The formal designation and full title for this standard that was published in April 2020 is, “CSA C392:20 Testing of Three-Phase Squirrel Cage Motors During Refurbishment.” This is the second edition of the standard and supersedes the previous edition published in 2011. The standard focuses on the identification of those tests that help to determine whether the efficiency of a motor is maintained after it is “refurbished,” without requiring a motor efficiency test.

The detailed descriptions of the tests to be performed make this standard very useful as a reference and a how-to document for any service center, not just those in Canada.

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Motor technicians may encounter instances where structural resonance is amplifying machine vibration. This webinar recording provides a good understanding of natural frequencies and the tests necessary to identify them.

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When rewinding synchronous field poles, especially if a wire size change is involved, make and install the top collar first. Wind the first layer, keeping it tight, then measure the thickness required for the bottom collar. 

As for the rectangular wire itself, keep the width to thickness ratio between 2:1 and 3:1 for an easier time winding. For collars wound using large round wire, consider changing to rectangular wire for the same reason.

Repairmen or tool room attendants should observe the following:

• “Ring test” and inspect each wheel for cracks or breaks. Never use a stone that shows signs of crack or other damage.
• Make sure the machine speed does not exceed the maximum operating speed of the abrasive wheel (shown on the manufacturer’s tag).
• Abrasive wheels should fit snugly  but not tight on the spindle or bushing. Never alter the hole in the wheel or force the wheel onto the spindle.