Basic Electrical Theory: Unit 15 - Protection Devices
Available short-circuit current is the current in amperes that is available at a given point in the electrical system. True or False
True
A GFCI-protection device contains an internal monitor that prevents the device from being turned on if there is a neutral-to-case connection downstream of the device. But this only occurs if there is a load on the circuit. True or False
False
Ground-fault protection devices protect equipment from damaging ground-fault currents by opening all ungrounded conductors of the faulted circuit. This device will also protect persons. True or False
False
Inverse time breakers operate on the principle that as the current decreases, the time it takes for the device to open decreases. True or False
False
A series arc can occur when the conductor in series with the load is unintentionally broken. A series arc-fault current is load limited. True or False
True
An AFCI-protection device provides protection from an arcing fault by recognizing the characteristics unique to a parallel arcing fault and by function to a de-energize the circuit when an arc fault is detected. True or False
True
Circuit breakers and fuses are intended to interrupt the circuit, and they must have an ampere interrupting rating (AIR) sufficient for the available short-circuit current. True or False
True
If the protection device is not rated to interrupt the available fault current at its listed voltage rating, it can explode while attempting to clear the fault. True or False
True
Severe electric shock or death can occur if a person touches the ungrounded and the neutral conductors at the same time, even if the circuit is GFCI protected. True or False
True
The opening time for a protection device is inversely proportional to the magnitude of the current. The greater the current value, the less time it takes for the protection device to open. True or False
True
Typically, when a GFCI-protection device fails, the switching contacts remain closed and the device will continue to provide power without GFCI protection. True or False
True
Unless marked otherwise, circuit breakers have a 5,000 AIC rating and fuses have a 10,000 AIC rating. True or False
True
Unsafe arcing faults can occur in one of two ways, as series arcing faults or as parallel arcing faults. The most dangerous is the parallel arcing fault. True or False
True
To help reduce the hazard of electrical fires from a parallel arcing fault, the NEC requires a listed AFCI-protection device to protect __________wiring in dwelling unit bedrooms. a. branch-circuit b. feeder c. service d. all of these
a. branch-circuit
________________ breakers operate on the principle that as the current increases, the time it takes for the device to open decreases. a. inverse time b. adjustable trip c. instantaneous trip d. all of these
a. inverse time
A(n) __________ is the operation of equipment or conductors in excess of their rated ampacity. a. overload b. short circuit c. ground fault d. all of these
a. overload
When a short circuit or ground fault occurs, __________ melt(s), removing the load from the source very quickly. a. several elements b. all of the elements c. a portion of the element d. none of these
a. several elements
_____________ breakers permit the thermal trip setting to be adjusted to coordinate the circuit breaker's operation with other protection devices. a. inverse time b. adjustable trip c. instantaneous trip d. all of these
b. adjustable trip
Equipment must have a(n)___________ current rating that permits the protection device to clear a short circuit or ground fault without extensive damage to the components of the circuit. a. overload b. short-circuit c. ground-fault d. none of these
b. short-circuit
According to a NEMA report, 11 percent of the GFCI breakers protecting indoor receptacles failed, and _______ percent protecting outdoor receptacles failed. a. 10 b. 15 c. 20 d. 25
c. 20
If the difference between the current leaving and returning through the current transformer of the GFCI-protection device exceeds __________, the solid-state circuitry deenergizes the circuit. a. 1 mA b. 3 mA c. 5 mA d. 10 mA
c. 5 mA
Arcing is a luminous discharge of electricity across an insulating medium. Electric arcs operate at temperatures between _______ and expel small particles of very hot molten material. a. 1,000 and 5,000 Fahrenheit b. 2,000 and 10,000 Fahrenheit c. 5,00 and 15,000 Fahrenheit d. 10,000 and 25,000 Fahrenheit
c. 5,00 and 15,000 Fahrenheit
A ground-fault type parallel arc can only occur when a ground path is present. This type of arcing fault can be quickly cleared by a(n) ________ circuit protective device. a. GFCI b. AFCI c. a or b d. none of these
c. a or b
As current flows through the element of a fuse, it generates heat. When a sustained overload occurs, the heat melts _________, stopping the flow of current. a. several elements b. all of the elements c. a portion of the element d. none of these
c. a portion of the element
To remove dangerous touch voltage on metal parts for a(n) _________, the fault-current path must have low impedance to allow the fault current to quickly rise to facilitate the opening of the protection device. a. overload b. short circuit c. ground fault d. all of these
c. ground fault
________ breakers operate on the principle of electromagnetism only and are used for very large motors. a. inverse b. adjustable trip c. instantaneous trip d. all of these
c. instantaneous trip
The _________ sensing element causes the circuit breaker to open when a predetermined calibration temperature is reached. a. magnetic b. electronic c. thermal d. none of these
c. thermal
The current in a short-circuit type arc 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 _______. a. 100A b. 220A c. 330A d. 450A
d. 450A
A short circuit is a _________ electrical connection between any two conductors of the electrical system. a. line-to-line b. line-to-neutral c. line-to-ground d. a or b
d. a or b
Factors that impact the available short-circuit current include circuit conductor _________. a. material b. size c. length d. all of these
d. all of these
Factors that impact the available short-circuit current include transformer _________. a. voltage b. kVA rating c. impedance d. all of these
d. all of these
The purpose of overcurrent protection is to protect conductors and equipment against excessive or dangerous temperatures because of over current. Overcurrent is current in excess of the rated current of equipment or conductors. It may result from a(n) _____________. a. overload b. short circuit c. ground fault d. all of these
d. all of these
To protect against electric shock or to prevent a fire, a dangerous _________ must quickly be removed by opening the circuit's overcurrent protection device. a. overload b. short circuit c. ground fault d. all of these
d. all of these
A thermal-magnetic circuit breaker typically clears fault current in less than 3 to 5 cycles when subjected to a(n)________. a. overload b. short circuit c. ground fault d. b or c
d. b or c
Magnetic time-delay circuit breakers operate on the solenoid principle where a movable core, held with a spring, is moved by the magnetic field of a (n) _________. a. overload b. short circuit c. ground fault d. b or c
d. b or c
When equipment does not have a withstand rating sufficient for the available fault current, the equipment can be protected by the use of _________. a. one-time fuses b. dual-element fuses c. instantaneous-type circuit breakers d. current-limiting fuses
d. current-limiting fuses
A fuse consists of an element electrically connected to end blades, which is enclosed in a tube and surrounded by a ____________ filler material. a. conductive b. foam c. light d. nonconductive
d. nonconductive
A GFCI is designed to protect persons against electric shock. It operates on the principle of monitoring the imbalance current of the circuit's ________ conductor. a. ungrounded b. neutral c. equipment d. ungrounded and neutral
d. ungrounded and neutral
The available short-circuit current is different at each point of the electrical system; it is highest at the __________. a. branch circuit b. feeder c. service d. utility transformer
d. utility transformer
