Article 210 Branch Circuits
Article 220 Branch Circuits, Feeder and Service Calculations
Article 250 Grounding
Article 320 Armored Cable
Article 410 Luminaires (Lighting Fixtures), Lampholders and Lamps
Article 430 Motors, Motor Circuits and Controllers
Volume 1 of the Fire Resistance Directory is also mentioned.
Insulating bushings for armored cable
Q:Is it necessary to install anti-short bushings at all armored cable terminations where insulated-throat connectors are used?
A:No, it is not. Third-party recognized testing laboratory-certified insulated-throat connectors are a suitable substitute for anti-short bushings provided that they are the proper size and the cut end of the cable is pushed into the connector so that the armor is against the insulated throat. Armored cable connectors should be selected in accordance with the outside diameter of the cable along with the number and size of conductors in the cable assembly.
The National Electrical Code reference for insulating bushings is 320.40. Part of the reference reads as follows: “At all points where the armor of the AC cable terminates, a fitting shall be provided to protect wires from abrasion, unless the design of the outlet boxes or fittings is such as to afford equivalent protection, and, in addition, an insulating bushing or its equivalent protection shall be provided between the conductors and the armor.”
Disconnecting means for evaporator fan motors
Q:Is a disconnecting means required within sight of evaporator fan motors in a walk-in commercial freezer? The compressor and condenser motors are outdoors and each has a disconnecting means.
A:A disconnecting means is required to be within sight (visible and not more than 50 feet away) of the evaporator motors to comply with 430.102(B), unless the installation is covered by either of the exceptions and the authority having jurisdiction considers individual disconnecting means for these fan motors as impractical or increases the chance of damage to the refrigeration equipment.
Size of service conductors
Q:I would like to make a comment to the answer to the sixth question in the April 2003 issue of ELECTRICAL CONTRACTOR magazine. This question asks for the minimum size service entrance conductors to supply a 15A branch circuit that supplies a school zone warning light.
Although the answer is correct based on the National Electrical Code, I have never seen a meter socket that would allow 14 AWG copper or even 8 AWG, for that matter. Most meter sockets have a minimum requirement of 6 AWG to be terminated in its lugs.
I believe a comment to this would have given the person asking the question more information as to the minimum size of the service entrance conductors allowed, not by the NEC, but by the manufacturer.
A:I agree the answer was not complete because it was based solely on the requirements in the National Electrical Code. Meter sockets are generally designed to accept 6 AWG and larger conductors. Terminals in some meter sockets will not clamp tight on 14 AWG conductors. Therefore, if this limited load is required to have a meter by the serving utility, it may be necessary to increase the service entrance conductors to 6 AWG because of the lugs in the meter base.
Because this is a predictable load that is probably seasonal, the serving utility may choose to flat-rate the installation. If this is the case, the electrical contractor should find out from the utility if 14 AWG copper is acceptable. If not, install the minimum size wire that is acceptable.
Receptacles in wall spaces
Q:I am estimating an electrical job for an apartment building. There are two rooms in each dwelling unit that have 2.5-foot walls behind open doors. Are receptacle outlets required in these walls, since furniture cannot be located in these spaces?
A:There is a requirement in 210.52(A)(1) for a receptacle in this space. It reads: “Wall space. As used in this section, a wall space shall include the following: Any space 600mm (2feet) or more in width including space measured around corners and unbroken along the floor line by doorways, fireplaces and similar openings.”
This might be the only receptacle in the room that is not obstructed by furniture, and available for a vacuum cleaner, rug cleaner or floor scrubber.
Grounding the neutral of a transformer
Q:If I bond the secondary neutral of a 75kVA transformer to its enclosure and run a grounding electrode conductor from the transformer neutral to buried metal water pipe, am I permitted to use a panelboard marked “Suitable Only For Use As Service Equipment” as the secondary overcurrent protection?
A:You are not allowed to ground the neutral at the transformer and install the secondary conductors in a metal cable assembly or metal raceway and use a panelboard marked “Suitable Only For Use As Service Equipment” because the neutral bus in this panelboard is factory-bonded to its metal enclosure. Such an arrangement provides a parallel path for neutral current; one through the wiring method (metal cable assembly or metal raceway), and the other through the neutral conductor. The bonding jumper is required to be connected to the same point as the grounding electrode conductor to prevent parallel paths for neutral current. This requirement appears in 250.30(A)(1) and (2)(a).
Branch circuit rating for lighting track
Q:What part or parts of the National Electrical Code are used to calculate the branch circuit size for track lighting? Also, what is the maximum length of lighting track that can be connected to a branch circuit?
A:Requirements for the installation, construction and overcurrent protection for lighting track are in 410.100 through 410.105. The Ampere rating marked on the track determines the size of the branch circuit conductors and overcurrent protection. This requirement appears in part (B) of 410.101. The second sentence in this part says, “Lighting track shall be supplied by a branch circuit having a rating not more than that of the track.”
There is no limit to the length of track that is permitted on a branch circuit. Although there is a load calculation for lighting track in other than dwelling units and hotel and motel guest rooms, this load calculation is used to size the feeder and service-entrance conductors. A load of 150VA for every two feet of lighting track must be included when calculating the size of the feeder and service-entrance conductors. However, this Volt-Ampere calculation for the load does not limit the length of track that may be supplied by the branch circuit. For example, a 15A, 120V, single-phase branch circuit can deliver (15 x 120) 1,800VA. If it is assumed that the load calculation determines the length of track permitted on this branch circuit (1,800 x 2 divided by 150), 24 feet of track would be the maximum length. But this is not the case; the load calculation has nothing to do with the length of track that may be supplied by a single branch circuit, since the branch circuit overcurrent device protects the lighting track from being overloaded. In other words, the length of lighting track on a branch circuit is not limited. The load calculation to be used to determine the size of the feeder and service for track lighting is in 220.12(B).
Nonmetallic device boxes in fire-rated construction
Q:Are there any nonmetallic device boxes that are suitable for installation in fire-rated walls and ceilings?
A:Volume 1 of the 2003 edition of the Fire Resistance Directory published by Underwriters Laboratories Inc. has many nonmetallic boxes that are classified for Fire Resistance. Here are some examples of the information that is part of the classification for nonmetallic outlet and switch boxes for one manufacturer: “For use in fire resistance walls constructed of wood or nonbearing steel studs and gypsum board with classification periods of two hours or less. Clearance between boxes and cutouts in wall shall not exceed one-eighth inch. The area of openings for boxes shall not aggregate more than 100 sq. in. per 100 sq. ft. of wall or partition area with no opening exceeding 28.0 sq. in. Outlet and switch boxes on opposite sides of a wall or partition shall be supported by a horizontal distance of not less than 24 inches.”
A list of catalog numbers for nonmetallic boxes is followed with this information: “For use in fire resistance floor, ceiling assemblies consisting of wood floor, solid or pre-engineered wood joists or trusses and gypsum board ceiling with Classification periods of two hours or less. Clearance between boxes and cutouts in ceiling shall not exceed one-eighth inch. The area of openings for boxes shall not aggregate more than 26.5 sq. in. per 100 sq. ft. of ceiling area, with no opening exceeding 12.5 sq. in. No box shall be located within 4.5 ft. of another box.” As can be seen from these short excerpts, the requirements are very detailed and specific.
There are about 14 pages of various types of nonmetallic boxes produced by various manufacturers with different requirements as to the sizes of the openings for boxes, minimum spacing between openings, types of construction, etc. Look through the Directory and pick out boxes that satisfy your needs. EC
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.