ch 2 Flashcards
The ? in an electrical circuit is the electromotive force of the circuit.
voltage
If the voltage of a DC circuit is 24 volts, and the resistance of the circuit is 10 ohms, what is the amount of current present in the circuit?
2.4 A
For current to be present in electrical circuits, the circuit has to be ? .
complete
Which of the following is included in the overall opposition to current in an AC circuit?
Inductive reactance
Capacitive reactance
Resistance
If an electrical circuit is not complete, there will be no current in the circuit.
true
The greater the resistance in a circuit, the ? the current present in the circuit.
lower
If a 2,500-watt heater is supplied by a 480-volt circuit, how much current is present in the circuit?
5.2 A
In a 60-cycle AC circuit, the voltage and current change amplitude and direction ? times per second.
120
In its simplest form, a capacitor is two conductors separated by insulation.
true
Kaufmann discovered that keeping the conductors of an AC circuit in close proximity to each other will keep the ? of the circuit low.
Impendance
Current in an AC circuit will take which of the following paths while attempting to return to the source?
All conductive paths
Equipment such as switchboards and panelboards installed in an electrical system must have adequate ? ratings to ensure that extensive damage to equipment will not result from a ground-fault or short-circuit condition.
short-circuit current
Fuses and circuit breakers are required to be marked with all but which of the following ratings?
resistance
The highest current at rated voltage that a device is identified to interrupt under standard test conditions best defines which of the following?
Interrupting rating
The ? of an electrical system is the maximum current a system is capable of delivering at any point on the wiring installation.
available fault current
An unintentional conducting connection between two ungrounded conductors of a circuit best describes which of the following?Short circuit
Short circuit
The amount of available fault current in an AC circuit is reduced by the overall ? of the circuit.
impedance
A(n) ? is defined as an unintentional, electrically conducting connection between an ungrounded conductor of an electrical circuit and the normally non–current-carrying conductors, metallic enclosures, metallic raceways, metallic equipment, or earth.
ground fault
Inverse time operation of overcurrent devices means that the ? the current, the ? the device will react to the ground fault or short circuit event.
higher / faster
Failure of conductor insulation is not a cause of failures in high-voltage and low-voltage electrical wiring.
false
Which of the following are common causes of conductor insulation failure?
Excessive voltage stress
Heat
Physical damage occurring during or after installation
Section ? requires conductors and wiring installations to be free of short circuits and any grounding connections other than grounding connections specifically permitted in the NEC.
110.7
According to the Insulated Cable Engineers Association (ICEA), the basic calculation for five-second insulated conductor current withstand ratings is as follows: For every ? area, an insulated conductor can safely carry one ampere for five seconds.
42.5
Which of the following organizations developed the formulas to determine insulated and bare conductor current withstand ratings?
Insulated Cable Engineers Association (ICEA)
Wire-type equipment grounding conductors must be capable of safely carrying high levels of available fault current for the duration of time it takes the overcurrent device for the circuit to open and clear the event.
true
Which NEC table provides the minimum sizes for wire-type equipment grounding conductors?
250.122
Which of the following test instruments is commonly used to determine the integrity of conductor insulation?
Megohmmeter
The time-current curves provided by overcurrent device manufacturers provide the graphic information about the operating characteristics of fuses or circuit breakers represented in time depending on current levels.
true
Which of the following symbols is not included in the formula for circuit impedance?
I
Basic Ohm’s Law includes all but which of the following components?
time
Wire-type equipment grounding conductors expressed in Table 250.122 of the NEC are approximately ? of the circuit conductor size.
25%
A(n) ? is defined as an electrically conductive path from the point of a ground fault on a wiring system through normally non–current-carrying conductors, equipment, or the Earth to the electrical supply source.
ground-fault current path
In the basic formula for impedance, XL represents the ? of the circuit.
inductive reactance
If the voltage of a circuit is 240 and the resistance of the circuit is 30 ohms, how much current would be present in the circuit?
8 A
Applying an overcurrent device (fuse or circuit breaker) within its marked interrupting rating will ensure that the overcurrent device can safely open the circuit in a ground fault condition.
true
The highest current at rated voltage that a device is identified to interrupt under standard test conditions best defines which of the following?
Interrupting rating
Using the time-current curve, determine the maximum 60-cycle clearing time for a 20-ampere, Squared D QO circuit breaker if a ground fault introduces 100 amperes in the circuit.
0.6 - 3 seconds
