Electrical principles
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ELECTRICAL PRINCIPLES. Electricity is the major power source of stationary equipment Uses: Driving Machinery Lighting Heating Cooling Knowledge of electricity is essential for safe use of electrical equipment.

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Electrical principles


Electricity is the major power source of stationary equipment


Driving Machinery




Knowledge of electricity is essential for safe use of electrical equipment

Electricity- a form of energy that can produce light, heat magnetism and chemical changes

Light- produced by heating a special metal element or filament in a vacuum tube called a “bulb”. Electricity flows through certain gases causing them to glow

Insulator- provides great resistance to the flow of electricity



Amperes- measure of the rate of flow of electricity in a conductor

Volts- measure of electrical pressure

Watts- measure of the amount of energy that can be completed by amps and volts


Watts=volts x amps

Volts=watts x amps

Amps=watts x volts




Fluorescent lamp- glows as a result of electricity flowing through a gas

Heat- is produced when electricity flows through metals with some difficulty

Resistance- tendency of a material to prevent electricity to flow

Conductor- metal permits electricity to flow easily



  • used in outdoors

  • used in wiring for homes

  • heat develops in implements

    Ohm’s Law: used to measure a material’s resistance to the flow of electrical current




E = I X R

Magnetism- force that attracts or repels iron or steel

- permanent magnet

- when iron or steel holds its magnetism

2 ends or poles

- north

- south

Opposites attract/likes repel

Magnetic field- force between 2 objects

Electric Motors- principle of magnetism is the basis upon which electric motors operate

Reverses the Polarity: reversing the direction of current flow

Electromagnet- unit is called

Commutator- reveres the current flow in an electric motor

Armature- rotating magnet

magnetic forces around the armature are called the “field”

Generators & Alternators- produce electricity

Generator- produces current (direct)

- flows one way

Alternator- produces current (alternating)

Turbine- high speed rotary engine driven by water-steam-gas

Circuits- circle of electricity

- open circuit- broken

- closed circuit- together

Short Circuit- “field” flow through the circle & back to the source too rapidly

Grounding- connection between a piece of equipment & the earth

- ground rod- steel or copper

- ground wire- bare

* channels stray electricity

Electricity Safety: 2 deadly hazards with current

- shock

- fire

Shock “field”- body’s reaction to a current

GFCI- Ground Fault Circuit Interrupter

-cuts off electricity if it leaves the pathway

Electrical Wiring: Systems have to be:

-safe -convenient -neat

-expandable -provide sufficient current

Service Entrance: Power company provides

-transformer -service drop -appropriate wiring

Entrance Head- “field” waterproof device used to attach exterior wires to interior wires

Transformer- converts high voltage to 240 volts-usable form for homes

- step up - step down

Service Drop- assembly of electrical wires- connectors & fasteners used to transmit electricity from the transformer to the entrance head

Service Entrance Panel- “field” box with fuses or breakers where electricity enters a building

Meter- measurement of electricity in kilowatt hours-Kilo means 1, 000

Watt Hour- use of 1 watt for 1 hour

Kilowatt Hour- use of 1, 000 watts for 1 hour

Reading a Meter: the last number passed by each pointer is read

1 “field”st & 3rd dials turn counterclockwise

2nd & 4th dials turn clockwise

Branch Circuits- branch out to a variety of places for many purposes

Fuse: plug or cartridge containing a strip of metal that melts when more than a specified amount of current passes through

Circuit Breaker:

switch that trips & breaks the circuit when more than specified amounts pass through it

- reset breaker after it trips

Types of Cables:

3 systems of wiring:

-Non-metallic sheathed

-Armored cable


Non-metallic Sheathed Cable: specified amounts pass through it



-approved for burial

Armored Cable:

-flexible metal sheath

-mechanical damage protection


Tubing consists of individual insulated wires

EMT-electrical metallic tube

Conduit can be: specified amounts pass through it



-provide the most protection

Wire Type & Size:



Wire size designated by gauge: lower the gauge larger the wire

Strands specified amounts pass through it- small wires placed together are called “bundles”

- improves conductivity & flexibility

- electricity carried on outside of wire

Voltage Drop- refers to a loss of voltage as the electricity travels along a wire

-larger the wire, less voltage drop

-longer the wire, more voltage drop

Wire ID: factors to determine wire

-outer covering

-number of wires

-individual wire covering specified amounts pass through it

-cable construction

Wire type is stamped on outside

Type T- dry locations

Type TW- dry or wet locations

Type THHN- dry locations, high temperatures

Type THW & THWN- wet locations, high temperatures

Type XHAW- high moisture & heat resistance

Type UF- buried in soil (not concrete) specified amounts pass through it

NEC- National Electric Code

Hot Wires- colors (positive)

-black -red -blue

Neutral Wires- color


Ground Wire- colors

-green -bare

Typical markings: 12-1, 12-2, 12-3 with ground

INSTALLING BRANCH CIRCUITS specified amounts pass through it

NEC- controls restrictions on wiring

Wiring Boxes:



-hold work in place

-nail or screw to framing

-contains all electrical connections


Wire Nuts- specified amounts pass through it insulated, solder-less connectors

Receptacle- device used for receiving electrical plugs

Switch- device used to stop the flow of electricity

Duplex Receptacle- both outlets are on same circuit

Single-Pole Switch- designed to be the only switch in the circuit

Knock Out- partially punched impression

Ground Clip- specified amounts pass through it attaches ground wire to a box

Testing a Circuit:

Continuity Tester- device used to determine if electricity can flow between 2 points

Continuity- connected-ness

3 way switch- permits a light/receptacle to be controlled from 2 locations