Look at the section of code on Motor circuits.
The circuit wiring needs to be rated at least 125% of the operating current.
The motor, it'self is protected by either internal overload protection or protection in the starter.
For a dedicated circuit the circuit overload protection can be much higher than the breaker can be much larger that "normal". I don't have time to look it up, but depending on the typie of overload device it can be 175 or 225% of normal operating current.
Common breakers have a 2 modes for triming. One is a time inverse heating element and bi-metalic trip. The other is a magnetic trip. For "shorts" the magnetic trip will be what protects the wiring and it is near instaneous.
CH and SQ D both show this in the breaker curves.
If this is not a dedicated circuit the 125% rule still holds, but the breaker is limited to the nominal size based on the wire size.
For home workshop these rules are often ignored and it works out OK. Except for air compressors most home workshop motors start with limited load so the starting current and time is fairly low.
They are used on a relatively low duty cycle.
And wiring with modern insulation can care more current than the size of the breaker allows for the #14, 12, 10 sizes. |
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