**One Ohm** = The resistance of a column of mercury (At the temperature of melting ice) of a uniform cross section of one square millimeter and a length of 106.30 centimeters.

**One Volt** = The electromotive force which produces a current of one ampere when steadily applied to a conductor the resistance of which is one Ohm.

**One Ampere** = The current which when passed through a solution of nitrate of silver in water in accordance with certain specifications, deposits silver at the rate of 0.001118+ of a gram per second.

**One Watt** = The power expended by a current of one Ampere in a resistance of one Ohm.

**One Coulomb** = The quantity of electricity transferred by a current of one Ampere in one second.

**One Farad** = The capacity of a condenser in which a potential difference of one volt causes it to have a charge of one Coulomb of electricity.

**One Henry** = The inductance in a circuit in which the electromotive force induced is one volt when the inducing current varies at the rate of one Ampere per second.

**One Joule** = The energy expended in one second by a flow of one Ampere in one Ohm.

The** Gram-Calorie** is the energy required to raise one gram of water one degree centigrade in temperature. One gram calorie is very nearly equal to 4.18 Joules.

The **Ampere-Hour** is the quantity of electricity transferred by a current of one ampere in one hour, and is therefore equal to 3600 Coulombs.

The **Circular Mil** is the unit of cross-section used in the American Wire Gauge. The term “Mil” means one thousandth of an inch (0.001 inch). It is the area of a circular wire having a diameter of one Mil.

The **Square Mil** is the area of a square each side of which is one Mil (0.001 inch).

The** Area of a Square Mil** is 0.000001 square inches.

The** Circular Mil-Foot** is a unit circular conductor one foot in length and one Mil in diameter.

The **Resistance** of such a unit of copper has been found experimentally to be 10.37 ohms at 20 degrees Celsius.

The **BTU or British Thermal Unit** is a unit of heat energy and is defined as the amount of heat necessary to raise the temperature of one pound of water one degree Fahrenheit.

The **Horsepower** is equal to 746 Watts.

**BASIC ELECTRICAL SYMBOLS**

**I** = Current in Amperes

**E** = Volts

**R** = Resistance in Ohms

**P** or **W** = power in Watts

**KW** = Power in Kilowatts

**1KW** = 1,000 watts

**VA** = Apparent Power in Volt-Amperes

**KVA** = Apparent power in Kilovolt-Amperes

**HP** = Output Power in number of Horsepower.

**EFF** = Efficiency, expressed in a decimal fraction (output divided by input)

**PF** = Power Factor expressed in a decimal fraction, the ratio of true power (P, W, or KW) divided by apparent power (VA or KVA)

**EQUATIONS for SINGLE PHASE AC CIRCUITS**

**I** = VA ÷ E or Amps equals volt-amperes, divided by volts.

**I** = 1,000 x KVA ÷ E or Amps equals one thousand, times kilovolt-amperes, divided by volts.

**I** = W ÷ E x PF or Amps equals watts, divided by volts, times power factor.

**I** = 1,000 x KW ÷ E x PF or Amps equals one thousand, times kilowatts, divided by volts, times power factor.

**I** = 746 x HP ÷ E x PF x EFF or Amps equals 746, times horsepower, divided by volts, times power factor, times efficiency.

**P** = E x I x PF or Power equals volts, times amps, times power factor.

**VA** = I x E or Volt-amperes equals amps, times volts.

**KW** = E x I x PF ÷ 1,000 or Kilowatts equals volts, times amps, times power factor, divided by 1000.

**KVA** = I x E ÷ 1,000 or Kilovolt-amperes equals amps, times volts, divided by 1000.

**HP** = I x E x PF x EFF ÷ 746 or Horsepower equals amps, times volts, times power factor, times efficiency, divided by 746

**EQUATIONS for DC CIRCUITS**

To find the Voltage, ( E )

E = P ÷ I Volts = Watts ÷ Amps

To find the Current, ( I )

I = P ÷ E Amps = Watts ÷ Volts

To find the Resistance, ( R )

R = E ÷ I Ohms = Volts ÷ Amps

To find the Watts, ( P )

P = E x I Watts = Volts x Amps

For additional DC Voltage Ohms Law equations, see the chart at the top of this page.