Chapter 3: Circuit Theory and Switches

Question 1

What is a slang term throughout the electrical industry as a replacement for the word “Conductor”?

Answer 1

Wire

Question 2

Which term is more commonly used throughout the National Electrical Code? Wire or Conductor?

Answer 2

Conductor

Question 3

Conductor in the NEC is defined as three things. What are they?

Answer 3

Conductor, Bare
Conductor, Covered
Conductor, Insulated

Question 4

What is a schematic diagram?

Answer 4

The circuit you see on paper. It depicts the systematic way current would flow through the wires, switches, and loads in a logical progression.

Question 5

What happens when the circuit is open?

Answer 5

No current flow

Question 6

How can an open circuit be created? 3 answers

Answer 6

Switch in an open position
A conductor that is broken or not complete
A mission connection at a terminal

Question 7

“Current takes the path of least resistance” back to the source. It is more correct to say,

Answer 7

“Current tries to take any path back to the source”

Question 8

The term “short circuit” comes from

Answer 8

Current has taken a shorter path back to the source, avoiding the opposition/resistance of the load

Question 9

A complete circuit allows

Answer 9

current to flow to the intended destination through the load and back to the source

Question 10

Switches are designated how?

Answer 10

How many paths from the source they make or break.

Question 11

A switch has what two characteristics?

Answer 11

A number or poles

A number of throws

Question 12

With switches, “Throws” refer to what?

Answer 12

The number of actions, or switch positions to CLOSE the circuit.

Question 13

With switches, “Poles” refer to what?

Answer 13

The number of circuit paths from the source we can control.

Question 14

A disconnect switch is used commonly in what applications?

Answer 14

Commercial and Industrial

Question 15

A more common style of switch is?

Answer 15

A toggle switch.

Question 16

What is a Relay?

Answer 16

Most common switch moved by electromagnetic means.

Question 17

The current rating on a switch is used to?

Answer 17

Design the conducting surface and material of the switch contacts. To allow the current to flow easily without overheating the contacts.

Question 18

The voltage rating on a switch tells? 2 Answers

Answer 18

The switch can safely break the circuit without a destructive arc.

Determines the distance we must separate the contact surfaces.

Question 19

Why/how is an Arc dangerous to equipment?

Answer 19

If the contacts do not move far enough apart, and fast enough apart, the arc will continue and the circuit current will continue to flow. The arc has a high temperatures and will burn and melt the switch contacts.

Question 20

Which Arc is more dangerous to equipment, with the same voltage and current? Direct Current or Alternating Current?

Answer 20

Direct Current, the arc is more difficult to extinguish.

Question 21

AC switches can be used for DC switches? True of False?

Answer 21

False

Question 22

What is the difference between and DC switch and an AC switch?

Answer 22

The mechanical design. A DC switch’s contacts must move apart faster and father than an AC switch with the same current and voltage rating.

Question 23

The common terminal in a switch is referred to as

Answer 23

The shunt terminal

Question 24

Why do some switching devices not have “ON/OFF” on the handle?

Answer 24

In some applications is cannot be determined unless the position of the other switches is known

Question 25

What are some troubleshooting problems with switches?

Answer 25

Faulty Switching Systems- Failed Mechanisms

Poor Connection Points- High Resistance Connection

Question 26

When a switch is closed properly and the connections are clean, what is the expected resistance in ohms across the switch?

Answer 26

0 ohms and no voltage drop

Question 27

An Open switch will read how many ohms?

Answer 27

Infinite Ohms

Question 28

Conductors must be sized to?

Answer 28

Carry the expected current

Question 29

Conductors are sized according to

Answer 29

American Wire Gauge or Circular Mil

Question 30

One Mil is equal to

Answer 30

.001 inch

Question 31

The area of a conductor is calculated as

Answer 31

square of the diameter

Question 32

The Cross Sectional Area of a conductor in CM is calculated by

Answer 32

(Diameter of the conductor in inches x 1,000)^2

Question 33

Internationally most conductor areas are expressed in ?

The formula is

Answer 33

mm^2

A= (3.14) r^2

Question 34

What affects the resistance of a conductor?

Answer 34

Cross-Sectional Area
Length
Temperature
Material Type

Question 35

How does length affect the resistance of a conductor?

Answer 35

The resistance is directly proportional to the length of the conductor.
Energy is given up a electrons strike each other of greater distances

Question 36

What is the relationship between resistance and conductor area?

Answer 36

The resistance of a conductor is inversely proportional to its area.
More valence electrons available to participate in current flow in larger conductors

Question 37

Specific resistance is also called ? and abbreviated with ?

Answer 37

Resistivity

K, to mean mils/foot

Question 38

To convert from square-mils to CM

Answer 38

Mil-inchs= 1,000 x inch
Square Area of the Rectangle= Width x Length in mil-inchs
Divide by constant .7854

Question 39

What is the Voltage Drop Formula?

Answer 39

VD= 2 x [ (KxL)/CM] x I

Question 40

What is power loss?

Answer 40

Energy loss in the form of Heat. Measured in Watts.

Question 41

What is the Power Loss Formula?

Answer 41

P=I^2x R

Question 42

Total Resistance of the wire is calculated with?

Answer 42

R= K x L/A