Principles of Electricity

Volt The measurement of electrical pressure

Ampere The rate of flow of electricity

Watt The measurement of electrical power

W = V x A Watts equal volts multiplied by amps

W = V x A This formulas is sometimes called the West Virginia formula

W = V x A How many watts of electricity will a 7.5 ampere electric motor use in 5 hours on a 120 volt circuit W=120x7.5x5 W=4500

V = W/A Volts equal watts divided by amps

V = W/A What volt circuit is needed for an 7.5 amp electric motor that uses 900 watts in one hour V=900/7.5 V=120

A = W/V Amps equal watts divided by volts

A = W/V What should the amp rating of an electric motor be if it uses 900 watts of electricity in one hour in a 120 volt circuit A=900/120 A=7.5

Kilowatt 1000 watts

Cost of Electricity Cost per kilowatt x number of kilowatts x hours of use

Cost of Electricity If electricity costs 12 cents per kilowatt hour, how much would it cost to use 2 kilowatts per hour for 10 hours.12 x 2 x 10 = $2.40

I = E/R Ohm’s Law Amps (I) = Volts (E) divided by Resistance (R)

Circuit Breaker Protects circuits form overload of current by tripping to break or open the circuit

Circuit breaker

Fuse Protects circuits from overload by melting a metal strip in the fuse

Conductors Materials such as copper, aluminum, or water that will carry or conduct electricity

Insulators Materials such as rubber and plastic that will not conduct electricity

Hot Wire A current carrying conductor under electrical pressure

Neutral Wire A current carrying conductor not under electrical pressure (has volts)

Ground Wire A conducting wire that transmits current to the earth to minimize the danger of electrical shock

Formulas to Compute Electrical Energy and Cost

Organizations National Fire Protection Association (NFPA) promotes and improves the science and methods of fire protection and publishes the National Electric Code (NES)

Organizations Underwriter Laboratories (UL) tests all types of wiring materials and electrical devices for safety

Safety Precautions Wear boots or shoes with rubber heels to insulate against shock

Safety Precautions Wear clothing made of materials low in flammability to prevent fires

Safety Precautions Ground all outlets, switches, service entrances to prevent shock

Solderless wire nut

Safety Precautions Extension cords should not be used under carpet because of fire danger

Safety Precautions Extension cords should not be used under carpet because of fire danger

Safety Precautions Standing in water or damp places or touching switches or receptacles with wet hands may cause electrical shock because water conducts electricity

Safety Precautions Do not touch someone undergoing electrical shock because both people will become part of circuit, and both will be shocked

Safety Precautions Always turn circuit breaker to “off” position before beginning work

Safety Precautions Use correct size fuses and circuit breakers to prevent fires

Safety Precautions Use only double insulated portable tools or those with three wire grounded cords to prevent shock

Safety Precautions The two deadliest hazards associated with electricity are shock and fire

Safety Precautions Precautions and common sense should be used to prevent conditions that will cause either

Principles of Electricity