EEP Unit 8
The opposition to current flow is greater for alternating-current circuits than for direct-current circuits because of _____.
All of these 1. Eddy Currents 2. Skin Effect 3. Inductive Reactance
The cross-sectional area of a conductor is commonly expressed in _____.
Circular Mils
The alternating-current conductor resistances listed in Chapter 9, Table 9 of the NEC are different for copper and aluminum, and for nonmagnetic and magnetic raceways.
True
What's the direct-current resistance of a 1 AWG copper conductor that's 100 ft long?
0.0154 ohms
What's the alternating-current ohms-to-neutral resistance for a 2/0 AWG copper conductor that's 300 ft long?
0.03 ohms
What's the direct-current resistance of a 1 AWG copper conductor that's 200 ft long?
0.0308 Ohms
What's the direct-current resistance of a 1/0 AWG aluminum conductor that's 800 ft long?
0.16 ohms
What's the direct-current resistance of a 3 AWG aluminum conductor that's 1,000 ft long?
0.403 ohms
The expanding and collapsing magnetic field induces a counter voltage within the conductors, which repels the flowing electrons toward the conductor surface. This is known as "_____ effect."
Skin
What's the voltage drop of two 12 AWG conductors that supply a 10A, 120V, single-phase load located 100 ft from the power supply?
4v
What's the maximum recommended continuous load that should be placed on 1/0 AWG aluminum conductors in a nonmetallic raceway to a panelboard located 200 ft from a 240V, single-phase power source so the NEC recommendation for voltage drop isn't exceeded?
90 A
What's the alternating-current ohms-to-neutral resistance for a 3 AWG copper conductor that's 100 ft long?
0.025 ohms
_____ currents are small independent currents that are produced as a result of the expanding and collapsing magnetic field. They flow erratically within the conductor opposing current flow and consuming power.
Eddy
In alternating-current circuits, the expanding and collapsing magnetic field within the conductor induces an electromotive force that opposes the flow of alternating current. This opposition to the flow of alternating current is called "inductive reactance."
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
The resistance of a conductor is directly proportional to its length.
True
According to Chapter 9, Table 8, what's the cross-sectional area in circular mils for a 3/0 AWG aluminum conductor?
167,800 cmil
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
What's the approximate distance a 480V, 45A, three-phase transformer, wired with 6 AWG copper can be located from a panelboard so the voltage drop doesn't exceed three percent?
375 Ft
A 100A, three-phase load is located 100 ft from the panelboard and is wired with 1 AWG aluminum conductors. What's the approximate voltage drop of the circuit conductors?
4.4 V
According to Chapter 9, Table 8, what's the cross-sectional area in circular mils for a 4 AWG conductor?
41,740 cmil
According to Chapter 9, Table 8, what's the cross-sectional area in circular mils for a 2 AWG conductor?
66,360 cmil
The National Electrical Code lists the resistance and area in circular mils for both direct-current and alternating-current conductors. Direct-current conductor resistances are listed in Chapter 9, Table _____ and alternating-current conductor resistances and reactance are listed in Chapter 9, Table _____.
8, 9
The larger the cross-sectional area of a conductor, the _____ the number of paths for electrons, which lowers the resistance of the conductor.
Greater
What's the alternating-current ohms-to-neutral resistance of a 500 kcmil copper conductor installed in PVC conduit that's 400 ft long?
0.0108 Ohms
What's the direct-current resistance in ohms for three 300 kcmil copper conductors in a parallel run that are 1,000 ft long?
0.014 ohms
What's the direct-current resistance of a 3 AWG aluminum conductor that's 500 ft long?
0.2015 Ohms
What's the approximate distance that a 240V, 31A, single-phase load can be located from a panelboard so the voltage drop doesn't exceed three percent? The load is wired with 8 AWG copper.
145 Ft
A 240V, 24A, single-phase load is located 160 ft from the panelboard. The load is wired with 10 AWG conductors. What's the approximate voltage drop of the branch-circuit conductors?
9.50 V
The resistance of a conductor changes with temperature. Temperature coefficient describes the effect temperature has on the resistance of a conductor. Conductors with a _____ temperature coefficient have an increase in resistance with an increase in temperature.
positive
