Theory Units 25-26 Flashcards
A(An) _____ is an electrical connection between any two phase wires, or a phase wire and neutral wire.
Answer 1: overload
Answer 2: short circuit
Answer 3: ground fault
Answer 4: all of these
short circuit
A(An) _____ occurs when an unintentional electrical connection occurs between a phase wire and metal parts of enclosures, raceways, and/or equipment.
Answer 1: overload
Answer 2: short circuit
Answer 3: ground fault
Answer 4: all of these
ground fault
Fuses consist of a _____ element connected to end blades or caps, surrounded by silica sand filler material enclosed in a tube.
Answer 1: conductive
Answer 2: foam
Answer 3: light
Answer 4: nonconductive
conductive
When a sustained overload occurs through the element(s) of a fuse, the heat melts _____, stopping the flow of current.
Answer 1: several elements
Answer 2: all of the elements
Answer 3: a portion of the element
Answer 4: none of these
portion of the element
When a short circuit or ground fault occurs through the element of a fuse, the heat in the element rises to a point where _____ in the fuse melt to stop electrical current flow.
Answer 1: multiple conductive segments
Answer 2: a small portion of the segment
Answer 3: all of the segments
Answer 4: none of these
multiple conductive segments
A _____ fuse is referred to as a nontime-delay fuse and is the least expensive type.
Answer 1: single-element
Answer 2: dual-element
Answer 3: current-limiting
Answer 4: all of these
single-element
A _____ fuse is designed to clear a short circuit or ground fault in less than one-half a cycle.
Answer 1: one-time fuses
Answer 2: dual-element fuses
Answer 3: special trip fuses
Answer 4: current-limiting
current-limiting
The _____ trip element of a circuit breaker operates on the time-current principle of being inversely proportional to the magnitude of the current, which means that as the overload current increases, the time it takes for the trip element to open decreases.
Answer 1: magnetic
Answer 2: electronic
Answer 3: thermal
Answer 4: none of these
thermal
_____ circuit breakers permit the thermal and electromagnetic trip current and/or time settings to be adjusted to provide the user with flexibility for specific applications.
Answer 1: Inverse time
Answer 2: Adjustable trip
Answer 3: Instantaneous trip
Answer 4: all of these
Adjustable trip
The time it takes for an overcurrent protective device to open is plotted on a _____ curve chart.
Answer 1: time-current characteristics
Answer 2: bar graph
Answer 3: pie chart
Answer 4: none of these
time-current characteristics
As the overload current _____, the time it takes for the thermal trip element to open decreases.
Answer 1: increases
Answer 2: decreases
Answer 3: remains the same
Answer 4: none of these
increases
To quickly clear a short circuit, the short-circuit _____ must rise to a level that is between ten and twenty times the rating of the circuit overcurrent protective device.
Answer 1: voltage
Answer 2: current
Answer 3: resistance
Answer 4: power
current
To quickly clear a(an) _____, the ground-fault current needs to rise to a level between ten and twenty times the rating of the circuit overcurrent protective device.
Answer 1: overload
Answer 2: arcing fault
Answer 3: ground fault
Answer 4: none of these
ground fault
Available short-circuit current is the _____ current in amperes that is available at a given point in the electrical system
Answer 1: phase
Answer 2: line
Answer 3: largest
Answer 4: smallest
largest
The available short-circuit current is highest at the utility transformer and lowest at the _____ load because of the impedance of the circuit.
Answer 1: branch-circuit
Answer 2: feeder
Answer 3: service
Answer 4: utility transformer
branch-circuit
The available short-circuit current at the _____ transformer is provided by the electric utility; no calculation is required.
Answer 1: occupancy
Answer 2: building
Answer 3: premises
Answer 4: utility
utility
What is the approximate available short-circuit current on the secondary of a 50 kVA, 480V to 240V transformer having an impedance rating of 1.20 percent?
Answer 1: 10,000A
Answer 2: 12,000A
Answer 3: 14,000A
Answer 4: 17,000A
17,000A
What is the approximate available short-circuit current on the secondary of a three-phase, 112.50 kVA, 480V to 208Y/120V transformer having an impedance rating of 2.40 percent?
Answer 1: 10,500A
Answer 2: 11,000A
Answer 3: 12,500A
Answer 4: 13,000A
13,000A
If the protective device is not rated to _____ the available fault current at its listed voltage rating, it can explode while attempting to clear the fault.
Answer 1: interrupt
Answer 2: withstand
Answer 3: hold
Answer 4: break
interrupt
Equipment must have a(an) _____ current rating that permits the protection device to clear a short circuit or ground fault without extensive damage to the equipment components.
Answer 1: overload
Answer 2: short-circuit
Answer 3: ground-fault
Answer 4: none of these
short-circuit
If the equipment is not rated to _____ the available short-circuit current, it can explode while waiting for the circuit protective device to clear the fault.
Answer 1: interrupt
Answer 2: withstand
Answer 3: hold
Answer 4: break
break
Selective coordination of overcurrent protective devices prevents _____ power losses to loads not part of the faulted circuit.
Answer 1: intended
Answer 2: unintended
Answer 3: excessive
Answer 4: none of these
unintended
Lack of selective coordination of overcurrent protective devices can result in unintended _____ to loads not part of the faulted circuit.
Answer 1: surges
Answer 2: power losses
Answer 3: blackouts
Answer 4: shutdowns
power losses
If the difference between the current leaving and returning through the current transformer of the GFCI protective device exceeds _____ (± 1 mA), the solid-state circuitry de-energizes the circuit.
Answer 1: 1 mA
Answer 2: 3 mA
Answer 3: 5 mA
Answer 4: 10 mA
5 mA
A(An) _____ wire is not necessary for the proper function of a GFCI device.
Answer 1: phase
Answer 2: grounded
Answer 3: neutral
Answer 4: equipment grounding
equipment grounding
GFCIs detect connections between the neutral wire and the metal parts of the electrical system (case). If a neutral connection to metal parts occurs, the GFCI protective device will _____.
Answer 1: open
Answer 2: explode
Answer 3: overload
Answer 4: none of these
open
Severe electric shock or death can occur if a person touches the _____ and neutral wires at the same time, even if the circuit is GFCI protected.
Answer 1: phase
Answer 2: service
Answer 3: equipment grounding
Answer 4: none of these
phase
GFCIs can only be properly tested by pressing the GFCI _____ button.
Answer 1: disconnect
Answer 2: reset
Answer 3: test
Answer 4: any of these
test
A special purpose GFCI device is used in circuits where the voltage-to-ground is greater than _____.
Answer 1: 30V
Answer 2: 50V
Answer 3: 120V
Answer 4: 150Vselected
150V
The current in an arcing fault is limited by the system impedance and the impedance of the arcing fault itself. Typically, at a receptacle, fault current will be above 75A, but not likely above _____.
Answer 1: 100A
Answer 2: 220A
Answer 3: 330A
Answer 4: 450A
450A
A _____ arcing fault occurs when the wire within a cord is unintentionally broken, causing the current to arc across the gap in the wire.
Answer 1: series
Answer 2: parallel
Answer 3: ground
Answer 4: neutral
series
_____ sources of transient voltage include the switching of utility power factor correction capacitors or lightning strikes.
Answer 1: Special
Answer 2: Interior
Answer 3: Exterior
Answer 4: any of these
Exterior
