How to Calculate Fuse Ratings for AC Motor Protection Based on Motor Full Load Amps Current

Using AC Motor Protection Tables to Select Fuse Ratings

Fuse ratings selected in accordance with the following recommendations also meet NEC® requirements for Motor Branch Circuit and Short Circuit Protection.

Selecting Fuses for Motor Running Protection Based on Motor Actual Full Load Currents

Better protection is achieved when fuse ratings are based on motor actual full load amps (FLA) as obtained from motor nameplates. Locate motor nameplate FLA in the column appropriate for the type of motor and type of protection required. Read to the left to obtain the recommended fuse ampere rating.

Fuse Selection for Dual Element Fuses (Fusetron)

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Full Load Amps: 0 - 2.5
Without Overload Relay
Motor Full Load Amps (FLA)
Fuse
Amp
Rating		 Service Factor
≥ 1.15 or with
Rise ≤ 40 ℃		 Service Factor
< 1.15 or with
Rise > 40 ℃
1/10 0.08 - 0.09 0.09 - 0.10
1/8 0.10 - 0.11 0.11 - 0.125
15/100 0.12 - 0.15 0.14 - 0.15
2/10 0.16 - 0.19 0.18 - 0.20
1/4 0.20 - 0.23 0.22 - 0.25
3/10 0.24 - 0.30 0.27 - 0.30
4/10 0.32 - 0.39 0.35 - 0.40
1/2 0.40 - 0.47 0.44 - 0.50
6/10 0.48 - 0.60 0.53 - 0.60
8/10 0.64 - 0.79 0.70 - 0.80
1 0.80 - 0.89 0.87 - 0.97
1 1/8 0.90 - 0.99 0.98 - 1.08
1 1/4 1.00 - 1.11 1.09 - 1.21
1 4/10 1.12 - 1.19 1.22 - 1.30
1 1/2 1.20 - 1.27 1.31 - 1.39
1 6/10 1.28 - 1.43 1.40 - 1.56
1 8/10 1.44 - 1.59 1.57 - 1.73
2 1.60 - 1.79 1.74 - 1.95
2 1/4 1.80 - 1.99 1.96 - 2.17
2 1/2 2.00 - 2.23 2.18 - 2.43
2 8/10 2.24 - 2.39 2.44 - 2.60
3 2.40 - 2.55 2.61 - 2.78

Full Load Amps: 0 - 2.5
With Overload Relay
Motor Full Load Amps (FLA)
Fuse
Amp
Rating		 Service Factor
≥ 1.15 or with
Rise ≤ 40 ℃		 Service Factor
< 1.15 or with
Rise > ℃
1/10 0.00 - 0.08 0.00 - 0.09
1/8 0.09 - 0.10 0.10 - 0.11
15/100 0.11 - 0.12 0.12 - 0.13
2/10 0.13 - 0.16 0.14 - 0.17
1/4 0.17 - 0.20 0.18 - 0.22
3/10 0.21 - 0.24 0.23 - 0.26
4/10 0.25 - 0.32 0.27 - 0.35
1/2 0.33 - 0.40 0.36 - 0.43
6/10 0.41 - 0.48 0.44 - 0.52
8/10 0.49 - 0.64 0.53 - 0.70
1 0.65 - 0.80 0.71 - 0.87
1 1/8 0.81 - 0.90 0.88 - 0.98
1 1/4 0.91 - 1.00 0.99 - 1.09
1 4/10 1.01 - 1.12 1.10 - 1.22
1 1/2 1.13 - 1.20 1.23 - 1.30
1 6/10 1.21 - 1.28 1.31 - 1.39
1 8/10 1.29 - 1.44 1.40 - 1.57
2 1.45 - 1.60 1.58 - 1.74
2 1/4 1.61 - 1.80 1.75 - 1.96
2 1/2 1.81 - 2.00 1.97 - 2.17
2 8/10 2.01 - 2.24 2.18 - 2.43
3 2.25 - 2.40 2.44 - 2.60
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Full Load Amps: 2.5 - 35
Without Overload Relay
Motor Full Load Amps (FLA)
Fuse
Amp
Rating		 Service Factor
≥ 1.15 or with
Rise ≤ 40 ℃		 Service Factor
< 1.15 or with
Rise > 40 ℃
2 8/10 2.24 - 2.39 2.44 - 2.60
3 2.40 - 2.55 2.61 - 2.78
3 2/10 2.56 - 2.79 2.79 - 3.04
3 1/2 2.80 - 3.19 3.05 - 3.47
4 3.20 - 3.59 3.48 - 3.91
4 1/2 3.60 - 3.99 3.92 - 4.34
5 4.00 - 4.47 4.35 - 4.86
5 6/10 4.48 - 4.79 4.87 - 5.21
6 4.80 - 4.99 5.22 - 5.43
6 1/4 5.00 - 5.59 5.44 - 6.08
7 5.60 - 5.99 6.09 - 6.52
7 1/2 6.00 - 6.39 6.53 - 6.95
8 6.40 - 7.19 6.96 - 7.82
9 7.20 - 7.99 7.83 - 8.69
10 8.00 - 9.59 8.70 - 10.00
12 9.60 - 11.99 10.44 - 12.00
15 12.00 - 13.99 13.05 - 15.00
17 1/2 14.00 - 15.99 15.22 - 17.39
20 16.00 - 19.99 17.40 - 20.00
25 20.00 - 23.99 21.74 - 25.00
30 24.00 - 27.99 26.09 - 30.00
35 28.00 - 31.99 30.44 - 34.78
40 32.00 - 35.99 34.79 - 39.12

Full Load Amperes: 2.5 - 35
With Overload Relay
Motor Full Load Amps (FLA)
Fuse
Ampere
Rating		 Service Factor
≥ 1.15 or with
Rise ≤ 40 ℃		 Service Factor
< 1.15 or with
Rise > 40 ℃
3 2.25 - 2.40 2.44 - 2.60
3 2/10 2.41 - 2.56 2.61 - 2.78
3 1/2 2.57 - 2.80 2.79 - 3.04
4 2.81 - 3.20 3.05 - 3.48
4 1/2 3.21 - 3.60 3.49 - 3.91
5 3.61 - 4.00 3.92 - 4.35
5 6/10 4.01 - 4.48 4.36 - 4.87
6 4.49 - 4.80 4.88 - 5.22
6 1/4 4.81 - 5.00 5.23 - 5.43
7 5.01 - 5.60 5.44 - 6.09
7 1/2 5.61 - 6.00 6.10 - 6.52
8 6.01 - 6.40 6.53 - 6.96
9 6.41 - 7.20 6.97 - 7.83
10 7.21 - 8.00 7.84 - 8.70
12 8.01 - 9.60 8.71 - 10.43
15 9.61 - 12.00 10.44 - 13.04
17 1/2 12.01 - 14.00 13.05 - 15.21
20 14.01 - 16.00 15.22 - 17.39
25 16.01 - 20.00 17.40 - 21.74
30 20.01 - 24.00 21.75 - 26.09
35 24.01 - 28.00 26.01 - 30.43
40 28.01 - 32.00 30.44 - 37.78
45 32.01 - 36.00 37.79 - 39.13
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Full Load Amps: 35 - 600
Without Overload Relay
Motor Full Load Amps (FLA)
Fuse
Amp
Rating		 Service Factor
≥ 1.15 or with
Rise ≤ 40 ℃		 Service Factor
< 1.15 or with
Rise > 40 ℃
40 32.00 - 35.99 34.79 - 39.12
45 36.00 - 39.99 39.13 - 43.47
50 40.00 - 47.99 43.48 - 50.00
60 48.00 - 55.99 52.17 - 60.00
70 56.00 - 59.99 60.87 - 65.21
75 60.00 - 63.99 65.22 - 69.56
80 64.00 - 71.99 69.57 - 78.25
90 72.00 - 79.99 78.26 - 86.95
100 80.00 - 87.99 86.96 - 95.64
110 88.00 - 99.99 95.65 - 108.69
125 100.00 - 119.99 108.70 - 125.00
150 120.00 - 139.99 131.30 - 150.00
175 140.00 - 159.99 152.17 - 173.90
200 160.00 - 179.99 173.91 - 195.64
225 180.00 - 199.99 195.65 - 217.38
250 200.00 - 239.99 217.39 - 250.00
300 240.00 - 279.99 260.87 - 300.00
350 280.00 - 319.99 304.35 - 347.82
400 320.00 - 359.99 347.83 - 391.29
450 360.00 - 399.99 391.30 - 434.77
500 400.00 - 479.99 434.78 - 500.00
600 480.00 - 600.00 521.74 - 600.00

Full Load Amps: 35 - 600
With Overload Relay
Motor Full Load Amps (FLA)
Fuse
Amp
Rating		 Service Factor
≥ 1.15 or with
Rise ≤ 40 ℃		 Service Factor
< 1.15 or with
Rise > 40 ℃
40 28.01 - 32.00 30.44 - 37.78
45 32.01 - 36.00 37.79 - 39.13
50 36.01 - 40.00 39.14 - 43.48
60 40.01 - 48.00 43.49 - 52.17
70 48.01 - 56.00 52.18 - 60.87
75 56.01 - 60.00 60.88 - 65.22
80 60.01 - 64.00 65.23 - 69.57
90 64.01 - 72.00 69.58 - 78.26
100 72.01 - 80.00 78.27 - 86.96
110 80.01 - 88.00 86.97 - 95.65
125 88.01 - 100.00 95.66 - 108.70
150 100.01 - 120.00 108.71 - 130.43
175 120.01 - 140.00 130.44 - 152.17
200 140.01 - 160.00 152.18 - 173.91
225 160.01 - 180.00 173.92 - 195.62
250 180.01 - 200.00 195.63 - 217.39
300 200.01 - 240.00 217.40 - 260.87
350 240.01 - 280.00 260.88 - 304.35
400 280.01 - 320.00 304.36 - 347.83
450 320.01 - 360.00 347.84 - 391.30
500 360.01 - 400.00 391.31 - 434.78
600 400.01 - 480.00 434.79 - 521.74
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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.