The 1999 National Electrical Code is different in many ways. There were 4262 proposals submitted to amend the 1996 NEC, so you can expect significant revisions to the text. Plus, the new size of the book (8 inches by 11 inches) will provide more legible type and wider margins for notations. This series of articles will summarize the most important revisions found in the 1999 NE Code. Please keep in mind that we are currently preparing for the next Code revision (2002) by assembling proposals. Code proposals are important for all users of the NEC, and I hope more people will contribute during this next cycle.
Chapter 1-General
Article 100-definitions
Branch-Circuit Appliance. The last part of this definition was revised to eliminate a rule contained within a definition. The meaning of the definition is the same, but the rule that "such circuits are to have no permanently connected lighting fixtures not part of the appliance" is rewritten to make the correction.
Listed. This definition is modified. The old wording "equipment or material meets appropriate designated standards" is now replaced with "equipment or materials or services, and whose listing states that either the equipment, material, or service meets identified standards," etc.
Service. This term is revised to read, "the conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served." This clarification is meant to distinguish this definition from nonutility supply systems, which would typically be separately derived systems. This revision will correlate with the change to the definition of the term "feeder," which makes reference to the circuit conductors supplied from the service equipment, separately derived system, or other power source (possibly an on-site generator).
Service conductors. This definition no longer makes a reference to "other power source" to correlate with the revisions to the terms "service" and "feeder."
Article 110-Requirements for electrical installations
Section 110-10. A new last sentence was added to indicate that "listed products applied in accordance with their listing shall be considered to meet the requirements of this section." This section deals with the protection of equipment and materials from the extensive damage associated with short-circuits and ground-faults. This last sentence serves as an explanation to the revised wording of the definition itself. The term "short-circuit withstand rating" is revised to "short-circuit current rating." The intention here is that the circuit protective device will operate to clear a fault in a circuit in order to prevent a hazard, which is the intention of Section 90-1(c), but the equipment or material in the circuit may not be operational.
Section 110-16(a), exception No. 1. This section is revised to indicate that where rear access is not required to service energized components from the rear or "sides," no working space is required from the back or "sides."
Section 110-16(a). The second paragraph of this Section, which deals with the minimum depth, width, and height of the working clearance space, was separated into individual subsections. Section 110-16(a)(3) permits equipment associated with the electrical installation, such as an auxiliary gutter beneath a panelboard(s), to extend as much as 6 inches beyond the front of the equipment.
Section 110-16(f). This relocated Section from Section 384-4 covers the clear zone above switchboards, panelboards, and motor control centers. The clear zone extends from floor to a height of 6 ft above the equipment or to the structural ceiling, whichever is lower. No piping, ducts, or equipment foreign to the electrical installation is permitted in this zone, without additional physical protection to guard against spillage or leakage.
Section 110-34(f). The provisions of the old Section 710-9 are relocated here. (Article 710 was deleted in 1999.) This Section deals with protection against spillage or leakage from piping or ducts that are in the vicinity of service equipment, power switchgear, or industrial control assemblies where the voltage exceeds 600 V.
Section 110-36. Information is relocated from Section 710-32 regarding the installation of circuit conductors at over 600 V where the installation is accessible to qualified persons only. Part F of Article 710 regarding tunnel installations is relocated to part C of Article 110.
Chapter 2-Wiring and Protection
Section 200-6(a). The old exceptions in this Section dealing with the identification of the grounded circuit conductor are now included in the general text. Also, the identification of the grounded conductor of a multiconductor cable is included in a new Section 200-6(e).
Section 210-11. Information on the number of branch circuits for dwelling occupancies is provided here. This includes the small appliance circuits, the laundry circuit, and the bathroom circuit. Branch circuits supplying lighting and appliances are to be provided in accordance with the calculated load as per Section 220-3. Section 210-19(a). Information concerning the sizing of conductors serving continuous loads or portions of continuous and noncontinuous loads was moved here from the old Section 210-22(c). The provisions of this Section are not applicable if the overcurrent device has a listed continuous rating.
Section 210-20(a). Information regarding the rating of an overcurrent device serving continuous loads or portions of continuous and noncontinuous is relocated from the old Section 210-22(c). If the overcurrent device is designed to operate at 100% of its rating, this provision does not apply.
Section 210-52(c)(5). The provisions for installing receptacles for island and peninsular countertops are covered in this Section. The exception recognizes the installation of receptacles not more than 12 inches below the countertop. These provisions include construction for the physically impaired and where there are no means provided to mount receptacles within 18 inches above the countertop. Where located below the counter top in accordance with this Section, the top must not extend more than 6 inches beyond its support base.
Section 210-52(d). This Section requires at least one wall receptacle within 36 inches of the outside edge of each basin in dwelling units. In 1996, this Section specified that the bathroom receptacle outlets were to be supplied by a 20-A branch circuit, and this circuit was to supply no other outlets. This provision has been moved to Section 210-11(c) (3), exception and revised to indicate that outlets for other equipment may be supplied from this 20-A circuit, provided the circuit supplies only one bathroom. Sometimes bathroom exhaust fans are required to be GFCI protected in accordance with their listing; therefore, it would be normal to connect this equipment on the load side of a GFCI receptacle in the bathroom.
Section 210-52(g). At least one receptacle is to be installed in an unfinished basement of a one family dwelling unit, in addition to the laundry receptacle outlet. Sometimes portions of basements are finished and other portions remain unfinished. This requirement would reduce the use of extension cords in the unfinished portion.
Section 210-60. Receptacles in hotels and motels must be installed to meet the requirements of Section 210-52(a) for normal dwelling units. However, they may be located to be convenient for the permanent furniture layout. At least two of these receptacles must be readily accessible and if located behind the bed(s), the receptacle(s) shall be so installed to prevent the bed(s) from contacting any attachment plug, or the receptacle(s) must be provided with a suitable guard, such as a "bubble type" cover.
Section 210-70(a)(3). At least one lighting outlet containing a switch or wall-switch control is to be located in storage or equipment spaces in dwelling units. The point of control for the light is to be at the usual point of entry and the lighting unit is to be at or near the equipment requiring service.
Article 215-Feeders
Section 215-2. This Section covers the sizing of feeder conductors where continuous loads or portions of continuous and noncontinuous loads are supplied. This information was in Section 220-10(b) in 1996.
Section 215-3. This Section covers the rating of the overcurrent device for a feeder supplying continuous loads or portions of loads that are continuous and noncontinuous. Once again, this information was in Section 220-10(b) in 1996. Neither Section 215-2 nor 215-3 applies where the overcurrent device is listed for operation at 100% of its rating.
Section 220-3(b). This Section is rearranged to include-in separate numbered sections-the minimum load for each outlet for general-use receptacles and outlets not provided for general illumination.
Section 220-35. The title of this Section is revised to "Determining Existing Loads." The exception to Part 1 is revised. It states that where the maximum demand data for one year is not available, the maximum demand is permitted to be determined over a continuous 30-day period (measure of average power demand over a 15-minute period) using a recording ammeter or power meter connected to the highest loaded phase of the feeder or service. This is essentially the same exception as in 1996; however, the wording was modified.
Table 220-36. Drop the word "between" from the Table to make it clear that the lower and upper ranges of the load factors are included. This Table covers the optional method of calculating the load for new restaurants to determine the service or feeder size.
Article 225-Outside Branch Circuits and Feeders
Section 225-8(a). This Section now includes a similar reference as Section 230-2(a), which states that where more than one building or structure is on the same property and under single management, each building or structure is to be supplied by only one branch circuit or feeder. The same exceptions apply for emergency services, fire pumps, multiple occupancy type buildings, where the capacity requirements are in excess of 2000 A at up to 600 V, etc.
Section 225-8(b), (c), (d),(e),(f),(g). This section includes the location of the building disconnect; the six-switch rule; the grouping of multiple disconnects; additional disconnects remotely located for fire pumps or emergency systems; suitability as service equipment requirement; and the identification of the disconnecting means where more than one feeder, branch circuit, or service supplies a building; and all the pertinent exceptions.
Article 230-Services
Section 230-46. This section permits service entrance conductors to be spliced or tapped by clamped or bolted connections. The splice must be made in accordance with Sections 110-14, 300-5, 300-13, and 300-15. Section 230-204(a). An isolating switch with "visible break contacts" is to be installed ahead of the service disconnect at voltages above 600 V. The old exception is revised to eliminate the need for the isolating switch where the disconnect or circuit breaker is mounted on removable truck panels or metal-enclosed switchgear units that cannot be opened unless the circuit is disconnected and all energized parts are automatically disconnected when the switch or breaker is removed.
Section 230-205(c). For multi-building, industrial installations under single management supplied at medium voltages, the service disconnect is permitted to be remotely located and electrically operated by a readily accessible remote-control device.
Article 240-Overcurrent Protection
Section 240-3. The subsections are rearranged, and some new references are included, such as the definition of "tap conductor" in Part (e). Also, the protection of transformer secondary conductors is now referenced in Section 240-21(c). Section 240-20(B). Circuit breakers used to protect line-to-line loads must have internal common-trip mechanisms. Handle-ties are not acceptable for this purpose.
Section 240-21. The tap rule references are rearranged for clarity with the conductor tap rules coming first, followed by the transformer tap rules. Also, a reference is included indicating a tap conductor cannot be tapped. In addition, Section 240-21(c), which covers the protection of transformer secondary conductors, is modified to exclude the protection of the secondary conductors of a three-phase, three-wire, Delta-to-Delta connected transformer from being protected by a primary overcurrent device. This change was made because of the possibility of a significant overload on one secondary conductor in the event of a single-phasing condition on the primary side of the transformer.
Section 240-83(c). This Section permits circuit breakers installed on circuits with available fault currents above their interrupting ratings to be protected on the line side by a suitable current-limiting device that has been selected "under engineering supervision." This highly controversial concept could be useful in systems where the available fault current has increased to a value above the interrupting rating of the circuit breaker. However, if the circuit breaker begins to operate before the current-limiting device ahead of it reaches its current-limiting range, the breaker may experience a fault current significantly above its interrupting rating. This new Section is going to be difficult (if not impossible) to use based on present conditions.
Section 240-92(c): Six grouped overcurrent devices nearest the point of entrance of conductors.
Article 240-Part H
This new Part of Article 240 recognizes some special allowances for industrial installations with proper maintenance and supervision with respect to the application of overcurrent devices. A definition of "Supervised Industrial Installation" is given in Section 240-91. Also, the facility is to be supplied by at least one service that is more than 150 V-to-ground and not more than 300 V phase-to-phase and 2500 kVA of load or greater.
Section 240-92(B)(1). This Section recognizes a transformer secondary tap rule where only short-circuit and ground-fault protection is provided for the secondary conductors when they are limited to a 50 ft length and the primary overcurrent device does not exceed 150% of the value determined by multiplying the secondary conductor ampacity by the secondary-to-primary transformer voltage ratio.
Or; The length is limited to 75 ft and is protected by a differential relay with a trip setting equal to or less than the secondary conductor ampacity. Or: The length is limited to 75 ft and the conductors are provided with short-circuit and ground-fault protection where it is determined under engineering supervision that these conductors are protected within time vs. current limits for all short-circuit and ground-fault conditions.
Section 240-92(c). This Section covers the unlimited length tap rule for outside conductors where they are tapped to a feeder or transformer secondary. These secondary conductors are permitted to be terminated into as many as six grouped overcurrent devices that are an integral part of a switch or located immediately adjacent to the switch. The switch or switches are to be installed in a readily accessible location either outside the building or structure, or inside nearest the point of entrance of the conductors.
Article 250-Grounding
Article 250 is rearranged into group-related issues that should make the Article more usable. A cross-reference guide is provided in Appendix E as an aid in locating the material from 1996 to 1999.
Section 250-24(a) [old Section 250-23(a)]. This Section contains significant rewording thatserve to clarify the intent. The old exceptions of Section 250-23(a) have been rolled over into the general text.
Section 250-30. This Section covers the grounding of separately derived systems, and the rewrite is done well. The emphasis is on excluding multiple connections to ground from the grounded conductor of the separately derived system. Where the grounded conductor is used as a means of grounding the metal enclosure of the first disconnect or overcurrent device supplied from the separately derived system, as permitted by Section 250-142, there can be no parallel path established for the grounded conductor. The grounding electrode for the separately derived system shall be the nearest one of the following: an effectively grounded structural metal member of the structure, an effectively grounded metal water pipe within 5 ft from the point of entrance into the building, or other electrodes as specified in Sections 250-50 and 52 (where the first two electrodes are not available).
Section 250-32(b). Covers the condition where two or more buildings or structures are supplied from a common service. Once again, a rewrite serves to clarify the intent of this Section. If there are any continuous metallic paths bonded to the grounding electrode systems in both buildings, or if GFP has been provided on the common service, an equipment grounding conductor must be installed in the supply circuit between buildings. Also, if an equipment grounding conductor has been provided in this supply circuit for grounding any noncurrent carrying metal equipment in the second (or third, etc.) building, then a connection to ground from the grounded circuit conductor is not permitted. This would prevent objectionable currents from returning through these conducting paths.
Section 250-122. This Section addresses the size of an equipment grounding conductor. For multiconductor cables the size of the equipment grounding conductor may be based on the trip rating of the GFP where this protection has been provided. This provision would apply where the equipment grounding conductors of the multiconductor cables were smaller than normally required for parallel circuits. The GFP would have to be set to trip at no more than the ampacity of a single ungrounded conductor of the cables in parallel.
Chapter 3-Wiring Methods and Materials
Article 300-Wiring Methods
Section 300-3(c)(2)(e). Conductors having nonshielded insulation (Section 310-6, exception) and operating at different voltages are not to occupy the same enclosure, cable, or raceway.
Table 300-5. A change was made in the burial depth requirements for rigid and intermediate metal conduits "in or under airport runways" from 18 inches to 6 inches. This change is made to correct an error made in 1990 when a modification to the Table for directly buried cables or conductors was specified at 18 inches and the same dimension was applied for rigid and intermediate metal conduits.
Section 300-11(a). This Section is once again modified as it addresses the supports for cables and raceways by support wires. The change for 1999 here is that "support wires and associated fittings that provide secure support and are installed in addition to the ceiling grid support wires, shall be permitted as the sole support. Secure support in this sense means that these wires are secured on both ends, such as one to the structural ceiling and one to the grid. If the wiring is located in the cavity of a fire-rated floor/ceiling or roof/ceiling assembly, and these same independent support wires are used as a supporting means, they must be distinguishable from the support wires for the fire-rated ceiling assembly by color, tagging, or other effective means.
Section 300-14. This revision serves to clarify an issue with regard to the free length of conductors at an outlet, junction, or switch point. The 6 inches of free conductor is measured from where the conductors emerge from the conduit, tubing, or cable sheath. But, if the opening of the box is less than 8 inches in any dimension, the conductors must be longenough to extend at least 3 inches outside the box opening.
Section 300-22(c). This section was reworded for clarity. It addresses the wiring methods permitted in "other space used for environmental air," such as an air-handling ceiling space.
Section 300-37. EMT may be used to enclose above ground conductors of medium voltage circuits. Recently, UL has recognized EMT as acceptable in the medium-voltage range. Table 300-50. The information from the old Table 710-4(b) regarding the minimum burial depths for circuits of over 600 V can be now found here.
Chapter 3 continues next month.