Sizing Overcurrent Protection for Motors
The charts below are based on the sections of National Electrical Code as noted. These charts are used to size the overcurrent protection for the power source. The overcurrent protection can be a circuit breaker, motor starter or disconnect switch. Typically the circuit breaker is sized 125% of the ampere rating but it is best to use the nameplate rating of the motor device to determine the overcurrent protection.
NEC Table 430.248
Full Load Current in Amperes,
Single Phase Alternating-Current Motors
|
|---|
| HORSEPOWER |
115 VOLTS
(120V) |
208 VOLTS |
230 VOLTS
(240V) |
| 1/6 |
4.4 |
2.4 |
2.2 |
| 1/4 |
5.8 |
3.2 |
2.9 |
| 1/3 |
7.2 |
4.0 |
3.6 |
| 1/2 |
9.8 |
5.4 |
4.9 |
| 3/4 |
13.8 |
7.6 |
6.9 |
| 1 |
16.0 |
8.8 |
8.0 |
| 1-1/2 |
20.0 |
11.0 |
10.0 |
| 2 |
24.0 |
13.2 |
12.0 |
| 3 |
34.0 |
18.7 |
17.0 |
| 5 |
56.0 |
30.8 |
28.0 |
| 7-1/2 |
80.0 |
44.0 |
40.0 |
| 10 |
100.0 |
55.0 |
50.0 |
NEC Table 430.250
Full Load Current in Amperes,
Three Phase Alternating-Current Motors
(Induction-Type Squirrel Cage
and Wound Rotors in Amperes)
|
|---|
| HORSEPOWER |
208 VOLTS |
230 VOLTS
(240V) |
460 VOLTS
(480V) |
| 1/2 |
2.4 |
2.2 |
1.1 |
| 3/4 |
3.5 |
3.2 |
1.6 |
| 1 |
4.6 |
4.2 |
2.1 |
| 1-1/2 |
6.6 |
6.0 |
3.0 |
| 2 |
7.5 |
6.8 |
3.4 |
| 3 |
10.6 |
9.6 |
4.8 |
| 5 |
16.7 |
15.2 |
7.6 |
| 7-1/2 |
24.2 |
22 |
11 |
| 10 |
30.8 |
28 |
14 |
| 15 |
46.2 |
42 |
21 |
| 20 |
59.4 |
54 |
27 |
| 25 |
74.8 |
68 |
34 |
| 30 |
88 |
80 |
40 |
| 40 |
114 |
104 |
52 |
| 50 |
143 |
130 |
65 |
| 60 |
169 |
154 |
77 |
| 75 |
211 |
192 |
96 |
| 100 |
273 |
248 |
124 |
| 125 |
343 |
312 |
156 |
| 150 |
396 |
360 |
180 |
| 200 |
528 |
480 |
240 |
| 250 |
-- |
-- |
302 |
| 300 |
-- |
-- |
361 |
| 350 |
-- |
-- |
414 |
| 400 |
-- |
-- |
477 |
| 450 |
-- |
-- |
515 |
| 500 |
-- |
-- |
590 |
|
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