By Mike Howell
EASA Technical Support Specialist

Right-sizing of three-phase induction motors for different applications – and striking a balance between reliability and efficiency – isn’t always easy, but it can be cost-effective. Before the days of comprehensive predictive and preventive maintenance programs, the conventional approach to reliability was conservatism, both in design and in application. That’s to say that on a 25 hp application, you’d find a very conservatively designed 60 hp motor that was really 75 hp “under the hood.” And yes, the motor would last a very long time, but it would have an inflated (and often ignored) operational cost. Many of these robustly engineered applications are still out there, and it can be well worth the effort to identify and correct them.

Some of the topics covered include:

• New vs existing applications
• Determining the actual load
• Determining typical loading by measuring the average input power
• Line amps
• Locked-rotor amps
• Starting torque
• Special applications

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