Section 15
Application Data
Contents
Reference Guide
15/2
Table 1:
Ampacities of Insulated Conductors
15/3
Table 2:
Correction Factors for Ambient Temperatures
15/3
Table 4A:
Motor Full-Load Currents of
Three Phase AC Induction Type Motors
15/4
Table 4B:
Motor Full-Load Currents in Amperes,
Single Phase AC
15/4
Table 4C:
Motor Full-Load Currents in Amperes, DC
15/4
Table 4D:
Conversion Table of Polyphase Design
15/4
Table 5:
Normal-Load and Fault Currents of
Three Phase Transformers
15/4
Table 6:
Electrical Formulas for Finding Amperes,
Horsepower Kilowatts, and kVA
15/5
Table 7:
Grounding Electrode Conductor for
AC Systems
15/5
Table 8:
Minimum Size Grounding Conductors for
Grounding Raceways and Equipment
15/5
Conversion Table
15/6
15
Application Data
REFERENCE GUIDE
General
In the application of fusible switches and
circuit breakers, consideration should be
given to the following factors:
1. Voltage of circuit.
2. Ampacity of circuit.
3. Frequency of power source.
4. Operating conditions.
5. Fault current available.
Voltage of Circuit — The system
voltage should not exceed the listed
voltage rating of the circuit breaker,
fuse or switch.
Ampacity of Circuit — The listed
continuous current rating of the fuse or
circuit breaker should not exceed the
allowable ampacity of the conductors.
Where the allowable ampacity of the
conductor does not correspond to
listed current ratings for fuses or circuit
breakers, the next larger rating of fuse
or circuit breaker is permitted providing it
does not exceed the conductor ampacity
by more than 25%. An exception to this
rule is permitted for motor circuits or
other circuits where high inrush currents
may persist for an appreciable time.
Frequency of Power Source — Circuit
breakers and fusible switches are
calibrated for use on direct current or
48–68-Hertz alternating current. For
frequencies above 62-Hertz, some fuses,
switches and circuit breakers must be
derated. The derating varies with each
type and size of protective device.
Consult your local representative for
specific information.
15
APPLICATION
DATA
15/2
Operating Conditions — Molded case
circuit breakers and fuses are calibrated
without any enclosure as specified by
the Underwriters’ Laboratories, Inc.
Sound engineering practice dictates that
continuous loads should not exceed 80%
of the breaker or fuse current rating for
most types of enclosures.
Electrical Connections — Molded Case
Circuit Breakers are to be connected
with 60 or 75°C wire for breakers having
a rated ampacity of 125 amperes or
less. For circuit breakers having a rated
ampacity greater 125 amperes, only 75°C
cable shall be used unless otherwise
indicated on the circuit breaker label.
Note: Exceptions to this rule are outlined
in Article 110-14-C(1) and C(2) of the 2002
National Electric Code.
Conductors should be derated in
accordance with the National Electrical
Code for both ambient temperature and
continuous loading. Table 2 on page
16-3 lists the correction factors to be
applied to the allowable current-carrying
capacities of conductors for application
in temperatures above 30°C. Conductors
which are loaded continuously should be
derated to 80% of their allowable currentcarrying capacity except when supplied
by an assembly including its overcurrent
device that is listed for continuous
operation at 100% of its rating.
When the type of load is unusual,
intermittent, or one which involves
momentary peak currents such as motor
loads, consideration should be given
to the heating effect on the protective
device over a period of time. The duty
cycle of a motor which is started and
stopped frequently may require a circuit
breaker or fuses with a higher rating than
an infrequently started motor.
The presence of excessive dust,
moisture, corrosive fumes, or
explosive atmosphere requires the
use of enclosures suitable for such
atmospheres. For applications in regions
where fungus growth may occur, some
circuit breakers should be treated with a
fungus and moisture resistant material.
Fault Current Available — The
interrupting rating of the circuit breaker
or fused switch should be greater than
the available short circuit current at the
point of application. The short circuit
current from some power sources, such
as engine driven generators, is limited,
and the protective device characteristics
should be selected to clear such faults
without delay.
Some systems require a study of
protective device characteristics to assure
proper protection and coordination for
any possible value of fault current. Your
representative is available to assist in
making coordination studies.
Application Data
general
Table 1
Ampacities of Insulated Conductors (From NEC Table 310-16)
Not More Than Three Conductors in Raceway or Cable or Earth (Directly Buried).
(Based on Ambient Temperature of 30°C, 86°F)
Size
Copper Conductors
60°C
75°C
(140°F)
(167°F)
Types
Types
AWG
Kcmil
0018
0016
0014
0012 
0010 
0008
0006
0004
0003
0002
0001
00001⁄0
00002⁄0
00003⁄0
00004⁄0
250
300
350
400
500
600
700
750
800
900
1000
1250
1500
1750
2000
TW
UF
—
—
020
025
030
040
055
070
085
095
110
125
145
165
195
215
240
260
280
320
355
385
400
410
435
455
495
520
545
560
RHW
THW
THWN
XHHW
USE
ZW
—
—
020
025
035
050
065
085
100
115
130
150
175
200
230
255
285
310
335
380
420
460
475
490
520
545
590
625
650
665
90°C
(194°F)
Types
TBS
SA
SIS
FEP
FEPB
RHH
THHN
THHW
XHHW
014
018
025
030
040
055
075
095
110
130
150
170
195
225
260
290
320
350
380
430
475
520
535
555
585
615
665
705
735
750
Aluminum Conductors
Copper-Clad Aluminum Conductors
60°C
75°C
90°C
(140°F)
(167°F)
(194°F)
Types
Types
Types
TBS,
SA, SIS,
THHN
RHW
THHW
THHW
THW-2, THWN-2,
THW
RHH, RHW-2
THWN
USE-2
TW
XHHW
XHH, XHHW
UF
USE
XHHW-2, ZW-2
—
—
—
—
—
—
—
—
—


020
020
025 
025
030 
035 
030
040
045
040
050
060
055
065
075
065
075
085
075
090
100
085
100
115
100
120
135
115
135
150
130
155
175
150
180
205
170
205
230
190
230
255
210
250
280
225
270
305
260
310
350
285
340
385
310
375
420
320
385
435
330
395
450
355
425
480
375
445
500
405
485
545
435
520
585
455
545
615
470
560
630
Size
AWG
Kcmil
—
—
—
12
10
8
6
4
3
2
1
00001⁄0
00002⁄0
00003⁄0
00004⁄0
250
300
350
400
500
600
700
750
800
900
1000
1250
1500
1750
2000
15
Table 2
Ambient
Temperature°C
21–25
26–30
31–35
36–40
41–45
46–50
51–55
56–60
61–70
71–80
For ambient temperature over 30°C, (86°F) multiply the ampacities shown above by the appropriate factor
shown below.
1.08
1.05
1.04
1.08
1.05
1.04
1.00
1.00
1.00
1.00
1.00
1.00
.91
.94
.96
.91
.94
.96
.82
.88
.91
.82
.88
.91
.71
.82
.87
.71
.82
.87
.58
.75
.82
.58
.75
.82
.41
.67
.76
.41
.67
.76
—
0.58
.71
—
0.58
.71
—
0.33
.58
—
0.33
.58
—
—
.41
—
—
.41
load current rating and the overcurrent protection
for conductor types shall not exceed 15 amperes for 14
AWG, 20 amperes for 12 AWG, and 30 amperes for 10
AWG copper; or 15 amperes for 12 AWG and 25 amperes
for 10 AWG aluminum and copper-clad aluminum after
any correction factors for ambient temperature and
number of conductors have been applied.
Ambient
Temperature°F
70–77
78–86
87–95
96–104
105–113
114–122
123–131
132–140
141–158
159–176
The
15/3
APPLICATION
DATA
Correction Factors for Ambient Temperature Over 30°C, 86°F
Application Data
GENERAL
Table 4A
Table 4B
Table 4C
Motor Full-Load Currents of Three
Phase AC Induction Type Motors 
Motor Full-Load Currents
In Amperes, Single-Phase, AC
Motor Full-Load Currents
In Amperes, DC
Motor
Rating
Horsepower
0001⁄4
0001⁄3
0001⁄2
0003⁄4
001
0011⁄2
002
003
005
0071⁄2
010
015
020
025
030
040
050
060
075
100
125
150
200
250
300
350
400
450
500
Current in Amperes
208V 230V 460V
575V
1.11
1.34
2.4
3.5
4.6
6.6
7.5
10.6
16.7
24.2
30.8
46.2
59.4
74.8
88
114
143
169
211
273
343
396
528
—0
—0
—0
—0
—0
—0
.38
.47
.9
1.3
1.7
2.4
2.7
3.9
6.1
9.0
11.0
17.0
22
27
32
41
52
62
77
99
125
144
192
242
289
336
382
412
472
.96
1.18
2.2
3.2
4.2
6
6.8
9.6
15.2
22.0
28.0
42.0
54
68
80
104
130
154
192
248
312
360
480
—0
—0
—0
—0
—0
—0
.48
.59
1.1
1.6
2.1
3
3.4
4.8
7.6
11.0
14.0
21.0
27
34
40
52
65
77
96
124
156
180
240
302
361
414
477
515
590
Horsepower
001⁄6
001⁄4
001⁄3
001⁄2
003⁄4
01
011⁄2
02
03
05
071⁄2
10
115V
4.4
5.8
7.2
9.8
13.8
16
20
24
34
56
80
100
230V
2.2
2.9
3.6
4.9
6.9
8
10
12
17
28
40
50
Horsepower
001⁄4
001⁄3
001⁄2
003⁄4
01
011⁄2
02
03
05
071⁄2
10
120V
3.1
4.1
5.4
7.6
9.5
13.2
17
25
40
58
76
240V
1.6
2.0
2.7
3.8
4.7
6.6
8.5
12.2
20
29
38
Table 4D
Conversion Table of Polyphase Design B, C, D, and E Maximum Locked-Rotor
Currents for Selection of Disconnecting Means and Controllers as Determined
from Horsepower and Voltage Rating and Design Letter For use only with
Sections 430-110, 440-12, 440-41, and 455-8(c) of the National Electric Code.
15
Maximum Motor Locked-Rotor Current Amperes
Two- and Three-Phase Design B, C, D, and E
Rated 115 Volts
200 Volts
208 Volts
230 Volts
HP B, C, D
E
B, C, D
E
B, C, D
E
B, C, D
E
0001⁄2
40
40
23
23
22.1
22.1
20
20
3
000 ⁄4
50
50
28.8
28.8
27.6
27.6
25
25
001
60
60
34.5
34.5
33
33
30
30
1
001 ⁄2
80
80
46
46
44
44
40
40
002
100
100
57.5
57.5
55
55
50
50
003
—0
—0
73.6
84
71
81
64
73
005
—0
—0
105.8 140
102
135
92
122
0071⁄2
—0
—0
146
210
140
202
127
183
010
—0
—0
186.3 259
179
249
162
225
015
—0
—0
267
388
257
373
232
337
020
—0
—0
334
516
321
497
290
449
025
—0
—0
420
646
404
621
365
562
030
—0
—0
500
775
481
745
435
674
040
—0
—0
667
948
641
911
580
824
050
—0
—0
834
1185
802
1139
725
1030
060
—0
—0 1001
1421
962
1367
870
1236
075
—0
—0 1248
1777
1200
1708
1085
1545
100
—0
—0 1668
2154
1603
2071
1450
1873
125
—0
—0 2087
2692
2007
2589
1815
2341
150
—0
—0 2496
3230
2400
3106
2170
2809
200
—0
—0 3335
4307
3207
4141
2900
3745
250
—0
—0 —00
—00
—00
—00
—00
—00
300
—0
—0 —00
—00
—00
—00
—00
—00
350
—0
—0 —00
—00
—00
—00
—00
—00
400
—0
—0 —00
—00
—00
—00
—00
—00
450
—0
—0 —00
—00
—00
—00
—00
—00
500
—0
—0 —00
—00
—00
—00
—00
—00
460 Volts
B, C, D
E
10
10
12.5
12.5
15
15
20
20
25
25
32
36.5
46
61
63.5
91.5
81
113
116
169
145
225
183
281
218
337
290
412
363
515
435
618
543
773
725
937
908
1171
1085
1405
1450
1873
1825
2344
2200
2809
2550
3277
2900
3745
3250
4214
3625
4682
575 Volts
B, C, D
E
8
8
10
10
12
12
16
16
20
20
25.6
29.2
36.8
48.8
50.8
73.2
64.8
90
93
135
116
180
146
225
174
270
232
330
290
412
348
494
434
618
580
749
726
936
868
1124
1160
1498
1460
1875
1760
2247
2040
2622
2320
2996
2600
3371
2900
3746
Table 5
Normal-Load and Fault Currents of Three-Phase Transformers
APPLICATION
DATA
 Values
may vary depending on manufacturer, type of
motor and NEMA design.
For full load currents of 200 volt motors, increase the
corresponding 230 volt motor full-load current by
15 percent.
Table 5 Notes:
1. Primary source available is assumed as 500 MVA at the
primary of the transformer with a source circuit X/R
ratio of 12.
2. Motor contribution is included in the table at twice
the full-load current for 208 volt transformers and
at 4 times the full-load current for 240 volt and 480
volt transformers. These values are derived from the
assumption that 208 volt systems are 50% motor load
and 240 and 480 volt systems are 100% motor load.
3. All short circuit current values are in symmetrical
RMS amperes.
15/4
Transformer
Characteristics
3 Phase
kVA
Rating
112.5
150
225
300
500
750
1000
1500
2000
2500
1000
1500
AC Voltage 3 Phase
280V
Normal Load Short
%
Continuous Circuit
Impedance Amperes
Current
2.25
312
14,491
3.00
416
14,699
4.50
625
15,139
5.00
834
18,326
5.00
1388
30,536
5.75
2080
40,373
5.75
2780
53,830
5.75
4162
80,745
5.75
—00
—0 0 0
5.75
—00
—0 0 0
8.00
—00
—0 0 0
8.00
—00
—0 0 0
240V
Normal Load
Continuous
Amperes
271
361
541
722
1203
1804
2406
3610
4812
6010
—00
—00
Short
Circuit
Current
13,128
13,477
14,186
17,328
28,872
38,590
51,467
77,201
102,914
128,647
—0000
—0000
480V
Normal Load
Continuous
Amperes
135
180
271
361
601
902
1203
1805
2406
3008
1203
1805
Short
Circuit
Current
6,540
6,720
7,106
8,664
14,424
19,295
25,734
38,590
51,467
64,324
19,850
29,766
Application Data
general
Table 6
Electrical Formulas for Finding Amperes, Horsepower, Kilowatts and kVA
Kilowatts
kVA
Horsepower
(Output)
Amperes when
Horsepower
is Known
Amperes when
Kilowatts
is Known
Amperes when
kVA is Known
Single-Phase
I x E x pf
1000
IxE
1000
I x E x % EFF x pf
746
Alternating Current
Two-Phase , Four-Wire
I x E x 2 x pf
1000
IxEx2
1000
I x E x 2 x % EFF x pf
746
Three-Phase
I x E x 1.73 x pf
1000
I x E x 1.73
1000
I x E x 1.73 x % EFF x pf
746
Direct Current
IxE
1000
I x E x % EFF
746
HP x 746
E x % EFF x pf
HP x 746
2 x E x % EFF x pf
HP x 746
1.73 x E x % EFF x pf
HP x 746
E x % EFF
KW x 1000
E x pf
KW x 1000
2 x E x pf
KW x 1000
1.73 x E x pf
KW x 1000
E
kVA x 1000
E
kVA x 1000
2xE
kVA x 1000
1.73 x E
Average Efficiency and Power Factor
Values of Motors
When the actual efficiencies and power
factors of the motors to be controlled are
not known, the following approximations
may be used.
Efficiencies:
DC motors, 35 horsepower
and less
80% to 85%
DC motors, above
35 horsepower
85% to 90%
Synchronous motors
(at 100% power factor)
92% to 95%
“Apparent” Efficiencies
( = Efficiency x Power Factor);
Three-phase induction motors,
25 horsepower and less
85%
Three-phase induction motors
above 25 horsepower
90%
These figures may be decreased slightly
for single-phase and two-phase
induction motors.
Fault-Current Calculation on LowVoltage AC Systems
In order to determine the maximum
interrupting rate of the circuit breakers
in a distribution system it is necessary
to calculate the current which could flow
under a three-phase bolted short circuit
condition. For a three-phase system the
maximum available fault current at the
secondary side of the transformer can be
obtained by use of the formula:
ISC =
kVA x 100
KV x √3 x % Z
where:
ISC = Symmetrical RMS amperes of fault
current.
kVA = Kilovolt-ampere rating of
transformers.
KV = Secondary voltage in kilovolts.
% Z = Percent impedance of primary line
and transformer.
Table 5 on page 15-4 has been prepared
to list the symmetrical RMS fault current
which is available at the secondary
terminals of the transformer.
Table 8 
Minimum Size Grounding Conductors
for Grounding Raceways and
Equipment (From NEC Table 250–122)
Rating or Setting of
Automatic Overcurrent
Device in Circuit Ahead
of Equipment, Conduit
etc., Not Exceeding
(Amperes)
15
20
30
40
60
100
200
300
400
500
600
800
1000
1200
1600
2000
2500
3000
4000
5000
6000
Size
Copper
Wire
Number
14
12
10
10
10
8
6
4
3
2
1
1/0
2/0
3/0
4/0
250 kcmil
350 kcmil
400 kcmil
500 kcmil
700 kcmil
800 kcmil
Aluminum or
Copper
Clad
Aluminum
Wire Number
12
10
8
8
8
6
4
2
1
1/0
2/0
3/0
4/0
250 kcmil
350 kcmil
400 kcmil
600 kcmil
600 kcmil
800 kcmil
1200 kcmil
1200 kcmil
15
To Find
Table 7 
Size of Largest Service Entrance Conductor or Equivalent Area for
Parallel Conductors
Copper
2 or smaller
1 or 1/0
2/0 or 3/0
Over 3/0 to 350 kcmil
Over 350 kcmil to 600 kcmil
Over 600 kcmil to 1100 kcmil
Over 1100 kcmil
Aluminum or Copper
Clad Aluminum
1/0 or smaller
2/0 or 3/0
4/0 or 250 kcmil
Over 250 kcmil to 500 kcmil
Over 500 kcmil to 900 kcmil
Over 900 kcmil to 1750 kcmil
Over 1750 kcmil
 In
three-wire, two-phase circuits the current in
the common conductor is 1.41 times that in either
other conductor.
E = Volts I = Amperes
% EFF = Per Cent Efficiency
APPLICATION
DATA
Grounding Electrode Conductor for AC Systems (From NEC Table 250–66)
Size of Grounding
Electrode Conductor
Aluminum or
Copper Clad
Copper
Aluminum
8
6
6
4
4
2
2
1/0
1/0
3/0
2/0
4/0
3/0
250 kcmil
 Additional
information and exceptions are stated in
Article 250 — Grounding, National Electric Code.
pf = Power Factor
15/5
Fraction, Decimal, and Millimeter Equivalents
Fractions to Decimals to Millimeters
15
APPLICATION
DATA
Fractions
1/64
1/32
3/64
1/16
5/64
3/32
7/64
1/8
9/64
5/32
11/64
3/16
13/64
7/32
15/64
1/4
17/64
9/32
19/64
5/16
21/64
11/32
23/64
3/8
25/64
13/32
27/64
7/16
29/64
15/32
31/64
1/2
33/64
17/32
35/64
9/16
37/64
19/32
39/64
5/8
41/64
21/32
43/64
11/16
45/64
23/32
47/64
3/4
49/64
25/32
51/64
13/16
53/64
27/32
55/64
7/8
57/64
29/32
59/64
15/16
61/64
31/32
63/64
1
 0.001”
= 0.0254 mm
1 mm = 0.03937”
15/6
Decimals
0.015625
0.03125
0.046875
0.0625
0.078125
0.09375
0.109375
0.1250
0.140625
0.15625
0.171875
0.1875
0.203125
0.21875
0.234375
0.2500
0.265625
0.28125
0.296875
0.3125
0.328125
0.34375
0.359375
0.3750
0.390625
0.40625
0.421875
0.4375
0.453125
0.46875
0.484375
0.500
0.515625
0.53125
0.546875
0.5625
0.578125
0.59375
0.609375
0.6250
0.640625
0.65625
0.671875
0.6875
0.703125
0.71875
0.734375
0.7500
0.765625
0.78125
0.796875
0.8125
0.828125
0.84375
0.859375
0.8750
0.890625
0.90625
0.921875
0.9375
0.953125
0.96875
0.984375
1.000
Millimeters
0.397
0.794
1.191
1.588
1.984
2.381
2.778
3.175
3.572
3.969
4.366
4.763
5.159
5.556
5.953
6.350
6.747
7.144
7.541
7.938
8.334
8.731
9.128
9.525
9.922
10.319
10.716
11.113
11.509
11.906
12.303
12.700
13.097
13.494
13.891
14.288
14.684
15.081
15.478
15.875
16.272
16.669
17.066
17.463
17.859
18.256
18.653
19.050
19.447
19.844
20.241
20.638
21.034
21.431
21.828
22.225
22.622
23.019
23.416
23.813
24.209
24.606
25.003
25.400
conversion tables
Millimeters to Inches 
Millimeters
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Inches
0.0039
0.0079
0.0118
0.0157
0.0197
0.0236
0.0276
0.0315
0.0354
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
0.0394
0.0787
0.1181
0.1575
0.1969
0.2362
0.2756
0.3150
0.3543
0.3937
0.4331
0.4724
0.5118
0.5512
0.5906
0.6299
0.6693
0.7087
0.7480
0.7874
0.8268
0.8661
0.9055
0.9449
0.9843
1.0236
1.0630
1.1024
1.1417
1.1811
1.2205
1.2598
1.2992
1.3386
1.3780
1.4173
1.4567
1.4961
1.5354
1.5748
1.6142
1.6535
1.6929
1.7323
1.7717
Millimeters
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
Inches
1.8110
1.8504
1.8898
1.9291
1.9685
2.0079
2.0472
2.0866
2.1260
2.1654
2.2047
2.2441
2.2835
2.3228
2.3622
2.4016
2.4409
2.4803
2.5197
2.5591
2.5984
2.6378
2.6772
2.7165
2.7559
2.7953
2.8346
2.8740
2.9134
2.9528
2.9921
3.0315
3.0709
3.1102
3.1496
3.1890
3.2283
3.2677
3.3071
3.3465
3.3858
3.4252
3.4646
3.5039
3.5433
3.5827
3.6220
3.6614
3.7008
3.7402
3.7795
3.8189
3.8583
3.8976
3.9370