Chapter 3: Circuit Theory and Switches Flashcards
What is a slang term throughout the electrical industry as a replacement for the word “Conductor”?
Wire
Which term is more commonly used throughout the National Electrical Code? Wire or Conductor?
Conductor
Conductor in the NEC is defined as three things. What are they?
Conductor, Bare
Conductor, Covered
Conductor, Insulated
What is a schematic diagram?
The circuit you see on paper. It depicts the systematic way current would flow through the wires, switches, and loads in a logical progression.
What happens when the circuit is open?
No current flow
How can an open circuit be created? 3 answers
Switch in an open position
A conductor that is broken or not complete
A mission connection at a terminal
“Current takes the path of least resistance” back to the source. It is more correct to say,
“Current tries to take any path back to the source”
The term “short circuit” comes from
Current has taken a shorter path back to the source, avoiding the opposition/resistance of the load
A complete circuit allows
current to flow to the intended destination through the load and back to the source
Switches are designated how?
How many paths from the source they make or break.
A switch has what two characteristics?
A number or poles
A number of throws
With switches, “Throws” refer to what?
The number of actions, or switch positions to CLOSE the circuit.
With switches, “Poles” refer to what?
The number of circuit paths from the source we can control.
A disconnect switch is used commonly in what applications?
Commercial and Industrial
A more common style of switch is?
A toggle switch.
What is a Relay?
Most common switch moved by electromagnetic means.
The current rating on a switch is used to?
Design the conducting surface and material of the switch contacts. To allow the current to flow easily without overheating the contacts.
The voltage rating on a switch tells? 2 Answers
The switch can safely break the circuit without a destructive arc.
Determines the distance we must separate the contact surfaces.
Why/how is an Arc dangerous to equipment?
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.
Which Arc is more dangerous to equipment, with the same voltage and current? Direct Current or Alternating Current?
Direct Current, the arc is more difficult to extinguish.
AC switches can be used for DC switches? True of False?
False
What is the difference between and DC switch and an AC switch?
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.
The common terminal in a switch is referred to as
The shunt terminal
Why do some switching devices not have “ON/OFF” on the handle?
In some applications is cannot be determined unless the position of the other switches is known
What are some troubleshooting problems with switches?
Faulty Switching Systems- Failed Mechanisms
Poor Connection Points- High Resistance Connection
When a switch is closed properly and the connections are clean, what is the expected resistance in ohms across the switch?
0 ohms and no voltage drop
An Open switch will read how many ohms?
Infinite Ohms
Conductors must be sized to?
Carry the expected current
Conductors are sized according to
American Wire Gauge or Circular Mil
One Mil is equal to
.001 inch
The area of a conductor is calculated as
square of the diameter
The Cross Sectional Area of a conductor in CM is calculated by
(Diameter of the conductor in inches x 1,000)^2
Internationally most conductor areas are expressed in ?
The formula is
mm^2
A= (3.14) r^2
What affects the resistance of a conductor?
Cross-Sectional Area
Length
Temperature
Material Type
How does length affect the resistance of a conductor?
The resistance is directly proportional to the length of the conductor.
Energy is given up a electrons strike each other of greater distances
What is the relationship between resistance and conductor area?
The resistance of a conductor is inversely proportional to its area.
More valence electrons available to participate in current flow in larger conductors
Specific resistance is also called ? and abbreviated with ?
Resistivity
K, to mean mils/foot
To convert from square-mils to CM
Mil-inchs= 1,000 x inch
Square Area of the Rectangle= Width x Length in mil-inchs
Divide by constant .7854
What is the Voltage Drop Formula?
VD= 2 x [ (KxL)/CM] x I
What is power loss?
Energy loss in the form of Heat. Measured in Watts.
What is the Power Loss Formula?
P=I^2x R
Total Resistance of the wire is calculated with?
R= K x L/A
