250 – Grounding and Bonding
250.25 – Grounding Systems Permitted to Be Connected on the Supply Side of the Disconnect
Change at a Glance:
New section created to cover the requirements for grounding of supply-side disconnects permitted to be connected on the supply-side of a service. Points user of the Code to 250.24.
250.25 Grounding Systems Permitted to Be Connected on the Supply Side of the Disconnect.
The grounding of systems connected on the supply side of the service disconnect, as permitted in 230.82, that are in enclosures separate from the service equipment enclosure shall comply with 250.25(A) or (B).
(A) Grounded System. If the utility supply system is grounded, the grounding of systems permitted to be connected on the supply side of the service disconnect and are installed in one or more separate enclosures from the service equipment enclosure shall comply with the requirements of 250.24(A) through (D).
(B) Ungrounded Systems. If the utility supply system is ungrounded, the grounding of systems permitted to be connected on the supply side of the service disconnect and are installed in one or more separate enclosures from the service equipment enclosure shall comply with the requirements of 250.24(E).
250.64(A) – Grounding Electrode Conductor Installation in Aluminum or Copper-Clad Aluminum Conductors
Change at a Glance:
Code language was formatted into a list format for improved clarity and usability and to clarify that terminations for aluminum or copper-clad aluminum conductors located in the interior of equipment “listed and identified for the environment” are separated from the earth and can be terminated within 450 mm (18 in.) of the earth.
250.64 Grounding Electrode Conductor Installation.
Grounding electrode conductors at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system shall be installed as specified in 250.64(A) through (F).
(A) Aluminum or Copper-Clad Aluminum Conductors. And identified for the enviroment
(1) Bare or covered conductors without an extruded polymeric covering shall not be installed where subject to corrosive conditions or be installed in direct contact with concrete.
(2) Terminations made within outdoor enclosures that are listed and identified for the environment shall be permitted within 450 mm (18 in.) of bottom of the enclosure.
(3)Bare Aluminum or copper-clad aluminum grounding electrode conductors external to buildings or equipment enclosures shall not be used where in direct contact with masonry or the earth or where subject to corrosive conditions. Where used outside, aluminum or copper-clad aluminum grounding electrode conductors shall not be terminated within 450 mm (18 in.) of the earth.
250.64(B)(2) and (B)(3) – Grounding Electrode Conductor Protection from Physical Damage
Change at a Glance:
Revision clarifies that Schedule 80 is required when PVC conduit is used for protection from physical damage for a grounding electrode conductor.
250.64 Grounding Electrode Conductor Installation
(B) Securing and Protection Against Physical Damage. Where exposed, a grounding electrode conductor or its enclosure shall be securely fastened to the surface on which it is carried. Grounding electrode conductors shall be permitted to be installed on or through framing members.
(1) Not Exposed to Physical Damage. A 6 AWG or larger copper or aluminum grounding electrode conductor not exposed to physical damage shall be permitted to be run along the surface of the building construction without metal covering or protection.
(2) Exposed to Physical Damage. A 6 AWG or larger copper or aluminum grounding electrode conductor exposed to physical damage shall be protected in rigid metal conduit (RMC), intermediate metal conduit (IMC), Schedule 80 rigid polyvinyl chloride conduit (PVC), reinforced thermosetting resin conduit Type XW (RTRC-XW), electrical metallic tubing (EMT), or cable armor.
(3) Smaller Than 6 AWG. Grounding electrode conductors smaller than 6 AWG shall be protected in RMC, IMC, Schedule 80 PVC, RTRC-XW, EMT, or cable armor.
250.68(C)(3) – Grounding Electrode Conductor Connections in Rebar System
Change at a Glance:
New provisions added to clarify that the rebar system in a footing or foundation is not suitable as the conductor to interconnect other grounding electrodes.
250.68(C)(3) Grounding Electrode Conductor and Bonding Jumper Connection to Grounding Electrodes.
The connection of a grounding electrode conductor at the service, at each building or structure where supplied by a feeder(s) or branch circuit(s), or at a separately derived system and associated bonding jumper(s) shall be made as specified 250.68(A) through (C).
(C) Grounding Electrode Conductor Connections. Grounding electrode conductors and bonding jumpers shall be permitted to be connected at the following locations and used to extend the connection to an electrode(s):
(1) Interior metal water piping…(see NEC for complete Code text)
(2) The metal structure frame of a building…(see NEC for complete Code text)
(3) A rebar-type concrete-encased electrode installed in accordance with 250.52(A)(3) with an additional rebar section extended from its location within the concrete foundation or footing to an accessible location that is not subject to corrosion shall be permitted for connection of grounding electrode conductors and bonding jumpers. The rebar extension shall not be exposed to contact with the earth without corrosion protection. in accordance with the following:
(a) The additional rebar section shall be continuous with the grounding electrode rebar or shall be connected to the grounding electrode rebar and connected together by the usual steel tie wires, exothermic welding, welding, or other effective means.
(b) The rebar extension shall not be exposed to contact with the earth without corrosion protection.
(c) Rebar shall not be used as a conductor to interconnect the electrodes of grounding electrode systems.
250.104(A)(1) – Bonding Jumpers used to Bond Metal Water Piping Systems Requirements
Change at a Glance:
Bonding jumper(s) used to bond metal water piping system(s) together are not required to be larger than 3/0 copper or 250 kcmil aluminum or copper- clad aluminum.
250.104 Bonding of Piping Systems and Exposed Structural Metal.
(A) Metal Water Piping. The metal water piping system shall be bonded as required in 250.104(A) (1), (A)(2), or (A)(3) of this section. (1) General. Metal water piping system(s) installed in or attached to a building or structure shall be bonded to any of the following:
(1) Service equipment enclosure
(2) Grounded conductor at the service
(3) Grounding electrode conductor, if of sufficient size
(4) One or more grounding electrodes used, if the grounding electrode conductor or bonding jumper to the grounding electrode is of sufficient size The bonding jumper(s) shall be installed in accordance with 250.64(A), 250.64(B), and 250.64(E). The points of attachment of the bonding jumper(s) shall be accessible. The bonding jumper(s) shall be sized in accordance with Table 250.102(C)(1) except that it shall not be required to be larger than 3/0 copper or 250 kcmil aluminum or copper-clad aluminum and except as permitted in 250.104(A) (2) and 250.104(A)(3).
250.104(A)(3) – Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s)
Change at a Glance:
Revision clarifies the sizing requirements for bonding jumper(s) used for bonding metal water piping systems when a building or structure is supplied by a feeder or branch circuit. Reference changed from Table 250.102(C)(1) to 250.102(D) (and Table 250.122).
250.104 Bonding of Piping Systems and Exposed Structural Metal.
(A) Metal Water Piping. The metal water piping system shall be bonded as required in 250.104(A) (1), (A)(2), or (A)(3) of this section.
(3) Multiple Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s). The metal water piping system(s) installed in or attached to a building or structure shall be bonded to any of the following:
(1) Building or structure disconnecting means enclosure where located at the building or structure
(2) Equipment grounding conductor run with the supply conductors
(3) One or more grounding electrodes used The bonding jumper(s) shall be sized in accordance with Table 250.102(C)(1), 250.102(D) based on the size of the feeder or branch-circuit conductors that supply the building or structure. The bonding jumper shall not be required to be larger than the largest ungrounded feeder or branch-circuit conductor supplying the building or structure.
250.109 – Metal Enclosures to Connect Bonding Jumpers or Equipment Grounding Conductors
Change at a Glance:
New section indicating metal enclosures can be used to connect bonding jumpers or equipment grounding conductors, or both, together to become a part of an effective ground-fault current path.
250.109 Metal Enclosures
Metal enclosures shall be permitted to be used to connect bonding jumpers or equipment grounding conductors, or both, together to become a part of an effective ground-fault current path. Metal covers and metal fittings attached to these metal enclosures shall be considered as being connected to bonding jumpers or equipment grounding conductors, or both.
250.121(B) – Restricted Use of Metal Frames as Equipment Grounding Conductors
Change at a Glance:
New sub-section prohibits the structural metal frame of a building or structure from being used as an equipment grounding conductor.
250.121 Restricted Use of Equipment Grounding Conductors.
(B) Metal Frame of Building or Structure. The structural metal frame of a building or structure shall not be used as an equipment grounding conductor.
250.122(B), Exception – Resizing ECG to Provide Effective Ground Fault Current Path
Change at a Glance:
Revisions clarify that adjustment and/or correction factors do not require an increase in the size of the EGC. New exception was added to allow the EGC to be sized by a qualified person, provided an effective ground fault current path can be established.
250.122 Size of Equipment Grounding Conductors.
(B) Increased in Size. If Where ungrounded conductors are increased in size for any reason other than as required in 310.15(B) or 310.15(C) from the minimum size that has sufficient ampacity for the intended installation, wire-type equipment grounding conductors, if where installed, shall be increased in size proportionately, according to the to the increase in circular mil area of the ungrounded conductors.
Exception: Equipment grounding conductors shall be permitted to be sized by a qualified person to provide an effective ground fault current path in accordance with 250.4(A)(5) or (B)(4).
250.148 – Continuity of Equipment Grounding Conductors in Boxes
Change at a Glance:
Revision clarifies that all wire-type equipment grounding conductors associated with any of those spliced circuit conductors must be connected within the box or to the box.
250.148 Continuity of Equipment Grounding Conductors and Attachment of Equipment Grounding Conductors to in Boxes.
If circuit conductors are spliced within a box or terminated on equipment within or supported by a box, all wire-type equipment grounding conductor( s) associated with any of those circuit conductors shall be connected within the box or to the box with devices suitable for the use in accordance with 250.8 and 250.148(A) through (E)(D).
Exception: The equipment grounding conductor permitted in 250.146(D) shall not be required to be connected to the other equipment grounding conductors or to the box.
(A) Connections and Splices. Connections and splices shall be made in accordance with 110.14(B) except that insulation shall not be required.
(B) Equipment Grounding Conductor Continuity. The arrangement of grounding connections shall be such that the disconnection or the removal of a luminaire, receptacle, luminaire, or other device fed from the box does not interfere with or interrupt the grounding electrical continuity of the equipment grounding conductor(s) providing an effective ground-fault current path.
(C) Metal Boxes. A connection used for no other purpose shall be made between the one or more equipment grounding conductors and a metal box by means of a grounding screw that shall be used for no other purpose, equipment listed for grounding, or a listed grounding device metal box and the equipment grounding conductor(s) in accordance with 250.8.
(D) Nonmetallic Boxes. One or more equipment grounding conductors brought into a nonmetallic outlet box shall be arranged such that a connection can be made to any fitting or device in that box requiring connection to an equipment grounding conductor. (E) Solder. Connections depending solely on solder shall not be used.
250.184(C), Exception – Exception for Multi-grounded Neutral Systems
Change at a Glance:
New exception added to relieve bonding the neutral conductor to a grounding electrode in an uninterrupted conductor exceeding 400 m (1300 ft) if the only purpose for removing the cable jacket is for bonding the neutral conductor to a grounding electrode in a multigrounded neutral system.
250.184 Solidly Grounded Neutral Systems
(C) Multigrounded Neutral Systems. Where a multigrounded neutral system is used, the following shall apply:
(1) The neutral conductor of a solidly grounded neutral system shall be permitted to be grounded at more than one point. Grounding shall be permitted at one or more of the following locations:
(a) Transformers supplying conductors to a building or other structure
(b) Underground circuits where the neutral conductor is exposed
(c) Overhead circuits installed outdoors
(2) The multigrounded neutral conductor shall be grounded at each transformer and at other additional locations by connection to a grounding electrode.
(3) At least one grounding electrode shall be installed and connected to the multigrounded neutral conductor every 400 m (1300 ft).
(4) The maximum distance between any two adjacent electrodes shall not be more than 400 m (1300 ft).
(5) In a multigrounded shielded cable system, the shielding shall be grounded at each cable joint that is exposed to personnel contact.
Exception: In a multipoint grounded system, a grounding electrode shall not be required to bond the neutral conductor in an uninterrupted conductor exceeding 400 m (1300 ft) if the only purpose for removing the cable jacket is for bonding the neutral conductor to a grounding electrode.
250.187 – Impedance Grounded Systems
Change at a Glance:
Impedance Grounded Neutral Systems. Revisions clarify that the conductor from the neutral point of a transformer to the grounding impedance device does not meet the definition of neutral conductor in Article 100 since it is not intended to carry current during normal operation.
250.187 Impedance Grounded Neutral Systems.
Impedance grounded neutral systems in which a grounding impedance, usually a resistor, limits the ground-fault current shall be permitted where all of the following conditions are met:
(1) The conditions of maintenance and supervision ensure that only qualified persons service the installation.
(2) Ground detectors are installed on the system.
(3) Line-to-neutral loads are not served. Impedance grounded neutral systems shall comply with the provisions of 250.187(A) through (D).
(A) Location. The grounding impedance shall be inserted in the grounding electrode conductor between the grounding electrode of the supply system and the neutral point of the supply transformer or generator.
(B) Identified and Insulated. The neutral conductor shall comply with both of the following: grounded conductor shall be insulated for the maximum neutral voltage. The neutral conductor shall be identified. The neutral conductor shall be insulated for the maximum neutral voltage.
Informational Note: The maximum neutral voltage in a three 3-phase wye system is 57.7 percent of the phase-to-phase voltage.
(C) Grounded System Neutral Conductor Connection. The system neutral grounded conductor shall not be connected to ground, except through the neutral grounding impedance.
(D) Equipment Grounding Conductors. Equipment grounding conductors shall be permitted to be bare and shall be electrically connected to the ground bus and grounding electrode conductor.