Motors room usually safeguarded by both fuses (or circuit breakers) and by heater coils in a magnetic starter. Fuses open up the circuit quickly in case of a huge overload or short circuit. Heater coils carry out a hold-up and open up the circuit if the mean current, over a duration of time, is greater than the circuit is draft for.

You are watching: How to calculate fuse rating for motor

In some situations it might be important to usage delayed action fuses. These administer a really short hold-up to stop blowing a fuse during the quick interval if the engine is increasing up come its normal rate after being started.

Current worths in this chart room approximate, and are compiled from data released by numerous motor manufacturers. They may be a little high or low for a particular motor. For choice of magnetic starter heater coils, the is better to monitor the nameplate present rating of the actual engine to be used rather than relying on this or any other table.

Wire and fuse size are provided for reference only, and also may differ with kind of insulation, number of conductors in a cable and also other factors. Because that a brand-new design, needs of the NEC (National electric Code) should be followed. Copies of the code have the right to be ordered with most book stores. Other local ordinances may likewise apply.

HPSpeedRPM230-Volt Service460-Volt Service HPSpeedRPM230-Volt Service460-Volt Service
FullLoadAmpsWireSizeFuseAmpsFullLoadAmpsWireSizeFuseAmpsFullLoadAmpsWireSizeFuseAmpsFullLoadAmpsWireSizeFuseAmps
11,2003.7614101.88146251,20065.6312032.86180
11,8003.5614101.78146251,80064.8312032.4680
13,6002.8014101.40146253,60060.8312030.4680
1-1/21,2005.2814152.641410301,20078.8115039.4680
1-1/21,8004.8614152.431410301,80075.6115037.8680
1-1/23,6004.3614152.181410303,60073.7115036.8680
21,2006.8415203.421410401,200102020050.64110
21,8006.4014203.201410401,800101020050.44110
23,6005.6014203.001410403,60096.4020048.24110
31,20010.214255.121415501,20012600025063.03120
31,8009.4014254.701415501,80012400025062.23120
33,6008.3414254.171415503,60012000025060.13120
51,20015.812307.911420601,20015000030075.02150
51,80014.412307.211420601,80014900030074.52150
53,60013.512306.761420603,60014300030071.72150
7-1/21,20021.8104010.91420751,20018430035092.00200
7-1/21,80021.5104010.71420751,80018330035091.60200
7-1/23,60019.510409.791420753,60017930035089.60200
101,20028.086014.012301001,200239500500120000250
101,80026.886013.412301001,800236500500118000250
103,60025.486012.712301003,600231500500115000250
151,20041.468020.710401251,200298- - -- - -1490000300
151,80039.268019.610401251,800293- - -- - -1470000300
153,60036.468018.210401253,600292- - -- - -1460000300
201,20052.8411026.48601501,200350- - -- - -174300350
201,80051.2411025.68601501,800348- - -- - -174300350
203,60050.4411025.28601503,600343- - -- - -174300350

 

For choosing ampere rating of heater coils for magnetic motor starters, pick the conventional coil closest come the rating ~ above 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 following larger current rating might work better.

For additional information, see Design Data sheet 11. See additionally Design Data sheet 33 and Design Data sheet 49 for result of high and low voltage on electric motors. An ext detailed info on magnetic engine starters including wiring diagrams, will be discovered in the Womack book “Electrical regulate of fluid Power".

 

TEMPERATURE counter - FAHRENHEIT and CELSIUS

Enter one of the columns significant “Temp” with the temperature, one of two people Fahrenheit or Celsius, i beg your pardon you great to convert. If converting to Celsius, review the tantamount value in the pillar to the left. If convert to Fahrenheit, check out the equivalent value in the shaft to the right. The table to be calculated from these formula:

°F = <°C × 9/5> + 32 or°C = 5/9 × <°F - 32>

 

Enter one of these columns through the temperature you great to convert

*

DegreeCTemp.DegreeF DegreeCTemp.DegreeF DegreeCTemp.

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DegreeF DegreeCTemp.DegreeF
-17.21 33.811.152125.646.1115239.0204.4400752
-16.6235.611.553127.448.9120248.0210.0410770
-16.1337.412.154129.251.7125257.0215.6420788
-15.5439.212.655131.054.4130266.0221.1430806
-15.0541.013.256132.857.2135275.0226.7440824
-14.4642.813.757134.660.0140284.0232.2450842
-13.9744.614.358136.462.8145293.0237.8460860
-13.3846.414.859138.265.6150302.0243.3470878
-12.7948.215.660140.068.3155311.0248.9480896
-12.21050.016.161141.871.1160320.0254.4490914
-11.61151.816.662143.673.9165429260.0500932
-11.11253.617.163145.476.7170338265.6510950
-10.51355.417.764147.279.4175347271.1520968
-10.01457.218.265149.082.2180356276.7530986
-9.41559.08.866150.885.0185365282.25401,004
-8.81660.819.367152.687.8190374287.85501,022
-8.31762.619.968154.490.6195383293.35601,040
-7.71864.420.469156.293.3200392298.95701,058
-7.21966.221.070158.096.1205401304.45801,076
-6.62068.021.571159.898.9210410310.05901,094
-6.12169.822.272161.6100212413315.66001,112
-5.52271.622.773163.4101.6215419321.16101,130
-5.02373.423.374165.2104.4220428326.76201,148
-4.42475.223.875167.0107.2225437332.26301,166
-3.92577.024.476168.8110.0230446337.86401,184
-3.32678.825.077170.6112.8235455343.36501,202
-2.82780.625.578172.4115.6240464348.96601,220
-2.22882.426.279174.2118.3245473354.46701,238
-1.62984.226.880176.0121.1250482360.06801,256
-1.13086.027.381177.8123.9255491365.66901,274
-0.63187.827.782179.6126.7260500371.17001,292
03289.628.283181.4129.4265509376.77101,310
0.53391.428.884183.2132.2270518382.27201,328
1.13493.229.385185.0135.0275527387.87301,346
1.63595.029.986186.8137.8280536393.37401,364
2.23696.830.487188.6140.6285545398.97501,382
2.73798.631.088190.4143.3290554404.47601,400
3.338100.431.589192.2146.1295563410.07701,418
3.839102.232.190194.0148.9300572415.67801,436
4.440104.032.691195.8151.7305581421.17901,454
4.941105.833.392197.6154.4310590426.78001,472
5.542107.633.893199.4157.2315599432.28101,490
6.043109.434.494201.2160.0320608437.88201,508
6.644111.234.995203.0162.8325617443.38301,526
7.145113.035.596204.8165.6330626448.98401,544
7.746114.836.197206.8171.1340644454.4 8501,562
8.247116.636.698208.4176.7350662460.08601,580
8.848118.437.199210.2182.2360680465.68701,598
9.349120.237.8100212.0187.8370698471.18801,616
9.950122.040.6105221.0193.3380716   
10.451123.843.3110230.0198.9390734