chapter 4 exam (14,15)
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 ____
450A
arcing is defined as a luminous discharge of electricity across an insulating medium. electric arcs operate at temp between _____
5k and 15k F
if the difference between the current leaving and returning through the current transformer of the gfci protection device exceeds ___ the solid state circuitry de energizes
5mA
the available short circuit current is different at each point of the electrical system, it is highest at the ___
branch circuit
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
branch circuit
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 there is a load on the circuit
false
a ground fault protection of equipment device is intended to provide protection from damaging ground fault currents by opening all ungrounded conductors of the vaulted circuit. this device will also protect persons
false
an afci protection device provides protection from an arcing fault by recognizing the characteristics unique to a parallel arcing fault and by functioning to de energize the circuit when an arc is detected
false
circuit breakers and fuses are intended to interrupt the circuit, and they must have an ampere intertupring rating sufficient for the available short circuit current
false
inverse time breakers operate on the principle that as the current decreases, the time it takes for the device to open decreases
false
to prevent fires and electric shock, the NEC specifies that neutral current can flow on metal parts of the electrical system
false
the most effective way to reduce conductor voltage drop and power loss is to lower the current flowing through the conductors. this is accomplished by _____ the transmission voltage
increasing
the voltage drop over a conductor is directly proportional to the ____ of the conductor
length
factors that impact the available short circuit current include circuit conductor ____
material, size, length
equipment must have an ____ current rating that permits the protection device to clear a short circuit or ground fault without extensive damage to the components of the circuit
short circuit
the magnetic time delay circuit breaker operates on the solenoid principle where a movable force held with a spring is moved by the magnetic field of a ___
short circuit and ground fault
the ___ sensing element causes the circuit breaker to open when a predwtermined calibration temp is reached
thermal
a series arc can occur whe the conductor in series with the load intentionally broken. a series circuit arc fault is load limited
true
available short circuit current is the current in amperes that is available at a given point in the electrical system
true
electrons leaving a power supply are always trying to return to the same power supply
true
if the protection device is not rated to interrupt the current at the available fault values at its listed voltage rating, it can explode while attempting to clear the fault
true
metal parts of premises wiring must be bonded to a low impedance path designed so that the circuit protection device will quickly open and clear a ground fault
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
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 to open
true
typically when a gfci fails the switching contacts remain closed and the device will continue to provide power without gfci protection
true
unsafe arcing faults can occur in one or two ways, as series arcing faults or as parallel arcing faults. the most dangerous is the parallel arcing fault
true
a gfci is designed to protect persons against electric shock it operates on the principle of monitoring the imbalance of current between the circuits ____ conductor
ungrounded and grounded
conductor power loses are directly proportional to the length of the conductor and the square of the current. If the current is doubled the power loss will be increased by ____ percent
400
ground fault type parallel arc only occurs when a ground path is present. this type of arcing fault can be quickly cleared by a ____ circuit protection device
AFCI
a ____ is the operation of equipment or conductors in excess of rated ampacity
overload
purpose of overcurrent protection is to protect the conductors against excessive or dangerous temperatures because of over current which is current in excess of the rated current of equipment or conductors may result from ____
overload, short cicuit and ground fault
to protect against electric shock or to prevent a fire, dangerous ____ must quickly be removed by opening the circuits overcurrent protection device
overload, short circuit and ground fault
because of the earths high resistance to current flow , it cannot be used for the purpose of clearing a line to case ground fault for ____ wiring
premises
factors that affect the available short circuit current include transformer ___
voltage, Kva rating, and impedance
