Wire Size and Fuse Ratings for 3-Phase Induction Motors

FLUID POWER - Design Data Sheet 78

Motors are usually protected by both fuses (or circuit breakers) and by heater coils in a magnetic starter. Fuses open the circuit quickly in case of a massive overload or short circuit. Heater coils provide a delay and open the circuit if the average current, over a period of time, is greater than the circuit is designed for.

In some cases it may be necessary to use delayed action fuses. These provide a very short delay to prevent blowing a fuse during the short interval while the motor is accelerating up to its normal speed after being started.

Current values in this chart are approximate, and are compiled from data published by several motor manufacturers. They may be a little high or low for a specific motor. For selection of magnetic starter heater coils, it is better to follow the nameplate current rating of the actual motor to be used rather than depending on this or any other table.

Wire and fuse sizes are listed for reference only, and may vary with type of insulation, number of conductors in a cable and other factors. For a new design, requirements of the NEC (National Electrical Code) should be followed. Copies of the code can be ordered through most book stores. Other local ordinances may also apply.

HP Speed
RPM
230-Volt Service 460-Volt Service   HP Speed
RPM
230-Volt Service 460-Volt Service
Full
Load
Amps
Wire
Size
Fuse
Amps
Full
Load
Amps
Wire
Size
Fuse
Amps
Full
Load
Amps
Wire
Size
Fuse
Amps
Full
Load
Amps
Wire
Size
Fuse
Amps
1 1,200 3.76 14 10 1.88 14 6 25 1,200 65.6 3 120 32.8 6 180
1 1,800 3.56 14 10 1.78 14 6 25 1,800 64.8 3 120 32.4 6 80
1 3,600 2.80 14 10 1.40 14 6 25 3,600 60.8 3 120 30.4 6 80
1-1/2 1,200 5.28 14 15 2.64 14 10 30 1,200 78.8 1 150 39.4 6 80
1-1/2 1,800 4.86 14 15 2.43 14 10 30 1,800 75.6 1 150 37.8 6 80
1-1/2 3,600 4.36 14 15 2.18 14 10 30 3,600 73.7 1 150 36.8 6 80
2 1,200 6.84 15 20 3.42 14 10 40 1,200 102 0 200 50.6 4 110
2 1,800 6.40 14 20 3.20 14 10 40 1,800 101 0 200 50.4 4 110
2 3,600 5.60 14 20 3.00 14 10 40 3,600 96.4 0 200 48.2 4 110
3 1,200 10.2 14 25 5.12 14 15 50 1,200 126 000 250 63.0 3 120
3 1,800 9.40 14 25 4.70 14 15 50 1,800 124 000 250 62.2 3 120
3 3,600 8.34 14 25 4.17 14 15 50 3,600 120 000 250 60.1 3 120
5 1,200 15.8 12 30 7.91 14 20 60 1,200 150 000 300 75.0 2 150
5 1,800 14.4 12 30 7.21 14 20 60 1,800 149 000 300 74.5 2 150
5 3,600 13.5 12 30 6.76 14 20 60 3,600 143 000 300 71.7 2 150
7-1/2 1,200 21.8 10 40 10.9 14 20 75 1,200 184 300 350 92.0 0 200
7-1/2 1,800 21.5 10 40 10.7 14 20 75 1,800 183 300 350 91.6 0 200
7-1/2 3,600 19.5 10 40 9.79 14 20 75 3,600 179 300 350 89.6 0 200
10 1,200 28.0 8 60 14.0 12 30 100 1,200 239 500 500 120 000 250
10 1,800 26.8 8 60 13.4 12 30 100 1,800 236 500 500 118 000 250
10 3,600 25.4 8 60 12.7 12 30 100 3,600 231 500 500 115 000 250
15 1,200 41.4 6 80 20.7 10 40 125 1,200 298 - - - - - - 149 0000 300
15 1,800 39.2 6 80 19.6 10 40 125 1,800 293 - - - - - - 147 0000 300
15 3,600 36.4 6 80 18.2 10 40 125 3,600 292 - - - - - - 146 0000 300
20 1,200 52.8 4 110 26.4 8 60 150 1,200 350 - - - - - - 174 300 350
20 1,800 51.2 4 110 25.6 8 60 150 1,800 348 - - - - - - 174 300 350
20 3,600 50.4 4 110 25.2 8 60 150 3,600 343 - - - - - - 174 300 350

 

For selecting ampere rating of heater coils for magnetic motor starters, select the standard coil closest to the rating on the motor nameplate. If motor operates in cold environment, the coil with next lower rating may be preferred. If in hot environment, the coil with next larger current rating may work better.

For additional information, see Design Data Sheet 11. See also Design Data Sheet 33 and Design Data Sheet 49 for effect of high and low voltage on electric motors. More detailed information on magnetic motor starters including wiring diagrams, will be found in the Womack book “Electrical Control of Fluid Power".

 

TEMPERATURE CONVERSIONS - FAHRENHEIT AND CELSIUS

Enter one of the columns marked “Temp” with the temperature, either Fahrenheit or Celsius, which you wish to convert. If converting to Celsius, read the equivalent value in the column to the left. If converting to Fahrenheit, read the equivalent value in the column to the right. The table was calculated from these formula:

°F = [°C × 9/5] + 32
or
°C = 5/9 × [°F - 32]

 

Enter one of these columns with the temperature you wish to convert

Illustration 78_1

Degree
C
Temp. Degree
F
  Degree
C
Temp. Degree
F
  Degree
C
Temp. Degree
F
  Degree
C
Temp. Degree
F
-17.2 1  33.8 11.1 52 125.6 46.1 115 239.0 204.4 400 752
-16.6 2 35.6 11.5 53 127.4 48.9 120 248.0 210.0 410 770
-16.1 3 37.4 12.1 54 129.2 51.7 125 257.0 215.6 420 788
-15.5 4 39.2 12.6 55 131.0 54.4 130 266.0 221.1 430 806
-15.0 5 41.0 13.2 56 132.8 57.2 135 275.0 226.7 440 824
-14.4 6 42.8 13.7 57 134.6 60.0 140 284.0 232.2 450 842
-13.9 7 44.6 14.3 58 136.4 62.8 145 293.0 237.8 460 860
-13.3 8 46.4 14.8 59 138.2 65.6 150 302.0 243.3 470 878
-12.7 9 48.2 15.6 60 140.0 68.3 155 311.0 248.9 480 896
-12.2 10 50.0 16.1 61 141.8 71.1 160 320.0 254.4 490 914
-11.6 11 51.8 16.6 62 143.6 73.9 165 429 260.0 500 932
-11.1 12 53.6 17.1 63 145.4 76.7 170 338 265.6 510 950
-10.5 13 55.4 17.7 64 147.2 79.4 175 347 271.1 520 968
-10.0 14 57.2 18.2 65 149.0 82.2 180 356 276.7 530 986
-9.4 15 59.0 8.8 66 150.8 85.0 185 365 282.2 540 1,004
-8.8 16 60.8 19.3 67 152.6 87.8 190 374 287.8 550 1,022
-8.3 17 62.6 19.9 68 154.4 90.6 195 383 293.3 560 1,040
-7.7 18 64.4 20.4 69 156.2 93.3 200 392 298.9 570 1,058
-7.2 19 66.2 21.0 70 158.0 96.1 205 401 304.4 580 1,076
-6.6 20 68.0 21.5 71 159.8 98.9 210 410 310.0 590 1,094
-6.1 21 69.8 22.2 72 161.6 100 212 413 315.6 600 1,112
-5.5 22 71.6 22.7 73 163.4 101.6 215 419 321.1 610 1,130
-5.0 23 73.4 23.3 74 165.2 104.4 220 428 326.7 620 1,148
-4.4 24 75.2 23.8 75 167.0 107.2 225 437 332.2 630 1,166
-3.9 25 77.0 24.4 76 168.8 110.0 230 446 337.8 640 1,184
-3.3 26 78.8 25.0 77 170.6 112.8 235 455 343.3 650 1,202
-2.8 27 80.6 25.5 78 172.4 115.6 240 464 348.9 660 1,220
-2.2 28 82.4 26.2 79 174.2 118.3 245 473 354.4 670 1,238
-1.6 29 84.2 26.8 80 176.0 121.1 250 482 360.0 680 1,256
-1.1 30 86.0 27.3 81 177.8 123.9 255 491 365.6 690 1,274
-0.6 31 87.8 27.7 82 179.6 126.7 260 500 371.1 700 1,292
0 32 89.6 28.2 83 181.4 129.4 265 509 376.7 710 1,310
0.5 33 91.4 28.8 84 183.2 132.2 270 518 382.2 720 1,328
1.1 34 93.2 29.3 85 185.0 135.0 275 527 387.8 730 1,346
1.6 35 95.0 29.9 86 186.8 137.8 280 536 393.3 740 1,364
2.2 36 96.8 30.4 87 188.6 140.6 285 545 398.9 750 1,382
2.7 37 98.6 31.0 88 190.4 143.3 290 554 404.4 760 1,400
3.3 38 100.4 31.5 89 192.2 146.1 295 563 410.0 770 1,418
3.8 39 102.2 32.1 90 194.0 148.9 300 572 415.6 780 1,436
4.4 40 104.0 32.6 91 195.8 151.7 305 581 421.1 790 1,454
4.9 41 105.8 33.3 92 197.6 154.4 310 590 426.7 800 1,472
5.5 42 107.6 33.8 93 199.4 157.2 315 599 432.2 810 1,490
6.0 43 109.4 34.4 94 201.2 160.0 320 608 437.8 820 1,508
6.6 44 111.2 34.9 95 203.0 162.8 325 617 443.3 830 1,526
7.1 45 113.0 35.5 96 204.8 165.6 330 626 448.9 840 1,544
7.7 46 114.8 36.1 97 206.8 171.1 340 644 454.4  850 1,562
8.2 47 116.6 36.6 98 208.4 176.7 350 662 460.0 860 1,580
8.8 48 118.4 37.1 99 210.2 182.2 360 680 465.6 870 1,598
9.3 49 120.2 37.8 100 212.0 187.8 370 698 471.1 880 1,616
9.9 50 122.0 40.6 105 221.0 193.3 380 716      
10.4 51 123.8 43.3 110 230.0 198.9 390 734      

 

 

Download a PDF of Fluid Power Design Data Sheet 78 - Wire Size and Fuse Ratings for 3-Phase Induction Motors

© 1990 by Womack Machine Supply Co. This company assumes no liability for errors in data nor in safe and/or satisfactory operation of equipment designed from this information.

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