Here are some common formulas that are frequently used in the field.

If you're mathematically challenged, using an online calculator can make these kinds of calculations super easy! You can access some great online calculators on your laptop computer when you're out in the field from the link near the bottom of this page. Just remember to check your preventive maintenance software updates often as well as your anti-virus software definitions to keep your computer running smoothly at all times.

Options:
- Motor Formulas
- Transformer 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
 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

E = Voltage / I = Amps /W = Watts / PF = Power Factor / Eff = Efficiency / HP = Horsepower

 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 = wattsI = amps R = ohms E = Volts

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. See Code chapter 9, Table 8

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

Check out these Online Calculators!

If there is anything you would like to add or if you have any comments please feel free to email E.T.E. at http://www.elec-toolbox.com/email.htm.

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