303
A 1200-Amp, 3Ø, 4-wire service and will have four parallel sets of conductors feeding it. Each set is in a separate conduit. What is the minimum size of the grounded conductor required in each conduit? Most of the loads are 3-phase.
1/0
A 208/120-volt, 3-ph, 4-wire panelboard will be fed with one conduit. This service panel contains a 350-Amp main breaker. The conductors supplying the service will consist of three 500 kcmil ungrounded conductors (one for AØ, one for BØ, and one for CØ) plus a grounded conductor. The calculated neutral load is 80 amps. The smallest neutral that can be run is a ___ AWG.
1/0
A 225 KVA, 480 delta to 208/120-volt, 3-ph, 4-w transformer is to be installed. One set of secondary conductors is installed from the transformer to a 400-A MB panelboard. There will be two parallel conduits to this 400-A panel. Each conduit will contain 3 each 3/0 ungrounded conductors and 1 each grounded conductor. The minimum size permitted grounded conductor will be installed in each conduit. A second set of secondary conductors is installed from the transformer to a 225-A MB panelboard. One conduit will be installed between this 225-amp panel and the transformer. The conduit will contain 4 each 4/0 conductors. The smallest grounded conductor you can install in each conduit to the 400-A PB is ___ AWG.
1/0
Which of the following secondary voltages would be indicated on a 4-wire, open delta using a voltmeter and measuring between any two ungrounded conductors, and between any ungrounded conductor and the neutral?
120 208 240
A 225 KVA, 480 delta to 208/120-volt, 3-ph, 4-w transformer is to be installed. One set of secondary conductors is installed from the transformer to a 400-A MB panelboard. There will be two parallel conduits to this 400-A panel. Each conduit will contain 4 each 3/0 conductors. A second set of secondary conductors is installed from the transformer to a 225-A MB panelboard. One conduit will be installed between this 225-amp panel and the transformer. The conduit will contain 3 each 4/0 ungrounded conductors and the smallest permitted size grounded conductor. Almost all the connected load is 3-phase. The smallest grounded conductor you can install in the conduit to the 225-A PB is ___ AWG.
2
An example of a system that is permitted to be grounded, but not required to be grounded, is a ___ system.
240-V, 3Ø, 3-W
An electrical system not required to be grounded is a ___.
240-volt, three-phase, 3-wire, delta system
Section ___ of the NEC® states that no overcurrent device shall be connected in series with any conductor that is intentionally grounded.
240.22
In a 277/480-volt, 3-phase, 4-wire system, the maximum voltage to ground is ___.
277 volts
A grounded conductor is to be pulled in with 500 kcmil THHN/THWN aluminum conductors as part of a 277/480-volt, 3Ø, 4-W service to a 300-amp fused safety switch. The maximum unbalanced load on the neutral will be 140 amps. The minimum size of the neutral is ___ AWG aluminum.
3/0
A 120/240-volt, 3-ph, 4-wire service is to be run to serve a 200-A main breaker panel. Each of the ungrounded conductors is a 3/0 AWG conductor. Most of the loads are 3-phase without neutrals. The smallest neutral that can be run is a ___ AWG conductor.
4
A 200-Amp, 120/208-volt, 3Ø, 4-wire service consists of three 3/0 AWG ungrounded conductors and one grounded conductor. The smallest grounded conductor that can be installed for this service is ___ AWG. Most of the connected loads are 3Ø and won't use a neutral.
4
In a 480-volt, corner-grounded delta system, the maximum voltage to ground is ___.
480
A 350-Amp, 277/480-volt, 3Ø, 4-wire service consists of three 500 kcmil ungrounded conductors and one grounded conductor. The smallest grounded conductor that can be installed for this service is ___ AWG or kcmil where the neutral load is unknown but could be the same as any ungrounded conductor since all the loads are 277-volt lighting.
500
A 150-Amp, 120/208-volt, 3Ø, 4-wire service consists of three 1/0 AWG ungrounded conductors and one grounded conductor. The smallest grounded conductor that can be installed for this service is ___ AWG. Most of the connected loads are 3Ø and won't use a neutral.
6
The smallest THHN/THWN copper grounded conductor that can be installed for a service is ___ when the ungrounded conductors are 1/0 THWN/THHN copper.
6
___ are not permitted to be grounded.
Circuits for electric cranes operating over combustible fibers
A single-phase transformer is supplied from a 480-volt circuit and delivers power to a 120-volt load. The secondary conductors are fused. If one of the secondary conductors is connected to a grounding electrode, the secondary fuses will open.
False
The grounded circuit conductor is always the neutral.
False
When a 3Ø, 3-W supply system delivers 240 volts, the system has a neutral.
False
When a 3Ø, 3-W supply system delivers 480 volts, the system has a neutral.
False
II
Generator ___ shown in Figure 304.03 is connected to a 4-Pole transfer switch.
I only
Generator ___ shown in Figure 304.03 would NOT be considered a separately derived system.
___ are required to be installed on ungrounded 3Ø, 3-wire systems.
Ground detectors
NEC® Sections 250.20, 250.21, and 250.22 state when a system is required, permitted, or not permitted to be grounded. Which of these transformer secondaries is not permitted to be grounded? I. the output conductors from a fluorescent ballast supplied from a 120-V circuit II. 120 to 12-volt AC transformer for a low-voltage lighting systemIII. 480 to 120-VAC for a motor control circuit
I & II only
Which of the following three-phase electrical distribution systems is grounded?I. 120/208-volt, three-phase, four-wireII. 277/480-volt, three-phase, four-wireIII. 480-volt, three-phase, three-wire
I & II only
NEC® Sections 250.20, 250.21, and 250.22 state when a system is required, permitted, or not permitted to be grounded. Which of these transformer secondaries is required to be grounded?I. 120 to 12 volt AC transformer installed outside overhead to tree-mounted, low-voltage lightingII. 480 to 120/240 VAC, 1Ø, 3-wire to a panelboardIII. 480 to 120 VAC for a motor control circuit
I, II & III
Which of the following voltage systems is solidly grounded?I. 120/208-volt, 3Ø, 4-wireII. 120/240-volt, 3Ø, 4-wireIII. 277/480-volt, 3Ø, 4-wire
I, II & III
NEC® Sections 250.20, 250.21, and 250.22 state when a system is required, permitted, or not permitted to be grounded. Which of these transformer secondaries is permitted or required to be grounded? I. 120 to 12-volt, AC transformer for a low-voltage lighting system II. 480 to 120/240-VAC, 1Ø, 3-wire to a panelboardIII. 480 to 120-VAC for a motor control circuit
II & III only
The secondary of a transformer delivers 12 volts. One of these secondary conductors must be grounded when the supply voltage to the transformer is from a ___. I. 2-pole breaker in a 120/208-volt, 3Ø, 4-wire panelboardII. 1-pole breaker in a 277/480-volt, 3Ø, 4-wire panelboard
II only
The grounded conductor is permitted to be ___ the GEC.I. a smaller size thanII. the same size asIII. a larger size than
II or III only
II only
NEC® Section 250.20 Informational Note refers to a corner-grounded delta transformer. A diagram of such a system is shown at ___ in Figure 304.02.
I only
NEC® Section 250.20(B)(3) requires that a three-phase, four-wire, delta-connected transformer, in which the midpoint of one phase winding is used as a circuit conductor, be grounded. A diagram of such a transformer is shown at ___ in Figure 304.02.
8
Refer to Figure 205.4. A 120/240-volt, 1-ph, 3-wire service is to be installed to serve a 100-Amp service. The conduit will have two ungrounded conductors and one grounded conductor. The ungrounded conductors will be 3 AWG copper conductors. All loads will be 240 volt. The smallest neutral that can be installed is a ___ AWG conductor.
4
Refer to Figure 205.4. A 120/240-volt, 1-ph, 3-wire service is to be installed to serve a 175-Amp service. The conduit will have two ungrounded conductors and one grounded conductor. The ungrounded conductors are to be 2/0 AWG. The neutral load will be 65 amps. The smallest grounded conductor that can be installed is a ___ AWG conductor.
2/0
Refer to Figure 304.06. The neutral loads supplied by the panel will not exceed 310 amps. The neutral in each conduit must be at least a ___ AWG or kcmil.
No
This "gutter service" is to be built on the exterior back wall of a free-standing building. Three fused safety switches, one main breaker panelboard, and one MLO (main-lug-only) panelboard are installed above the gutter.Refer to the installation shown in Figure 304.21. A ground rod is driven below the gutter and bonded to the grounded conductor inside the gutter. The service is 120/240-volt, 3Ø, 4-wire. Safety switch C is rated at 400 A and fused at 350 A and will feed MLO 3Ø, 4-wire panelboard D. Does the NEC® permit the grounded conductor to be bonded to panelboard D enclosure?
A transformer is supplied by a 277-volt circuit. The transformer delivers 120 volts for use in a control circuit. One of the two 120-volt wires is required by the NEC® to be grounded.
True
When a 3Ø, 4-W supply system delivers 120/208 volts, the system has a neutral.
True
When a 3Ø, 4-W supply system delivers 277/480 volts, the system has a neutral.
True
A 480-volt, 3-phase service panel is to be installed to serve only 3-phase motors. The power company has set a pad-mounted 277/480-volt, 3Ø transformer for the new service. You will need to install which of the following between the transformer and the service panel?I. three ungrounded conductors II. one grounded conductor
both I & II
The minimum size of a grounded conductor in a conduit is based on ___. I. the size of the largest ungrounded conductor in that conduitII. the load the neutral must carry
both I & II
A three-phase, four-wire, wye-connected system is normally ___ grounded.
center (at the point where the common leads of each transformer are connected together)
Ground detectors for ungrounded system must be installed as ___ where the system receives its supply.
close as practicable to
When a 3Ø, 3-W supply system delivers 240 volts, the system is ___ connected.
delta
A separately derived AC system ___ with any supply circuit conductor from another system.
does not share any circuit conductor
The NEC® requires that the ___ not be smaller than the grounding electrode conductor.
grounded conductor
An emergency or standby power generator is classified as a separately derived system provided that its neutral ___ common with that of the normal supply.
is not
When a 120 to 12-volt, AC transformer is a component of a low-voltage lighting system, ___ secondary conductor(s) is/are permitted to be grounded.
neither
A ___ would be considered a source of a separately derived system. 5 KW, 120/240-V, 1Ø generator, fed through a 2 pole transfer switch utility company pole-mounted 150 KVA, 277/480-V transformer bank
neither a nor b
Section 250.24(C) requires that the grounded (neutral) conductor be ___.
routed with the phase conductors
Refer to Figure 304.20. The neutral bar in the ___ should be connected to its metal enclosure.
safety switch
Where installed as overhead conductors outside of a building, AC systems of less than 50 volts ___ grounded.
shall be
An alternating current system of 50 to 1000 volts is required to be grounded where ___.
the maximum voltage to ground does not exceed 150 volts the system is 3-phase, 4-wire, wye-connected in which the neutral is used as a circuit conductor the system is 3-phase, 4-wire, delta-connected in which the midpoint of one phase winding is used as a circuit conductor
Where a grounded service conductor is run in parallel conduits and is used as a circuit conductor, its minimum size is determined based on ___.
the size of the largest ungrounded conductor in each conduit the load current that it will be required to carry
Three 120-volt circuits will be installed to serve receptacles that are required to be GFCI protected. The three circuits will be installed in one conduit to a J-box, and then MC cable will be run from there to the receptacles. Three GFCI circuit breakers will be installed in a 120/208-volt, 3-phase, 4-wire panelboard. The fewest number of neutrals that can be installed in the conduit is ___.
three
When a 3Ø, 4-W supply system delivers 277/480 volts, the system is ___ connected.
wye
