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Transformer Selection Steps D r y - T y p e D i s t r i b u t i o n T r a n s f o r m e r s
① When motor service factor is greater than 1, increase
full load amps proportionally. Example: If service factor is
1.15, increase above amp values by 15%.
1 Phase kVA =
Volts x Amps
1000
Note: If motors are started more than once per hour,
increase minimum transformer kVA by 20%.
Table 1
Full Load Current in Amperes–
Single Phase Circuits
Horsepower 115V 208V 230V Minimum Transformer KVA
1/6 4.4 2.4 2.2 .53
1/4 5.8 3.2 2.9 .70
1/3 7.2 4.0 3.6 .87
1/2 9.8 5.4 4.9 1.18
3/4 13.8 7.6 6.9 1.66
1 16 8.8 8 1.92
1.5 20 11.0 10 2.40
2 24 13.2 12 2.88
3 34 18.7 17 4.10
5 56 30.8 28 6.72
7.5 80 44 40 9.6
10 100 55 50 12.0
Table 2
Full Load Amperes
Single Phase A.C. Motors ①
kVA 120V 208V 240V 277V 380V 440V 480V 600V
.050 0.4 0.2 0.2 0.2 0.1 0.1 0.1 0.1
.100 0.8 0.5 0.4 0.3 0.2 0.2 0.2 0.2
.150 1.2 0.7 0.6 0.5 0.4 0.3 0.3 0.3
.250 2.0 1.2 1.0 0.9 0.6 0.5 0.5 0.4
.500 4.2 2.4 2.1 1.8 1.3 1.1 1.0 0.8
.750 6.3 3.6 3.1 2.7 2.0 1.7 1.6 1.3
1 8.3 4.8 4.2 3.6 2.6 2.3 2.1 1.7
1.5 12.5 7.2 6.2 5.4 3.9 3.4 3.1 2.5
2 16.7 9.6 8.3 7.2 5.2 4.5 4.2 3.3
3 25 14.4 12.5 10.8 7.9 6.8 6.2 5.0
5 41 24.0 20.8 18.0 13.1 11.3 10.4 8.3
7.5 62 36 31 27 19.7 17 15.6 12.5
10 83 48 41 36 26 22.7 20.8 16.7
15 125 72 62 54 39 34 31 25
25 208 120 104 90 65 57 52 41
37.5 312 180 156 135 98 85 78 62
50 416 240 208 180 131 114 104 83
75 625 360 312 270 197 170 156 125
100 833 480 416 361 263 227 208 166
167 1391 802 695 602 439 379 347 278
250 2083 1203 1041 902 657 568 520 416