How to Calculate Fuse Ratings for AC Motor Protection Based on Motor Horsepower (hp)

Motor horsepower and motor full load amps (FLA) shown are taken from NEC® Tables 430.248 and 430.250 covering standard speed AC motors with normal torque characteristics. Fuse ratings for motors with special characteristics may need to vary from given values.

If motor running protection will be provided by the fuses, select fuse ratings for corresponding motor type from the tables labeled "Without Overload Relays."

If overload relays will provide principle motor running protection, select fuse ratings for corresponding motor type from the tables labeled "With Overload Relays." Fuse ratings selected from these columns coordinate with most UL Class 10 and 20 overload relays which cover over 90% of the motor applications.

Without Overload Relays:

With Overload Relays:

120 VOLT, 1 PHASE MOTORS – 120V CIRCUIT
Without Overload Relays
Motor HP Full Load Amps Horsepower (HP) Switch or
Fuse Clip Rating
Service Factor
≥ 1.15 or with
Rise ≤ 40°C		 Service Factor
< 1.15 or with
Rise > 40°C
1/6 4.4 5 5 30
1/4 5.8 7 6 1/4 30
1/3 7.2 9 8 30
1/2 9.8 12 10 30
3/4 13.8 15 15 30
1 16.0 20 17 1/2 30
1 1/2 20.0 25 20 30
2 24.0 30 25 30
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120 VOLT, 1 PHASE MOTORS - 120V CIRCUIT
With Overload Relays
Motor HP Full Load Amps Horsepower (HP) Switch or
Fuse Clip Rating
Service Factor
≥ 1.15 or with
Rise ≤ 40°C		 Service Factor
< 1.15 or with
Rise > 40°C
1/6 4.4 5 6/10 5 6/10 30
1/4 5.8 7 1/2 7 30
1/3 7.2 9 9 30
1/2 9.8 15 12 30
3/4 13.8 17 1/2 17 1/2 30
1 16.0 20 20 30
1 1/2 20.0 25 25 30
2 24.0 30 30 30
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230 VOLT, 1 PHASE MOTORS - 240V CIRCUIT
Without Overload Relays
Motor HP Full Load Amps Horsepower (HP) Switch or
Fuse Clip Rating
Service Factor
≥ 1.15 or with
Rise ≤ 40°C		 Service Factor
< 1.15 or with
Rise > 40°C
1/6 2.2 2 1/2 2 1/2 30
1/4 2.9 3 1/2 3 2/10 30
1/3 3.6 4 1/2 4 30
1/2 4.9 5 6/10 5 6/10 30
3/4 6.9 8 7 1/2 30
1 8.0 10 9 30
1 1/2 10.0 12 10 30
2 12.0 15 12 30
3 17.0 20 17 1/2 30
5 28.0 35 30* 60
7 1/2 40.0 50 45 60
10 50.0 60 50 60
*Fuse reducers required
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230 VOLT, 1 PHASE MOTORS - 240V CIRCUIT
With Overload Relays
Motor HP Full Load Amps Horsepower (HP) Switch or
Fuse Clip Rating
Service Factor
≥ 1.15 or with
Rise ≤ 40°C		 Service Factor
< 1.15 or with
Rise > 40°C
1/6 2.2 2 8/10 2 8/10 30
1/4 2.9 4 3 1/2 30
1/3 3.6 4 1/2 4 1/2 30
1/2 4.9 6 1/4 6 30
3/4 6.9 9 8 30
1 8.0 10 10 30
1 1/2 10.0 15 12 30
2 12.0 15 15 30
3 17.0 25 20 30
5 28.0 35 35 60
7 1/2 40.0 50 50 60
10 50.0 70 60 60
*Fuse reducers required
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200 VOLT, 3 PHASE MOTORS - 208V CIRCUIT
Without Overload Relays
Motor HP Full Load Amps Horsepower (HP) Switch or
Fuse Clip Rating
Service Factor
≥ 1.15 or with
Rise ≤ 40°C		 Service Factor
< 1.15 or with
Rise > 40°C
1/2 2.5 2 6/10 2 1/2 30
3/4 3.7 4 3 1/2 30
1 4.8 5 4 1/2 30
1 1/2 6.9 7 6 1/4 30
2 7.8 9 8 30
3 11.0 12 12 30
5 17.5 20* 20 30
7 1/2 25.3 30* 25* 60
10 32.2 40 35 60
15 48.3 60 50 60
20 62.1 75 70 100
25 78.2 90 80 100
30 92.0 110 100* 200
40 120.0 150 125 200
50 150.0 175* 150 200
60 177.0 200* 200* 400
75 221.0 250 250 400
100 285.0 350* 300 400
125 359.0 400* 400* 600
150 415.0 500 450 600
*Fuse reducers required
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200 VOLT, 3 PHASE MOTORS - 208V CIRCUIT
With Overload Relays
Motor HP Full Load Amps Horsepower (HP) Switch or
Fuse Clip Rating
Service Factor
≥ 1.15 or with
Rise ≤ 40°C		 Service Factor
< 1.15 or with
Rise > 40°C
1/2 2.5 3 2 8/10 30
3/4 3.7 4 1/2 4 30
1 4.8 5 6/10 5 30
1 1/2 6.9 7 1/2 7 30
2 7.8 10 9 30
3 11.0 15 15 30
5 17.5 25 25 30
7 1/2 25.3 35 30* 60
10 32.2 45 40 60
15 48.3 70** 60 60
20 62.1 80 75 100
25 78.2 100 90 100
30 92.0 125 110 200
40 120.0 150 150 200
50 150.0 200 175 200
60 177.0 225 225 400
75 221.0 300 300 400
100 285.0 400 350 400
125 359.0 450 450 600
150 415.0 600 500 600
*Fuse reducers required | **100 Amp switch required
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230 VOLT, 3 PHASE MOTORS - 240V CIRCUIT
Without Overload Relays
Motor HP Full Load Amps Horsepower (HP) Switch or
Fuse Clip Rating
Service Factor
≥ 1.15 or with
Rise ≤ 40°C		 Service Factor
< 1.15 or with
Rise > 40°C
1/2 2.2 2 1/2 2 1/4 30
3/4 3.2 3 1/2 3 2/10 30
1 4.2 4 1/2 4 30
1 1/2 6.0 6 1/4 5 6/10 30
2 6.8 8 7 1/2 30
3 9.6 12 10 30
5 15.2 17 1/2 17 1/2 30
7 1/2 22.0 25 25 30
10 28.0 35 30* 60
15 42.0 50* 45 60
20 54.0 60* 60* 100
25 68.0 80 75 100
30 80.0 100 90 100
40 104.0 125 110 200
50 130.0 150 150 200
60 154.0 175 175 200
75 192.0 255 200* 400
100 248.0 300 250 400
125 312.0 350 350 400
150 360.0 450 400* 600
200 480.0 600 500 600
*Fuse reducers required
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230 VOLT, 3 PHASE MOTORS - 240V CIRCUIT
With Overload Relays
Motor HP Full Load Amps Horsepower (HP) Switch or
Fuse Clip Rating
Service Factor
≥ 1.15 or with
Rise ≤ 40°C		 Service Factor
< 1.15 or with
Rise > 40°C
1/2 2.2 2 1/2 2 1/2 30
3/4 3.2 3 1/2 3 1/2 30
1 4.2 4 1/2 4 1/2 30
1 1/2 6.0 7 6 30
2 6.8 9 8 30
3 9.6 12 12 30
5 15.2 20 17 1/2 30
7 1/2 22.0 30 30 30
10 28.0 35 35 60
15 42.0 60 50 60
20 54.0 70 70 100
25 68.0 90 80 100
30 80.0 100 100 100
40 104.0 150 125 200
50 130.0 175 150 200
60 154.0 200 200 200
75 192.0 250 225 400
100 248.0 350 300 400
125 312.0 400 400 400
150 360.0 450 450 600
200 480.0 600 600 600
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460 VOLT, 3 PHASE MOTORS - 480V CIRCUIT
Without Overload Relays
Motor HP Full Load Amps Horsepower (HP) Switch or
Fuse Clip Rating
Service Factor
≥ 1.15 or with
Rise ≤ 40°C		 Service Factor
< 1.15 or with
Rise > 40°C
1/2 1.1 1 1/4 1 1/8 30
3/4 1.6 1 6/10 1 6/10 30
1 2.1 2 1/4 2 30
1 1/2 3.0 3 2/10 2 6/10 30
2 3.4 4 3 1/2 30
3 4.8 5 6/10 5 30
5 7.6 9 8 30
7 1/2 11.0 12 12 30
10 14.0 17 1/2 15 30
15 21.0 25 20 30
20 27.0 30* 30* 60
25 34.0 40 35 60
30 40.0 50 45 60
40 52.0 60* 60* 100
50 65.0 80 70 100
60 77.0 90 80 100
75 96.0 110 110 200
100 124.0 150 125 200
125 156.0 175 175 200
150 180.0 225 200* 400
200 240.0 300 250 400
*Fuse reducers required
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460 VOLT, 3 PHASE MOTORS - 480V CIRCUIT
With Overload Relays
Motor HP Full Load Amps Horsepower (HP) Switch or
Fuse Clip Rating
Service Factor
≥ 1.15 or with
Rise ≤ 40°C		 Service Factor
< 1.15 or with
Rise > 40°C
1/2 1.1 1 1/4 1 1/4 30
3/4 1.6 1 8/10 1 8/10 30
1 2.1 2 1/4 2 1/4 30
1 1/2 3.0 3 1/2 3 30
2 3.4 4 1/2 4 30
3 4.8 6 5 6/10 30
5 7.6 10 9 30
7 1/2 11.0 15 15 30
10 14.0 17 1/2 17 1/2 30
15 21.0 30 25 30
20 27.0 35 35 60
25 34.0 45 40 60
30 40.0 50 50 60
40 52.0 70 60* 100
50 65.0 90 75 100
60 77.0 100 90 100
75 96.0 125 125 200
100 124.0 175 150 200
125 156.0 200 200 200
150 180.0 225 225 400
200 240.0 300 300 400
*Fuse reducers required
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575 VOLT, 3 PHASE MOTORS - 600V CIRCUIT
Without Overload Relays
Motor HP Full Load Amps Horsepower (HP) Switch or
Fuse Clip Rating
Service Factor
≥ 1.15 or with
Rise ≤ 40°C		 Service Factor
< 1.15 or with
Rise > 40°C
1/2 0.9 1 8/10 30
3/4 1.3 1 1/4 1 1/4 30
1 1.7 1 8/10 1 6/10 30
1 1/2 2.4 2 1/2 2 1/4 30
2 2.7 3 2/10 2 8/10 30
3 3.9 4 1/2 4 30
5 6.1 7 1/2 7 30
7 1/2 9.0 10 10 30
10 11.0 12 12 30
15 17.0 20 17 1/2 30
20 22.0 25 25 30
25 27.0 30* 30* 60
30 32.0 40 35 60
40 41.0 50 45 60
50 52.0 60 60 60
60 62.0 75 70 100
75 77.0 90 80 100
100 99.0 110 110 200
125 125.0 150 125 200
150 144.0 175 150 200
200 192.0 225 200* 400
*Fuse reducers required
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575 VOLT, 3 PHASE MOTORS - 600V CIRCUIT
With Overload Relays
Motor HP Full Load Amps Horsepower (HP) Switch or
Fuse Clip Rating
Service Factor
≥ 1.15 or with
Rise ≤ 40°C		 Service Factor
< 1.15 or with
Rise > 40°C
1/2 0.9 1 1 30
3/4 1.3 1 4/10 1 4/10 30
1 1.7 1 8/10 1 8/10 30
1 1/2 2.4 2 8/10 2 1/2 30
2 2.7 3 1/2 3 2/10 30
3 3.9 5 4 1/2 30
5 6.1 8 7 1/2 30
7 1/2 9.0 12 12 30
10 11.0 15 15 30
15 17.0 25 20 30
20 22.0 30 30 30
25 27.0 35 35 60
30 32.0 40 40 60
40 41.0 60 50 60
50 52.0 70** 60 60
60 62.0 80 75 100
75 77.0 100 90 100
100 99.0 125 125 200
125 125.0 175 150 200
150 144.0 200 175 200
200 192.0 250 225 400
**100 Amp switch required
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Warning: When using this information to perform electrical work, call a licensed electrician and consult the NEC® for safety. All licensed electricians have passed examinations covering the National Electric Code®, know state and local building codes, and may carry insurance to cover damages.