Article 250 Grounding and Bonding

250.20 (D) Impedance Grounded Neutral Systems.

Impedance grounded neutral systems shall be grounded in accordance with 250.36 or 250.187.

Part II. System Grounding 250.20 Alternating-Current Systems to Be Grounded. (A) Alternating-Current Systems of Less Than 50 Volts.

Alternating-current systems of less than 50 volts shall be groun- ded under any of the following conditions: 1) Where supplied by transformers, if the transformer supply system exceeds 150 volts to ground. 2) Where supplied by transformers, if the transformer supply system is ungrounded 3) Where installed outside as overhead conductors.

250.20 (C) Alternating-Current Systems of over 1000 Volts.

Alternating-current systems supplying mobile or portable equipment shall be grounded as specified in 250.188. Where supplying other than mobile or portable equipment, such systems shall be permitted to be grounded.

250.24 Grounding of ServiceSupplied Alternating-Current Systems. (A) System Grounding Connections. (3) Dual-Fed Services.

For services that are dual fed (double ended) in a common enclosure or grouped together in sepa- rate enclosures and employing a secondary tie, a single ground- ing electrode conductor connection to the tie point of the grounded conductor(s) from each power source shall be permitted.

250.21 Alternating-Current Systems of 50 Volts to 1000 Volts Not Required to Be Grounded. (B) Ground Detectors.

Ground detectors shall be installed in accordance with 250.21 (B) (1) and (B) (2). 1) Ungrounded ac systems as permitted in 250.21(A) (1) through (A) (4) operating at not less than 120 volts and at 1000 volts or less shall have ground detectors installed on the system. 2) The ground detection sensing equipment shall be connected as close as practicable to where the system receives its supply.

250.4 General Requirements for Grounding and Bonding. (A) Grounded Systems. (2) Grounding of Electrical Equipment.

Normally non- current-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth so as to limit the voltage to ground on these materials.

250.24 (C) Grounded Conductor Brought to Service Equipment. (2) Parallel Conductors in Two or More Raceways or Cables.

The grounded conductor shall not be smaller than specified in Table 250.102 (C) (1).

250.24 (D) Grounding Electrode Conductor.

A grounding electrode conductor shall be used to connect the equipment grounding conductors, the service-equipment enclosures, and, where the system is grounded, the grounded service conductor to the grounding electrode(s) required by Part III of this article. This conductor shall be sized in accordance with 250.66. High-impedance grounded neutral system connections shall be made as covered in 250.36.

250.20 (B) (3)

Where the system is 3-phase, 4-wire, delta connected in which the midpoint of one phase winding is used as a circuit conductor

Part II. System Grounding 250.20 Alternating-Current Systems to Be Grounded.

Alternating-current systems shall be grounded as provided for in 250.20(A), (B). (C), or (D). Other systems shall be permitted to be grounded. If such systems are grounded, they shall comply with the applicable provisions of this article. Informational Note: An example of a system permitted to be grounded is a corner-grounded delta transformer connection. See 250.26(4) for conductor to be grounded.

250.28 Main Bonding Jumper and System Bonding Jumper. (D) Size. (1) General.

Main bonding jumpers and system bonding jumpers shall not be smaller than specified in Table 250.102(C) (1).

250.12 Clean Surfaces.

Nonconductive coatings (such as paint, lacquer, and enamel) on equipment to be grounded or bonded shall be removed from threads and other contact surfa- ces to ensure good electrical continuity or shall be connected by means of fittings designed so as to make such removal unnecessary.

250.4 General Requirements for Bonding. (A) Grounded Systems. (3) Bonding of Electrical Equipment.

Normally non-current- carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the electrical supply source in manner that establishes an effective ground-fault current path.

250.4 General Requirements for Grounding and Bonding. (A) Grounded Systems. (4) Bonding of Electrically Conductive Materials and Other Equipment.

Normally поп-сurrent-carrying electrically conductive materials that are likely to become energized shall be connected together and to the electrical supply source in manner that establishes an effective ground-fault current path. Path. Electrical

250.30 Grounding Separately Derived Alternating-Current Systems. (3) Grounded Conductor.

If a grounded conductor is installed and the system bonding jumper connection is not located at the source, 250.30(A) (3) (a) through (A) (3) (d) shall apply. The grounded conductor shall not be required to be larger than the derived ungrounded conductors. a) Sizing for a Single Raceway. The grounded conductor shall not be smaller than specified in Table 250.102 (C) (1). b) Parallel Conductors in Tioo or More Raceuxrys. If the ungrounded conductors are installed in parallel in two or more raceways, the grounded conductor shall also be installed in parallel. The size of the grounded conductor in each raceway shall be based on the total circular mil area of the parallel derived ungrounded conductors in the raceway as indicated in 250.30(A)(3) (a), but not smaller than 1/0 AWG. Informational Note: See 310.10(G) for grounded conductors connected in parallel. c) Delta-Connected System. The grounded conductor of a 3-phase, 3-wire delta system shall have an ampacity not less than that of the ungrounded conductors. d) Impedance Grounded System. The grounded conductor of an impedance grounded neutral system shall be installed in accordance with 250.36 or 250.187, as applicable.

250.6 Objectionable Current. (B) Alterations to Stop Objectionable Current.

If the use of multiple grounding connections results in objectionable current and the requirements of 250.4(A)(5) or (B) (4) are met, one or more of the following alterations shall be permit- ted: 1) Discontinue one or more but not all of such grounding connections. 2) Change the locations of the grounding connections. 3) Interrupt the continuity of the conductor or conductive path causing the objectionable current. 4) Take other suitable remedial and approved action.

250.24 (C) Grounded Conductor Brought to Service Equipment. (4) High Impedance.

The grounded conductor on a high- impedance grounded neutral system shall be grounded in accordance with 250.36.

250.6 Objectionable Current. (A) Arrangement to Prevent Objectionable Current.

The grounding of electrical systems, circuit conductors, surge arresters, surge-protective devices, and conductive normally non-current-carrying metal parts of equipment shall be installed and arranged in a manner that will prevent objectionable current.

250.24 Grounding of ServiceSupplied Alternating-Current Systems. (A) System Grounding Connections. (2) Outdoor Transformer.

Where the transformer supplying the service is located outside the building, at least one additional grounding connection shall be made from the grounded service conductor to grounding electrode, either at the transformer or elsewhere outside the building. Exception: The additional grounding electrode conductor connection shall not be made on high-impedance grounded neutral systems. The system shall meet the requirements of 250. 36.

250.4 Genral requirements for bonding and grounding B) Ungrounded System 4) Path for Current Fault

Electrical equipment, wiring, and other electrically conductive material likely to become ener- gized 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 overcur- rent devices should a second ground fault from a different phase occur on the wiring system. The earth shall not be considered as an effective fault-current path.

250.4 General Requirements for grounding and bonding (B) Ungrounded System (3) Bonding of Electrical Conductive Material and other Equipment

Electrically conductive materials that are likely to become energized 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.

250.8 Connection of Grounding and Bonding Equipment. (A) Permitted Methods.

Equipment grounding conductors, grounding electrode conductors, and bonding jumpers shall be connected by one or more of the following means: 1) Listed pressure connectors 2) Terminal bars 3) Pressure connectors listed as grounding and bonding equipment 4) Exothernmic welding process 5) Machine screw-type fasteners that engage not less than two threads or are secured with a nut. 6) Thread-forming machine screws that engage not less than two threads in the enclosure 7) Connections that are part of a listed assembly 8) Other listed means

250.26 Conductor to Be Grounded Alternating-Current Systems.

For grounded ac premises wiring systems, the conductor to be grounded shall be as specified in the follow- ing: 1) Single-phase, 2-wire - one conductor 2) Single-phase, 3-wire - the neutral conductor 3) Multiphase systems having one wire common to all phases - the neutral conductor 4) Multiphase systems where one phase is grounded - that phase conductor 5) Multiphase systems in which one phase is used as in (2) - the neutral conductor

250.30 Grounding Separately Derived Alternating-Current Systems. (2) Supply side bonding jumper

If the source of a separately derived system and the first disconnecting means are located in separate enclosures, a supplyside bonding jumper shall be installed with the circuit conductors from the source enclosure to the first disconnecting means enclosure. A supply-side bond- ing jumper shall not be required to be larger than the derived ungrounded conductors. The supply-side bonding jumper shall be permitted to be of nonflexible metal raceway type or of the wire or bus type as follows: 1) A supply-side bonding jumper of the wire type shall comply with 250.102(C), based on the size of the derived ungrounded conductors. 2) A supply-side bonding jumper of the bus type shall have a cross-sectional area not smaller than a supply-side bond- ing jumper of the wire type as determined in 250.102(C). Exception: A supply-side bonding jumper shall not be required betuven enclosures for installations made in compliance with 250.30(A)(1). Exception No. 2.

250.24 (C) Grounded Conductor Brought to Service Equipment. (2) Parallel Conductors in Two or More Raceways or Cables.

If the ungrounded service-entrance conductors are installed in parallel in two or more raceways or cables, the grounded conductor shall also be installed in parallel. The size of the grounded conductor in each raceway or cable shall be based on the total circular mil area of the parallel ungrounded conductors in the raceway or cable, as indicated in 250.24(C)(1) , but not smaller than 1/0 AWG. Informational Note: See 310.10(G) for grounded conductors connected in parallel.

250.4 General Requirements for Grounding and Bonding. (B) Ungrounded Systems. (1) Grounding Electrical Equipment.

Non-current-carrying conductive materials enclosing electrical conductors or equip- ment, or forming part of such equipment, shall be connected to earth in a manner that will limit the voltage imposed by lightning or unintentional contact with higher-voltage lines and limit the voltage to ground on these materials. Informational Note: See NFPA 780-2017, Standard for the Installa- tion of Lightning Protection Systems, for information on installation of grounding and bonding for lightning protection systems.

250.24 Grounding of ServiceSupplied Alternating-Current Systems. (A) System Grounding Connections. (1) General.

The grounding electrode conductor connection shall be made at any accessible point from the load end of the overhead service conductors, service drop, underground service conductors, or service lateral to, including the terminal or bus to which the grounded service conductor is connected at the service disconnecting means. Informational Note: See definitions of Service Conductors, Overhead; Service Conductors, Underground; Service Drop; and Service Lateral in Article 100.

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).

250.24 (C) Grounded Conductor Brought to Service Equipment.

Where an ac system operating at 1000 volts or less is grounded at any point, the grounded 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. A main bonding jumper shall connect the grounded conductor(s) to each service disconnecting means enclosure. The grounded conductor(s) shall be installed in accordance with 250.24(C) (1) through (C)(4). Exception: Where tuo or more service disconnecting means are located in a single assembly listed for use as service equipment, it shall be permitted to connect the grounded conductor(s) to the assembly common grounded conductor(s) terminal or bus. The assembly shall include a main bonding jumper for connecting the grounded conductor(s) to the assembly enclosure.

250.6 Objectionable Current. (E) Isolation of Objectionable Direct-Current Ground Currents.

Where isolation of objectionable de ground currents from cathodic protection systems is required, a listed ac coupling/de isolating device shall be permitted in the equipment grounding conductor path to provide an effective return path for ac ground-fault current while blocking dc current.

250.24 Grounding of ServiceSupplied Alternating-Current Systems. (A) System Grounding Connections. (2) Outdoor Transformer.

Where the transformer supplying the service is located outside the building, at least one additional grounding connection shall be made from the grounded service conductor to a grounding electrode, either at the transformer or elsewhere outside the building. Exception: The additional grounding electrode conductor connection shall not be made on high-impedance grounded neutral systems. The system shall meet the requirements of 250. 36.

250.25 Grounding Systems Permitted to Be Connected on the Supply Side of the Disconnect. (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 enclo- sure shall comply with the requirements of 250.24(A) through (D).

250.25 Grounding Systems Permitted to Be Connected on the Supply Side of the Disconnect. (B) Ungrounded Systems.

If the utility supply system is ungrounded, the grounding of systems permitted to be connec- ted on the supply side of the service disconnect and are instal- led in one or more separate enclosures from the service equipment enclosure shall comply with the requirements of 250.24(E).

Part I. General 250.1 Scope.

This article covers general requirements for grounding and bonding of clectrical installations, and the specific requirements in (1) through (6). 1) Systems, circuits, and equipment required, permitted, or not permitted to be grounded 2) Circuit conductor to be grounded on grounded systems 3) Location of grounding connections 4) Types and sizes of grounding and bonding conductors and electrodes 5) Methods of grounding and bonding 6) Conditions under which guards, isolation, or insulation may be substituted for grounding Informational Note: See Figure 250.1 for information on the organization of Article 250 covering grounding and bonding requirements.

250.6 Objectionable Current. (D) Limitations to Permissible Alterations.

This section shall not be considered as permitting electronic equipment to be operated on ac systems or branch circuits that are not connec- ted to an equipment grounding conductor as required by this article. Currents that introduce electromagnetic interference or data errors in electronic equipment shall not be considered the objectionable currents addressed in this section.

250.28 Main Bonding Jumper and System Bonding Jumper. (D) Size. (3) Separately Derived System with More Than One Enclosure.

Where a separately derived system supplies more than a single enclosure, the system bonding jumper for each enclosure shallbe sized in accordance with 250.28 (D) (1) based on the largest ungrounded feeder conductor serving that enclosure, or a single system bonding jumper shall be installed at the source and sized in accordance with 250.28 (D) (1) based on the equivalent size of the largest supply conductor determined by the largest sum of the areas of the corresponding conductors of each set.

250.30 Grounding Separately Derived Alternating-Current Systems. (A) Grounded Systems.

A separately derived ac system that is grounded shall comply with 250.30(A) (1) through (A) (8). Except as otherwise permitted in this article, a grounded conductor shall not be connected to normally non-current- carrying metal parts of equipment, be connected to equipment grounding conductors, or be reconnected to ground on the load side of the system bonding jumper. Informational Note: See 250,32 for connections at separate buildings or structures and 250.142 for use of the grounded circuit conductor for grounding equipment. Exception: Impedance grounded neutral system grounding connections shali be made as specified in 250, 36 or 250. 187, as applicable.

250.30 Grounding Separately Derived Alternating-Current Systems. (A) Grounded Systems. (1) System Bonding Jumper.

An unspliced system bonding jumper shall comply with 250.28(A) through (D). This connec- tion 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). The system bonding jumper shall remain within the enclosure where it originates. If the source is located outside the building or structure supplied, a system bonding jumper shall be installed at the grounding electrode connection in compliance with 250.30(C). Exception No. 1: For systems installed in accordance with 450.6, a single system bonding jumper connection to the tie point of the grounded circuit conductors from each pouer source shall be permitted. Exception No. 2: 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 parallel path for the grounded conductor. If grounded conductor is used in this manner, it shall not be smaller than the size specified for the system bonding jumper but shall not be required to be larger than the ungrounded conductor(s). For the purposes of this exception, connection through the earth shall not be considered as providing a paralled path. Exception No. 3: The size of the system bonding jumper for a system that supplies a Class 1, Class 2, or Class 3 circuit, and is derived from a transformer rated not more than 1000 volt-amperes, shall not be smaller than the derived ungrounded conductors and shall not ie smaller than 14 AWG copper or 12 AWG aluminum. a) Installed at the Source. The system bonding jumper shall connect the grounded conductor to the supply-side bonding jumper and the normally non-current-carrying metal enclosure. b) Installed at the First Disconnecting Means. The system bonding jumper shall connect the grounded conductor to the supply-side bonding jumper, the disconnecting means enclosure, and the equipment grounding conductor(s). Exception: Separately derived systems consisting of multiple sources of the same type that are connected in parallel shall be permitted to have the system bonding jumper installed at the paralleting switchgear, switchboard, or other paralleling connection point instead of at the disconnecting means located at each separate source.

250.30 Grounding Separately Derived Alternating-Current Systems.

In addition to complying with 250.30(A) for groun- ded systems, or as provided in 250.30(B) for ungrounded systems, separately derived systems shall comply with 250.20, 250,21, 250,22, or 250.26, as applicable. Multiple power sources of the same type that are connected in parallel to form one system that supplies premises wiring shall be considered as a single separately derived system and shall be installed in accordance with 250.30. Informational Note No. 1: An alternate ac power source, such as an on-site generator, is not a separately derived system if f the grounded conductor is solidly interconnected to a service- supplied system grounded conductor. An example of such a situation is where alternate source transfer equipment does not include a switching action in the grounded conductor and allows it to remain solidly connected to the service-supplied grounded conductor when the alternate source is operational and supplying the load served. Informational Note No. 2: See 445.13 for the minimum size of conductors that carry fault current.

250.24 Grounding of ServiceSupplied Alternating-Current Systems. (A) System Grounding Connections. (5) Load-Side Grounding Connections.

A grounded conductor shall not be connected to normally non-current-carrying metal parts of equipment, to equipment grounding conductor(s), or be reconnected to ground on the load side of the service disconnecting means except as otherwise permitted in this article. Informational Note: See 250.30 for separately derived systems, 250.32 for connections at separate buildings or structures, and 250.142 for use of the grounded circuit conductor for grounding equipment.

250.24 Grounding of ServiceSupplied Alternating-Current Systems. (A) System Grounding Connections.

A premises wiring system supplied by a grounded ac service shall have a grounding electrode conductor connected to the grounded service conductor, at each service, in accordance with 250.24(A) (1) through (A) (5).

250.24 (E) Ungrounded System Grounding Connections.

A premises wiring system that is supplied by an ac service that is ungroun- ded shall have, at each service, a grounding electrode conduc- tor connected to the grounding electrode(s) required by Part III of this article. The grounding electrode conductor shall be connected to a metal enclosure of the service conductors at any accessible point from the load end of the overhead service conductors, service drop, underground service conductors, or service lateral to the service disconnecting means.

250.20 Alternating-Current Systems to Be Grounded. (B) Alternating-Current Systems of 50 Volts to 1000 Volts.

Alternating-current systems of 50 volts to 1000 volts that supply premises wiring and premises wiring systems shall be grounded under any of the following conditions: 1) Where the system can be grounded so that the maximum voltage to ground on the ungrounded conductors does not exceed 150 volts 2) Where the system is 3-phase, 4-wire, wye connected in which the neutral conductor is used as a circuit conductor.

250.8 Connection of Grounding and Bonding Equipment. (B) Methods Not Permitted.

Connection devices or fittings that depend solely on solder shall not be used.

250.4 General Requirements for Grounding and Bonding. (A) Grounded Systems. (5) Effective Ground-Fault Current Path.

Electrical equip- ment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a low-impedance circuit facilitating the operation of the overcurrent device or ground detector for high-impedance grounded systems. It shall be capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply source. The earth shall not be consid- ered as an effective ground-fault current path.

250.4 General Requirements for Grounding and Bonding. (A) Grounded Systems. (1) Electrical System Grounding.

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.

250.24 Grounding of ServiceSupplied Alternating-Current Systems. (B) Main Bonding Jumper.

For a grounded system, an unspliced main bonding jumper shall be used to connect the equipment grounding conductor(s) and the service-disconnect enclosure to the grounded conductor within the enclosure for each service disconnect in accordance with 250.28.

250.28 Main Bonding Jumper and System Bonding Jumper.

For a grounded system, main bonding jumpers and system bonding jumpers shall be installed as follows:

250.3 Application of Other Articles.

For other articles apply- ing to particular cases of installation of conductors and equip- ment, grounding and bonding requirements are identified in Table 250.3 that are in addition to, or modifications of, those of this article. Part I General Part II System grounding Part VIII Direct-current systems ----------- Part X Grounding of systems and circuits of over 1000 volts Part III Grounding electrode system and grounding Part V Bonding electrode conductor Part IV Enclosure, raceway, and service cable connections Part VI Equipment grounding and equipment grounding conductors Part VII Methods of equipment grounding conductor connections Part IX Instruments, meters, and relays

250.10 Protection of Ground Clamps and Fittings.

Ground clamps or other fittings exposed to physical damage shall be enclosed in metal, wood, or equivalent protective covering.

250.28 Main Bonding Jumper and System Bonding Jumper. (D) Size. (2) Main Bonding Jumper for Service with More Than One Enclosure.

If a service consists of more than a single enclosure as permitted in 230.71 (B), the main bonding jumper for each enclosure shall be sized in accordance with 250.28 (D) (1) based on the largest ungrounded service conductor serving that enclosure.

250.28 Main Bonding Jumper and System Bonding Jumper. (C) Attachment.

Main bonding jumpers and system bonding jumpers shall be connected in the manner specified in 250,8.

250.28 Main Bonding Jumper and System Bonding Jumper. (A) Material.

Main bonding jumpers and system bonding jumpers shall be of copper, aluminum, copper-clad aluminum, or other corrosion-resistant material. A main bonding jumper and a system bonding jumper shall be a wire, bus, screw, or similar suitable conductor.

250.28 Conductor to Be Grounded Alternating-Current Systems. (D) Size.

Main bonding jumpers and system bonding jumpers shall be sized in accordance with 250.28(D) (1) through (D) (3).

250.4 General Requirements for Grounding and Bonding. (B) Ungrounded Systems. (2) Bonding of Electrical Equipment

Non-current-carrying conductive materials enclosing electrical conductors or equip- ment, 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.

250.6 Objectionable Current. (C) Temporary Currents Not Classified as Objectionable

Temporary currents resulting from abnormal condi- tions, such as ground faults, shall not be classified as objection- able current for the purposes specified in 250.6(A) and (B).

250.21 Alternating-Current Systems of 50 Volts to 1000 Volts Not Required to Be Grounded. (A) General.

The following ac systems of 50 volts to 1000 volts shall be permitted to be grounded but shall not be required to be grounded: 1) Electrical systems used exclusively to supply industrial electric furnaces for melting. refining, tempering, and the like 2) Separately derived systems used exclusively for rectifiers that supply only adjustable-speed industrial drives 3) Separately derived systems supplied by transformers that have a primary voltage rating of 1000 volts or less if all the following conditions are met: a. The system is used exclusively for control circuits. b. The conditions of maintenance and supervision ensure that only qualified persons service the installation. c. Continuity of control power is required. 4) Other systems that are not required to be grounded in accordance with the requirements of 250.20 (B)

250.22 Circuits Not to Be Grounded.

The following circuits shall not be grounded: (1) Circuits for electric cranes operating over combustible fibers in Class III locations, as provided in 503.155 (2) Circuits in health care facilities as provided in 517.61 and 517.160 (3) Circuits for equipment within electrolytic cell line work- ing zones as provided in Article 668 (4) Secondary circuits of lighting systems as provided in 411.6(A)(5) Secondary circuits of lighting systems as provided in 680.23(A) (2) (6) Class 2 load side circuits for suspended ceiling low-voltage power grid distribution systems as provided in 393.60(B)

250.4 General Requirements for Grounding and Bonding.

The following general requirements identify what grounding and bonding of electrical systems are required to accomplish. The prescriptive methods contained in Article 250 shall be followed to comply with the performance requirements of this section.

250.20 (C) Grounded Conductor Brought to Service Equipment. (3) Delta-Connected Service.

The grounded conductor of a 3- phase, 3-wire delta service shall have an ampacity not less than that of the ungrounded conductors.

250.21 Alternating-Current Systems of 50 Volts to 1000 Volts Not Required to Be Grounded. (C) Marking.

Ungrounded systems shall be legibly marked "Caution: Ungrounded System Operating - Volts Between Conductors" at the source or first disconnecting means of the system. The marking shall be of sufficient durabil- ity to withstand the environment involved.

250.28 Main Bonding Jumper and System Bonding Jumper. (B) Construction.

Where a main bonding jumper or a system bonding jumper is a screw only, the screw shall be identified with a green finish that shall be visible with the screw installed.

250.28 Main Bonding Jumper and System Bonding Jumper. (B) Construction.

Where a main bonding jumper or a system bonding jumper is a screw only, the screw shall be identified with a green finish that shall be visible with the screw installed.

250.24 Grounding of ServiceSupplied Alternating-Current Systems. (A) System Grounding Connections. (4) Main Bonding Jumper as Wire or Busbar.

Where the main bonding jumper specified in 250.28 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 grounding electrode conductor shall be permitted to be connected to the equipment grounding terminal, bar, or bus to which the main bonding jumper is connected.