Motors should be fused with a time-delay fuse rated 175% of the motor’s full load operating amperage, 250% of the full load operating amperage if a circuit breaker is used. The wire to a motor must be rated to carry 25% more amperage than the motor draws when operating at full load.
How do you choose the size of a fuse?
In order to select the right amperage of the fuse, you first need to know the full-load steady-state current of the circuit at an ambient temperature of 25º C (68º F). Once the current value is determined, then a fuse rating should be selected as to be 135% of this value (taken to the next standard value).
What is the standard fuse size?
Standard sizes for fuses and fixed trip circuit breakers, per 240.6, are 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000 5000, and 6000 amps.
What should be checked whenever a low voltage fuse is changed?
Any time a fuse is replaced or a breaker is reset, the operation of the system should be checked carefully. Before operat- ing the system, check all major line voltage loads for shorts or grounds and check the main power wire connections.
What size breaker do I need for a 40 hp motor?
Full-Load Current and Circuit Protection Data for Three-Phase AC Motors
| Motor Horsepower | Breaker Size | |
|---|---|---|
| 20 | 230 V 460 V | 100 50 |
| 25 | 230 V 460 V | 100 50 |
| 30 | 230 V 460 V | 125 70 |
| 40 | 230 V 460 V | 175 100 |
What size breaker do I need for a 30 amp motor?
Any circuit fused for 30 amps must use a minimum of 10 ga copper or 8 ga alu. Longer runs may require an upgrade of wire size.
What size breaker do I need for a 3 HP motor?
Full Load Current: Three Phase AC Motors
| Motor Horsepower | Size Breaker | |
|---|---|---|
| 1-1/2 | 230V 460V | 15 15 |
| 2 | 230V 460V | 15 15 |
| 3 | 230V 460V | 15 15 |
| 5 | 230V 460V | 15 15 |
Will 6 gauge wire fit in a 30 amp breaker?
“Twelve-gauge wire is good for 20 amps, 10-gauge wire is good for 30 amps, 8-gauge is good for 40 amps, and 6-gauge is good for 55 amps,” and “The circuit breaker or fuse is always sized to protect the conductor [wire].”