Energy Management

Billions of dollars in energy could be lost annually due to poor motor sizing


Jul 10, 2008

WEG Electric Motors Corp. (, a supplier of motors, drives, controls, generators and transformers, explains how proper motor sizing could easily save vast amounts of energy. Energy efficiency losses through over-sizing of pump electric motors by engineers are commonplace and, if the motor specification far exceeds the application, it could be costing industry billions of dollars in wasted energy.

“Industry figures suggest that around 80% of pump motors could be the incorrect size,” says Andrew Glover, product manager for WEG Motors. “The majority are overspecified by as much as 10% or 15% by engineers wanting to be ‘on the safe side.’ Pumps typically account for around 30% of an industrial country’s energy usage, and this represents a serious loss of energy. This takes no account for the extra cost of a larger motor with all the associated equipment, drives, cabling, etc. Electric motor manufacturers are forever striving to increase energy efficiency by 1 or 2 percentage points, but incorrect specification by an application engineer can mean that is wasted effort. Where a single percentage point increase in energy efficiency can save the equivalent of the purchase price of an electric motor over its design life, it seems ludicrous to waste energy through poor specification.”

Undersizing also is relatively common and should not be ignored. An electric motor can operate above its rated output, thus allowing for temporary overloads. However, such a motor will run hotter as a result, and overheating will cause damage and/or shorten its useful life.

Two points where this can directly affect the motor life are the bearings, which influence the motor reliability, and the coil insulation. Overheating degrades the insulation more rapidly and encourages discharges, which further degrade the insulation, thus shortening the motor’s life.

Specification of motor size should include starting condition, as well as running torque. Method of starting also is important; direct on-line starting methods will create high torque that also imposes mechanical stresses on the pump and hydraulic components. Star delta starting delivers lower torque and current.

Including a variable-speed drive or soft starter in the system specification, matched to the requirements of the motor and pump, will easily overcome these problems. Variable-speed drives also improve energy efficiency in the long term by matching application requirements with the correct motor speed. This avoids energy wasted by, for example, belt drives, clutches and gears.

For more information, visit or call (800) ASK-4WEG.