Ch 4 Flashcards
If there is a neutral-to-case connection on the load side of f the GFCI protection device, the sensors detect the imbalance of the current returning on the _______ and prevents the GFCI device from being turned on
ECG or Equipment Grounding Conductor
A current-limiting type fuse is a fuse designed for operations relating to only what?
Short circuits
The electrical connection between any two conductors of the electrical system from line-to-line- or from line-to-neutral is called:
Short Circuit
What are the two ways in which power is transferred from the utility distribution transformer?
Overhead service drop : underground service lateral
The NEC requires a listed AFCI-protection device to be installed to protect the branch-circuit wiring for ______
Dwelling unit bedrooms
A GFCI operates on the principle of monitoring the imbalance of ____ between the circuits _____ and _____
Current : Ungrounded : Neutral
The opening time for an overcurrent protection device is _____ proportional to the ______ of the current
Inversely : Magnitude
A fault must quickly be removed by doing what?
Opening the circuit’s overcurrent protection device
Would you use a GFCI or AFCI to clear a Ground Fault Parallel Arc?
Either
What happens to a fuse when a sustained overload occurs?
A portion of the element is overheated and breaks, which prevents current from going through the fuse.
Electromagnetic circuit breakers open on the principle of ________ and _______
Thermal Energy and Electromagnetism
Ground-fault protection of equipment is a system intended to provide protection of equipment from damaging ground-fault currents by _____ all ungrounded conductors of the faulted circuit.
Opening
What kinds of protection do Instantaneous breakers offer?
Short circuit and ground fault. Not overload
This type of circuit breaker depends upon temperature rise in the sensing element for actuation. It has a predetermined calibration temperature.
Thermal Trip Element
The purpose of overcurrent protection is to protect equipment and the conductors from what?
Dangerous temperatures
What is a more dangerous arc fault, parallel or series?
Parallel
Typically, when a GFCI protection device fails, the switching contacts remain closed and the device will continue to provide power _____ GFCI protection
Without
What does “AIR” stand for?
Ampere Interrupting Rating
The most effective way to reduce conductor voltage drop and power loss is to:
Lower the current flowing through the conductors by increasing the circuit voltage
What are the two ways parallel arcing faults occur?
Short circuit or ground fault
Typically, circuit breakers and fuses are designed to open or clear short-circuit and ground-circuit fault current in how many cycles?
Less than 1
The electrical connection between any ungrounded conductors of the electrical system and any non-current-carrying metal object is called:
Ground Fault
Typically, a steam turbine is directly connected to an electrical generator, which produces _______ kV, three-phase power
13.80
What are the two most common types of overcurrent protection?
Fuses and Circuit Breakers
A series arc-fault current is ____ limited; the arc’s current cannot be greater than the load current the conductor serves.
Load
What temperature do electric arcs operate at?
Between 5,000 and 15,000 F
Conductor power losses are directly proportional to the length of the conductor and the ______ of the current
Square
Various distribution feeders transfer the primary distribution voltage from step-down substations to ________ ________
Distribution transformers
Metal parts of premises wiring are bonded to a low-impedance path designed and intended to carry fault current from _______ to _______
The point of a line-case fault on a wiring system : the neutral conductor at the electrical supply source
This type of breaker operates on the principle that as the current increases, the time it takes for the device to open decreases
Inverse time breaker
Step-down substations reduce the voltage from the high-voltage transmission lines to 34.50 kV, 13.80 kV, or sometimes as low as 4160V. This reduced voltage is knows as ________
Primary distribution voltage
Thermal circuit breakers depend on ________ _______ in the sensing element for actuation.
Temperature rise
Electrical connection between any two conductors of the electrical system from line-to-line or line-to-neutral
Short Circuit
The magnetic time-delay circuit breaker operates under which principle and how does that work?
Solenoid Principle. A movable core held with a spring, in a tube, is moved by the magnetic field caused by a short circuit or ground fault.
A condition where equipment or conductors carry current in excess of their rated ampacity is called:
Overload
The most economical way to transfer electrical power over long distances is with ______ ________
High voltage
Is short-circuit current higher at the utility transformer or the branch-circuit load?
Utility transformer
A ground fault parallel arc can only occur when a ___ path is present.
Ground
An AFCI-protection device protects again arcing faults by recognizing the characteristics unique to an arcing fault and by functioning to _____ the circuit when a parallel arc fault is detected
de-energize
The current flow in a short-circuit type arc is limited by the system _____ and the impedance of the arcing fault itself.
Impedance
What are two ways to solve the problem of excessive available fault current?
1) Install equipment with a higher short-circuit rating
2) Install a fast-clearing fuse to protect components in the circuit.
Electrons leaving a power supply are always trying to go where?
Back to the power supply, not to Earth
Overcurrent protection devices such as circuit breakers and fuses are intended to ________ the circuit
Interupt
Electrical connection between any ungrounded conductors of the electrical system and any non-current-carrying metal object
Ground Fault
Why does the electric utility ground the primary and secondary neutral in multiple locations?
To create a parallel path as to reduce the impedance of the return neutral current path
The voltage drop of a conductor is directly proportional to the _____ of the conductor because conductor ______ is directly proportional to the conductor lenght
Length : resistance
What might cause a short-circuit parallel arc?
Damage to the wire’s insulation
What do you call the element electrically connected to the end blades on a fuse?
Ferrules
Neutral current should only flow on the ______, not on the metal parts of the electrical installation
Neutral conductor
Adjustable trip breakers permit the ____ _____ to be adjusted
Thermal Trip
Condition where equipment or conductors carry current in excess of their rated ampacity
Overload
Electrical equipment must have a ______ _____ current rating that permits the circuit overcurrent protection device to clear a short circuit or ground fault
Short-circuit
To remove dangerous touch voltage on metal parts from a ground fault, the fault current path must have sufficiently low _______ to allow the fault current to quickly rise to facilitate the opening of the branch circuit overcurrent protection device
Impedance
This type of breaker operates on the principle of electromagnetism only and is used for very large motors and sometimes called motor-circuit protectors
Instantaneous trip breakers
An inverse time breaker provides overcurrent for what kinds of faults?
Overload : Short Circuit : Ground Fault
(T/F) At the step-up substation, the 13.80 kV generated voltage is transformed to 69 kV, 500 kV or even higher.
True
(T/F) f you touch the neutral and ungrounded conductors at the same time the GFCI protection device will turn turn on.
False
Distribution transformers further reduce the primary distribution voltage from 34.50 kV or 13.80 kV to 240V or 480V, three-phase for the average commercial or small industrial customer. What is that called?
Secondary distribution voltage
Electric power is typically generated and transmitted across _____ ______ lines to the electrical substation
Long transmission
The electrical system begins at a generating plant that converts energy from ______, _______, or _______, power to ____, which turns the turbine of an electric generator.
Coal : Oil : Nuclear : Steam
What is the purpose of grounding and bonding metal parts of the electric utility equipment to the neutral conductor?
To provide a low-impedance parallel path for the purpose of clearing a line-to-case ground fault
What is the purpose of a GFCI?
To protect persons agains electrical shock
