Article 210 Branch Circuits; Article 250 Grounding and Bonding; Article 300 Wiring Methods; Article 330 Metal Clad Cable: Type MC; Article 404 Switches; Article 422 Appliances; Article 450 Transformers and Transformer Vaults Including Secondary Ties; Article 590 Temporary Installations; Article 690 Solar Photovoltaic Systems; Portions of the 2007 edition of the Guide Information for Electrical Equipment (White Book), published by Underwriters Laboratories Inc., also are mentioned.
Neutral conductor for grounding
I installed a feeder to a new two-car garage, which also contains a clothes washer and electric clothes dryer. Three conductors were used as the feeder, and the neutral conductor of this 120/240 volt, single-phase feeder was used to ground the system at the garage. There is no metal of any kind that is connected to both buildings, but the electrical inspector turned the job down and said I could not use the neutral to ground the equipment in the garage. Is this a change in the 2008 edition of the National Electrical Code (NEC)?
The 2005 edition of the NEC and previous editions allowed grounding the neutral at another structure or building provided there was not metal interconnecting the two buildings or structures and ground-fault protection was not provided. This method of grounding is no longer permitted in the 2008 edition. The grounded-feeder conductor cannot be used to ground enclosures and other electrical equipment at the building or structure. Part (B)(2) of 250.32 has been removed from the 2008 edition. This was the part of 250.32(B) that allowed regrounding the grounded-circuit conductor (neutral). An exception now appears in part (B) that allows the grounded-circuit conductor to ground equipment in the building or structure in existing installations only.
The size of the equipment-grounding- conductor cannot be smaller than given in Table 250.122 and must be included with the feeder conductors. For a 50-ampere feeder, the equipment-grounding conductor cannot be smaller than 10 AWG copper. However, it can be one of the wiring methods in 250.118 that are listed as suitable for grounding.
The grounded-circuit conductors in the feeder and branch circuits cannot be connected to the equipment-grounding conductor. One sentence in part (B) reads, “Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode.”
Wire ties for multiwire branch circuits
I installed a few multiwire branch circuits using Type MC cable in double barrel connectors. The electrical inspector said I must use wire ties to separate the multiwire branch circuits. Does the 2008 edition of the NEC require this?
Under the title “Multiwire Branch Circuits” in 210.4, a new requirement appears in part (B), which reads, “Grouping. The ungrounded and grounded conductors of each multiwire branch circuit shall be grouped by wire ties or similar means in at least one location within the panelboard or other point of origination.” Where a single multiwire branch circuit enters a panelboard through a single connector, wire ties or other means are not required to identify the multiwire branch circuit.
Another change for multiwire branch circuits involves the disconnecting means. The 2008 edition requires a disconnecting means that will simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates. This change is in Part (B) of 210.4.
GFCIs for drinking fountains
Is there a requirement for ground-fault circuit interrupter (GFCI) protection of electrical drinking fountains in commercial occupancies?
Yes, there is a requirement for GFCI protection for electric drinking fountains in all occupancies. New Section 422.52 reads, “Electric Drinking Fountains. Electric drinking fountains shall be protected with ground-fault circuit-interrupter protection.”
Fine stranded conductors
Are there any requirements for the use of fine stranded conductors or connectors in solar photovoltaic systems?
Yes. A new part (F) has been added to 690.31 that points out restrictions that are placed on terminations of fine stranded conductors. New part (F) to 690.31 reads, “Flexible, Fine-Stranded Cables. Flexible fine-stranded cables shall be terminated only with terminals, lugs, devices, or connectors that are identified and listed for such use.” Termination fittings that are not marked for fine stranded conductors usually do not capture all of the strands on fine stranded conductors.
Use of multipole snap switches
Is there anything in the NEC that prohibits the use of a two-pole snap switch for controlling a 277-volt fluorescent luminaire and a 120-volt exhaust fan in a bathroom in a commercial building?
A new part (C) has been added to 404.8 that clarifies the installation of multipole snap switches, which reads, “Multipole Snap Switches. A multipole general-use snap switch shall not be permitted to be fed from more than a single branch circuit unless it is listed and marked as a two-circuit or three-circuit switch or unless the voltage rating is not less than the nominal line-to-line voltage of the system supplying the circuits.”
The 2007 edition of the Guide Information for Electrical Equipment Directory (White Book) published by Underwriters Laboratories Inc. contains this information among other things under the title “Snap Switch.” (W.SOR): “Multipole general use snap switches have not been investigated for more than single circuit operation unless worked ‘2-circuit’ or ‘3-circuit.’”
The voltage rating of the switch must be at least 277 volts, and the switch must be marked “2-circuit” or “3-circuit” to comply with 404.8(C).
Portable generator on construction site
Are 15- and 20-ampere, 125-volt receptacles required to have GFCI protection where supplied by a portable generator on a construction site? Does the neutral have to be grounded?
All 15-, 20- and 30-ampere, 125-volt receptacles supplied from the portable generator must have GFCI protection unless the construction site has only qualified individuals. When qualified individuals are on the site, an assured equipment-grounding conductor program is permitted, and GFCI protection is not required. This requirement is in 590.6.
The generator neutral does not have to be connected to a grounding electrode under the following conditions: “The generator supplies only equipment mounted on the generator, cord and plug connected equipment through receptacles mounted on the generator or both.” And the noncurrent-carrying metal parts of equipment and the equipment-grounding conductor terminals of the receptacles are connected to the generator frame.
Where receptacles are located remote from the generator, a grounding electrode must be provided. The neutral conductor of a three-wire, single-phase generator must be grounded to comply with 250.26(2). The grounding-electrode conductor must be connected to the neutral conductor of the generator and the grounding electrode. It must be sized to comply with 250.66. This requirement appears in 250.34(C).
Transformers in hollow spaces
May a 50 kilovolt-ampere, 120/208 volt, three-phase dry-type transformer be installed in the air handling space in the ceiling of an office building?
The answer is yes provided that the transformer has adequate ventilation to prevent the transformer from reaching its maximum temperature rating when delivering its rated output.
The installation of the wiring methods and transformer must be made so that the possible spread of fire or products of combustion will not be substantially increased to comply with 300.21.
In the air handling, ceiling wiring methods to and from the transformer are generally limited to metal raceways and metal cable assemblies. These include totally enclosed unventilated insulated busway with no provisions for plug-in connections, Type MI cable, Type MC cable without an overall nonmetallic covering, Type AC cable, or other factory-assembled multiconductor control or power cable that is specifically listed for the use or listed prefabricated cable assemblies of metallic manufactured wiring systems without nonmetallic sheath. Other types of cables, conductors and raceways shall be permitted to be installed in electrical metallic tubing, flexible metallic tubing, intermediate metal conduit, rigid metal conduit without an overall nonmetallic covering, flexible metal conduit, or where accessible surface metal raceway or metal wireway with metal covers or solid bottom metal cable tray with solid metal covers.
The transformer must meet the requirements of part (2) of 300.22(C)(2) which reads: “Equipment. Electrical equipment with a metal enclosure or with a nonmetallic enclosure listed for the use and having adequate fire-resistant and low smoke producing characteristics and associated wiring material suitable for the ambient temperature shall be permitted to be installed in such other spaces unless prohibited elsewhere in this Code.”
Branch circuit for microwave oven
Does the NEC permit a microwave oven to be supplied from a 15-ampere duplex receptacle protected by a 15-ampere branch circuit? The microwave oven has a nameplate load current of 13.6 amperes and is provided with a flexible cord and a 15-ampere, 125-volt attachment cap.
No, the cord and attachment cap (plug) must be changed to 20-amperes to comply with 210.21(B)(2) and Table 210.21(B)(2). This part of Section 210.21 limits the total cord-and-plug connected load on a 15-ampere receptacle to 12 amperes. Therefore, the 15-ampere cord and plug must be changed to 20-amperes, and the branch circuit must be 12 AWG copper, and the receptacle must have an ampere rating of 20-amperes.
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.