Square D Digest 179

Motor Protection Selection Tables Motor Circuit Protection Selection

Motor Circuit Protectors

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Table 7.91 Selection Tables for Conductors, Safety Switches and Thermal-Magnetic Circuit Breakers Based on 2017 NEC ® Tables 430.247, 430.248 & 430.250 (cont'd.) Horsepower Ratings

Amperage of Thermal-Magnetic [11] Inverse Time Circuit Breaker

Minimum Size metallic Conduit 75° C, C Wire Field-Installed Sized for 125% FLA [13]

QMB and Heavy Duty Switch with Time Delay Fuses [12]

Squirrel-Cage and Wound Rotor Motors with Norm. Torque Characteristics Operating at Usual Speeds

Average Direct Current Motors Operating at BaseSpeed

For Motor Code Letter B to E

Full Load Amperage [10]

1Ø 10Hzac

For Motor Code LetterF toV [14]

Conduit 3W

3Ø60Hz

AWG kcmil

Ordinary Service [15]

Heavy Service andEnergy Efficient [16]

THHN THWN XHHW

200 Vac [17]

200 Vac [17]

THW

230 Vac

460 Vac

575 Vac

115 Vac

230 Vac

120 Vdc

240 Vdc

30

92.0A 96.0A 99.0A 100.0A 104.0A 106.0A 120.0A 124.0A 125.0A 130.0A 140.0A 144.0A 150.0A 154.0A 156.0A 173.0A 177.0A 180.0A 192.0A 221.0A 240.0A 242.0A 248.0A 285.0A 289.0A 302.0A 312.0A 336.0A 359.0A 360.0A 361.0A 382.0A 414.0A 472.0A 477.0A 480.0A 552.0A 590.0A

75

200A

250A

100

1

1-1/4 in.

1-1/2 in.

10

150A

40

225A

30

300A

175A

1/0

1-1/4 in.

1-1/2 in.

40

250A 250A

100

125

350A

2/0

1-1/2 in.

1-1/2 in.

50

200A

40

300A

150

50

3/0

1-1/2 in.

2 in.

60

400A

225A

125

350A

50

60

4/0

2 in.

2 in.

250A

150

400A

500A

75

200

250 300

2 in. 2 in.

2 in.

75

300A

450A

2-1/2 in.

600A

200

250

350A

500A

350

2-1/2 in.

2-1/2 in.

400A

700A

100

100

600A

300

400A

500

3 in.

3 in.

800A

250

(2) 3/0 (2) 2-1/2 in. (2) 2 in.

125

450A 500A

700A

350

900A

125

(2) 4/0 (2) 2 in.

(2) 2 in.

150

800A

300

600A

1000A

400

(2)300 (2) 2 in.

(2) 2-1/2 in.

600A

150

350

900A

500

1200A

(2) 350 (2) 2-1/2 in. (2) 2-1/2 in.

400

1000A

800A

200

200

(3) 2-1/2 in.

500

1200A

1600A

— (3) 300 (3) 2 in.

900A

250

602.0A Contact your local Field Office for circuit breaker selection on constant horsepower multi speed motors.

[10] Motor full load currents thru 200 hp are taken from NEC Tables 430.247, 248 and 250. Above 200 hp from UL 98. Select wire size, circuit breakers, or fuses on basis of hp rather than nameplate full load current per NEC 430.6. Do not use these values to select overload relay thermal units. See Digest pages 16-129—16152 for selection of thermal units when actual full load current is not known. Voltages listed are rated motor voltages. Corresponding nominal system voltages are 110–120 V, 200–208 V, 220–240 V, 440–480 V and 550–600 V [11] Thermal-magnetic circuit breaker ampere ratings recommended are approximate for average conditions, based on trip characteristics of Square D circuit breakers and NEC Table 430.52. Under some conditions, the next size larger switch or circuit breaker rating may be necessary to accommodate the motor starting current and is permitted by NEC 430.52(C)(1) Exception 2. High starting currents are anticipated with Design E and other energy efficient motors. For explanation of Code letter markings, see NEC 430.7(B). For Busway Plug-in units, see page 9-7. [12] Switch size only is shown in table. Selected fuses should not exceed maximum percent of full-load current as given in NEC Table 430.52. Above 50 hp dc switches are not hp rated by UL as Motor Circuit Switches, but as General Use Switches only and are not necessarily capable of interrupting the max. operating overload current of a motor. See NEC 100 for definition of General Use Switch. When protecting a 3Ø, Design E energy efficient motor, the switch is required by NEC 430.109 to have a hp rating of not less than 1.4 times that of a motor rated 3–100 hp, or not less than 1.3 times that of a motor rated over 100 hp. Switches shown in this table do not necessarily comply with that requirement. [13] NEC 430.22 for Single Motor, Smaller conductors may be permitted for light duty-cycle service per 430.22 (B) Exception No. 1. DC motors operating from rectified 1Ø power supply will require larger conductors per 430.22 (A) Exception No. 1. For motor-generator arc welders, see 630.11 [14] Thermal-magnetic breaker ampere ratings recommended are approximate for average conditions and based on trip characteristics of Square D circuit breakers and NEC Tables 430.7(B) and 430.52. [15] Ordinary service for normal starting duty only, acceleration time of 10 sec. or less. [16] Heavy service is jogging or plugging duty or cycling load with over 25 starts per hour or over 5 starts per minute. Energy efficient motors are polyphase motors defined in NEMA Standard MG1 and exhibit high starting current. [17] 200 V motors are commonly used on 208 V services.

CIRCUIT BREAKERS

7 MINIATURE AND MOLDED CASE

7-51

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