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Electricians' toolbox
Useful Formulas
E = Voltage / I = Amps /W = Watts / PF = Power Factor / Eff
= Efficiency / HP = Horsepower
| AC/DC
Formulas |
To Find |
Direct Current |
AC / 1phase
115v or 120v |
AC / 1phase
208,230, or 240v |
AC 3 phase
All Voltages |
Amps when
Horsepower is Known |
HP x 746
E x Eff |
HP x 746
E x Eff X PF |
HP x 746
E x Eff x PF |
HP x 746
1.73 x E x Eff x PF |
Amps when
Kilowatts is known |
kW x 1000
E |
kW x 1000
E x PF |
kW x 1000
E x PF |
kW x 1000
1.73 x E x PF |
Amps when
kVA is known |
|
kVA x 1000
E |
kVA x 1000
E |
kVA x 1000
1.73 x E |
| Kilowatts |
I x E
1000 |
I x E x PF
1000 |
I x E x PF
1000 |
I x E x 1.73
PF
1000 |
| Kilovolt-Amps |
|
I x E
1000 |
I x E
1000 |
I x E x 1.73
1000 |
Horsepower
(output) |
I x E x Eff
746 |
I x E x Eff x PF
746 |
I x E x Eff x PF
746 |
I x E x Eff x 1.73 x
PF
746 |
| Voltage
Drop Formulas |
Single Phase
(2 or 3 wire) |
VD = |
2 x K x I x L
CM |
K = ohms per
mil foot
(Copper = 12.9 at 75°)
(Alum = 21.2 at 75°)
| Note: |
K value
changes with temperature. |
L = Length of conductor in feet
I = Current in conductor (amperes)
CM = Circular mil area of conductor |
| CM= |
2K x L x I
VD |
| Three Phase |
VD= |
1.73 x K x I x L
CM |
| CM= |
1.73 x K x
L x I
VD |
| Three
Phase Values |
| For 208 volts
x 1.732, use 360 |
| For 230 volts
x 1.732, use 398 |
| For 240 volts
x 1.732, use 416 |
| For 440 volts
x 1.732, use 762 |
| For 460 volts
x 1.732, use 797 |
| For 480 Volts
x 1.732, use 831 |
|
|
| AC
Efficiency and Power Factor Formulas |
| To Find |
Single Phase |
Three Phase |
| Efficiency |
746 x HP
E x I x PF |
746 x HP
E x I x PF x 1.732 |
| Power Factor |
Input Watts
V x A |
Input Watts
E x I x 1.732 |
|
| Power
- DC Circuits |
| Watts = E xI |
| Amps = W / E |
|
|
| Ohm's
Law / Power Formulas |
 |
P = watts
I = amps
R = ohms
E = Volts |
|
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