In keeping with a tradition of translating the NEC's changes every three years and keeping you informed of revisions that will affect you, EC&M presents the first of four installments in its 2002 NEC analysis. This month, we cover changes that affect the Code as a whole, as well as revisions to Chapters 1 and 2.Global Changes. Specific changes to articles and sections aren't the only thing necessary to keep the Code up-to-date. The following revisions have been made to make the NEC easier to read.
Numbering System - The numbering system for the NEC no longer uses the “hyphen” system; the 2002 Code employs the “dot” system. For example, 110-26 will now be 110.26. No more than three levels of division will be used, the first letter will be capitalized, and the following characters will be lower case. For example: 110.26(A), 110.26(A)(1), 110.26(A)(1)(a).
New Articles - The 2002 NEC includes the following Articles:
Art. 80 - Administration and Enforcement
Art. 285 - Transient Voltage Surge Suppressors
Art. 406 - Receptacles
Art. 647 - Sensitive Electronic Equipment
Art. 692 - Fuel Cells
Parts - Article parts in the 1999 NEC were identified as Part A, Part B, and Part C. The 2002 NEC identifies Article parts as Part I, Part II, and Part III.
Sections - Many Code sections were moved, and to achieve a uniform numbering system, several articles were renumbered (See Sidebar on page 24).
Wire Identifiers - The term “AWG” will now replace “No.” for describing conductor size throughout the NEC. For example, “a No. 8” is now identified as “8 AWG.”
Now it's time to examine some of the most notable changes to the Code and why they've been made. (NOTE: As you make your way through each change, keep in mind that paraphrased excerpts from the NEC are shown as indented text, with new material or changes underlined. An explanation for the revision also follows each discussion.)Art. 80 - Administration and Enforcement
A new Article 80 was added to the 2002 NEC to provide a model administrative and enforcement ordinance. The requirements contained in this Article are only informative and cannot be enforced by the Authority Having Jurisdiction (AHJ), unless it is specifically adopted by the local jurisdiction.
Intent: Art. 80 will help promote uniform administrative provisions throughout the U.S. and other countries that have adopted, or will be adopting, the NEC. In addition, the Article provides model administrative and enforcement requirements for jurisdictions that are adopting the Code for the first time.Art. 90 - Introduction
90.2 Scope of the NEC
This subsection was revised to group similar types of installations together and to make it easier to read. It clarifies the fact that the Code's scope covers signaling and communications conductors and equipment. Signaling and communications cable and raceway must be in compliance with the NEC.
In addition, the rule that exempts electric utilities from complying with the requirements of the NEC was revised to include service drops and laterals. However, service laterals not under the exclusive control of an electric utility installed by the electrical contractor must be installed in accordance with the NEC.90.4 Enforcement (Inspection)
This Code is intended to be suitable for enforcement by governmental bodies that exercise legal jurisdiction over electrical installations, for power, lighting, signaling, and communications systems.
Intent: The Communications Systems Task Group indicated some Code users did not think their installations were subject to inspection. The new words clarify that scope of enforcement (inspection) includes signaling and communications conductors and associated equipment. The requirements for the following systems are contained in the corresponding articles:
|CATV, MATV, and CCTV||820|
|Control and Signaling Circuits||725|
|Optical Fiber Cables and Raceways||770|
|Satellite and Antenna||810|
By special permission, the Authority Having Jurisdiction (AHJ) can waive specific NEC requirements or permit alternate methods where it is assured that safety objectives can be achieved.
Intent: By requiring written consent whenever a Code rule is waived or an alternate method is permitted, this change ensures accountability when the AHJ allows alternate methods of installation that may be contrary to the NEC.90.9 Units of Measurement
(A) Measurement System of Preference. The metric unit is the preferred measurement system.
(B) Dual Systems of Units. Dual measurement unit systems must be showed in the NEC, with the metric units to appear first, and the imperial units to immediately follow in parentheses.
(D) Compliance. Installing electrical systems in accordance with the metric system or the imperial system is considered compliance with the Code.
Intent: The change ensures the NEC will be recognized and accepted as an international standard for electrical installations.Art. 100 - Definitions
The following definitions have been added or changed for the 2002 NEC.
Authority Having Jurisdiction. The organization, office, or individual responsible for approving equipment, materials, an installation, or a procedure.
FPN: *The Authority Having Jurisdiction may be a federal, state, local government, or individual such as a fire chief; fire marshal; chief of a fire prevention bureau, labor department or health department; building official or electrical inspector; or others having statutory authority. In some circumstances, the property owner or his/her agent assumes the role, and at government installations, the commanding officer or departmental official may be the AHJ.
*The text for the FPN above was shortened for this article.
Intent: The term “Authority Having Jurisdiction (AHJ)” can be found more than 40 times in the NEC, yet it has never been defined. This definition clarifies that the AHJ can be a public entity, individual, nonpublic person, or designated agent. Many believe the AHJ should have an electrical engineering background or an electrical contractor's license, and in some states this is a legal requirement. See Sec. 80.27 for Inspectors' Qualifications.
Ground-Fault Circuit Interrupter. A device intended to protect persons by functioning to de-energize a circuit within a short period of time when a current to ground exceeds the value established for a Class A device.
FPN: A Class A ground-fault circuit interrupter opens the circuit when the current to ground has a value between 4mA to 6mA.
Intent: This change clarifies that the term “GFCI” refers to a device that opens the circuit at a value between 4mA and 6mA (Class A GFCI). It does not apply to a Class B GFCI device, which is designed to open a circuit at 20mA.
Luminaire. A complete lighting unit that consists of a lamp or lamps together with the parts designed to distribute the light.
Intent: “Luminaire” replaces the terms “fixture” and “lighting fixture,” which were used throughout the 1999 NEC but never defined. The Illuminating Engineering Society of North America and most manufacturers use this new term.
Qualified Person. A person who has the skill and knowledge related to the construction and operation of the electrical equipment and its installation. This person has received safety training on the hazards involved with electrical systems.
Intent: The 1999 NEC used the term “Qualified Person(s)” in about 65 sections, and the revision clarifies that a qualified person must have received safety training on the hazards involved. No longer is a person considered qualified simply by being familiar with the construction and operation of the equipment and the hazards involved.Art. 110 - Requirements for Electrical Installations
110.16 Flash Protection
Switchboards, panelboards, industrial control panels, and motor control centers in commercial and industrial occupancies that are likely to require examination, adjustment, servicing, or maintenance while energized must be field marked to warn qualified persons of the danger of electric arc flash. The marking must be clearly visible to qualified persons before they examine, adjust, service, or perform maintenance on the equipment.
FPN No. 1: NFPA 70E-2000, Electrical Safety Requirements for Employee Workplaces, provides assistance in determining the severity of potential exposure, planning safe work practices, and selecting personal protective equipment.
FPN No. 2: ANSI Z535.4-1998, Product Safety Signs and Labels, provides guidelines for the design of safety signs and labels.
Intent: This new section addresses the concern of protecting qualified persons who work on energized electrical systems by ensuring they are notified of the arc flash hazards and assisting in the selection of proper personal protective equipment.110.26 Spaces About Electrical Equipment
(C) Entrance to Working Space
(2) Large Equipment. There must be one entrance to the required working space not less than 24 in. wide and 6.5 ft high at each end of the working space for equipment rated 1200A or more having a width of over 6 ft containing overcurrent devices, switching devices, or control devices. Where the entrance to the working space has a door(s), the door(s) must open in the direction of egress and it must be equipped with panic hardware or other devices that will open the door under simple pressure.
Intent: This change addresses the concern for the safety of persons who work on energized equipment. The personnel door to an area that houses equipment must allow an injured worker to exit the area without having to operate a doorknob. Since this requirement is contained in the NEC, electrical contractors are responsible for installing panic hardware at these locations.
(F) Dedicated Equipment Space. All switchboards, panelboards, distribution boards, and motor control centers must be located in dedicated spaces and protected from damage.
(1) Indoors. Indoor installations must comply with the following.
(a) Dedicated Electrical Space. The space equal to the width and depth of the equipment extending from the floor to a height of 6 ft above the equipment or to the structural ceiling, whichever is lower, must be dedicated to the electrical installation. No piping, ducts, or other equipment foreign to the electrical installation can be installed in this dedicated space.
Exception: Suspended ceilings with removable panels can be in the dedicated space.
(b) Foreign Systems. The area above the dedicated space can contain foreign systems, provided protection is installed to protect electrical equipment from condensation, leaks, or breaks in such foreign systems.
(c) Sprinkler Protection. Sprinkler protection is permitted to spray water into the dedicated space, but the sprinkler piping itself must not be located within the dedicated space area.
Intent: The revised text makes it easier to understand that the dedicated space above switchboards, panelboards, distribution boards, and motor control centers (up to 6 ft), must be kept clear of foreign items. However, suspended ceilings with lift-out panels are permitted in this space.Art. 200 - Use and Identification of Grounded (Neutral) Conductor
200.6 Means of Identifying Grounded (Neutral) Conductor
(A) Identifying Grounded (Neutral) Conductors, 6 AWG or Smaller. A grounded (neutral) conductor 6 AWG or smaller must be identified by a continuous white or gray outer finish along its entire length.
(B) Identifying Grounded (Neutral) Conductors Larger than 6 AWG. A grounded (neutral) conductor larger than 6 AWG must be identified by a continuous white or gray outer finish along its entire length, or it can be identified by distinctive white markings such as tape, paint, or by other effective means at its terminations.
(D) Mixing Grounded (Neutral) Conductors from Different Systems in the Same Raceway or Enclosure. Where conductors from different systems are installed in the same raceway, cable, or enclosure, one system grounded (neutral) conductor must have an outer covering of white or gray. The other system grounded (neutral) conductor must have an outer covering of white with a readily distinguishable different color stripe (not green) running along its entire length.
FPN: Care should be taken when working on existing systems because the color gray may have been used as an ungrounded (hot) conductor.
Intent: This revision addresses the concern that the Code does not define the term “natural gray.” The FPN warns individuals there may be electrical systems where a gray conductor was used as an ungrounded (hot) conductor.Art. 210 - Branch Circuits
210.7 Branch Circuit Receptacle Requirements
(A) Receptacle Requirements. Receptacle outlets must be located on branch circuits in accordance with the requirements listed in Part III of Article 210.
(B) Receptacle Requirements. Specific receptacle requirements are covered in Article 406.
Intent: Usability of the Code has become important to the Code-making panels. They believed relocating the installation requirements for receptacles and cord connectors to Art. 406 would make the Code easier to use. Art. 406 also includes the installation requirements for receptacles and cord connectors that were located in Art. 410, Part L of the 1999 Code.210.7 Branch Circuit Receptacle Requirements
(C) Multiple Branch Circuits. Where more than one branch circuit supplies more than one receptacle on the same yoke, a means at the branch circuit panelboard must be provided to simultaneously disconnect the ungrounded (hot) circuit conductors supplying the receptacles.
Intent: The change makes it necessary for all ungrounded (hot) circuit conductors terminating on multiple receptacles (duplex) on the same yoke to be disconnected simultaneously regardless of type of occupancy. The rule prevents persons from working on energized circuits they thought were disconnected. The 1999 NEC only required the circuit disconnect to simultaneously interrupt the multiwire circuit to multiple receptacles on the same yoke if the receptacle was located in a dwelling unit.210.12 Arc-Fault Circuit-Interrupter (AFCI) Protection
(A) AFCI Definition. An AFCI protection device provides protection from an arc fault by recognizing the characteristics unique to an arcing fault and by functioning to de-energize the circuit when an arc fault is detected.
(B) Dwelling Unit Bedrooms. All branch circuits supplying 15 or 20A, single-phase 125V outlets installed in dwelling unit bedrooms must be AFCI protected by a listed device that protects the entire branch circuit.
Intent: The change extends AFCI protection to all 125V outlets in dwelling unit bedrooms, whereas the 1999 NEC only required AFCI protection for all branch circuits that supply 15A or 20A, single-phase 125V receptacle outlets in dwelling unit bedrooms. The Code defines an outlet as “a point on the wiring system at which current is taken to supply utilization equipment” [Art. 100]. This includes openings for receptacles, luminaires, or smoke detectors.
The practice of separating the lighting from the receptacle circuits in dwelling unit bedrooms will now require two AFCI circuit breakers. The 125V limitation to the requirement means AFCI protection would not be required for a 240V baseboard electric heater.210.63 Heating, Air-Conditioning, and Refrigeration Equipment Outlet
A 15 or 20A, single-phase 125V receptacle outlet must be installed at an accessible location for the servicing of heating, air-conditioning, and refrigeration equipment on rooftops and in attics and crawl spaces. The receptacle must be located within 25 ft and on the same level of the heating, air-conditioning, and refrigeration equipment. The receptacle outlet must not be connected to the load side of the equipment disconnecting means.
Intent: The changes require a 15A or 20A, single-phase 125V receptacle outlet to be located within 25 ft of heating, air-conditioning, and refrigeration equipment for all occupancies, including one- and two-family dwellings. This receptacle must be GFCI protected if it is located outdoors [210.8(A)(3)] or in crawl spaces at or below grade [210.8(A)(4)].Art. 225 - Outside Branch Circuits and Feeders 225.32 Disconnecting Means
The disconnecting means for a building or structure must be installed either inside or outside of the building or structure. The disconnecting means must be at a readily accessible location nearest the point of entrance of the conductors.
Exception No. 1: For installations under single management, where documented safe switching procedures are established and maintained and where the installation is monitored by qualified persons, the building/structure disconnecting means can be located elsewhere on the premises.
Intent: The revised exception is intended to ensure that in addition to safe switching procedures, the installation be monitored by qualified persons who have the skills and knowledge related to the construction and operation of the electrical equipment and installation, and who have received safety training on the hazards involved with electrical systems.Art. 240 - Overcurrent Protection 240.21 Location in Circuit
(C) Transformer Secondary Conductors
(6) Secondary Conductors Not Over 25 ft. Secondary conductors can be run up to 25 ft if installed in accordance with the following:
(1) The secondary conductors have an ampacity that (when multiplied by the ratio of the secondary-to-primary voltage) is at least one-third of the rating of the overcurrent device protecting the primary of the transformer.
(2) The secondary conductors terminate in a single circuit breaker or set of fuses that have a rating not greater than the conductor ampacity.
(3) The secondary conductors are protected from physical damage.
Intent: The new subsection provides the language necessary for secondary conductors longer than 10 ft but not more than 25 ft. This rule was missing in the previous editions of the NEC. The 1999 Code contained the requirement for secondary conductors up to 25 ft for industrial installations only [240-21(c)(3)].240.24 Location in or on Premises
(B) Occupancy. Each occupant must have ready access to all overcurrent devices protecting the conductors supplying that occupancy.
Exception No. 2: Branch circuit overcurrent protection devices are not required to be accessible to occupants of guest rooms of hotels and motel, if electric maintenance is provided in a facility that is under continuous building management.240.83 Marking
(D) Used as Switches. Circuit breakers used to switch 120V or 277V fluorescent lighting circuits must be listed and marked ‘SWD’ or ‘HID’. Circuit breakers used to switch high intensity discharge lighting circuits must be listed and must be marked as ‘HID’.
Intent: Circuit breakers marked “HID” are listed to switch electric discharge and fluorescent luminaires. Circuit breakers marked “SWD” are listed to switch fluorescent luminaires, not HID luminaires. You do not need to mark circuit breakers used to switch incandescent lighting.240.85 Applications
A circuit breaker with a straight voltage rating (240V or 480V) can be used on a circuit where the nominal voltage between any two conductors does not exceed the circuit breaker's voltage rating. A two-pole circuit breaker must not be used for protecting a 3-phase, corner-grounded delta circuit unless the circuit breaker is marked 1- or 3-phase to indicate such suitability.
A circuit breaker with a slash rating such as 120V/240V or 480V/277V can be used on a solidly grounded circuit where the nominal voltage of any one conductor to ground does not exceed the lower of the two values and the nominal voltage between any two conductors does not exceed the higher value.
FPN: Circuit breakers on systems other than on a solidly grounded wye, particularly on corner grounded delta systems, should consider the individual pole interrupting capability.
Intent: This clarifies that slash-rated circuit breakers must be applied on solidly grounded systems. A slash-rated breaker cannot be used on the high-leg phase of a solidly 120V/240V grounded delta system because the phase-to-ground voltage is 208V. In addition, these breakers cannot be used on a resistance grounded or ungrounded system because the full phase-to-phase voltage could cross one pole.Art. 250 - Grounding Part I. General 250.2 Definitions
Effective Ground-Fault Current Path. An intentionally constructed, permanent, low impedance path designed and intended to carry fault current from the point of a line-to-case fault on a wiring system to the grounded (neutral) at the electrical supply source.
FPN: An effective ground-fault current path is created when all electrically conductive materials that are likely to be energized are bonded together and to the grounded (neutral) at the electrical supply. Effective bonding is accomplished through the use of equipment grounding conductors, bonding jumpers, metallic raceways, connectors and couplings, metallic sheathed cable and cable fittings, and other approved devices recognized for the purpose. A ground-fault path is effective when it is properly sized so that it will safely carry the maximum ground-fault current likely to be imposed on it.
Ground-Fault. A ground-fault is an unintentional electrical connection between an ungrounded (hot) conductor and metal enclosures, raceways, equipment, or earth.
Ground-Fault Current Path. An electrically conductive path from the point of a line-to-case fault on a wiring system through conductors, equipment, or the earth extending to the grounded (neutral) terminal at the electrical supply source.
FPN: The ground-fault current paths could consist of equipment grounding conductors, metallic raceways, metallic cable sheaths, electrical equipment, and other electrically conductive material such as metal water and gas piping, steel framing members, stucco mesh, metal ducting, reinforcing steel, shields of communications cables, or the earth itself.
Intent: The addition of these definitions will help Code users understand the performance requirements contained in Art. 250.250.4 General Requirements for Grounding and Bonding
To ensure a safe electrical system, the following requirements identify the purpose of grounding and bonding of electrical systems. The requirements contained in other sections of Art. 250 must be followed so that the electrical system will be safe from dangerous voltage.
(A) Grounded Systems.
(1) Electrical System Grounding.
Grounded electrical systems (transformer, generators, etc.) must be connected to earth for the purpose of limiting the voltage imposed by lightning, line surges, or unintentional contact with higher voltage lines, by shunting the energy to the earth. In addition, electrical systems (power supplies) are grounded to the earth for the purpose of stabilizing the voltage to earth during normal operation.
“Electrical system” refers to the “source,” such as the transformer/generator.
(2) Grounding of Electrical Equipment. Noncurrent-carrying conductive metal parts of the electrical system in a building or structure must be connected to earth for the purpose of limiting the voltage imposed by lightning, line surges, or unintentional contact with higher voltage lines, by shunting the energy to the earth.
(3) Bonding of Electrical Equipment. Noncurrent-carrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, must be connected together and to the grounded (neutral) terminal at the electrical supply source in a manner that establishes an effective ground-fault current path.
(4) Bonding of Electrically Conductive Materials and Other Equipment. Electrically conductive materials that are likely to become energized must be connected together and to the grounded (neutral) terminal at the electrical supply source in a manner that establishes an effective ground-fault current path.
(5) Effective Ground-Fault Current Path. Electrical equipment and other electrically conductive material likely to become energized must be installed in a manner that creates a permanent, low impedance circuit capable of safely carrying the maximum ground-fault current likely to be imposed on it from where a ground-fault may occur to the grounded (neutral) terminal at the electrical supply source.
The earth cannot be used as the sole equipment grounding conductor or effective ground-fault current path.
Intent: Sec. 250-2 of the 1999 NEC was revised and relocated to 250.4. The changes to this section clarify the grounding and bonding requirements in Art. 250. The most significant change includes the explanation that, in order to clear a fault, the fault current must have an effective low-impedance ground-fault current path back to the grounded (neutral) terminal at the power supply.Part II. Circuit and System Grounding
250.30 Grounding Separately Derived Alternating-Current Systems
(A) Grounded Systems
(2) Grounding Electrode Conductor. The grounding electrode conductor for a separately derived system (transformer and sometimes a generator) must be installed in accordance with (a) or (b) below. Where taps are connected to a common grounding electrode conductor as permitted in 250.30(A)(2)(b), the installation must comply with 250.30(A)(3).
(a) Single Separately Derived System. A grounding electrode conductor for a single separately derived system must be sized in accordance with 250.66 for the derived phase conductors and it must connect the grounded (neutral) conductor of the derived system to the grounding electrode as specified in 250.30(A)(4).
(b) Multiple Separately Derived Systems. Where more than one separately derived system is connected to a common grounding electrode conductor as provided in 250.30(A)(3), the common grounding electrode conductor shall be sized in accordance with 250.66 based on the total circular mil area of the derived phase conductor from all separately derived systems.
Intent: This rule addresses the grounding electrode conductor requirements for multiple separately derived systems.250.30 Grounding Separately Derived Alternating-Current Systems
(A) Grounded Systems
(3) Grounding Electrode Taps. Grounding electrode taps from a separately derived system to a common grounding electrode conductor must connect the grounded conductor of the separately derived system to the common grounding electrode conductor and must be installed in accordance with (a) through (d) below.
(a) Tap Conductor Size. Each tap conductor must be sized in accordance with 250.66 for the derived phase conductors of the separately derived system it serves.
(b) Connections. All connections must be made at an accessible location by an irreversible compression connector listed for the purpose, listed connections to copper busbars not less than 0.25 in. × 2 in., or by the exothermic welding process. Tap conductors must be connected to the common grounding electrode conductor as specified in 250.30(A)(2)(b) in such a manner that the common grounding electrode conductor is not spliced.
(c) Installation. The common grounding electrode conductor and the taps to each separately derived system must comply with 250.64(A), (B), (C) and, (E).
(d) Bonding. Where exposed structural steel that forms the building frame or interior metal piping exists in the area served by the separately derived system, it must be bonded to the grounding electrode conductor in accordance with 250.104(C).
Intent: This new section addresses grounding electrode conductor taps for grounding multiple separately derived systems as permitted by 250.30(A)(2)(b). The change permits an alternate method of grounding multiple separately derived systems in cases where an effectively grounded steel building or metal water pipe is not in the vicinity of the systems.250.30 Grounding Separately Derived Alternating-Current Systems
(A) Grounded Systems
(6) Grounded (neutral) Conductor. Where a grounded (neutral) conductor is installed and the neutral-to-case bond is not located at the source of the separately derived system, the following must apply:
(a) Routing and Sizing. The grounded (neutral) conductor must be routed with the secondary conductors and it must not be smaller than the required grounding electrode conductor as specified in Table 250.66 based on the largest ungrounded supply conductor, but it is not required to be larger than the largest ungrounded derived phase conductor. For secondary phase conductors larger than 1100 kcmil copper or 1750 kcmil aluminum, the grounded (neutral) conductor must not be smaller than 12.5% of the area of the largest derived phase conductor.
(b) Parallel Conductors. If the secondary conductors are in parallel, the grounded (neutral) secondary conductor must be sized based on the total circular mil area of all of the parallel conductors per phase. Where installed in two or more raceways, the size of the grounded (neutral) conductor in each raceway must be based on the size of the ungrounded (hot) conductors in the raceway but it must not be any smaller than 1/0 AWG.
Intent: This new requirement provides guidance on how to properly size the grounded (neutral) conductor to the first system disconnecting means or overcurrent device if the neutral-to-case bond is not located at the source of the separately derived system. Because this conductor will carry line-to-case fault current, it must be sized in accordance with Table 250.66. This new rule requires the grounded (neutral) conductor to be large enough to carry the maximum unbalanced load as required by 188.8.131.52(B)(2) Buildings or Structures Supplied with Feeder
The size of the grounded conductor shall not be smaller than the larger of: (1) That required by 220.22 (maximum unbalanced neutral load), or (2) That required by 250.122 (equipment grounding conductor size).
Intent: The new sentence specifies how to size the grounded (neutral) conductor to a building or structure when an equipment grounding conductor does not run to the separate building or structure. When an equipment grounding conductor does not run to a separate building or structure, the grounded (neutral) conductor must be used to provide the effective fault current path required to clear any line-to-case faults in addition to carrying any unbalanced neutral current.250.32 Two or More Buildings or Structures Supplied with Feeder
(E) Grounding Electrode Conductor. The size of the grounding electrode conductor for a building or structure supplied by a feeder must not be smaller than that identified in 250.66 based on the largest ungrounded supply conductor. The grounding electrode conductor must be installed in accordance with the requirements for grounding electrode conductors in Part III of Art. 250, specifically Secs. 250.62 through 250.70.
Intent: The title to this subsection was changed from “Grounding Conductor” to “Grounding Electrode Conductor,” and the reference to 250-122 was changed to 250.66. In the 1999 NEC, this conductor to the grounding electrode was called a “grounding conductor” and it was sized in accordance with Table 250-122 for equipment grounding.Part III. Grounding Electrode System and Grounding Electrode Conductor
250.54 Supplementary Grounding Electrodes (Signal Reference Ground)
Supplementary grounding electrodes (often called signal reference ground) can be installed and they can be connected to the equipment grounding conductors. Signal reference grounding electrodes and their conductors are not required to comply with the bonding requirements of 250.50 and 250.53(C), or the 25 ohm resistance requirement of 250.56 does not apply. However, the earth cannot be used as the sole equipment grounding conductor [250.4(A)(5)].
Intent: These changes clarify that you are not required to bond a supplemental electrode to the grounding electrode system, the bonding jumper to the supplemental electrode can be any size, and the 25-ohm resistance requirement of 250.56 does not apply.Part V. Bonding
250.102 Equipment Bonding Jumpers
(E) Installation. The equipment bonding jumper can be installed inside or outside of a raceway or enclosure. Where installed on the outside, the length of the equipment bonding jumper must not exceed 6 ft and it must be routed with the raceway or enclosure. Where installed inside a raceway, the equipment bonding jumper must be properly identified [250.119] and terminated and/or spliced [250.148].
Exception: An equipment bonding jumper longer than 6 ft is permitted at utility pole locations for the purposes of bonding isolated sections of metal service raceways or elbows installed in exposed risers.
Intent: Service lateral conductors and raceways not owned by the utility company at the time of installation are subject to the rules of the NEC. Often the serving utility mandates a metal elbow and/or metal raceway at the pole, and many times these metal parts are not bonded. This new rule provides a method for the electrician to bond the isolated parts to the grounded (neutral) conductor at the pole, making the installation safe and Code-compliant.250.104(A)(4) Bonding of Piping Systems and Exposed Structural Steel
Exception: Bonding the metal water pipe system to the separately derived system grounded (neutral) terminal is not required if the metal water piping in the areas served by the separately derived system is bonded to the effectively grounded metal frame of a building or structure that serves as the grounding electrode for the separately derived system.
Intent: This exception makes it no longer necessary to bond water piping to the separately derived system grounded (neutral) terminal if the metal frame of the building or structure serves as the grounding electrode for the system, and the metallic water piping in the areas served by the separately derived system is bonded to the effectively grounded metal frame of the building.250.104 Bonding of Piping Systems and Exposed Structural Steel
(B) Other Metal Piping Systems. Metal piping, including gas piping, that may become energized must be bonded to:
The service equipment enclosure,
The grounded (neutral) conductor at the service,
The grounding electrode conductor where of sufficient size, or
Any grounding electrodes used to form the grounding electrode system.
The metal piping bonding jumper must be sized in accordance with Table 250.122 using the rating of the circuit that may energize the piping. The equipment grounding conductor for the circuit that may energize the piping can serve as the bonding means.
Intent: The revised text makes it clear that an equipment grounding conductor can bond all metal piping, including gas piping. As a result, an additional bonding jumper is not required for gas or other metal piping.250.104 Bonding of Piping Systems and Exposed Structural Steel
(C) Structural Steel. Exposed structural steel that is interconnected to form a steel building frame and is not effectively grounded and may become energized must be bonded to:
The service equipment enclosure,
The grounded (neutral) conductor at the service,
The grounding electrode conductor where of sufficient size, or
Any grounding electrodes used to form the grounding electrode system.
The bonding jumper is sized in accordance with Table 250.66 and the attachment of the jumper must be accessible.
Intent: The new language requires all structural steel (whether interior or exterior) to be bonded where it is likely to become energized. The 1999 NEC did not require exterior structural steel systems to be bonded. In addition, the sizing of this bonding jumper now must be in accordance with Table 250.66, instead of Table 250.122.Part VI. Equipment Grounding and Equipment Grounding Conductors
250.118 Types of Equipment Grounding Conductors
(11) MC Cable. The outer metal sheath of smooth or corrugated tube type MC cable can serve as an equipment grounding conductor.
Intent: There are three forms of MC cable: (a) spiral interlocked metal sheath, (b) smooth metal sheath, and (c) corrugated metal sheath. The change to this section makes it clear that interlocked metal MC cable (which looks like flex with wires) is not listed as an equipment grounding conductor, and it must contain an internal equipment grounding conductor. However, the sheath of smooth or corrugated tube MC cable (which is rarely used) is suitable for equipment grounding. But an internal equipment grounding conductor is not required within this type of cable. The metal armor of MC interlocked cable is not suitable as a fault current path, so an equipment grounding conductor is required.250.148 Continuity and Attachment of Equipment Grounding Conductors to Metal Boxes
Where circuit conductors are spliced, or terminated on equipment within a box, any separate equipment grounding conductors associated with those circuit conductors must be spliced or joined within or to the box with devices suitable for the use. Splices shall be made in accordance with Sec. 110.14(b) except that insulation shall not be required. The arrangement of grounding connections shall be such that the disconnection or the removal of a receptacle, fixture, or other device fed from the box will not interfere with or interrupt the grounding continuity.
Exception: The equipment grounding conductor permitted in Sec. 250.146(D) is not required to be connected to the other equipment grounding conductors or to the box.
Intent: The revised text clarifies that equipment grounding conductors are only required to terminate to the box if the circuit conductors terminate to equipment within the box or if they are spliced within the box.Art. 285 - Transient Voltage Surge Suppressors (TVSS)
The Code panel added a new Article to cover the installation requirements for transient voltage surge suppressors (TVSS). A TVSS is a listed protective device that limits transient voltages by diverting or limiting surge current.
Intent: Art. 280 in the 1999 NEC contained the installation requirements for “surge arresters,” which are installed at service equipment (main disconnect). However the Code did not include any rules for TVSS devices, which are typically installed at panelboards. The new Article does not apply to devices that incorporate a TVSS device, such as cord-and-plug connected TVSS units, a receptacle, or an appliance that has integral TVSS protection.
285.1 Scope. This Article covers the installation and connection requirements for TVSSs that are permanently installed on premises wiring systems.
A TVSS must be a listed device.
TVSSs are currently tested to UL 1449 2nd edition.
285.6 Short Circuit Current Rating. TVSSs must be marked with their short circuit current rating, and they cannot be installed where the available fault current is in excess of that rating.
TVSSs installed on the load side of service equipment are susceptible to high fault currents when near service equipment. TVSSs not listed for the available fault current present a hazard.
285.12 Routing of Connections. The conductors for the TVSS must not be any longer than necessary and unnecessary bends should be avoided.
285.21 Connection. Where a TVSS is installed, it must be connected as follows:
(1) Service Supplied Building or Structure. A TVSS can be connected anywhere on the premises wiring system, but not on the line side of service disconnect overcurrent device.
Ensure no more than one conductor terminates to a terminal, unless it is identified otherwise, according to 110.14(A).
Exception: If the TVSS is rated as a surge arrester, the TVSS can be connected to the line side of the service overcurrent device.
TVSSs are listed to be located only on the load side of service equipment, because there is concern they might be exposed to lightning-induced surges if installed on the line side. Because surge arresters are tested to a more stringent standard (ANSI/IEEE C62.41), they can be installed on the supply (line) side of service equipment [230.82(3)].
(2) Feeder Supplied Building or Structure. A TVSS can be connected anywhere on the premises wiring system, but not on the line side of the building or structure disconnect overcurrent device.
TVSS devices cannot be installed on the line side of the building or structure overcurrent device because there is concern that the TVSS devices might be exposed to lightning-induced surges.
(3) Separately Derived System. A TVSS can be connected anywhere on the premises wiring of the separately derived system, but not on the line side of the separately derived system overcurrent device.
This analysis is excerpted from the author's book, Mike Holt's Illustrated Guide to Code Changes Based on the 2002 National Electrical Code. For more info, see www.mikeholt.com.
Editors' Note: We will continue our analysis of the most important changes to the 2002 NEC next month in Part 2.
|312||373||Cabinets and Cutout Boxes|
|324||328||Flat Conductor Cable|
|342||345||Intermediate Metal Conduit|
|344||346||Rigid Metal Conduit|
|348||350||Flexible Metal Conduit|
|350||351A||Liquidtight Flexible Metal|
|352||347||Rigid Nonmetallic Conduit|
|358||348||Electrical Metallic Tubing|
|362||331||Electrical Nonmetallic Tubing|
|372||358||Cellular Concrete Raceway|
|374||356||Cellular Metal Floor Raceway|
|384||352C||Strut-Type Channel Raceways|
|386||352A||Surface Metal Raceways|
|388||352B||Surface Nonmetallic Raceways|
|396||321||Messenger Supported Wiring|
|398||320||Open Wiring on Insulators|
For more information on Code changes or for any questions on the Code, visit www.mikeholt.com.