Article 250- Grounding and Bonding
Where service-entrance conductors are installed in parallel in two or more raceways or cables, the size of the grounded conductor in each raceway or cable shall be based on the total circular mil area of the parallel ungrounded service-entrance conductors in the raceway or cable, sized in accordance with 250.24(C)(1), but not smaller than _____ AWG.
1/0
Grounding electrodes of bare or electrically conductive coated iron or steel plates shall be at least _____ in. thick.
1/4
Bonding jumper(s) from grounding electrode(s) shall be permitted to be connected to an aluminum or copper busbar not less than _____ and of sufficient length to accommodate the number of terminations necessary for the installation in accordance with 250.64(F)
1/4 in. thick x 2 in. wide
One or more metal in-ground support structure(s) in direct contact with the earth vertically for _____ ft or more, with or without concrete encasement is permitted to be a grounding electrode in accordance with 250.52.
10
In order for a metal underground water pipe to be used as a grounding electrode, it shall be in direct contact with the earth for _____.
10 ft or more
Aluminum or copper-clad aluminum conductors external to buildings or equipment enclosures shall not be terminated within _____ in. of the earth.
18
A bare 4 AWG copper conductor installed horizontally near the bottom or vertically, and within that portion of a concrete foundation or footing that is in direct contact with the earth, can be used as a grounding electrode when the conductor is at least _____ ft in length.
20
The grounded conductor brought to service equipment shall be routed with the phase conductors and shall not be smaller than specified in Table _____ when the service-entrance conductors are 1,100 kcmil copper and smaller.
250.102(C)(1)
Each tap conductor to a common grounding electrode conductor for multiple separately derived systems shall be sized in accordance with _____, based on the derived ungrounded conductors of the separately derived system it serves.
250.66
The common grounding electrode conductor installed for multiple separately derived systems shall not be smaller than _____ AWG copper when using a wire-type conductor
3/0
The largest size grounding electrode conductor required is _____ copper.
3/0 AWG
What size copper grounding electrode conductor is required for a service that has three sets of 600 kcmil copper conductors per phase?
3/0 AWG
The common grounding electrode conductor installed for multiple separately derived systems shall be permitted to be the metal structural frame of the building or structure that complies with 250.68(C)(2) or is connected to the grounding electrode system by a conductor not smaller than _____.
3/0 AWG copper or 250 kcmil aluminum
When a ground ring is used as a grounding electrode, it shall be installed at a depth below the earth\'s surface of not less than _____.
30 in
In an ac system, if the size of the grounding electrode conductor or bonding jumper connected to a concrete-encased electrode does not extend on to other types of electrodes that require a larger size of conductor, the grounding electrode conductor shall not be required to be larger than _____ AWG copper.
4
Grounding electrodes of the rod type shall be at least _____ in. in diameter, unless listed.
5/8
A(An) _____ AWG or larger copper or aluminum grounding electrode conductor exposed to physical damage shall be protected in rigid metal conduit, IMC, Schedule 80 PVC conduit, reinforced thermosetting resin conduit Type XW (RTRC-XW), EMT, or cable armor.
6
Grounding electrode conductors _____ AWG and larger that are not exposed to physical damage can be run along the surface of the building construction without metal covering or protection.
6
Grounding electrode conductors smaller than _____ AWG shall be protected in rigid metal conduit, IMC, PVC conduit, electrical metallic tubing, or cable armor.
6
A service consisting of 12 AWG service-entrance conductors requires a grounding electrode conductor sized no less than _____ AWG.
8
_____ shall not be used as grounding electrodes.
Metal underground gas piping systems and aluminum
_____ on equipment to be grounded shall be removed from contact surfaces to ensure good electrical continuity.
Paint, Lacquer, Enamel
Main bonding jumpers and system bonding jumpers shall not be smaller than specified in _____.
Table 250.102(C)(1)
__________ or more grounding electrodes bonded together are considered a single grounding electrode system.
Two
_____ alternating-current systems operating at 480V shall have ground detectors installed on the system.
Ungrounded
Tap connections to a common grounding electrode conductor for multiple separately derived systems shall be made at an accessible location by _____.
a connector listed as grounding and bonding equipment, listed connections to aluminum or copper busbars, or the exothermic welding process
For a separate building or structure supplied by a separately derived system when overcurrent protection is provided where the conductors originate, the supply conductors shall contain _____.
an equipment grounding conductor
For grounded systems, electrical equipment and other electrically conductive material likely to become energized shall be installed in a manner that creates a _____ from any point on the wiring system where a ground fault may occur to the electrical supply source.
circuit facilitating the operation of the overcurrent device, low-impedance circuit, and circuit capable of safely carrying the ground-fault current likely to be imposed on it
Bare or covered aluminum or copper-clad aluminum grounding electrode conductors without an extruded polymeric covering shall not be installed where subject to corrosive conditions or be installed in direct contact with _____.
concrete
Grounding electrode conductors shall be installed in one continuous length without a splice or joint, unless spliced by _____.
connecting together sections of a busbar, irreversible compression-type connectors listed as grounding and bonding equipment, or the exothermic welding process
For ungrounded systems, noncurrent-carrying conductive materials enclosing electrical conductors or equipment shall be connected to the _____ in a manner that will limit the voltage imposed by lightning or unintentional contact with higher-voltage lines.
earth
Auxiliary grounding electrodes can be connected to the _____.
equipment grounding conductor
Ungrounded alternating-current systems from 50V to 1,000V or less that are not required to be grounded in accordance with 250.21(B) shall have _____.
ground detectors installed for ac systems operating at not less than 120V and at 1,000V or less, and have the ground detection sensing equipment connected as close as practicable to where the system receives its supply
Equipment grounding conductors, grounding electrode conductors, and bonding jumpers shall be connected by _____.
listed pressure connectors, terminal bars, exothermic welding
A grounded conductor shall not be connected to normally noncurrent-carrying metal parts of equipment on the _____ side of the system bonding jumper of a separately derived system except as otherwise permitted in Article 250.
load
For a grounded system, an unspliced _____ shall be used to connect the equipment grounding conductor(s) and the service disconnect enclosure to the grounded conductor of the system within the enclosure for each service disconnect.
main bonding jumper
High-impedance grounded neutral systems shall be permitted for three-phase ac systems of 480V to 1,000V where _____.
the conditions of maintenance and supervision ensure that only qualified persons service the installation, ground detectors are installed on the system, line-to-neutral loads are not served
If a building or structure is supplied by a service or feeder with _____ or more disconnecting means in separate enclosures, the grounding electrode connections shall be made in accordance with 250.64(D)(1), 250.64(D)(2), or 250.64(D)(3).
two
Where used outside, aluminum or copper-clad aluminum grounding electrode conductors shall not be terminated within _____ in. of the earth.
18
A buried iron or steel plate used as a grounding electrode shall expose not less than _____ sq ft of surface area to exterior soil.
2
The size of the grounding electrode conductor for a building or structure supplied by a feeder shall not be smaller than that identified in _____, based on the largest ungrounded supply conductor.
250.66
The connection of the system bonding jumper for a separately derived system shall be made _____ on the separately derived system from the source to the first system disconnecting means or overcurrent device.
any single point
An electrode encased by at least 2 in. of concrete, located horizontally near the bottom or vertically and within that portion of a concrete foundation or footing that is in direct contact with the earth, shall be permitted as a grounding electrode when it consists of _____.
bare copper conductor not smaller than 4 AWG
Where practicable, rod, pipe, and plate electrodes shall be installed _____.
below permanent moisture level
For grounded systems, normally noncurrent-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the _____ to establish an effective ground-fault current path.
electrical supply source
Ferrous metal raceways and enclosures for grounding electrode conductors shall be bonded at each end of the raceway or enclosure to the grounding electrode or grounding electrode conductor to create a(an) _____ parallel path.
electrically
Concrete-encased electrodes of _____ shall not be required to be part of the grounding electrode system where the steel reinforcing bars or rods aren't accessible for use without disturbing the concrete.
existing buildings or structures
Where _____, a grounding electrode conductor or its enclosure shall be securely fastened to the surface on which it is carried.
exposed
Where an alternating-current system operating at 1,000V or less is grounded at any point, the _____ conductor(s) shall be routed with the ungrounded conductors to each service disconnecting means and shall be connected to each disconnecting means grounded conductor(s) terminal or bus.
grounded
The building or structure grounding electrode system shall be used as the _____ electrode for the separately derived system.
grounding
For grounded systems, normally noncurrent-carrying conductive materials enclosing electrical conductors or equipment shall be connected to earth so as to __________ on these materials.
limit the voltage-to-ground
Grounded electrical systems shall be connected to earth in a manner that will _____.
limit voltages due to lightning, line surges, or unintentional contact with higher-voltage lines and stabilize the voltage-to-ground during normal operation
Where an ac system operating at 1,000V or less is grounded at any point, a(an) _____ shall connect the grounded conductor(s) to each service disconnecting means enclosure.
main bonding jumper
Swimming pool structures and structural _____ [680.26(B)(1) and (B)(2)] shall not be used as a grounding electrode.
reinforcing steel
Alternating-current systems of 50V to 1,000V that supply premises wiring systems shall be grounded where supplied by a three-phase, 4-wire, delta-connected system in which the midpoint of one phase winding is used as a circuit conductor
shall be grounded
When installing auxiliary electrodes, the earth ___________ be used as an effective ground-fault current path.
shall not
For ungrounded systems, noncurrent-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying _____.
the maximum fault current likely to be imposed on it
Where the resistance-to-ground of 25 ohms or less is not achieved for a single rod electrode, _____.
the single rod electrode shall be supplemented by one additional electrode
Where the supplemental electrode is a rod, that portion of the bonding jumper that is the sole connection to the supplemental grounding electrode shall not be required to be larger than _____ AWG copper wire.
6
Electrically conductive materials that are likely to _____ in ungrounded systems shall be connected together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying the maximum fault current likely to be imposed on it.
become energized
Reinforcing bars for use as a concrete-encased electrode _________ together by the usual steel tie wires or other effective means.
can be bonded
Where a main bonding jumper is a screw only, the screw shall be identified with a(an) _____ that shall be visible with the screw installed.
green finish
Ferrous metal raceways and enclosures for grounding electrode conductors _______ electrically continuous from the point of attachment to cabinets or equipment to the grounding electrode.
shall be
Grounding electrode conductors of the wire type shall be _____.
solid, stranded, or insulated/bare
For a separate building or structure supplied by a separately derived system when overcurrent protection is not provided for the supply conductors to the building/structure as permitted by 240.21(C)(4), the installation shall be _____ in accordance with 250.30(A)
grounded and bonded
A grounding electrode conductor, sized in accordance with 250.66, shall be used to connect the equipment grounding conductors, the service-equipment enclosures, and, where the system is grounded, the ____________ to the grounding electrode(s).
grounded service conductor
The frame of a portable generator shall not be required to be connected to a(an) _____ if the generator only supplies equipment mounted on the generator, cord-and-plug-connected equipment using receptacles mounted on the generator, or both.
grounding electrode
The frame of a vehicle-mounted generator shall not be required to be connected to a(an) _____ if the generator only supplies equipment mounted on the vehicle or cord-and-plug-connected equipment, using receptacles mounted on the vehicle.
grounding electrode
Buildings or structures supplied by multiple services or feeders shall use the same _____ to ground enclosures and equipment in or on that building
grounding electrode system
The grounding electrode conductor connection shall be made at any accessible point from the load end of the overhead service conductors, _____ to, including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means.
service drop, underground service conductors, or service lateral
A grounding electrode_______ required if a building or structure is supplied by a feeder.
shall be
A main bonding jumper shall be a _____ or similar suitable conductor.
wire, bus, or screw
Where the main bonding jumper is a wire or busbar and is installed from the grounded conductor terminal bar or bus to the equipment grounding terminal bar or bus in the service equipment, the _____ shall be permitted to be connected to the equipment grounding terminal, bar, or bus to which the main bonding jumper is connected.
grounding electrode conductor
An important consideration for limiting imposed voltage on electrical systems is to remember that bonding and ____________ should not be any longer than necessary and unnecessary bends and loops should be avoided.
grounding electrode conductors
Local metal underground systems or structures such as underground tanks are permitted to serve as ______________.
grounding electrodes.
For grounded systems, the earth ______ considered an effective ground-fault current path.
is NOT
Where bonding jumper(s) are used to connect the grounding electrodes together to form the grounding electrode system, rebar ________ permitted to be used as a conductor to interconnect the electrodes.
is not
Ground clamps and fittings that are exposed to physical damage shall be enclosed in _____ or equivalent protective covering.
metal or wood
The common grounding electrode conductor installed for multiple separately derived systems shall be permitted to be a _____ pipe that complies with 250.68(C)(1).
metal water
Where a building or structure contains more than one service disconnect in separate enclosures, grounding electrode conductor connections shall be permitted to be _____.
multiple individual grounding electrode conductors, one grounding electrode conductor at a common location, a common grounding electrode conductor and taps
Where the supply conductors are larger than 1,100 kcmil copper or 1,750 kcmil aluminum, the main bonding jumper shall have an area that is _____ the area of the largest phase conductor when of the same material.
not less than 12 1/2 percent of
If a building or structure is supplied by a feeder from an outdoor separately derived system, a system bonding jumper at both the source and the first disconnecting means shall be permitted if doing so does not establish a(an) _____ path for the grounded conductor.
parallel
Grounding electrode conductor taps from a separately derived system to a common grounding electrode conductor are________ when a building or structure has multiple separately derived systems, provided that the taps terminate at the same point as the system bonding jumper.
permitted
A ground ring encircling the building or structure can be used as a grounding electrode when the _____.
ring is in direct contact with the earth, ring consists of at least 20 ft of bare copper conductor, bare copper conductor is not smaller than 2 AWG
In ungrounded systems, electrical equipment, wiring, and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit from any point on the wiring system to the electrical supply source to facilitate the operation of overcurrent devices should a(an) _____ fault from a different phase occur on the wiring system.
second ground
A grounding electrode at a separate building or structure _______ required where one multiwire branch circuit serves the building or structure.
shall NOT be
A grounding electrode conductor_________ permitted to be run to any convenient grounding electrode available in the grounding electrode system where the other electrode(s), if any, is connected by bonding jumpers that are installed in accordance with 250.53(C).
shall be
The grounding of electrical systems, circuit conductors, surge arresters, surge-protective devices, and conductive normally noncurrent-carrying metal parts of equipment_______ installed and arranged in a manner that will prevent objectionable current.
shall be
When supplying a grounded system at a separate building or structure, an equipment grounding conductor shall be run with the supply conductors and connected to the building or structure disconnecting means and to the grounding electrode(s).
shall be
Alternating-current circuits of less than 50V _____________ if supplied by a transformer whose supply system exceeds 150 volts-to-ground.
shall be grounded
Alternating-current systems of 50V to 1,000V that supply premises wiring systems ____________ where the system is three-phase, 4-wire, wye-connected, with the neutral conductor used as a circuit conductor.
shall be grounded
In an area served by a separately derived system, the _____ shall be connected to the grounded conductor of the separately derived system.
structural steel and metal piping
For a single separately derived system, the grounding electrode conductor connects the grounded conductor of the derived system to the grounding electrode at the same point on the separately derived system where the _____ is connected.
system bonding jumper
The connection of an unspliced _____ complying with 250.28(A) through (D) shall be made at any single point on the separately derived system from the source to the first system disconnecting means or overcurrent device, or it shall be made at the source of a separately derived system that has no disconnecting means or overcurrent devices, in accordance with 250.30(A)(1)(a) or (A)(1)(b).
system bonding jumper
Grounding electrode conductors and grounding electrode bonding jumpers in contact with _____ shall not be required to comply with 300.5 but shall be buried or otherwise protected if subject to physical damage.
the earth
If the source of a separately derived system and the first disconnecting means are located in separate enclosures, a supply-side bonding jumper of the wire type shall comply with 250.102(C), based on _____.
the size of the derived ungrounded conductors
Ungrounded alternating-current systems from 50V to less than 1,000V shall be legibly marked \"Caution: Ungrounded System - Operating _____ Volts Between Conductors\" at _____ of the system, with sufficient durability to withstand the environment involved.
the source or the first disconnecting means
For a separate building or structure supplied by a feeder or branch circuit, the grounded conductor can serve as the ground-fault return path for the building/structure disconnecting means for existing installations made in compliance with previous editions of the Code as long as the installation continues to meet the condition(s) that _____.
there are no continuous metallic paths between buildings and structures, ground-fault protection of equipment is not installed on the supply side of the feeder, the neutral conductor is sized no smaller than the larger required by 220.61 or 250.122
In grounded systems, normally noncurrent-carrying electrically conductive materials that are likely to become energized shall be connected _____ in a manner that establishes an effective ground-fault current path.
together and to the electrical supply source
Where a metal underground water pipe is used as a grounding electrode, the continuity of the grounding path or the bonding connection to interior piping shall not rely on _____ and similar equipment.
water meters or filtering devices