardous Area electrical installations in water and waste water pipeline and pumping facilities, offshore platforms, hydrocarbon process plants and pipelines including related facilities. Hazardous area classification and design certification (UEENEEM015B, UEENEEM016B, UEENEEM017B).