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APPENDIX B — IMPORTANT FORMULA
OHMS LAW:
OHMS = VOLTS / AMPS ( R = E / I)
AMPS = VOLTS / OHMS (I = E / R)
VOLTS = AMPS / OHMS (E = IR)
3 Phase
Resistance = (V² X 2) / W
Amperage = W / (V X 1.732)
208V KW
1
5
10
20
25
40
50
100
200
250
400
500
RES 86.5 17.3 8.6
4.3
3.46 2.16 1.73 0.865 0.432 0.346 0.276 0.173
AMP 2.77 13.9 27.8 55.5 69.4 111
139
278
555
694
1110 1388
240V KW
1
5
10
20
25
40
50
100
200
250
400
500
RES
115 23.0 11.5 5.76 4.61 2.88 2.30 1.15 0.576 0.461 0.288 0.230
AMP 2.41 12.0 24.0 48.0 60.0 96.2 120 240
480
600
962
1200
380V KW
1
5
10
20
25
40
50
100 200 250
400
500
RES
289 57.7 28.8 14.4 11.5 7.22 5.77 2.88 1.44 1.15 0.722 0.577
AMP 1.51 7.59 15.2 30.4 37.9 60.7 75.9 152 304 380
608
760
480V KW
1
5
10
20
25
40
50
100 200 250
400
500
RES 460.8 92.2 46.1 23.0 18.4 11.5 9.22 4.61 2.30 1.84
1.15 0.922
AMP 1.20 6.01 12.0 24.0 30.0 48.1 60.0 120 240 300
481
600
1 Phase
Resistance = V² / W
Amperage = W/ V
120V KW
1
5
10
20
25
50
100
200
250
500
RES 57.6 28.8 14.4 7.20 4.80 3.60 2.88 1.44 0.720 0.360
AMP 2.08 4.16 8.33 16.7 25.0 33.3 41.7 83.3
167
333
208V KW
1
5
10
20
25
50
100
200
250
500
RES 43.3 8.65 4.33 2.16 1.73 0.865 0.432 0.216 0.173 0.086
AMP 4.80 24.0 48.1 96.1 120
240
481
962
1202 2404
240V KW
1
5
10
20
25
50
100
200
250
500
RES 57.6 11.5 5.8 2.88 2.30 1.15 0.576 0.288 0.230 0.115
AMP 4.16 20.8 41.6 83.3 104 208
417
833
1042 2083
KVA: 1 phase VOLTS X AMPS
3 phase 1.732 X VOLTS X AMPS
Derating KW:
KW(
V2
/
V1
)² = derated KW;
EX. 50KW (
200
/
240
)² = 34.722KW
Derating KW and Hz:
KW (
V2
/
V1
)² X (
F1
/
F2
) = Derated KW at different Hz
3 Phase Henrys: V²/(Kvar X 3.14 X freq)
1 Phase Henrys: V²/(2 X 3.14 X freq X vars)
1 Phase Farads: Kvar / (2 X 3.14 X freq X V²)
MA Output
amps: amps / (833 X 16 + 4) volt: (V2 / V1) X 16 + 4
Heater Current (Wye)
I
H
= W
H
* (V
L-H
/(X
H
*V
H
²))
I
H
= Heater Current
W
H
= Wattage of 1 Heater
X
H
= # of Heaters from Line to Neutural
V
H
= Rated Voltage of 1 Heater
Fuses for Transformer
Total Amperage = V*A / Source Voltage
