Grounding II
A 400-ampere feeder made up of four 600 kcmil copper conductors and one size 3 AWG copper equipment grounding conductor is installed to supply a separate building. The only grounding electrode present is a metal in-ground support structure for the building. What is the minimum size grounding electrode conductor required for the building served?
1/0 AWG copper
If PVC conduit is installed for an 800-ampere feeder supplying a separate building, what is the minimum size wire-type copper equipment grounding conductor required to be installed with the feeder conductors?
1/0 AWG copper
If the grounding electrode conductor for a separate building or structure is connected to only a concrete-encased electrode(s), the maximum size required is a(n) ? .
4 AWG copper conductor
A ? equipment grounding conductor is the minimum size required for a 1,000-ampere feeder supplying a separate building or structure.
4/0 AWG aluminum
Where the grounding electrode for a separate building or structure is only a single ground rod or two ground rods, what is the maximum-size copper grounding electrode conductor required if the feeder supplying the separate building or structure is sized at 2,500 amperes?
6 AWG
From the choices below, identify the grounding electrodes permitted by 250.52(A) for use as grounding electrodes at a separate building or structure.
All but I. and V.
If present, which of the following grounding electrodes must be used to form a grounding electrode system for a building or structure served by a feeder or branch circuit?
All of the above must be used
Which of the following is not considered an effective ground-fault current path?
Earth
Class 2 load-side circuits for suspended ceiling low-voltage power grid distribution systems are required to be supplied by grounded systems.
False
If a feeder to a separate building or structure is installed in rigid metal conduit, the conduit is not permitted to serve as the required equipment grounding conductor.
False
If the overcurrent protective device is located on a generator outside that supplies a separate building or structure, then the feeder is on the load side of an overcurrent device. In this case, the equipment bonding jumper (load side) with the feeder is sized based on the requirements in Section 250.102(C).
False
If the transfer switch for a generator switches the grounded (neutral) conductor, the generator has to be grounded as a separately derived system in accordance with Section 250.30(B).
False
On an ungrounded system, the occurrence of the first ground fault (not a short circuit or line-to-line fault) on the system will cause the overcurrent protective device for the service, feeder, or branch circuit to open.
False
The connection of the grounding electrode conductor to the grounded conductor of the separately derived system is required to be made at a different location than the system bonding jumper connection.
False
The disconnecting means installed in the feeder supplying a separate building or structure has to always be suitable for use as service equipment.
False
The grounding electrode for a separately derived system must be one of the grounding electrodes used for the building or structure. It must be as near as practicable, preferably in the same area, and must be the nearest of either a metal water pipe electrode or a structural metal electrode, unless neither of the above electrodes is available.
False
The size of a DC system bonding jumper has to be not less than the system grounding electrode conductor based on Section 250.66.
False
The system bonding jumper for a separately derived system is permitted to extend beyond the enclosure where it originates.
False
Where a delta-connected system over 1,000 volts is used to supply portable or mobile equipment, a neutral point and system neutral are not permitted to be derived for grounding purposes.
False
Where a separately derived system is installed outside the building or structure it supplies, a grounding electrode connection is not required at the outdoor source location.
False
Where supplying portable or mobile equipment, electrical systems of over 1,000 volts must not be grounded.
False
NEC ? provides the requirements for grounding of electrical systems and equipment at buildings or structures that are supplied from a feeder(s) or branch circuit(s).
Section 250.32
Which section of Article 250 requires the electrodes present at any building or structure served to be bonded together to form a grounding electrode system?
Section 250.50
According to the NEC, that which is built or constructed, other than equipment, best defines which of the following?
Structure
A connection to ground through a grounding electrode system is generally required at separate buildings or structures to establish a reference to ground at that location.
True
A grounding electrode system is generally required for each building or structure served by a feeder.
True
A structure is constructed or built and does not include electrical equipment.
True
Electrical systems that are grounded shall be connected to earth in a manner that will limit the voltage imposed by lightning, line surges, or unintentional contact with higher-voltage lines and that will stabilize the voltage to earth during normal operation.
True
Electrical systems that supply only industrial electric furnaces for melting, refining, tempering, and so forth are permitted to be grounded, but not required to be grounded.
True
Ground detectors are required for 480-volt, 3-phase, ungrounded, delta-connected systems.
True
Ground-fault detection is required for ungrounded DC systems but permitted for grounded DC systems.
True
If a generator is installed on a premises wiring system, it must be grounded as a separately derived system if there is a switching action in the grounded conductor through the transfer switch.
True
If the overcurrent protective device is not located on a generator outside that supplies a separate building or structure, then the feeder is on the line side of an overcurrent device. In this case, the supply-side bonding jumper with the feeder is sized based on the requirements in 250.102(C).
True
In health care facilities, those isolated powered circuits in hazardous (classified) inhalation anesthetizing locations are required to be supplied by an isolation transformer or other ungrounded source and are not permitted to be grounded.
True
It is never Code-compliant to install a feeder to a separate building or structure without an equipment grounding conductor or supply-side bonding jumper for a new installation.
True
Systems supplying cranes that operate over combustible fibers in Class III locations are not permitted to be grounded.
True
The neutral of a high-impedance grounded neutral system is required to be fully insulated, and no equipment grounding or equipment bonding connections are permitted on the supply side of the impedance device.
True
Ungrounded systems are required to be marked "Caution: Ungrounded System Operating Volts Between Conductors" at the source or first disconnecting means of the system, and the marking must be of sufficient durability for the environment in which it is installed.
True
Where a building or structure is supplied by an ungrounded system, the feeder from the ungrounded system must include an equipment grounding conductor or supply-side bonding jumper with the conductors to the building disconnecting means, and it must be connected to the disconnecting means enclosure as well as to the grounding electrode conductor.
True
Where a system bonding jumper for a separately derived system is a wire type, it is required to be sized using Table 250.102(C)(1) or the 12.5% rule based on the size of the largest derived ungrounded phase conductor(s) or the total circular mil (cm) area of all conductors connected to any one ungrounded phase at the source.
True
Where equipment such as a luminaire at a light pole base in a parking lot is supplied by a single branch circuit, an auxiliary grounding electrode is permitted to be installed, but not required.
True
Where grounding electrode conductor taps are used for multiple separately derived systems, each grounding electrode conductor tap must be sized using Table 250.66 based on the largest ungrounded derived phase conductor(s) of the individual derived system it serves.
True
Where no grounding electrodes are present at a separate building or structure served by a feeder, a grounding electrode in accordance with 250.50 is required to be installed.
True
Not connected to ground or to a conductive body that extends the ground connection defines which of the following Code terms?
Ungrounded
If the overcurrent protective device is not located on a generator outside that supplies a separate building or structure, then the feeder is on the line side of an overcurrent device. What is the minimum size supply-side bonding jumper (copper) required with a 400-ampere feeder from an outdoor generator to the building disconnecting means? (Note: The size of the largest ungrounded phase conductor supplied by the generator is 750 kcmil aluminum or copper-clad aluminum.)
a. 1/0 AWG
Which of the following electrical systems is required to be grounded?
a. 120V, single-phase system
Which of the following systems is required to be grounded?
a. 120V, single-phase system
Performance requirements for grounded electrical systems are provided in ? of the NEC.
a. 250.4(A)
If the voltage on the secondary side of a transformer is less than ? and the voltage on the primary side of the transformer exceeds ? to ground, the secondary side shall be grounded.
a. 50 V / 150 V
Which of the following is typically not a separately derived system?
a. Autotransformer with a grounded conductor common to both the primary and secondary
The size of the grounding electrode conductor for a separate building or structure shall generally not be smaller than the sizes provided in ? .
a. Table 250.66, based on the size of the largest ungrounded conductor of the feeder
A separately derived system is required to be grounded in accordance with 250.30(A), and it is located 50 feet from a building structural metal electrode and 100 feet from a metal water pipe electrode. Which of the following grounding electrodes is required to be used to meet the minimum requirements in the NEC?
a. The system shall be grounded by connection to the building grounding electrode system.
A(n) ? is an intentionally constructed, low-impedance electrically conductive path designed and intended to carry current during ground-fault conditions from the point of grounding on a wiring system to the electrical supply source, and is intended to facilitate the operation of the overcurrent protective device or ground-fault detectors on a high-impedance system.
a. effective ground-fault current path
A(n) ? is a premises wiring system where power is derived from a source of electric energy or equipment other than a service. Such systems have no direct connection from circuit conductors of one system to circuit conductors of another system, other than those established through bonding or grounding connections.
a. separately derived system
What is the minimum size copper bonding jumper required for a metal water piping system (not a grounding electrode) in a building or structure supplied by a 400-ampere feeder when the largest ungrounded feeder conductor is 600 kcmil copper?
b. 3 AWG
Where more than one separately derived system is grounded using a common grounding electrode conductor, the common grounding electrode conductor shall be sized based at not less than ? copper or ? aluminum.
b. 3/0 AWG / 250 kcmil
If a generator has a 1,200-ampere overcurrent device installed at the generator set, a minimum size of ? is required for the EGCs installed in a parallel set of four-inch PVC conduits routed from the generator to the first system overcurrent device enclosure.
b. 3/0 AWG copper
For a 3-phase, 3-wire, corner-grounded, separately derived system that has 500 kcmil copper ungrounded derived phase conductors, the grounded conductor must be sized not smaller than ? .
b. 500 kcmil copper
If the grounding electrode for a separate building or structure is a single ground rod as permitted in 250.53(A)(2) Exception, the largest size grounding electrode conductor required is ? , regardless of the size of the feeder supplying the building or structure served.
b. 6 AWG copper
Which of the following conditions is not required to qualify for installation and use of a high-impedance grounded neutral system?
b. Continuity of power is required.
Identify three Code-compliant methods for connecting the grounding electrode conductor taps to the common grounding electrode conductor at an accessible location.
b. I., IV., and V.
Which part of Article 250 provides the specific requirements for system grounding?
b. Part II
If overcurrent protection is not provided where the conductors originate at a grounded separately derived system source supplying a separate building or structure, the installation must comply with ? .
b. Section 250.30(A)
The general requirements for grounding and bonding for both grounded and ungrounded systems are located in ? .
b. Section 250.4
The grounding electrode conductor for a single separately derived system is required to be sized using which NEC table?
b. Table 250.66
Which of the following locations is permitted for installing the system bonding jumper for a separately derived system (transformer type)?
b. b., e., and f.
An insulated grounded conductor of a system is required to be identified by any of the following methods except ? .
b. green insulation
The ? for an ungrounded system is required to be connected to the system as close as practicable to where the system receives its supply.
b. ground detection sensing equipment
A ? is defined as the circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).
branch circuit
If a separately derived system has 600 kcmil copper secondary ungrounded phase conductors, what is the minimum size required for a copper, wire-type system bonding jumper?
c. 1/0 AWG
Where the derived phase conductors (secondary conductors) from a transformer separately derived system are sized at 500 kcmil copper and installed in flexible metal conduit from the transformer to a panelboard, what is the minimum size copper supply-side bonding jumper required to be installed in the flexible metal conduit?
c. 1/0 AWG
What is the minimum size grounding electrode conductor required for a 400-ampere feeder supplying a panelboard installed in a structure, if the size of the largest ungrounded conductor of the feeder is 600 kcmil aluminum, and the grounding electrode is a metal in-ground support structure (building steel)?
c. 1/0 AWG copper
A separately derived system is installed and has 4/0 AWG copper conductors installed from the secondary of the system to a 225-ampere panelboard. What is the minimum-size copper bonding jumper for a metal water piping system that serves the same area served by the separately derived system?
c. 2 AWG
What size copper grounding electrode conductor is required for a separately derived system with 4/0 AWG copper ungrounded derived phase conductors if the grounding electrode is a metal building frame electrode in accordance with 250.52(A)(2)?
c. 2 AWG
The grounding electrode conductor for a single separately derived system in accordance with ? must be sized at a minimum in accordance with the sizes in ? , based on the circular mil area of the largest ungrounded system conductor.
c. 250.30(A)(5) / Table 250.66
Where a DC system, other than a 3-wire balancer set, has a 250 kcmil copper grounded (neutral) conductor connected, the grounding electrode conductor shall not be required to be larger than ? .
c. 3/0 copper
If overcurrent protection is provided where the conductors originate at a grounded separately derived system source supplying a separate building or structure, the installation must comply with ? .
c. Section 250.32(B)(1)
Where an alternate power source is provided with transfer equipment that includes a switching action in the grounded conductor, which of the following applies?
c. Shall be grounded according to 250.30(A)
Metal water piping and interconnected metal building framing that exists in the area served by a separately derived system is required to be bonded to the grounded conductor of that separately derived system, and ? is used to size this bonding jumper or conductor.
c. Table 250.102(C)(1)
The ? is the conductor connected to the neutral point of a system that is intended to carry current under normal conditions.
c. neutral conductor
The ? is a conductor installed on the supply side of a service or within a service equipment enclosure(s), or for a separately derived system that ensures the required electrical conductivity between metal parts required to be electrically connected.
c. supply-side bonding jumper
Section 250.188 requires grounding all portable or mobile high-voltage equipment that is supplied from an AC system of greater than ? .
d. 1,000 V
What does the NEC indicate that the phase-to-ground voltage should be for an ungrounded 240-volt, delta-connected system?
d. 240 V
Which of the following AC systems is permitted to be grounded, but not required to be grounded?
d. 480-volt delta, 3-phase, 3-wire system
Which of the following systems is not required to be grounded because, if grounded, the phase-to-ground voltage would exceed 150?
d. 480V, 3-phase delta system
An AC system operating at less than 50 volts is required to be grounded under which of the following conditions?
d. All of the above
When an ungrounded system (source) supplies separate buildings or structures by a feeder, the requirements in ? apply.
d. All of the above
Where an ungrounded system is installed ground detectors shall be installed in accordance with which of the following?
d. All of the above
An exception applying only to existing premises wiring systems permits the continued use of the grounded conductor for grounding at separate buildings under which of the following restrictive conditions?
d. All of the above.
Metal water piping systems in separate buildings or structures shall be bonded to which of the following?
d. Any of the above
Systems operating at 50 volts to 1,000 volts are required to be grounded under which of the following conditions?
d. Any of the above
Where a system is grounded, the grounded (usually neutral) conductor(s) in sizes 4 AWG and larger must be identified generally by which of the following means?
d. Any of the above
If a generator supplies standby power for a separate building, a separate disconnecting means where the feeder arrives at the building or structure is not required if ? .
d. Both a. and c.
Where the grounded conductor is used for grounding in accordance with the provision of 250.32(B)(1) Exception No. 1, the size of the grounded conductor shall not be smaller than the larger of which of the following?
d. Either a. or c.
What is the minimum size required for the grounded (neutral) conductor of a separately derived system where there is no load on the neutral conductor? (Note: The system bonding jumper is not located at the source enclosure.)
d. Not smaller than the values in Table 250.102(C)(1), based on the size of the largest ungrounded derived phase conductor connected to the system
Secondary circuits for underwater lighting installed in swimming pools or spas are not permitted to be grounded under which of the following conditions?
d. a. and either b. or c.
A(n) ? is the connection between the grounded circuit conductor and the supply-side bonding jumper or the equipment grounding conductor, or both, at a separately derived system.
d. system bonding jumper
A high-impedance grounded neutral system rated 480 volts to 1,000 volts is only permitted under which of the following conditions?
e. None of the above
Separately derived systems supplied by transformers that have a primary voltage rating less than 1,000 volts are not required to be grounded ? .
e. all of the above
A ? includes all circuit conductors between the service equipment, the source of a separately derived system, or other power supply source, and the final branch-circuit overcurrent device.
feeder
