Electrical Terms and Equations 2019

Ohms Law

Dear Mr. Electrician:  I have purchased several books on home wiring so that I can do some electrical work around my house.  The books use words and terms that I do not understand and cannot find in the dictionary.  Do you have any suggestions?

Answer:  If you plan to do electrical work you should have a basic understanding of wiring methods and code requirements.  Article 100 in the National Electrical Code is entitled Definitions.  It defines all electrical terms used for electrical installations.  See below for a short list of some common electrical terms.  NOTE: Links below go to applicable products on Amazon.

Electrical Terms and Definitions

Neutral or Neutral Conductor refers to the return path of electricity back to the utility company power transformer.  In the National Electrical Code this wire is called the grounded conductor because it is bonded to earth ground in the main disconnect for the home or building.  Sometimes electricians will just call it the return.  The wire color for the neutral in the USA is usually white, but gray is sometimes used.

Hot or LINE refers to the current carrying conductors (Wires) that have electricity flowing in them to power things such as lights and appliances.  These wires are also called ungrounded conductors.  Wire colors for hot conductors can be anything but white, gray, or green.  A typical electrical receptacle outlet in your home will have a NEUTRAL and a LINE connected to it.  Anything that is plugged into the outlet is considered a LOAD.

LOAD is what is powered by electricity.  Anything that consumes electricity to operate is a load on the electrical system.  Lights, appliances, machinery, and computers are all examples of a load.  A typical single pole wall switch that operates a ceiling light will have a LOAD wire on one screw and a LINE wire on the other screw.

Ground or Earthing refers to a wire known as the grounding electrode conductor that is connected directly to the planet Earth via water pipes and/or ground rods, or other means.  There is no color code for the GEC and it can also be a bare un-insulated wire.  This provides lightning protection and voltage stabilization.  In the USA the ground is also connected (Bonded) to the neutral in the main electrical disconnect for a home or building to provide short circuit protection, also known as fault protection.  In your outlet and switch boxes the ground wire is known as the equipment grounding conductor (EGC).  Article 250 in the National Electrical Code covers all types of grounding.  The equipment grounding conductor color is green or can also be an un-insulated bare wire.  Article 100 for definitions is also helpful.

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 unit of current strength.  It is 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.  The flow of electrical Current is measured in Amperes or Amps using an ammeter.

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.

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.

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.  BTU’s x 2.93 + 10,000 = Kilowatt hours.

Horsepower is equal to 746 Watts.  A one horsepower electric motor consumes approximately 746 watts.

One Watt = The power expended by a current of one Ampere in a resistance of one Ohm.  Watts is the amount of power consumed.  It is a unit of electrical power required to do work at the rate of one Joule per second.  It is the power expended when one ampere of direct current (DC) flows through a resistance load of one Ohm.  Watts are called true power.  The electric meter on your house measures Kilowatt hours which is how many thousands of Watts were used per hour.

Kilowatt is 1000 watts.  Kilowatts x 1.341 = Horsepower.

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BASIC ELECTRICAL SYMBOLS

I = Current in Amperes

E = Volts

R = Resistance in Ohms

P or W = power in Watts

KW = Power in Kilowatts

1 KW = 1,000 watts

VA = Apparent Power in Volt-Amperes

KVA = Apparent power in Kilovolt-Amperes

HP = Output Power in number of Horsepower.  One horsepower is equal to 746 watts.

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 ELECTRICAL 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 ELECTRICAL 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 equations, see the circular Ohms Law chart at the top of this page.

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