THEA 120 - Part 1: Electricity

Electricity vs. Electronics

Electricity: The use of electromotive forces to do work.

Electronics: Low voltage circuits and devices used to control the flow of electricity.

Electromotive force (EMF)

Like charges repel and opposite charges attract.

Valence / Free electrons

Electrons in the outer shell.

Elements with these electrons are considered conductors.

The movement of these electrons in large groups is what creates electricity.

The flow of electricity

Free electrons pass from one atom to the next moving toward the positive charge.

Terms, units, and symbols

V - volts - voltage - The potential energy or force to do work

A - amps - current - The rate of flow of the current

W - watts - power - How much work an appliance can do

Ω - ohms - resistance - The resistance of the current

The Power Formula

W = V x A

• W is watts

• V is volts

• A is amperes

Ohm’s Law

V = I x R

• V is voltage

• I is current

• R is resistance

Conductors

Any material that allows electric current to pass through it

Ex: water, copper, aluminum, steel, etc

Insulators

Any material that does not allow electric current to pass through it

Ex: ceramic/porcelain, plastic, rubber, glass, cloth, wood

Series circuit

Electricity passes through one resistance before going to the next one.

If one light burns out, they all go out.

Less efficient since the current slows down going through each filament.

Switches are always wired…

…always wired in series.

Parallel circuit

Electricity goes to each resistance at the same time, and then returns.

If one light burns out, the rest keep working.

More efficient since they are using maximum power they can get.

Circuit breaker

A switch at the panel which creates an open circuit when too much current runs through (“trips”)

Fuse

Screws into the panel and has a metal wire inside it which burns out when too much current runs through (“blows”)

Ground wire

Routes the overload current to the ground pole in the earth

Overload

When too many appliances are placed on the circuit causing the circuit to try to draw too much amperage from the voltage pool.

Short

When there is a broken part of the circuit (perhaps physical damage to a wire casing creating a bare wire) allowing the electricity to leave the otherwise closed circuit.

Usually create sparks, smoke, and sometimes flames.

Electrical safety

• If you don’t know what it is or how to handle it, DON’T!!!!

• Turn off circuit breaker before fixing any architectural wiring.

• Unplug appliance before trying to fix it.

  • If you need to work live, (which is never recommended), keep one hand in your pocket and be sure you are well insulated from the ground.

Standardization: Wire Colors

National Electric Code (NEC)

• Green —> ground

• White (formerly black) —> neutral/return

• Black (formerly red) —> hot/live

Standardization: Screw Terminal Colors

• Green - ground

• Silver - neutral

• Brass - hot

BX cable

Seen in industrial applications today.

Has metal sheath used to ground the wire.

Hard to tell which wire is which.

Knob and tube wiring

In some buildings from around 1880-1940 in the US

Each wire is a single insulated wire

One is hot, other is neutral/return. No ground wire.

DC - direct current

Flows directly in one direction.

Loses power over long distances.

AC - alternating current

Flows back and forth, allowing it to be delivered further.

Wire gauges

Smaller number = bigger gauge

Smaller gauge = more resistance

Wire ratings for service wire

S = Standard; rated at 600 VAC

SJ = Junior; rated at 300 VAC

E = Elastomer; (thermoplastic rubber)

T = Thermoplastic insulation

O = Oil-resistant outer jacket

OO = Oil-resistant insulation and outer jacket

P = Parallel construction (flat)

W = Approved for outdoor use (water resistant)

V = Lightweight, round vacuum cleaner cord

Incandescent light bulb

• Glass sheath with inert gas vacuum sealed inside

• Electricity travels through wire to filament (tungsten) which has a high electrical resistance

• Filament gets very hot causing metal to glow brightly

• Doesn’t burn up because of inert gas

LED light bulb (Light Emitting Diode)

• Made by putting two semi-conductors together (aluminum-gallium-arsenide) which when enough voltage passes through it, it creates light by a process called electroluminescence

• Basically the electrons pass from one semi-conductor to the

  next and the excitement of the electrons causes the metal

  material to glow.

• It is more efficient and you get a lot more light from a tiny

  device.