AC and MC bushings

Q: Sections 320.17 and 330.17 indicate that Types AC and MC cables must be installed in accordance with 300.4, which includes protection of the cables by listed bushings or listed grommets that cover all metal edges of metal studs. There is no requirement for this protection for flexible metal conduit in Article 348. Is this an oversight? Should those requirements for Types AC and MC cables also apply to FMC?

A: A change in the 2005 edition of the National Electrical Code (NEC) makes it clear that bushings or grommets are not required where Types AC and MC cables are installed in holes or slots of metal framing members. The change in 320.17 and 330.17 removes part (B) of 300.4 from the requirement for protection of the cables.

This is what 320.17 says: “Through or Parallel to Framing Members. Type AC cable shall be protected in accordance with 300.4(A), (C), and (D) where installed through or parallel to framing members.” This same revision was made to 330.17. Part (B) of 300.4 has this requirement: “Nonmetallic-Sheathed Cable. In both exposed and concealed locations where nonmetallic-sheathed cables pass through either factory or field punched, cut, or drilled slots or holes in metal members, the cable shall be protected by listed bushings or listed grommets covering all metal edges that are securely fastened in the opening prior to installation of the cable.”

I believe that similar requirements to those in 300.4(A), (C), and (D) should apply to flexible metal conduit because this wiring method must be protected from physical damage. Type FMC is not permitted, by 348.12(7), where subject to physical damage.

Apartment receptacles outdoors

Q: Is it permissible to install outdoor receptacles for a six-unit apartment building from a “house” panelboard or must these receptacles be supplied from each individual dwelling unit panelboard? How many receptacles are required? If more than one receptacle is required, how many receptacles are permitted on a single branch circuit?

A: In the 2005 NEC, a second paragraph was added to 210.52(E) that reads: “For each dwelling unit of a multifamily dwelling where the dwelling unit is located at grade level and provided with individual exterior entrance/egress, at least one receptacle outlet accessible from grade level and not more than 2.0 m (6.5 ft.) above grade shall be installed.”

Although the number of receptacles is not mentioned, each tenant should have access to at least one outdoor receptacle. This may require more than one outdoor receptacle. However, there is no limit to the number of receptacles that may be installed on a single branch circuit because there is no unit load assigned to general use receptacles installed in dwellings units. These receptacles may be supplied from the house-meter service.

Depending on the number of branch circuits, all 125-volt, 15- and 20-ampere outdoor receptacles provided for dwelling units must be protected by one or more ground-fault circuit interrupters. This requirement is in 210.8(A)(3).

Panelboards above stairways

Q: An electrical inspector turned my job down because I located a branch circuit panelboard on a wall above the stairs to the second floor in a single-family dwelling. What section of the NEC prohibits this installation? Is there anything in the Code that requires the working surface to be flat and level? What are the minimum dimensions for this working surface?

A: I answered a similar question on this subject in a previous column. In the answer I stated that although there were no dimensions in the NEC for the size of working surfaces in front of switchboards and panelboards, a relatively flat surface equal to the minimum working depth listed in Table 110.26(A)(1) and width mentioned in 110.26(A)(2) should be provided to ensure that an electrician working on energized equipment does not have to be concerned about standing on an uneven or narrow surface.

In the past, Code-making panel No. 1 has rejected proposals that have advocated a level work area below electrical equipment. It is not necessary to have a level surface, but the surface should be relatively flat but may slope to a drainage ditch or storm drain.

Dishwasher disconnect switches

Q: Does the on/off switch on a dishwasher installed in an apartment building require a separate disconnect within sight of the appliance?

A: Where the dishwasher is permanently connected to the premise-wiring system, a branch circuit switch or circuit breaker is required within sight or it must be capable of being locked in the off position [see 422.31(B)].

If the appliance is connected to an accessible receptacle with a flexible cord and has a unit switch with an “off” position, another disconnect is required, and the location is determined by the number of dwelling units in the building.

In a multifamily dwelling, the other disconnect for the dishwasher may be located inside or outside of the dwelling unit in which the appliance is installed. Where there are more than two dwelling units in the building, the other disconnecting means must be within the dwelling unit or on the same floor as the dwelling unit in which the appliance is installed. These requirements appear in 422.34(A) and (B).

Track lighting calculations

Q: How are branch-circuit and feeder load calculations made for 120-volt, and three-wire, 120/240-volt track lighting?

A: Load calculations for track lighting are based on the length of the track. No load calculations apply to lighting track installed in dwelling units or in guest rooms or guest suites in hotels and motels, but in other occupancies, a load of 150 volt-amperes for each two feet or fraction thereof of lighting track must be added to the feeder and service only. Therefore, the length of track permitted on a branch circuit is not limited.

For example, a 15-ampere branch circuit could supply 36 feet of 120-volt lighting track. This design or one that is similar is often used in museums where very few lamps are connected to the lighting track to highlight temporary exhibits. For this installation, a feeder and service load of 36 divided by 2 times 150 would be added to the calculated loads. Although 2,700 volt-amperes are added to the feeder and service, only one 15-ampere, 120-volt circuit is provided for the track lighting.

For 120- to 240-volt multiwire track, a load of 300 volt-amperes is added to the feeder and service calculations for each two feet or fraction thereof of lighting track. This interpretation of the language in 220.43(B) is based on 210.4, which reads in part: “A multi-wire circuit shall be permitted to be considered as multiple circuits.”

This reference is in contrast with Article 225—Outside Branch Circuits and Feeders, which recognizes a multiwire branch circuit as a single circuit.

Since the actual lighting load can vary over time, the branch circuit overcurrent device must protect the track from overloading. Limiting the length of lighting track on a branch circuit does not guarantee that the track will not be overloaded, and therefore, is not required.

Relamping wet-niche lighting fixtures

Q: Is there a rule in the NEC that requires a minimum length of flexible cord on a wet-niche lighting fixture in a swimming pool to allow relamping by removal of the lamp housing from the pool wall to the deck?

A: Yes, there is. Requirements for the installation of underwater luminaires (lighting fixtures) in swimming pools are covered in 680.23. Generally, a wall-mounted luminaire (lighting fixture) must be installed a minimum of 18 inches below the normal water level and must be removable from the water for relamping and normal maintenance without disconnecting any wires from the power source. This sentence appears in 680.23(B)(6) under the title, “Servicing. Luminaires shall be installed in such a manner that personnel can reach the luminaire for relamping, maintenance, or inspection while on the deck or equivalently dry location.”

To satisfy this requirement, about six feet of flexible cord is supplied and connected to the luminaire (lighting fixture) housing. There is enough space in the forming shell for storage of the flexible cord.

Optional standby generators

Q: An optional standby generator will be connected into the premise-wiring system as a separately derived system through a four-pole transfer switch. Is the grounding-electrode conductor size based on Table 250.66 or Table 250.122? Where the generator is outdoors, are disconnects and overcurrent protection required where the conductors enter the building? How many disconnects are permitted? Must the disconnects be marked “suitable for use as service equipment?”

A: The size of the grounding- electrode conductor is based on Table 250.66. This information is in 250.30 (A)(3). A separately derived optional standby generator is required by 702.10 to be grounded.

Article 445—Generators generally requires overcurrent protection in the form of circuit breakers or fuses, and 445.18 requires one or more disconnects for the generator. Up to six disconnects are permitted for the generator by 225.30(A), 225.31 and 225.33. These disconnects must be grouped at one location and must be marked “suitable for use as service equipment” (see 225.36). EC

FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.