Full Load Full Load Full Load
Full Load
X-Former X-Former X-Former per phase per phase per phase
208V 3Ø per phase
480V 3Ø
Nominal
Resist. Reactance Impedance
@ 120V
@ 240V
@ 208V Transformer
@ 480V Transformer
%jX
KVA
%R
%Z
1Ø
1Ø
3Ø Short Circuit
3Ø Short Circuit
3
6
9
15
30
45
75
112.5
150
225
300
500
750
1000
1500
2000
2500
3000
3750
5000
7500
10000
15000
3.76
2.72
2.31
2.1
3.75
2.73
2.42
2.56
1.94
1.95
1.7
1
1
1
1
1
1
1
1
1
1
1
1
1
1.72
1.16
1.82
2.04
1.97
2.1
3.69
4.07
4.8
4.96
4.8989
4.8989
5.6623
5.6623
5.6623
5.6623
6.9282
6.9282
6.9282
6.9282
6.9282
6.9282
3.89
3.22
2.58
2.78
4.27
3.37
3.20
4.49
4.51
5.18
5.24
5.00
5.00
5.75
5.75
5.75
5.75
7.00
7.00
7.00
7.00
7.00
7.00
25
50
75
125
250
375
625
938
1,250
1,875
2,500
4,167
6,250
8,333
12,500
16,667
20,833
25,000
31,250
41,667
62,500
83,333
125,000
13
25
38
63
125
188
313
469
625
938
1,250
2,083
3,125
4,167
6,250
8,333
10,417
12,500
15,625
20,833
31,250
41,667
62,500
8
17
25
42
83
125
208
312
416
625
833
1,388
2,082
2,776
4,164
5,551
6,939
8,327
10,409
13,879
20,818
27,757
41,636
214
518
966
1,498
1,951
3,710
6,497
6,953
9,235
12,054
15,882
27,758
41,636
48,274
72,411
96,548
120,685
118,960
148,699
198,266
297,399
396,532
594,798
4
7
11
18
36
54
90
135
180
271
361
601
902
1,203
1,804
2,406
3,007
3,608
4,511
6,014
9,021
12,028
18,042
93
224
419
649
845
1,608
2,815
3,013
4,002
5,224
6,882
12,028
18,042
20,919
31,378
41,838
52,297
51,549
64,436
85,915
128,873
171,831
257,746
Dimensions
(WxDxH) & BTU Heat BTU Heat
Weight of 480 to Loss No Loss Full
208Y/120
Load
Load
15x9x14 - 120#
15x9x14 - 145#
19x12x15 - 235#
20x16x27 - 200#
20x16x27 - 250#
20x20x30 - 340#
30x20x30 - 500#
30x24x37 - 750#
32x27x44 - 800#
35x29x50 - 1025#
41x32x50 - 1450#
48x36x71 - 2100#
56x41x74 - 3950#
72x54x94 - 6300#
376
495
666
529
854
1,024
1,366
2,048
2,390
3,073
3,755
5,121
7,169
563
939
1,280
2,270
6,128
5,753
8,654
13,076
15,124
19,784
24,120
23,471
34,447
This information is provided as a free engineering resource by Design & Construction Engineers. Transformer characteristics were compiled
from various industry sources available from Cutler-Hammer, GE, Siemens, and Square D. Impedance is the vector sum of the listed DC
resistance and the inductive reactance. The full load amperage is (KVA)(1000)/(Voltage). This is multiplied by the square root of 3 (1.73) for
three-phase transformers. The short circuit current is the full load amperage divided by the impedance. The dimensions and weight are
based on general purpose Square D 3-phase transformers.
www.dcengineers.com
6/13/2004
! "#
"
$ #
%
kVA
10
15
25
50
75
100
167
250
333
Conductor
14
12
10
8
6
4
3
2
1
1/0
2/0
3/0
4/0
250
300
350
400
500
600
750
1000
X-Former Full Load per
Impedance
Phase @ Fault Current
%Z
240/120V
@ 240V
1.16
42
3,600
1.60
63
3,900
1.55
104
6,700
1.68
208
12,400
1.63
313
19,200
1.50
417
27,800
1.50
696
46,400
1.61
1,042
64,500
2.80
1,388
49,500
PVC or AL
Conductor
Conduit Steel Conduit
Resistance
Reactance X Reactance X (DC @75° C)
0.058
0.073
3.07
0.054
0.068
1.93
0.050
0.063
1.21
0.052
0.065
0.778
0.051
0.064
0.491
0.048
0.060
0.308
0.047
0.059
0.245
0.045
0.057
0.194
0.046
0.057
0.154
0.044
0.055
0.122
0.043
0.054
0.0967
0.042
0.052
0.0766
0.041
0.051
0.0608
0.041
0.052
0.0515
0.041
0.051
0.0429
0.040
0.050
0.0367
0.040
0.049
0.0321
0.039
0.048
0.0258
0.039
0.048
0.0214
0.038
0.048
0.0171
0.037
0.046
0.0129
kVA
75
150
225
300
500
750
1000
1500
2000
2500
!
PVC or AL
Conduit Steel Conduit
Impedance Z Impedance Z
2.7
2.7
1.7
1.7
1.1
1.1
0.69
0.70
0.44
0.45
0.29
0.30
0.23
0.24
0.19
0.20
0.16
0.16
0.13
0.13
0.11
0.11
0.088
0.094
0.074
0.080
0.066
0.073
0.059
0.065
0.053
0.060
0.049
0.056
0.043
0.050
0.040
0.047
0.036
0.043
0.032
0.040
X-Former Full Load per
Full Load per
Impedance
Phase @ Fault Current
Phase @ Fault Current
%Z
208Y/120V
@ 208V
480Y/277V
@ 480V
1.8
208
11,600
90 Don't Stock
1.8
416
23,200
180
10,100
1.6
625
39,100
271
17,000
1.6
833
52,100
361
22,600
2.2
1,388
63,100
601
27,400
5.75
2,082
36,200
902
15,700
5.75
2,776
48,300
1,203
21,000
5.75
4,164 Don't Stock
1,804
31,400
5.75
5,551 Don't Stock
2,406
41,900
5.75
6,939 Don't Stock
3,007
52,300
This information is provided as a free engineering service
by Design & Construction Engineers. The transformer
information was compiled from figures provided by OPPD
which were current at the time but that are subject to
change. The wire properties information is basically that
which is found in Table 8 and 9 of the 2004 NEC. The
conductor resistance is the DC resistance from Table 8
while the reactance and impedance (at 85% power factor)
is from Table 9. Note that wire properties are much
different from 20°C to 75°C. Voltage drops are based on
wire impedance at 75° while short circuits are based on
20° C. This is because the greatest voltage drops occur
when the wire is hot. In contrast, most short circuits occur
when the circuit is first energized and the conductors are
cold.
www.dcengineers.com
6/13/2004