What is the selection procedure for fuse wire for motor load?

Answer 1

An easy way to do this is to get yourself an "Ugly's" book. Its a small electrical reference guide for circuit protection, (sold at Home Depot & some electrical supply houses). Buss, and other fuse makers usually can supply you with a similar guide.

You will also need to find the right size Motor Starter & Overload Heater within the Motor Starter. But to answer your question;

To select wire, or fuse/breakers for a Motor Load, you need to look at the Motor's FLA (Full Load Amps), take that number and multiply it by 1.25 (this is a 'rule of thumb' & not Absolutely necessary),

-Now you have the maximum amperage that the motor will draw under NORMAL OPERATING CONDITIONS. Go to the NEC section on conductors (i.e. wires) and find a suitable gage wire (in the 75 deg column) and find a wire that will handle the amount of current the your load requires.

Now find a fuse or breaker that is permitted for the WIRE, not the load.

For example: if you have a motor that draws 10 amps (full load), you might use 16 gage wire, 16 gage wire may be rated for 20A, use a breaker, or fuse rated for 20A.

Its always best to use the lowest temperature column in the NEC book because you have to account for all connections in the circuit (i.e. lugs, crimps, spades, terminal blocks, etc.)

YOU NEED TO SELECT A FUSE, OR BREAKER BASED ON THE WIRE SIZE, NOT THE LOAD ! !