and Training Doug Conaway Director C. A.<br><br> Phillips Deputy Director Tom Harmon Electrical Inspector John Scott Electrical Inspector Bob Thornsbury Electrical Inspector March 2003 Revised July 2003 VOLTS FULL-LOAD CURRENT X 400% Operating voltage. Motor full-load current X 400% to determine maximum allowable short circuit protection if MOTOR HORSEPOWER thermal circuit breaker or fuses are used. Horsepower of the motor.<br><br> FULL-LOAD CURRENT x 700% MOTOR FLC To determine low setting for short circuit Full-load current of the motor. protection using a magnetic CB. FLC X 125% FULL-LOAD CURRENT X 1300% Motor full-load current x 125% to determine To determine short circuit protection using a required cable size and overload protection.<br><br> magnetic circuit breaker, try to start at (Some manufacturers have the 125% already 700% of motor full-load current. If motor will not calculated into their heater charts). start, keep increasing but do not exceed 1300% of motor full-load current.<br><br> CABLE SIZES Power cables are rated at different temperatures. BREAKER TRIP RANGE Normally the mining industry uses 75 and 90 The variable adjustable short circuit protection degree insulation ratings. Underground mining of a circuit breaker.<br><br> cables listed have been calculated for the underground ambient temperature factors. The TRIP RANGE SET ON surface charts utilize the standardization of the From 700% to 1300% of motor full-load current National Electrical Code for jacketed-cables or (For a magnetic CB). enclosed in conduit.<br><br> HEATER SIZE CIRCUIT BREAKER AND FUSE SIZE No greater than 125% of motor full load current. Standard Listings 15-20-25-30-35-40-45-50-60- 70-80-90-100-110-125-150-175-200-225-250- HEATER AMPS 300 350-400-450-500-600-700-800-1000-1200- Set point of heaters which will open 1600-2000-2500-3000-4000-5000 and 6000. the circuit.<br><br> FULL-LOAD CURRENT X 250% CT RATIO Motor full-load current X 250% to determine low Current transformer used in conjunction with setting for short circuit protection if thermal thermal overloads to provide motor overload circuit breaker or fuses are used. protection. STARTER SIZE Minimum size starter.<br><br> DEFINITIONS Page 1 S U THERMAL BK OR FUSE SIZE 90 ( SURFACE ) This example utilizes a U N FLC X 250% = 85 amps ( a standard thermal circuit breaker or fuses R D size 90 amp thermal CB or fuse although a thermal magnetic circuit F E is acceptable). breaker is acceptable. A R FLC X 700% 238 C G FLC X 700% = 238 amps is low ( UNDERGROUND ) This example E R setting for short circuit protection utilizes a magnetic circuit O (magnetic CB).<br><br> breaker. U FLC X 1300% 442 N FLC X 1300% = 442 amps is maximum D setting for short circuit protection VOLTS 460 460 (magnetic CB). Operating voltage.<br><br> BREAKER TRIP RANGE 150 HORSEPOWER 25 25 Magnetic CB with 480 Rated motor horsepower. adjustable trip range between MOTOR FLC 34 34 150 to 480 amps. Motor full-load current.<br><br> TRIP RANGE SETTING 250 FLC X 125% 43 43 CB with 150 to 480 trip range and 13 Motor full-load current X 125% = 43 settings set on No.4 (250 amps ) amps. would be acceptable. CABLE SIZE 8 8 CT RATIO No.<br><br> 8 AWG copper rated for 50 amps Normally not used in motors below surface or No.8 copper rated for 70 100 HP. amps underground. HEATER SIZE FH56 FH56 CABLE AMPACITY 50 70 FH 56 rated for 41.5 amps.<br><br> Rating No. 8 copper rated for 50 amps not to exceed 125% of motor FLC. surface and 70 amps underground.<br><br> HEATER AMPS 41.5 41.5 FLC X 250% 85 FH 56 will open circuit if amperage FLC 34 amps X 250% = 85 amps low reaches 41.5 amps. setting for short circuit protection STARTER SIZE 2 2 (thermal circuit breaker or fuses). Minimum size starter.<br><br> FLC X 400 % 136 FLC 34 amps X 400% = 136 amps Maximum setting for short circuit protection (thermal circuit breaker or fuses). SINGLE MOTOR EXAMPLE Page 2 VOLTS 460 MOTOR HORSEPOWER 150 150 System operating voltage. Rated motor horsepower.<br><br> MOTOR FLC 180 MOTOR FLC 180 180 Motor full-load current. Motor full-load current. FLC X 125% 225 FLC X 125% 225 225 Motor FLC x 125% = 225 amps.<br><br> Motor FLC 180 X 125% = 225 amps. FLC + (FLC X 125%) 405 BRANCH CIR CABLE SIZE 4/0 4/0 To determine required size feeder conductor Minimum size cable for motors receiving power in a multi-motor installation. The largest HP from feeder circuit 125% of motor FLC.<br><br> FLC X 125% + FLC of other motors connected BR. CIR CABLE AMPAC. 230 230 to the feeder circuit.<br><br> EXAMPLE: Installation Rated ampacity of branch circuit cable. Contains two (2) 460 volt, 150 HP, 180 amp FLC X 250% 450 450 motors. Multiply (180 amps by 125% = 225 FLC 180 X 250% = 450, low setting for short amps + 180 amps = 405 amps).<br><br> Circuit protection (fuses or thermal CB). FEEDER SIZE 600 FLC X 400% 720 720 A 600 MCM copper cable would be the FLC 180 X 400% = 720, maximum setting for minimum size for surface installation. If this short circuit protection (fuses or thermal CB).<br><br> Circuit were to be installed underground, referring FLC X 700% 1260 1260 to the underground cable ampacity chart 0-2K FLC of motor X 700% low setting for volts, a 300 MCM 90 degree cable rated at 421 magnetic CB. Amps would be acceptable. FLC X 1300% 2340 2340 FEEDER AMPACITY 420 FLC of motor X 1300% maximum setting for Rated ampacity of cable from power magnetic CB.<br><br> Source to beginning of branch circuits. CT RATIO 300/5 300/5 TRIP RANGE 15-3 A 300/5 CT=60/1 (300 divided by 5 = 60/1) Thermal magnetic CB with adjustable trip range. Low setting 1500 high 3000 amps.<br><br> A motor operating at 60 amps, the secondary output would be 1 amp. TRIP RANGE SETTING 1500 HEATER SIZE FH 30 FH 30 150 HP 180 amps 180 X 700% = 1260, set Multiply CT ratio (60/1) by FH-30 (3.73 amps) = trip range on low (1500 amps). 224 amps.<br><br> This is 1 amp under 225 amp max. FUSE & THERMAL CB SZ 450 HEATER AMPS 3.73 3.73 Fuse or (thermal CB only) for short circuit Rated amperage for heater strips will open protection of feeder cable, try to start at 250%. Circuit if overload condition occurs.<br><br> If motors will not start, increase up to STARTER SIZE 5 5 400% max. Minimum size starter. MULTI-MOTOR EXAMPLE Page 3 CT RATIO HEATER SIZE FOR MOTOR PROTECTION Normally motors over 100 horsepower use current transformers (CT) to provide overload protection.<br><br> Overload protection shall not be greater than 125% of the motor rated full-load current. EXAMPLE: A 300/5 CT=60/1 (300 divided by 5=60). If a motor is operating at 60 amps, the secondary amperage of the CT would be 1 amp.<br><br> The chart above has been calculated to determine the maximum overload heater size for proper overload protection not to exceed 125% of motor full-load operating current. EXAMPLE: A 150 horsepower, 460 volt motor operates at 180 amps full-load current. 180 amps X 125% = 225 amps.<br><br> Overload protection shall not exceed 225 amps. The heater size FH-30 is rated for 3.73 amps. Multiply CT ratio (60/1) by FH-30 (3.73 amps) = 224 amps.<br><br> This is one amp under the 225 amp maximum. If FH series heaters are not used, this chart can be used to cross reference amperage rating of other heaters. 460V 100 HP 125 HP 150 HP 200 HP 250 HP FLC X 125% 155 195 225 300 378 100/5 = 20/1 FH-37 FH-40 FH-41 FH-45 FH-47 150/5 = 30/1 FH-33 FH-36 FH-37 FH-40 FH-43 200/5 = 40/1 FH-30 FH-33 FH-34 FH-37 FH-40 250/5 = 50/1 FH-27 FH-30 FH-32 FH-35 FH-37 300/5 = 60/1 FH-26 FH-28 FH-30 FH-33 FH-35 350/5 = 70/1 FH-24 FH-26 FH-28 FH-31 FH-34 400/5 = 80/1 FH-22 FH-25 FH-26 FH-30 FH-32 450/5 = 90/1 FH-21 FH-24 FH-25 FH-28 FH-31 500/5 = 100/1 FH-20 FH-23 FH-24 FH-27 FH-30 600/5 = 120/1 FH-18 FH-21 FH-22 FH-25 FH-28 Page 4 H F 1 2 4 7 1 H S P L 2 5 0 0 3 T T 4 C 5 0 0 0 0 6 % % % % 0 S S 0 % Z Z 0.5 1.1 1.3 2.75 4.4 7.7 14.3 FH 18 0 0.75 1.6 2 4 6.4 11.2 21 FH 23 0 1 2.1 2.6 5.25 8.4 14.7 27 FH 26 0 1.5 3 3.75 7.5 12 21 39 FH 30 0 2 3.4 4.25 8.5 13.6 23.8 44 FH 31 0 3 4.8 6 12 19.2 33.6 62 FH 35 0 5 7.6 9.5 19 30.4 53.2 99 FH 40 0 7.5 11 14 27.5 44 77 143 FH 44 1 10 14 17.5 35 56 98 182 FH 47 1 15 21 26.3 52.5 84 147 273 FH 50 2 20 27 34 67.5 108 189 351 FH 53 2 25 34 43 85 136 238 442 FH 56 2 30 40 50 100 160 280 520 FH 81 3 40 52 65 130 208 364 676 FH 83 3 50 65 81 163 260 455 845 FH 86 3 60 77 96 193 308 539 1001 FH 88 4 75 96 120 240 384 672 1248 FH 90 4 100 124 155 310 496 868 1612 FH 93 4 125 156 195 390 624 1092 2028 5 150 180 225 450 720 1260 2340 5 200 240 300 600 960 1680 3120 5 250 302 378 755 1208 2114 3926 6 300 361 451 902 1444 2527 4693 6 350 414 517 1035 1656 2898 5382 6 400 477 596 1192 1908 3339 6201 6 450 515 644 1287 2060 3605 6695 7 500 590 738 1475 2360 4130 7670 7 H F 1 2 4 7 1 H S P L 2 5 0 0 3 T T 5 C 5 0 0 0 0 7 % % % % 0 S S 5 % Z Z 0.5 0.9 1.2 2.25 3.6 6.3 11.7 FH17 0 0.75 1.3 1.62 3.25 5.2 9.1 16.9 FH 21 0 1 1.7 2.12 4.25 6.8 11.9 22.1 FH 23 0 1.5 2.4 3 6 9.6 16.8 31.2 FH 27 0 2 2.7 3.3 6.7 10.8 18.9 35.1 FH 28 0 3 3.9 4.8 9.75 15.6 27.3 50.7 FH 32 0 5 6.1 7.6 15 24.4 42.7 79.3 FH 37 0 7.5 9 11.2 22.5 36 63 117 FH 41 1 10 11 13.75 27.5 44 77 143 FH 44 1 15 17 21.25 42 68 119 221 FH 48 2 20 22 27.5 55 88 154 286 FH 51 2 25 27 33.7 67 108 189 351 FH 53 2 30 32 40 80 128 224 416 FH 78 3 40 41 51 102 164 287 533 FH 79 3 50 52 65 130 208 364 676 FH 83 3 60 62 77 155 248 434 806 FH 85 4 75 77 96 192 308 539 1001 FH 88 4 100 99 124 247 396 693 1287 FH 91 4 125 125 156 312 500 875 1625 5 150 144 180 360 576 1008 1872 5 200 192 240 480 768 1344 2496 5 250 242 302 605 968 1694 3146 6 300 289 361 722 1156 2023 3756 6 350 336 420 840 1344 2352 4368 6 400 382 477 955 1528 2674 4966 6 450 412 515 1030 1648 2884 5356 7 500 472 590 1180 1888 3304 6136 7 Page 5 MAGNETIC TRIP RANGE 150 300 500 750 800 1500 2000 2500 480 700 1000 1500 1600 3000 4000 5000 LO 150 300 500 750 800 1500 2000 2500 1 191 350 562 844 900 1688 2250 2812 2 232 400 625 938 1000 1875 2500 3125 3 274 450 687 1031 1100 2063 2750 3437 4 315 500 750 1125 1200 2250 3000 3750 5 356 550 812 1219 1300 2438 3250 4062 6 397 600 875 1313 1400 2625 3500 4375 7 439 650 937 1407 1500 2813 3750 4687 HI 480 700 1000 1500 1600 3000 4000 5000 50 66 150 150 190 480 UNDERGROUND COND.<br><br> LO 50 66 150 0-2000V 2 TO 8 K 1 58 75 175 AWG 75C 90C 75C 90C 2 65 85 200 14 17 17 3 73 94 225 12 22 22 4 80 104 250 10 28 28 5 88 113 275 8 63 70 6 95 123 300 6 81 93 99 110 7 103 132 325 4 106 123 130 144 8 111 142 350 3 125 142 9 118 151 375 2 144 163 170 188 10 126 161 400 1 163 190 196 217 11 134 170 425 1/0 181 219 226 249 HI 142 180 450 2/0 213 254 260 287 3/0 244 294 299 329 SC TRAIL. CABLES 4/0 275 329 343 379 10 150 1 1000 250 306 378 379 419 8 200 1/0 1250 300 344 421 423 470 6 300 2/0 1500 350 381 465 465 513 4 500 3/O 2000 400 406 507 500 555 3 600 4/0 2500 500 469 575 571 632 2 800 SURFACE CONDUCTORS AWG COPPER ALUMINUM 75C 75C 14 20+ 12 25+ 20+ 10 35+ 30+ 8 50 40 6 65 50 4 85 65 3 100 75 2 115 90 1 130 100 1/0 150 120 2/0 175 135 3/0 200 155 4/0 230 180 250 255 205 300 285 230 350 310 250 400 335 270 500 380 310 600 420 340 700 460 375 750 475 385 800 490 395 900 520 425 1000 545 445 1250 590 485 1500 625 520 1750 650 554 2000 665 560 Page 6 HEATER SIZE FH-3 0.27 FH-26 2.58 FH-49 21.7 FH-4 0.31 FH-27 2.83 FH-50 23.9 FH-5 0.34 FH-28 3.11 FH-51 26.2 FH-6 0.38 FH-29 3.42 FH-52 28.7 FH-7 0.42 FH-30 3.73 FH-53 31.4 FH-8 0.46 FH-31 4.07 FH-54 34.5 FH-9 0.5 FH-32 4.39 FH-55 37.9 FH-10 0.55 FH-33 4.87 FH 56 41.5 FH-11 0.62 FH-34 5.3 FH 78 37.5 FH-12 0.68 FH-35 5.9 FH-79 41.5 FH-13 0.75 FH-36 6.4 FH-80 46.3 FH-14 0.83 FH-37 7.1 FH-81 50 FH-15 0.91 FH-38 7.8 FH-82 55 FH-16 1 FH-39 8.5 FH-83 61 FH-17 1.11 FH-40 9.4 FH-84 66 FH-18 1.22 FH-41 10.3 FH-85 73 FH-19 1.34 FH-42 11.3 FH-86 78 FH-20 1.47 FH-43 12.4 FH-87 84 FH-21 1.62 FH-44 13.5 FH-88 92 FH-22 1.78 FH-45 14.9 FH-89 101 FH-23 1.95 FH-46 16.3 FH-90 110 FH-24 2.15 FH-47 18 FH-91 122 FH-25 2.35 FH-48 19.8 FH-92 129 FH-93 133 CT RATIO HEATER SIZE FOR MOTOR PROT. 460 V 100HP 125HP 150HP 200HP 250HP FLC X 125% 155 195 225 300 378 100/5=20/1 FH-37 FH-40 FH-41 FH-45 FH-47 150/5=30/1 FH-33 FH-36 FH-37 FH-40 FH-43 200/5=40/1 FH-30 FH-33 FH-34 FH-37 FH-40 250/5=50/1 FH-27 FH-30 FH-32 FH-35 FH-37 300/5=60/1 FH-26 FH-28 FH-30 FH-33 FH-35 350/5=70/1 FH-24 FH-26 FH-28 FH-31 FH-34 400/5=80/1 FH-22 FH-25 FH-26 FH-30 FH-32 450/5=90/1 FH-21 FH-24 FH-25 FH-28 FH-31 500/5=100/1 FH-20 FH-23 FH-24 FH-27 FH-30 600/5=120/1 FH-18 FH-21 FH-22 FH-25 FH-28 CT RATIO HEATER SIZE FOR MOTOR PROT.<br><br> 575 V 100HP 125HP 150HP 200HP 250HP FLC X 125% 124 156 180 240 302 100/5=20/1 FH-35 FH-38 FH-39 FH-42 FH-45 150/5=30/1 FH-31 FH-33 FH-35 FH-38 FH-40 200/5=40/1 FH-27 FH-30 FH-32 FH-35 FH-37 250/5=50/1 FH-25 FH-28 FH-29 FH-32 FH-35 300/5=60/1 FH-23 FH-26 FH-27 FH-30 FH-33 350/5=70/1 FH-21 FH-24 FH-25 FH-29 FH-31 400/5=80/1 FH-20 FH-23 FH-24 FH-27 FH-30 450/5=90/1 FH-19 FH-21 FH-23 FH-26 FH-28 500/5=100/1 FH-18 FH-20 FH-22 FH-25 FH-27 600/5=120/1 FH-16 FH-18 FH-20 FH-23 FH-25 STANDARD FUSE AND THERMAL BREAKER SZ 15 50 125 350 1000 5000 20 60 150 400 1200 6000 25 70 175 450 1600 30 80 200 500 2000 35 90 225 600 2500 40 100 250 700 3000 45 110 300 800 4000 Page 7 LOCATION VOLTS HORSEPOWER MOTOR FLC FLC X 125% CABLE SIZE CABLE AMPACITY FLC X 250 % FLC X 400 % THERM. BKR OR FUSE SZ FLC X 700 % FLC X 1300 % BKR TRIP RANGE TRIP RANGE SETTING CT RATIO HEATER SIZE HEATER AMPS STARTER SIZE LOCATION VOLTS HORSEPOWER MOTOR FLC FLC X 125% CABLE SIZE CABLE AMPACITY FLC X 250 % FLC X 400 % THERM BKR OR FUSE SZ FLC X 700 % FLC X 1300 % BKR TRIP RANGE TRIP RANGE SETTING CT RATIO HEATER SIZE HEATER AMPS STARTER SIZE LOCATION VOLTS HORSEPOWER MOTOR FLC FLC X 125% CABLE SIZE CABLE AMPACITY FLC X 250 % FLC X 400 % THERM. BKR OR FUSE SZ FLC X 700 % FLC X 1300 % BKR TRIP RANGE TRIP RANGE SETTING CT RATIO HEATER SIZE HEATER AMPS STARTER SIZE LOCATION VOLTS HORSEPOWER MOTOR FLC FLC X 125% CABLE SIZE CABLE AMPACITY FLC X 250 % FLC X 400 % THERM BKR OR FUSE SZ FLC X 700 % FLC X 1300 % BKR TRIP RANGE TRIP RANGE SETTING CT RATIO HEATER SIZE HEATER AMPS STARTER SIZE Page 8 LOCATION VOLTS MOTOR FLC MOTOR FLC X 125% FLC + (FLC X 125%) FEEDER SIZE FEEDER AMPACITY TRIP RANGE TRIP RANGE SETTING FUSE OR TH BKR SZ HORSEPOWER MOTOR FLC MOTOR FLC X 125% BR CIR CABLE SZ BR CIR CABLE AMP.<br><br> FLC X 250% FLC X 400% FLC X 700% FLC X 1300% CT RATIO HEATER SIZE HEATER AMPS STARTER SIZE LOCATION VOLTS MOTOR FLC MOTOR FLC X 125% FLC + (FLC X 125%) FEEDER SIZE FEEDER AMPACITY TRIP RANGE TRIP RANGE SETTING FUSE OR TH BKR SZ HORSEPOWER MOTOR FLC MOTOR FLC X 125% BR CIR CABLE SZ BR CIR CABLE AMP. FLC X 250% FLC X 400% FLC X 700% FLC X 1300% CT RATIO HEATER SIZE HEATER AMPS STARTER SIZE LOCATION VOLTS MOTOR FLC MOTOR FLC X 125% FLC + (FLC X 125%) FEEDER SIZE FEEDER AMPACITY TRIP RANGE TRIP RANGE SETTING FUSE OR TH BKR SZ HORSEPOWER MOTOR FLC MOTOR FLC X 125% BR CIR CABLE SZ BR CIR CABLE AMP. FLC X 250% FLC X 400% FLC X 700% FLC X 1300% CT RATIO HEATER SIZE HEATER AMPS STARTER SIZE LOCATION VOLTS MOTOR FLC MOTOR FLC X 125% FLC + (FLC X 125%) FEEDER SIZE FEEDER AMPACITY TRIP RANGE TRIP RANGE SETTING FUSE OR TH BKR SZ HORSEPOWER MOTOR FLC MOTOR FLC X 125% BR CIR CABLE SZ BR CIR CABLE AMP.<br><br> FLC X 250% FLC X 400% FLC X 700% FLC X 1300% CT RATIO HEATER SIZE HEATER AMPS STARTER SIZE Page 9

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