Motor Calculations — Part 2

Motor Calculations — Part 2

How to correctly size devices that protect motor systems from overcurrent.

In Part 1, we saw why we must separate overload protection from fault and short circuit protection for motor circuits. But correctly sizing these different devices can be confusing. And if you follow the rules for one while doing the other, you’re likely to burn something up.

When sizing motor overload protection devices (OPDs), two numbers you don’t use for other types of circuits are vitally important.

1. You must know the motor nameplate service factor (SF). An SF

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