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



HORSEPOWER115 VOLTS
(120V)
208 VOLTS 230 VOLTS
(240V)
1/64.42.4 2.2
1/45.83.2 2.9
1/37.24.0 3.6
1/29.85.4 4.9
3/413.87.6 6.9
116.08.8 8.0
1-1/220.011.0 10.0
224.013.2 12.0
334.018.7 17.0
556.030.8 28.0
7-1/280.044.0 40.0
10100.055.0 50.0








NEC Table 430.250

Full Load Current,
 Three Phase Alternating-Current Motors 
(Induction-Type Squirrel Cage
and Wound Rotors in Amperes)



HORSEPOWER208 VOLTS230 VOLTS
(240V)
460 VOLTS
(480V)
1/22.42.2 1.1
3/43.53.2 1.6
14.64.2 2.1
1-1/26.66.0 3.0
27.56.8 3.4
310.69.6 4.8
516.715.2 7.6
7-1/224.222 11
1030.828 14
1546.242 21
2059.454 27
2574.868 34
308880 40
40114104 52
50143130 65
60169154 77
75211192 96
100273248 124
125343312 156
150396360 180
200528480 240
250---- 302
300---- 361
350---- 414
400---- 477
450---- 515
500---- 590









Search This Site



Subscribe!
XML RSS
Add to Google
Add to My Yahoo!
Add to My MSN
Subscribe with Bloglines




Copyright © 2009 – electrical-design-tutor.com – All Rights Reserved
Home    Site Map    Disclaimer    Contact