Tom Bishop, P.E.
EASA Senior Technical Support Specialist

The tongue-in-check saying “If it’s in black and white, it must be right” is a helpful reminder that not everything we read (or hear) is accurate or complete. It’s always best to check sources and verify facts before accepting consequential statements as true. A similar adage underscores the importance of this advice in the digital age: “If it’s on the Internet, it must be true.” With these things in mind, here’s a random collection of common misconceptions about three-phase squirrel-cage motors and the facts that deny them.

Myths discussed include:

• Soft starting motors reduces utility demand charges.
• Higher current means a motor is less efficient.
• Power factor correction capacitors can reduce motor energy consumption.
• A motor can be loaded up to its service factor.
• A 230V motor can be used on a 208V electrical system.
• Oversized motors, especially motors operating at less than 60% of rated load, are not efficient and should be replaced with appropriately-sized premium efficiency (IE3) motors.
• It doesn't matter which of the three line-to-line voltages in a three-phase system you measure to see if a motor is supplied with the proper voltage.
• Hand contact on a motor surface is a reliable way to judge operating temperature.
• Winding burnout is the most common cause of motor failure.

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