Article 110 Requirements for Electrical Installations; Article 210 Branch Circuits; Article 225 Outside Branch Circuits and Feeders; Article 250 Grounding and Bonding; Article 338 Service-Entrance Cable: Type SE and Types USE; Article 396 Messenger-Supported Wiring; Article 404 Switches; Article 408 Switchboards and Panelboards
Portions of the 2007 edition of the Guide Information for Electrical Equipment (White Book) published by Underwriters Laboratories Inc. also are mentioned.
Type SE cable underground
Is service-entrance (Type SE) cable-permitted to be installed underground in rigid metal conduit?
No, it is not. New Section 338.12 in the 2008 National Electrical Code (NEC) includes a list of prohibited uses of service-entrance cable, and Item 2 says Type SE cable cannot be used underground with or without a raceway.
Is the insulated equipment-grounding conductor that supplies isolated-grounding receptacles suitable for grounding metal boxes that contain the isolated-ground receptacles? This grounding conductor is not required to be connected to panelboard enclosures by 250.146(D), but does not mention boxes or other enclosures. Clarification is requested.
The insulated equipment-grounding conductor that is used to ground the terminal on an isolated-grounding receptacle should not be used to ground anything except the receptacle.
A sentence has been added at the end of Section 250.146(D) to clarify the use of this insulated equipment-grounding conductor and is new in the 2008 edition of the NEC. It reads, “Where installed in accordance with the provisions of this section, this equipment-grounding conductor shall also be permitted to pass through boxes, wireways, or other enclosures without being connected to such enclosures.”
Where the branch-circuit wiring method does not include an equipment-grounding conductor, one must be provided to ground metal boxes and metal enclosures.
Grounding of panelboards is covered by 408.40, and the exception allows the insulated equipment-grounding conductor that supplies insulated ground-type receptacles to pass through a panelboard without making a connection to the panelboard equipment-grounding conductor terminal bar.
Please explain the changes made in the requirements in arc-fault circuit interrupters (AFCI) in the 2008 NEC.
Code-Making Panel Number 2 studied and reviewed at least 49 proposals to modify or remove the requirements for arc-fault circuit interrupters (AFCIs) as covered by 210.12 in the 2005 edition of the NEC. Some proposals were to remove Section 210.12 from the NEC. Some requested no change except for deletion of the second paragraph in 210.12(B) in the 2005 edition, which reads, “Branch/feeder AFCIs shall be permitted to be used to meet the requirements of 210.12(B) until January 1, 2008.” And others supported expansion of the requirement for AFCI protection to other rooms in dwelling units or other occupancies. For example, proposals were received to include dormitories, lodging and rooming houses and similar occupancies to require AFCI protection.
Code-Making Panel Number 2 accepted these words at the end of the proposal period: “210.12(B). All 120 volt, single-phase 15- and 20-ampere branch circuits installed in dwelling units shall be protected by a listed arc-fault circuit interrupter combination type installed to provide protection of the branch circuit.”
During the public comment period, Code-Making Panel No. 2 reviewed, discussed and acted on 67 comments. In addition to those that recommended accepting or rejecting some of the proposals, others suggested expanding the requirements for AFCI protection to existing residential installations where the electric service to the structure is increased and a modification to the proposal that was accepted during the Code-Making Panel meeting to review and act on proposals. The accepted proposal was changed during the comment period to require AFCI protection in dwelling unit family rooms, dining rooms, living rooms, parlors, libraries, dens, bedrooms, sun rooms, recreation rooms, closets, hallways, or similar rooms or areas. These rooms are similar to those mentioned in 210.52(A) except for the kitchen that is not mentioned, and the addition of closets and hallways were added. Notice that garages, bathrooms and outdoor locations are not included.
Additional changes in 210.12 include permission to eliminate AFCI protection for fire alarm circuits where the wiring method to the first outlet is installed in metal raceways, such as rigid metal conduit, intermediate metal conduit, electrical metallic tubing, or Type AC cable with steel armor. Metal outlet and junction boxes also are required to remove the requirements for AFCI protection.
Fine Print Notes 2 and 3 point out requirements for power supplies to fire alarm systems. Two sections in Article 760—Fire Alarm Systems prohibit AFCI protection for the power supply.
May the bare messenger in a messenger--supported wiring assembly be used as a neutral in a 120/240-volt single-phase feeder service? Service-entrance cable will be used.
Yes, provided that the installation meets all requirements of Article 396—Messenger-Supported Wiring and related regulations. Where installed outdoors, the insulated conductors must be suitable for wet locations and sunlight resistance.
An exception to 225.4 allows a bare grounded circuit conductor for outdoor wiring under limited conditions. Overhead clearances also must be met. See Article 225—Outside Branch Circuits and Feeders and Article 230—Services. There are many sections that must be considered for an installation of messenger--supported wiring for services and feeders.
Bonding metal water piping
Is it permissible to bond the interior copper water pipe in a single-family dwelling to the equipment-grounding terminal bus in a feeder panel, or must the grounding connection be made at the service panel? The interior copper water pipe is supplied by underground plastic pipe.
The ungrounded interior metal water pipe can be grounded to comply with 250.104(A) by installing a bonding conductor from the water pipe to the service--equipment enclosure, the grounded conductor at the service, the grounding-electrode conductor where of sufficient size, or to one or more of the grounding electrodes used. The bonding jumper cannot be installed from the water pipe to the feeder panel-board equipment-grounding terminal bar. The bonding jumper must be sized to comply with 250.66
Another recognized method for bonding the interior metal water pipe is in 250.104(B). This part recognizes another method for bonding the water piping to the grounding-electrode system. This method in 250.104(B) enables the branch circuit that supplies electrical equipment connected to the water piping system to allow the equipment-grounding conductor of the branch circuit supplying the equipment to serve as the bonding conductor for the water pipe. Regardless of the method used, the connections of the bonding jumper must be accessible at both ends.
Receptacle GFCI protection
Does a receptacle connected to a 120-volt, 20-ampere receptacle installed outdoors for a pump at an office building require GFCI protection?
The answer is probably yes. A revision to 210.8(B) changes the requirement for outdoor receptacles in 210.8(B)(4). Item (4) in 210.8(B) was revised, and an exception was added to recognize an assured equipment--grounding conductor program in lieu of a GFCI-protected receptacle in industrial establishments where qualified people maintain the equipment. A lack of power at the receptacle could create a greater hazard. If the installation does not meet this requirement, AFCI protection is required.
Two-pole snap switches
Is it permissible to use a two-pole snap switch to control an exhaust fan and a ceiling light in a bathroom in a commercial building? Both circuits are 20 amperes, 120 volts.
The answer is no unless the switch is marked for two-circuit use. Part (C) of 404.8 was added to the 2008 edition of the NEC and reads, “Multipole Snap Switches. A multipole, general-use snap switch shall not be permitted to be fed from more than a single circuit unless it is listed and marked as a two-circuit or three-circuit switch, or unless its voltage rating is not less than the nominal line-to-line voltage of the system supplying the circuits.”
In the 2007 edition of the White Book under the title Snap Switches (WJQR), the following information appears: “Multi-pole general-use snap switches have not been investigated for more than single circuit operation unless marked ‘2-circuit’ or ‘3-circuit.’”
A two-pole snap switch with a 240-volt rating also could be used.
How many equipment-grounding conductors are permitted to be connected in a single terminal in a service panel? How many grounded branch-circuit conductors are permitted to be connected to a single terminal on a neutral bus?
The maximum number of equipment-grounding conductors that may be terminated in a single terminal on the bus in the service panelboard is marked on the panelboard. If no marking is provided, the number of equipment-grounding conductors permitted in a single terminal is one.
There are requirements for the location of the equipment-grounding conductor termination as covered in 408.40. Part of this section indicates that equipment-grounding conductors cannot be connected to a terminal bar that is provided for grounded conductors or neutral conductors unless the bar is identified for the purpose and the panel-board is located where interconnection of the equipment-grounding conductor and neutral conductor is permitted by Article 250.
Each grounded conductor must terminate in an individual terminal within the panelboard. This requirement is in 408.41. An exception allows grounded conductors in parallel to terminate in a single terminal that is identified for acceptance of more than one conductor. Also, 110.14(A) contains this statement that limits wire terminals to a single conductor unless marked: “Terminals for more than one conductor and terminals used to connect aluminum shall be so identified.”
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.