jtinge
Senior Member
- Location
- Hampton, VA
- Occupation
- Sr. Elec. Engr
Scenario:
Similar to an October 14, 2015 post entitled “Fence around substation with no live parts”, I have an electrical equipment yard adjacent to a recent constructed data center building that has a 22kV pad mount SF6 switchgear that feeds two 22kV to 480 unit substations, and three-1MW, 480 back-up generators. There are no exposed live parts and all exposed non-current carrying enclosures are bonded to an equipment yard grounding grid. The equipment yard is enclosed by a security fence with vinyl coated fabric and the posts are grounded via the concrete post foundations but not bonded to the interior grounding grid. The grounding grid for the electrical yard is interior to the plan of the fence and does not extend past the fence.
The electrical equipment yard adjacent to the building is owned and operated by the customer and is fed by an underground 22kV feeder that is part of the customer’s owned and operated campus wide distribution system. The POCO service connection is the 115kV supply into the main customer owned substation.
The scope of both the NEC and NESC clearly delineate that for campus or industrial complex electrical distribution systems, everything on the line side of the service point is covered by the NESC, and everything downstream is covered by the NEC. This being said, it is still common to still hear the argument from engineers that the supply to the building is a service and is covered by the NESC, despite being downstream of the service point in the main substation.
Based on the above information and code references below regarding the definition of substations and substation fence grounding requirements, I have the following questions:
1) Does the electrical equipment yard described above constitute a “substation” that requires the perimeter security fence to be grounded?
2) Is my interpretation that NEC requirements and not NESC requirements are applicable correct based on the location of the service point?
3) Does the installation meet the requirements of NEC 250.190 and 250.194?
4) Are the NESC requirements for grounding of fences around electrical supply stations applicable to this installation?
Additional information for consideration:
Definition of substation in applicable codes and standards:
Not defined in applicable OSHA 29 CFR 1910 and 29 CFR 1926 requirements.
Not defined in IEEE 80, IEEE Guide for Safety in AC Substation Grounding.
Substation. An enclosed assemblage of equipment (e.g., switches, interrupting devices, circuit breakers, buses, and transformers) through which electric energy is passed for the purpose of distribution, switching, or modifying its characteristics. (NEC 2014)
Substation. An enclosed assemblage of equipment, e.g., switches, circuit breakers, buses, and transformers, under the control of qualified persons, through which electric energy is passed for the purpose of switching or modifying its characteristics to increase or decrease voltage or control frequency or other characteristics. (NESC 2017)
Electric supply station. Any building, room, or separate space within which electric supply equipment is located and the interior of which is accessible, as a rule, only to qualified persons. This includes generating stations and substations, including their associated generator, storage battery, transformer, and switchgear rooms or enclosures, but does not include facilities such as pad-mounted equipment and installations in manholes and vaults. (NESC 2017)
Requirements for grounding substation fences:
29 CFR 1910.269(u)(3) Substation fences. Conductive fences around substations shall be grounded. When a substation fence is expanded or a section is removed, fence sections shall be isolated, grounded, or bonded as necessary to protect employees from hazardous differences in electric potential.
29 CFR 1926.966.269(d) Substation fences. Conductive fences around substations shall be grounded. When a substation fence is expanded or a section is removed, fence sections shall be isolated, grounded, or bonded as necessary to protect employees from hazardous differences in electric potential.
NEC 250.190 Grounding of Equipment
(A) Equipment Grounding. All non–current-carrying metal parts of fixed, portable, and mobile equipment and associated fences, housings, enclosures, and supporting structures shall be grounded.
NEC 250.194 Grounding and Bonding of Fences and Other Metal Structures
Metallic fences enclosing, and other metal structures in or surrounding, a substation with exposed electrical conductors and equipment shall be grounded and bonded to limit step, touch, and transfer voltages.
(A) Metal Fences. Where metal fences are located within 5 m (16 ft) of the exposed electrical conductors or equipment, the fence shall be bonded to the grounding electrode system with wire-type bonding jumpers as follows :
(1) Bonding jumpers shall be installed at each fence corner and at maximum 50 m (160 ft) intervals along the fence.
(2) Where bare overhead conductors cross the fence, bonding jumpers shall be installed on each side of the crossing.
(3) Gates shall be bonded to the gate support post, and each gate support post shall be bonded to the grounding electrode system.
(4) Any gate or other opening in the fence shall be bonded across the opening by a buried bonding jumper.
(5) The grounding grid or grounding electrode systems shall be extended to cover the swing of all gates.
(6) The barbed wire strands above the fence shall be bonded to the grounding electrode system.
Alternate designs performed under engineering supervision shall be permitted for grounding or bonding of metal fences.
Informational Note No. 1: A non-conducting fence or section may provide isolation for transfer of voltage to other areas.
Informational Note No. 2: See IEEE 80-2000, IEEE Guide for Safety In AC Substation Grounding, for design and installation of fence grounding.
(B) Metal Structures. All exposed conductive metal structures, including guy wires within 2.5 m (8 ft) vertically or 5 m (16 ft) horizontally of exposed conductors or equipment and subject to contact by persons, shall be bonded to the grounding electrode systems in the area.
NESC 092 E. Fences
Conductive electric supply station fences that are required to be grounded by Part 1 of this Code shall be designed to limit touch, step, and transferred voltages in accordance with industry practices.
NOTE: IEEE Std 80™-2000 [B32] is one source that may be utilized to provide guidance in meeting these requirements.
The grounding connections of electrical supply station fences shall be made either to the grounding system of the enclosed equipment or to a separate ground.
1. Conductive supply station fences shall be grounded at each side of a gate or other opening.
2. Conductive supply station fence gates shall be bonded to the grounding conductor, jumper, or fence.
3. A buried bonding jumper shall be used to bond across a gate or other opening in the supply station fence, unless a nonconducting fence section is used.
4. If barbed wire strands are used above the supply station fence fabric, the barbed wire strands shall be bonded to the grounding conductor, jumper, or fence.
5. When supply station fence posts are of conducting material, the grounding conductor shall be connected to the fence post or posts, as required, with suitable connecting means.
6. When supply station fence posts are of nonconducting material, suitable bonding connection shall be made to the fence mesh strands and the barbed wire strands at each grounding conductor point.
Similar to an October 14, 2015 post entitled “Fence around substation with no live parts”, I have an electrical equipment yard adjacent to a recent constructed data center building that has a 22kV pad mount SF6 switchgear that feeds two 22kV to 480 unit substations, and three-1MW, 480 back-up generators. There are no exposed live parts and all exposed non-current carrying enclosures are bonded to an equipment yard grounding grid. The equipment yard is enclosed by a security fence with vinyl coated fabric and the posts are grounded via the concrete post foundations but not bonded to the interior grounding grid. The grounding grid for the electrical yard is interior to the plan of the fence and does not extend past the fence.
The electrical equipment yard adjacent to the building is owned and operated by the customer and is fed by an underground 22kV feeder that is part of the customer’s owned and operated campus wide distribution system. The POCO service connection is the 115kV supply into the main customer owned substation.
The scope of both the NEC and NESC clearly delineate that for campus or industrial complex electrical distribution systems, everything on the line side of the service point is covered by the NESC, and everything downstream is covered by the NEC. This being said, it is still common to still hear the argument from engineers that the supply to the building is a service and is covered by the NESC, despite being downstream of the service point in the main substation.
Based on the above information and code references below regarding the definition of substations and substation fence grounding requirements, I have the following questions:
1) Does the electrical equipment yard described above constitute a “substation” that requires the perimeter security fence to be grounded?
2) Is my interpretation that NEC requirements and not NESC requirements are applicable correct based on the location of the service point?
3) Does the installation meet the requirements of NEC 250.190 and 250.194?
4) Are the NESC requirements for grounding of fences around electrical supply stations applicable to this installation?
Additional information for consideration:
Definition of substation in applicable codes and standards:
Not defined in applicable OSHA 29 CFR 1910 and 29 CFR 1926 requirements.
Not defined in IEEE 80, IEEE Guide for Safety in AC Substation Grounding.
Substation. An enclosed assemblage of equipment (e.g., switches, interrupting devices, circuit breakers, buses, and transformers) through which electric energy is passed for the purpose of distribution, switching, or modifying its characteristics. (NEC 2014)
Substation. An enclosed assemblage of equipment, e.g., switches, circuit breakers, buses, and transformers, under the control of qualified persons, through which electric energy is passed for the purpose of switching or modifying its characteristics to increase or decrease voltage or control frequency or other characteristics. (NESC 2017)
Electric supply station. Any building, room, or separate space within which electric supply equipment is located and the interior of which is accessible, as a rule, only to qualified persons. This includes generating stations and substations, including their associated generator, storage battery, transformer, and switchgear rooms or enclosures, but does not include facilities such as pad-mounted equipment and installations in manholes and vaults. (NESC 2017)
Requirements for grounding substation fences:
29 CFR 1910.269(u)(3) Substation fences. Conductive fences around substations shall be grounded. When a substation fence is expanded or a section is removed, fence sections shall be isolated, grounded, or bonded as necessary to protect employees from hazardous differences in electric potential.
29 CFR 1926.966.269(d) Substation fences. Conductive fences around substations shall be grounded. When a substation fence is expanded or a section is removed, fence sections shall be isolated, grounded, or bonded as necessary to protect employees from hazardous differences in electric potential.
NEC 250.190 Grounding of Equipment
(A) Equipment Grounding. All non–current-carrying metal parts of fixed, portable, and mobile equipment and associated fences, housings, enclosures, and supporting structures shall be grounded.
NEC 250.194 Grounding and Bonding of Fences and Other Metal Structures
Metallic fences enclosing, and other metal structures in or surrounding, a substation with exposed electrical conductors and equipment shall be grounded and bonded to limit step, touch, and transfer voltages.
(A) Metal Fences. Where metal fences are located within 5 m (16 ft) of the exposed electrical conductors or equipment, the fence shall be bonded to the grounding electrode system with wire-type bonding jumpers as follows :
(1) Bonding jumpers shall be installed at each fence corner and at maximum 50 m (160 ft) intervals along the fence.
(2) Where bare overhead conductors cross the fence, bonding jumpers shall be installed on each side of the crossing.
(3) Gates shall be bonded to the gate support post, and each gate support post shall be bonded to the grounding electrode system.
(4) Any gate or other opening in the fence shall be bonded across the opening by a buried bonding jumper.
(5) The grounding grid or grounding electrode systems shall be extended to cover the swing of all gates.
(6) The barbed wire strands above the fence shall be bonded to the grounding electrode system.
Alternate designs performed under engineering supervision shall be permitted for grounding or bonding of metal fences.
Informational Note No. 1: A non-conducting fence or section may provide isolation for transfer of voltage to other areas.
Informational Note No. 2: See IEEE 80-2000, IEEE Guide for Safety In AC Substation Grounding, for design and installation of fence grounding.
(B) Metal Structures. All exposed conductive metal structures, including guy wires within 2.5 m (8 ft) vertically or 5 m (16 ft) horizontally of exposed conductors or equipment and subject to contact by persons, shall be bonded to the grounding electrode systems in the area.
NESC 092 E. Fences
Conductive electric supply station fences that are required to be grounded by Part 1 of this Code shall be designed to limit touch, step, and transferred voltages in accordance with industry practices.
NOTE: IEEE Std 80™-2000 [B32] is one source that may be utilized to provide guidance in meeting these requirements.
The grounding connections of electrical supply station fences shall be made either to the grounding system of the enclosed equipment or to a separate ground.
1. Conductive supply station fences shall be grounded at each side of a gate or other opening.
2. Conductive supply station fence gates shall be bonded to the grounding conductor, jumper, or fence.
3. A buried bonding jumper shall be used to bond across a gate or other opening in the supply station fence, unless a nonconducting fence section is used.
4. If barbed wire strands are used above the supply station fence fabric, the barbed wire strands shall be bonded to the grounding conductor, jumper, or fence.
5. When supply station fence posts are of conducting material, the grounding conductor shall be connected to the fence post or posts, as required, with suitable connecting means.
6. When supply station fence posts are of nonconducting material, suitable bonding connection shall be made to the fence mesh strands and the barbed wire strands at each grounding conductor point.
