Article 210 Branch Circuits
Article 220 Branch-Circuit, Feeder, and Service Calculations
Article 230 Services
Article 250 Grounding
Article 404 Switches
Article 410 Luminaires (Lighting Fixtures) Lampholders, and Lamps
Article 445 Generators
Article 702 Optional Standby Systems
Volume I of the Fire Resistance Directory published by Underwriters Laboratories Inc. is also mentioned.
Branch circuit for a refrigerator
Q: May a 15-ampere, 125-volt branch circuit supply a refrigerator in a kitchen in an apartment building and also supply an under-counter refrigerator in the dining area?
A: The exception in 210.52(B)(1) limits the use of a 15-ampere branch circuit for refrigeration equipment to an “individual” branch circuit. And the definition of an Individual Branch Circuit as given in Article 100 is “A branch circuit that supplies only one utilization equipment.” Because the exception says, “The receptacle outlet for refrigeration equipment shall be permitted to be supplied from an individual branch circuit rated 15 amperes or greater,” additional outlets are not permitted on this 15-ampere circuit. This branch circuit should terminate on a single 15-ampere, 125-volt receptacle.
Although at least one member of the Code Panel responsible for Article 210 has said that it was not the intent of the panel to limit this branch circuit to a single receptacle, the use of the word “individual” along with the definition does restrict the branch circuit to a single outlet.
Some electrical inspectors will allow a duplex receptacle to be used for this branch circuit provided that the tabs connecting one receptacle to the other are broken off, and a plastic cap is inserted in the receptacle that is not energized.
If both refrigerators are to be supplied from the same branch circuit, use a 20-ampere circuit that can also supply other receptacle outlets in the kitchen and dining area. This circuit would be in addition to the two required by 210.11(C)(1).
Outlet boxes in fire-rated walls
Q: Are there any listed nonmetallic outlet boxes that can be used in a wall that separates a four-car garage from the living space of a two-family dwelling unit?
A: Yes, there are nonmetallic outlet boxes that have been tested and classified for fire resistance. A number of nonmetallic outlet box manufacturers have their boxes classified for Fire Resistance. A list of manufacturers and catalog numbers of boxes begins on page 960 of Volume I of the Fire Resistance Directory, 2001 edition. Nonmetallic outlet and switch boxes are generally classified for use in fire resistance walls constructed of wood or nonbearing steel studs and gypsum wallboard with a classification period of two hours or less. To maintain the integrity of the wall, clearance between boxes and cutouts in the wall cannot exceed 1/8 inch. The total area of openings in the wall cannot exceed 100 square inches in 100 square feet of wall, and the maximum single opening is limited to 21 to 28 square inches, depending on the product. Horizontal spacing between boxes also varies from one box manufacturer to another, and changes where some types of insulation is placed in the wall cavity.
For more information, consult a nonmetallic outlet box manufacturer or read the material starting on page 959 in Volume I of the 2001 Fire Resistance Directory published by Underwriters Laboratories, Inc.
Standby generator installation
Q: I am wiring a new home in an area where a city water system is not available. If a power outage occurs, there will be no water because an electric pump supplies water from a well. The owner is concerned, and has suggested that I provide an on-site generator for the well pump and other loads. Where do I find requirements for the installation of a generator in the National Electrical Code (NEC)? How do I size the generator?
A: The NEC classifies this generator as an Optional Standby System in Article 702. The Article applies to permanently installed and portable generators that can be connected to a premises wiring system. In addition to the requirements in Article 702, you must also comply with the rules in Article 445—Generators. This Article requires overcurrent protection for the generator. The feeder conductors from the generator terminals to the first overcurrent device must have an ampacity that is equal to or greater than 115 percent of the nameplate current rating of the generator. And live parts of generators operating at more than 50 volts to ground cannot be exposed to accidental contact.
Transfer equipment, either manual or automatic, must be provided to prevent inadvertent interconnection of the normal and standby power sources. This can be a transfer switch or double-throw safety switch with proper voltage and current ratings.
A sign is required at the service that indicates the type and location of the on-site generator. A sign is also required at the location where the generator grounded circuit conductor is connected to the grounding electrode system where this connection is remote from the generator. However, there is no requirement to separately ground the generator grounded circuit conductor is this conductor is not switched in the transfer equipment. These rules are in 702.8(A) and (B).
If the generator grounded circuit conductor (neutral) is switched with the ungrounded conductors of the generator at the transfer equipment, a separately derived system is created and 702.10(A) requires compliance with 250.30. If the neutral of the generator is not switched, part (B) of 702.10 applies, and the generator equipment grounding conductor must be bonded to the system grounding electrode.
To properly size the generator, the owner has to decide what loads will be operated simultaneously. Nonmotor loads should be calculated using nameplate volt-amperes. Motor loads may be calculated at 0.5 kVA per horsepower or 0.75 kVA per horsepower, or 1 kVA per horsepower depending on the method used for starting the motor and the characteristics of the motor-generated set. Rather than guess, a generator field representative or knowledgeable employee of a generator manufacturer should be consulted to determine the proper size of the generator.
Installing lighting track
Q: What parts of the NEC are used to calculate the branch circuit size and load for track lighting?
A: The size or rating of a branch circuit is determined by the ampere rating of the overcurrent device. This information appears in 210.3. The size or rating of the branch circuit is governed by the ampere rating of the track. Part of 410-101(B) has the statement: “Lighting track shall be supplied by a branch circuit having a rating not more than that of the track.” Therefore, the maximum rating for a branch circuit that supplies a 20-ampere track is 20 amperes.
No load is added for track lighting in dwelling units and guestrooms in hotels and motels. In all other occupancies a load of 150-volt-amperes is added to the feeder and service calculations for every 2 feet or fraction of track. (See 220.12.) For example, 33 feet of lighting track installed in a museum would add 2,250 volt-amperes of load to the feeder conductors and service-entrance conductors. Notice that this load calculation is the same whether the lighting track is 15-ampere, 20-ampere, or 30-ampere. Also, the load calculation does not limit the length of track that can be connected to a branch circuit. For example, 50 feet of lighting track can be connected to a 20-ampere branch circuit provided that the continuous load does not exceed 16 amperes.
Maximum height of service disconnecting means
Q: What is the maximum height for overcurrent protective devices and the disconnecting means for service equipment?
A: For services operating at 600 volts or less, the service disconnecting means must be readily accessible and located outside of a building or structure or inside at the nearest point of entrance of the conductors. Overcurrent devices must also be readily accessible. These requirements appear in 230.70(A)(1) and 240.24. However, there are some conditions that do not require that overcurrent devices be readily accessible.
All switches and circuit breakers used as switches must be readily accessible to comply with 404.8(A). The center of the grip or operating handle of the switch or circuit breaker cannot be more than 6 feet 7 inches above the floor or platform when in its highest position. The three exceptions do not apply to this question.
Application of these rules results in a maximum height of 6 feet 7 inches to the operating handle of the switch or circuit breaker used as the service disconnecting means.
Bonding liquid-tight flexible metal conduit
Q: A 2-inch liquidtight flexible metal conduit services a 15-horsepower, 208-volt, three-phase motor. The wiring method is rigid metal conduit. The length of liquidtight conduit is 4 feet. The electrician has installed a bonding conductor by wrapping it around the conduit about 12 times. I turned the job down. Was I right?
A: Yes you were. Wrapping the bonding jumper around the liquidtight flexible metal conduit increases the impedance of the ground return path. A bonding jumper installed on the outside of a raceway cannot exceed 6 feet in length. The arrangement described results in a bonding jumper that is more than 10 feet long. The 6-foot limitation is in 250.102(E). EC
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.254.2132.