Article 110—Requirements for Electrical Installations; Article 210—Branch Circuits; Article 250—Grounding and Bonding; Article 314—Outlet, Device, Pull, and Junction Boxes; Conduit Bodies; Fittings; and Handhole Enclosures; Article 682—Natural and Artificially Made Bodies of Water; Article 695—Fire Pumps; Article 700—Emergency Systems; Article 701—Legally Required Standby Systems, Annex G. The 2006 Guide Information for Electrical Equipment (White Book) published by Underwriters Laboratories Inc is also mentioned.
Q: A homeowner has a pond with a small island. He wants to provide a fountain on the island. Does the National Electrical Code (NEC) recognize any wiring methods that are suitable for this application? What type of wire insulation is required for this submerged conduit?
A: Article 682—Natural and Artificially Made Bodies of Water applies to this installation as well as articles that apply to the wiring methods used. Schedule 80 PVC conduit should be used for direct burial in the soil below the water. Multiconductor UF cable should be a suitable cable in PVC conduit for this application, but check with the cable manufacturer to make sure the cable is suitable for submersion.
According to the 2006 edition of the Guide Information for Electrical Equipment (White Book) published by Underwriters Laboratories Inc., submersible water pump cable is a multiconductor cable with 2, 3 or 4 conductors. It is a UF cable in a flat or twisted conductor assembly and available in sizes from 14 AWG to 4/0 AWG copper or 12 AWG to 4/0 AWG aluminum or copper-clad aluminum. The UF cable and PVC conduit must be installed in accordance with Article 340 for UF cable and Article 352—Rigid Nonmetallic Conduit: Type RNC. An insulated 12 AWG or larger copper conductor must be included in the cable assembly to comply with 682.30, and an equipotential plane must be provided if required by 682.33.
Q: Is a ground-fault circuit interruptor (GFCI) receptacle required by 210.63 when an outdoor air conditioning unit is replaced at a commercial property?
A: The answer is generally no, but it is a decision that should be made by the authority having jurisdiction (AHJ). The National Electrical Code is not retroactive, and unless the AHJ judges that a hazard exists because a GFCI protected 15- or 20-ampere, 125-volt receptacle is not installed within 25 feet of the air conditioning, the answer is no.
Although Annex G Administration and Enforcement is not an enforceable part of the NEC, it contains information that is useful in this particular instance. Existing installations are mentioned in 80.9(B), and part of it reads, “Existing electrical installations that do not comply with the provisions of this Code shall be permitted to be continued in use unless the authority having jurisdiction determines that the lack of conformity with this Code presents an imminent danger to occupants.”
I do not believe that the lack of GFCI-protected receptacle at an air conditioner is an imminent danger to occupants.
Q: Do box extensions have to be flush with the wall surface, or can they be recessed? If they can be recessed, is there a maximum recessed depth?
A: Yes, box extensions have to be flush with the wall surface where combustible material is used for the surface finish. The answer is no where the wall-finish is noncombustible.
The requirements for the location of boxes in walls and ceilings are in 314.20: “In Wall or Ceiling. In walls or ceilings with a surface of concrete, tile, gypsum, plaster, or other noncombustible material, boxes employing a flush-type cover or faceplate shall be installed so that the front edge of the box, plaster ring, extension ring, or listed extender will not be set back of the finished surface more than 6 mm (0.25 in).
“In walls and ceilings constructed of wood or other combustible surface material, boxes, plaster rings, extension rings or listed extenders shall be flush with the finished surface or project therefrom.”
Q: Where there is no grounding electrode for a feeder and disconnect switch at a second building, is one ground rod adequate for grounding this equipment?
A: Requirements for grounding this equipment are located in 250.32. Part (A) requires a grounding-electrode system at the building served. And part (B) requires that an equipment-grounding conductor be included with the feeder conductors. The equipment-grounding conductor may be rigid metal conduit, intermediate metal conduit, electrical metallic conduit or any other type of equipment-grounding conduit recognized in 250.118. Where the equipment-grounding conductor is a wire, its size must conform with Table 250.122. The feeder-grounded conductor (may be a neutral conductor) must be isolated from the panel enclosure and equipment-grounding conductor at the building served.
Where an equipment-grounding conductor is not part of the feeder, and there are no continuous metallic paths between the two structures, and ground-fault protection is not installed on the supply side of the feeder, the feeder-grounded circuit conductor is permitted to be grounded by connection to the grounding electrode(s) at the building served. The grounded-feeder conductor cannot be smaller than calculated as required by 220.64 or Table 250.122.
A proposal for the 2008 edition of the National Electrical Code to delete permission to reground the feeder-grounded conductor at the building served was accepted in principle. Code Making Panel 5 modified the proposal by making an Exception to 250.32(B)(2), which would allow grounding the grounded conductor in the feeder in “existing premises wiring systems only, new or existing structures only.” This is another effort to reduce multipoint grounding of the grounded-circuit conductor in premises wiring systems.
The answer to the question (are two ground rods required if one has a resistance of more than 25 ohms?) is yes. As required by 250.56, a driven rod that has a resistance of more than 25 ohms must be augmented by an additional electrode, which may be a second rod driven at least 6 feet away from the first rod.
Q: Are recessed luminaires (lighting fixtures) permitted in the ceiling above a bath tub? The ceiling is 8 feet above the floor. If the answer is yes, must they be protected by a GFCI?
A: There is no requirement in the NEC for GFCI protection for recessed luminaires (lighting fixtures) installed in the ceiling above a bath tub in a dwelling unit. However, there is a requirement for GFCI protection for a receptacle that is part of a luminaire (lighting fixture) installed in a bathroom of a mobile home or manufactured home. The luminaire (lighting fixture) must be marked “suitable for damp locations” or “suitable for wet locations” where subject to water spray.
If the luminaire (lighting fixture) manufacturer specifies ground-fault circuit interrupter protection for the luminaire (lighting fixture), GFCI protection must be provided by the electrician making the installation to comply with 110.3(B) of the National Electrical Code.
Q: I installed a 20-ampere dedicated branch circuit for a microwave oven in the kitchen of a one-family dwelling unit. This circuit was terminated in a 15-ampere duplex receptacle in the cabinet space. The electrical inspector asked for a single 20-ampere receptacle for this branch circuit. Is this required by the Code?
A: A “dedicated branch circuit” is not defined in the NEC. An individual branch circuit is defined in Article 100 as one that supplies only one utilization equipment.
The 15-ampere duplex receptacle is permitted on the 20-ampere branch circuit by 210.21(B)(3) where the maximum cord-and-plug-connected load does not exceed 12 amperes. This load may be increased to 16 amperes where 20-ampere receptacles are used.
The ampere rating of the individual branch circuit cannot be less than the marked ampere rating on the appliance, and the microwave oven must be protected from overcurrent in accordance with the full load current marked on the nameplate. The only reason for requiring a 20-ampere receptacle that I can think of is the microwave oven has a nameplate load current greater than 12 but not more than 16 amperes.
Q: We have a job to install an emergency generator in a large office building. Where should the generator, feeders, transfer switch and panelboard be located to comply with all codes?
A: NFPA 110 has some requirements for the location of components of the emergency system in addition to the National Electrical Code in Article 700—Emergency Systems. Emergency equipment must be designed and located to minimize the hazards that might cause complete failure due to flooding, fires, icing and vandalism. Where emergency equipment is located in occupancies that can accommodate more than 1,000 people or in a building above 75 feet in height with assembly, educational, residential, detention, correctional, business and mercantile occupancies, the equipment must be installed in spaces that are fully protected by approved automatic fire suppression systems or in spaces with a one-hour fire rating.
Transfer switches must comply with 700.6, and emergency generators must meet the requirements of 700.12(B).
Q: Is a tap ahead of the service-disconnecting means of a legally required standby service acceptable as the power source for an electric motor-driven fire pump?
A: Yes, provided that all the requirements in Article 695—Fire Pumps and Article 701—Legally Required Standby Systems are satisfied. A separate service for the legally required system is permitted by 701.11(D). The service for the fire pump must be from a connection located ahead of and not within the same cabinet, enclosure or vertical switchboard section as the legally required service-disconnecting means. The tap ahead of the legally required service-disconnecting means must be capable of delivering locked rotor current of the fire pump motor indefinitely and adhere to the voltage-drop requirements of not more than 15 percent of controller-rated voltage during starting and not more than 5 percent of motor nameplate voltage when operating at 115 percent of motor nameplate full-load current. EC
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.