Theory 2 Final
If the protection device is not rated to interrupt the current at the available fault values at its listed voltage rating, it could explode while attempting to clear the fault.
true
In the ac induction motor, the stator produces a rotating magnetic field that induces current in the rotor windings. The rotor current generates a magnetic field in opposition to the magnetic field of the stator, thereby causing the rotor to turn.
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 current flowing on a neutral conductor of a multi wire branch circuit is called unbalanced current.
true
The energy transfer ability of a transformer is accomplished because the primary electromagnetic lines of force induce a voltage in the secondary winding.
true
The heating from harmonic currents is proportional to the square of the harmonic current.
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
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
Voltage induced in the secondary winding of a transformer is dependent on the number of secondary turns as compared to the number of primary turns.
true
beer
true power (kW)
Swapping ______of of the line conductors can reverse a three-phase ac motor's rotation.
two
When describing the relationship between voltage and current, the reference waveform is always _______.
voltage
Factors that impact the available short-circuit current include transformer
voltage, KVA rating, impedance
Three-phase ac generators have three equally spaced windings______ out-of-phase with each other.
120 degrees
If the output is 1,600W and the equipment is 88 percent efficient, what are the input amperes at 120V?
15 A
What size transformer is required for a 100A, 240V, single-phase noncontinuous load that has a power factor of 85%
24,000VA/85% = 25kVA
how many 20A 120V circuits are required for forty two, 300W luminaire's (noncontinuous load) that have a power factor of 85%?
2400VA/(300W/85%)= 6 lights per circuit... 42(lights total)/6(lights per cicuit) = 7 circuits
If the primary phase voltage is 480V and the secondary phase voltage is 240V, the turns ratio is _____
2:1
Three-phase,____, wye connected systems can overheat because of circulating odd triplen harmonic currents.
4 wire
Arcing is defined as a luminous discharge of electricity across an insulating medium. Electric arcs operate at temperatures between _____ and expel small particles of very hot molten
5,000 and 15,000 degrees
What is the nameplate FLA for a 20 hp, 208V, three-phase motor with 90 percent power far and 80 percent efficiency?
58A
When a motor starts, the current drawn is approximately_______ times the motor FLA; this is known as motor locked-rotor amperes (LRA).
6
The induced voltage in a conductor carrying alternating current opposes the change in current flowing through the conductor. The induced voltage that opposes the current flow is called
CEMF, conter-electromotive force, back EMF
If the rotating part of the motor winding is jammed so that it cannot rotate, no CEMF will be produced in the motor winding. Result the motor operates at ______ and the windings will be destroyed by excessive heat.
LRC
In a(n)____ motor, the rotor is locked in step with the rotating stator field and is dragged along at the speed of the rotating magnetic field
Synchronous
______ motors are fractional horsepower motors that operate equally well on ac and de and are used for vacuum cleaners, electric drills, mixers, and light household appliances.
Universal
Self-induced voltage opposes the change in current flowing in the conductor. This is called inductive reactance and it is abbreviated ______.
XL
The opposition offered to the flow of ac current by a capacitor is called capacitive reactance, which is expressed in ohm and abbreviated
Xc
The abbreviation for impedance is
Z
Beer Glass
apparent power (kVA)
_____ can be reduced by dividing the core into many flat sections or laminations.
eddy currents
For ac circuits, the ac _____ of a conductor must be taken into consideration.
eddy currents, skin effect, resistance
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.
false
AC inductive or capacitive reactive loads cause the voltage and current to be in-phase with each other.
false
Available short-circuit current is the current in amperes available at a given point in the electrical system.
false
Inverse time breakers operate on the principle that as the current decreases, the time it takes for the device to open decreases.
false
The motor FLA rating is used when sizing motor conductor size or circuit protection.
false
To prevent fires and electric shock, the NEC specifies that neutral current can flow on metal parts of the electrical system.
false
Because of the dangers associated with an open neutral conductor, the continuity of the ___ conductor cannot be dependent upon the receptacle.
grounded
A GFCI is designed to protect persons against electric shock. It operates on the principle of monitoring the imbalance of current between the circuit's ______ conductor
grounded and ungrounded
As current flows through the transformer, the iron core is temporarily magnetized. The energy required to realign the core molecules to the changing electromagnetic field is called ______ loss
hysteresis
Wasteful circulating _____ in the iron core cause(s) the core to heat up without any useful purpose.
hysteresis losses
The total opposition to current flow in ac circuits is called _____ and measured in ohm.
impedance
Transformers are rated in
kVA
Factors that impact the available short-circuit current include circuit conductor
material, size, length
A non-sinusoidal waveform is created when ______ loads distort the voltage and current sine wave.
nonlinear
To protect against electric shock or to prevent a fire, a dangerous _____ must quickly be removed by opening the circuit's overcurrent protection device.
overload, short circuit, and ground fault
The purpose of overcurrent protection is to protect the conductors and equipment against excessive or dangerous temperatures because of overcurrent. Overcurrent is current in excess of the rated current of equipment or conductors. It may result from a(n).
overload, short current, or ground fault
Improper Wiring or Mishandling of multiwire Branch Circuits can cause ___ connected to the circuit.
overloading of the neutral and ruining equipment due to over voltage
Dual-voltage ac motors are made with two field windings. The field windings are connected in _____for low-voltage operation and in ______for high-voltage operation.
paralell, series
Because of the earth's high resistance to current flow, it cannot be used for the purpose of clearing a line-to-case ground fault for______ wiring.
premesis
foam
reactive power (kVAr)
The______ of an ac generator contains the electromagnetic field, which cuts through the stationary conductor coils
rotor
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.
short circuit
The magnetic time-delay circuit breaker operates on the solenoid principle where a movable core, held with a spring, is moved by the magnetic field of a(n) ______
short circuit or ground fault
The expanding and collapsing magnetic field within the conductor induces a voltage in the conductors (CEMF) that repels the flowing electrons toward the surface of the conductor. This is called ______.
skin effect
The sensing element causes the circuit breaker to open when a predetermined calibration temperature is reached.
thermo
The effective value is equal to the peak value_____.
times .707
An AFC protection device provides protection from an arcing fault by recognizing the characteristics unique to an arcing fault and by functioning to de-energize the circuit when an arc fault is detected.
true
Because of conductor resistance, flux leakage, eddy currents, and hysteresis losses, not all of the input power is transferred to the secondary winding for useful purposes.
true
Circuit breakers and fuses are intended to interrupt the circuit, and they shall have an ampere interrupting rating (AIR) sufficient for the available short-circuit current
true
Electrons leaving a power supply are always trying to return to the same power supply; they are not trying to go into the earth.
true
Even when power is removed from the circuit, capacitors can store large amounts of energy for a long period of time. They can discharge and arc if inadvertently shorted or grounded out.
true
