Electrical Midterm Review.
If the output power is 1,600W and the equipment is 88 percent efficient, what are the input amperes at 120V?
15A
A self-induced voltage waveform, also known as counter-electromotive force (CEMF), is _____ out-of-phase with the applied voltage waveform.
180°.
A transformer having a 208Y/120 volt 3-phase secondary is to supply a panelboard with a 130 ampere demand load. The feeder conductors are size 1/0 AWG THWN copper. What is the MAXIMUM approximate distance the panelboard can be located from the transformer so that the voltage drop does not exceed three percent?
225 feet.
At least one receptacle outlet shall be located within _____ ft of the outer end of a peninsular countertop or work surface.
2ft.
Three capacitors, a 12 μF, a 20 μF, and a 30 μF, are connected in parallel to a 60 Hz source. What is the total XC?
442.09 Ω.
How many 20A, 120V circuits are required for forty-two, 300W incandescent luminaires (noncontinuous load)?
6 circuits
How many 20A, 120V circuits are required for forty-two, 300W incandescent luminaires (noncontinuous load)?
6 circuits.
Three capacitors, a 12 μF, a 20 μF and a 30 μF, are connected in series. What is the total capacitance?
6 μF
What is the approximate MAX distance a 120 volt single phase 1800 VA load suppled with 12 AWG copper branch circuit conductors can be located from the panelboard, when the permitted voltage drop is to be not more than three percent?
60 feet
Three capacitors, a 12 μF, a 20 μF and a 30 μF, are connected in parallel. What is the total capacitance?
62 μF
How many 20A, 120V circuits are required for forty-two, 300W luminaires (assume this is a noncontinuous inductive load) that have a power factor of 85 percent?
7 circuits
If the output power is 1,320W and the input power is 1,800W, what is the efficiency of the equipment?
73%
If the output power is 1,320W and the input power is 1,800W, what is the efficiency of the equipment?
73%.
An inductor has an inductive reactance of 64 Ω, and a wire resistance of 36 Ω. What is the impedance of the inductor?
73.4 Ω
The load, in amperes, on a size 6 AGW THHN copper conductor is permitted to be no more than ______ where connected to a fusible disconnect switch with terminals rated at 75 degrees C
75
A capacitor is connected to a 240 V supply. An ammeter indicates 3 A. What is the capacitive reactance of the capacitor?
80 Ω.
A 240-volt single phase feeder with size 2/0 AWG aluminum conductors is supplying an existing panelboard located 260 feet from the main switchboard. What is the MAX load that can be placed on the panelboard so that the voltage drop is limited to three percent?
87 amps.
If a transformer is 97 percent efficient, for every 1 kW input, there will be _____ output.
970W
A waveform image is used to display the level and direction of current, but not voltage.
False.
Conductor resistance is directly proportional to the conductor's length and cross-sectional area.
False.
The resistance of a conductor is directly proportional to its length.
True.
When the alternating current decreases, the polarity of the induced voltage within the conductor tries to prevent the current from decreasing.
True.
Self-induced voltage is 180° out-of-phase with the _____. When the applied voltage is at its maximum in one direction, the induced voltage is at its maximum in the opposite direction.
applied voltage.
A common practical use of induction is for _____.
motors transformers generators
The NEC requires that conductors 8 AWG and larger must be ____ when installed in a raceway.
stranded.
When describing the relationship between voltage and current waveforms, the reference waveform (the one used to compare against) is the _____.
voltage.
What does it cost per year (at 9 cents per kWh) for ten 150W recessed luminaires to operate if they are turned on for six hours per day?
$300
What does it cost per year (at 9 cents per kWh) for ten 150W recessed luminaires to operate if they are turned on for six hours per day?
$300.
An inductor is connected to a 240-V, 60-Hz supply. The current in the circuit is 5 A. What is the inductance of the inductor?
.127 H
What's the alternating-current ohms-to-neutral resistance for a 500 kcmil copper conductor installed in an aluminum raceway that's 1,000 ft long?
0.032 ohms
An inductor is connected to a 60 Hz circuit. The inductive reactance is 75.4 Ω. What is the inductance of the inductor?
0.2 H
An inductor is connected to a 60 Hz circuit. The inductive reactance is 75.4 Ω. What is the inductance of the inductor?
0.2 H.
Two capacitors, a 20 μF and a 30 μF, are connected in series. What is the total capacitance?
12 μF.
Where a 100 amp load is to be supplied with THWN copper conductors in an area where the ambient temp will reach 110 deg. F size _____ THWN conductors are required to serve the load.
1 AWG
What is the allowable ampacity of a size 1/0 awg THW copper conductor installed in a conduit longer than 24 inches, when there are three other current carrying conductors contained in the same pipe?
120
Two inductors are connected in parallel to a 120-V, 60-Hz supply. The values of the inductors are 1.5 H and 2.5 H. The total inductive reactance is _____.
1508 Ω.
Two inductors are connected in series to a 120-V, 60-Hz supply. The values of the inductors are 1.5 H and 2.5 H. The total inductive reactance is _____.
1508 Ω.
A 100 ampere load is located in an environment where the temperature reaches 115 deg. F. and is to be supplied with four (4) 75 deg. C copper current carrying conductors. Determine the proper size wire to serve the load. All terminations are rated at 75 deg. C
2/0 AWG
An inductor has an inductive reactance of 12 Ω, and a wire resistance of 16 Ω. What is the impedance of the inductor?
20 Ω
What size transformer is required for a 100A, 240V, single-phase noncontinuous load (unity power factor)?
25 kVA.
A single-phase, 5 hp motor is located 110 ft from a panelboard in a dry location. The nameplate indicates that the voltage is 115V and the FLA is 52A. What size conductor is required? Note: Apply the NEC recommended voltage-drop limit for this branch circuit.
3 AWG
Two inductors are connected in parallel to a 120-V, 60-Hz supply. The values of the inductors are 0.15 H and 0.225 H. The total inductive reactance is _____
3.54 A
"_____" is the value of the voltage or current at a moment of time.
Instantaneous
When electrons move, the magnetic fields of the individual electrons combine to produce an overall magnetic field. The greater the current flow, the greater the overall magnetic field around the conductor.
True
Even when power is removed from the circuit, capacitors can store large amounts of energy for a long period of time, and can discharge and arc if inadvertently shorted or grounded out.
True.
Root-Mean-Square (RMS) describes the calculation steps (in reverse) necessary to determine the effective ac voltage or ac current value of a waveform.
True.
The intensity of a magnetic field depends on the intensity of alternating current. The greater the current flow, the greater the overall magnetic field.
True.
As the alternating current through a conductor increases, an expanding and collapsing electromagnetic field through the conductor induces a voltage within the conductor. This is known as "_____ voltage."
self-induced.
Two inductors are connected in series to a 120-V, 60-Hz supply. The values of the inductors are 0.175 H and 0.255 H. The total circuit current is _____.
0.74 A
Two inductors are connected in parallel to a 120-V, 60-Hz supply. The values of the inductors are 0.15 H and 0.225 H. The total inductive reactance is _____.
3.54 A
A 208Y/120 volt, 3 phase 150 ampere load is located two hundred and fifty (250) feet from the main distribution switchboard. What is the MINIMUM size copper feeder conductors required to supply he load when the voltage drop is limited to 3%?
3/0 AWG.
The vertical clearance of final spans of overhead service conductors above, or within _____ ft measured horizontally of platforms, projections, or surfaces that will permit personal contact shall be maintained in accordance with 230.24(B).
3ft.
Determine the allowable ampacity of size 2 AWG THWN aluminum conductor installed in a 20 foot long conduit with 7 other current carrying conductors of the same size and insulation where the ambient temperature is 99 deg. F.
55
The load on a size 6 AWG THHN copper conductor is limited to _____ where connected to a circuit breaker with a termination rated at 60 degree C
55 amps.
An inductor is connected to a 120-V, 60-Hz supply. The current in the circuit is 2.4 A. What is the inductive reactance?
57.08 Ω
An existing 208Y/120 volt three phase 4 wire panelboard is supplied with a size 2 AWG copper feeder conductor from the main switchboard. The panelboard is located three hundred (300) feet from the main switchboard. What is the MAX load in amperes the conductors can carry without exceeding a three percent voltage drop?
62 amps
If the input power of a 1 hp dc motor is 1,128W and the output power is 746W, what is the efficiency of the motor?
66%
If the input power of a 1 hp dc motor is 1,128W and the output power is 746W, what is the efficiency of the motor?
66%.
If the feeder supply voltage is 240V, the maximum recommended voltage drop of the feeder shouldn't be more than _____.
7.20V
When a size 3 awg copper conductor, with THW insulation is installed in an area where the ambient temperature is 114 deg. F the wire has an allowable ampacity of____?
75 amps.
If a transformer is 97 percent efficient, for every 1 kW input, there will be _____ output.
970W.
When a size 1/0 AWG THWN aluminum conductor is installed in an ambient temperature of 45 deg. C the conductor has an allowable ampacity of ______.
98 amps
The opposition to current flow is greater for alternating-current circuits than for direct-current circuits because of _____.
eddy currents skin effect inductive reactance
Where the lighting load for a nondwelling building is designed and constructed to comply with an energy code adopted by the local authority, the lighting load shall be permitted to be calculated using the unit values specified in the _____.
energy code.
120V, single-phase, 15A and 20A branch circuits supplying outlets and devices installed in _____ of hotels and motels shall be protected by any of the means described in 210.12(A)(1) through (6).
guest rooms
Factors that determine the capacitance of a capacitor are the _____ the plates.
surface area of distance between dielectric between
