Testing & TroubleshootingQuestion 514 of 521
Using the rule of thumb of 1 megohm minimum per 1,000 V of rating, what is the minimum acceptable insulation resistance for a 4,160 V motor?
a.0.24 megohms
b.1 megohm
c.416 megohms
d.About 4 to 5 megohms
Explanation
The 1-megohm-per-kV guideline gives roughly 4,160 V / 1,000 = about 4.16 megohms, often rounded up (some add 1 megohm) to about 4-5 megohms minimum. Readings below this suggest degraded insulation. Option a inverts the ratio and c multiplies incorrectly.
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