Article 110 Requirements for Electrical Installations
Article 210 Branch Circuits
Article 230 Services
Article 240 Overcurrent Protection
Article 300 Wiring Methods
Article 342 Intermediate Metal Conduit: Type IMC
Article 352 Rigid Nonmetallic Conduit: Type RNC
Article 408 Switchboards and Panelboards
Article 430 Motors, Motor Circuits, and Controllers
Article 511 Commercial Garages, Repair and Storage
Q: Does a wall switch in a residential bedroom that controls an outside floodlight require arc-fault circuit-interrupter protection? The circuit that supplies the wall switch does not supply any loads in the bedroom. Do branch circuits that supply junction boxes in the bedroom require AFCI protection? These branch circuits do not supply any loads in the bedroom.
A: According to 210.12(B), arc-fault circuit-interrupters are required on all 15- and 20-ampere, 125V, single-phase outlets in dwelling-unit bedrooms. Notice that the requirement applies to "outlets," which are defined in Article 100: "Outlet. A point on the wiring system at which current is taken to supply utilization equipment." Since junction boxes and switches do not qualify as outlets, they are not required to have AFCI protection. Junction boxes and switches fit the definition of "device," which reads as follows: "Device. A unit of an electrical system that is intended to carry but not utilize electric energy."
Nonmetallic Conduit in a Parking Structure
Q: Does the NEC permit the use of rigid nonmetallic (PVC) conduit in a parking garage? The floor is concrete, and the walls are concrete block.
A: Article 511 covers Commercial Garages, Repair and Storage, which may apply to this installation. The scope of this article indicates that it applies to occupancies that are used for service and repair operations of passenger cars, buses, trucks, tractors and other vehicles that use flammable liquids of flammable gases for fuel or power. However, 511.3 indicates parking garages used for parking or storage where no repair work is performed except for exchange of parts and routine maintenance and do not require the use of electrical equipment, open flame, welding or the use of volatile flammable liquids are not classified. Because major repairs are generally not done in parking structures as described in the question, it is assumed that the building is not a classified location. Therefore, rigid nonmetallic conduit is a permitted wiring method, and the rules in Article 352-Rigid Nonmetallic Conduit: Type RNC apply. Where the conduit is installed and is subject to physical damage, Schedule 80 PVC is required to comply with 300.5(D)(4).
Protecting Secondary Conductors
Q: An electrical contractor installed a new 480Y/277V service and a transformer connected delta/wye for 208Y/120V circuits in an industrial office building. The distance from the transformer to the secondary distribution panel is about 17 feet. The panel contains 24 circuit breakers of various ratings without a main. Should a main be installed?
A: The question indicates this is an industrial office building, which I interpret to mean is an office building used in conjunction with an industrial plant. If the authority having jurisdiction determines this to be an industrial installation, a main circuit breaker in the secondary panelboard is not required provided all of the requirements in 240.21(C)(3) are satisfied. These are:
1. The secondary conductors do not exceed 25 feet in length
2. The ampacity of the secondary conductors is equal to or greater than the secondary current rating of the transformer
3. The sum of the ampere ratings of the secondary overcurrent devices does not exceed the ampacity of the secondary conductors
4. All secondary overcurrent devices are grouped
5. The secondary conductors are protected from physical damage. If the installation does not meet all of these requirements, a main circuit breaker or switch and fuses must be provided to comply with 240.21(C)(6).
To comply with 240.21(C)(6) the following rules apply:
1. The secondary conductors must have an ampacity that when multiplied by the ratio of the secondary-to-primary voltage is at least one-third the rating of the overcurrent device protecting the primary
2. The secondary conductors terminate in a single overcurrent device that limits the load current to not more than the ampacity of the conductors
3. The secondary conductors are protected from physical damage. As can be seen from these requirements, a main circuit breaker or switch and fuses ahead of the secondary panelboard depends on whether the electrical inspector classifies this installation as industrial or the panelboard is classified as a lighting-and-appliance or power panelboard.
Although 240.21 may not require individual overcurrent protection for the panelboard, one or two mains with overcurrent protection are probably required by 408.16 (A) or (B) to protect the panelboard.
Q: What has changed in the disconnect requirements for motors in the 2002 National Electrical Code? Some inspectors seem to be confused about lockable circuit breakers supplying motor branch circuits.
A: There were some changes in 430.102 for disconnecting means located in sight from motor controllers and motors. The requirement in 430.102(A) specifies that a disconnecting means be located within sight of the motor controller. There are two exceptions to this rule-one is for motors operating at more than 600 volts and the other is for several motors that drive a single machine. Part (B) of 430.102 requires a disconnecting means to be located within sight of the motor. An exception to this part (B) allows the disconnect to be out of sight from the motor where additional hazards are introduced and in industrial installations if the disconnecting means is capable of being individually locked in the off position. The exception further states the locking means must be permanently installed on or at the switch or circuit breaker. The language indicates the locking means must be permanently installed on the disconnect switch or circuit breaker and cannot be mounted on the trim of a circuit breaker panelboard.
Q: I am using intermediate metal conduit (IMC) to wire a machine shop. The ceiling is open bar joists and machines are located in open spaces around the floor. The only way to wire this equipment is from the ceiling joists down to the machines. The ceiling is 18 feet above the floor. Does the NEC require any intermediate supports between the bar joists and the disconnects located on the machines?
A: Probably not. Item (3) in 342.30(B) allows support for IMC to be increased to 20 feet under specific conditions. This is what the Code says: "Exposed vertical risers from industrial machinery or fixed equipment shall be permitted to be supported at intervals not exceeding 6m (20 feet), if the conduit is made up with threaded couplings, the conduit is firmly supported at the top and bottom of the riser, and no other means of intermediate support is readily available."
Service Disconnecting Means
Q: Where a 480Y/277V, 400-ampere, 3-phase, 4-wire service is metered through a self-contained meter in a meter socket, the utility company requires a disconnect switch ahead of the meter. The electrical contractor wants to provide a 400-ampere panelboard with a 400-ampere main on the inside wall of the building directly in back of the meter socket. The disconnect switch ahead of the meter has no overcurrent protection. Does this arrangement satisfy the National Electrical Code?
A: The disconnecting means located ahead of the meter is installed to allow utility personnel to remove the meter from the socket while the meter terminals are not energized. This is a safety issue. Also, the switch should not be operated under load.
Part (2) of 230.82 allows meter disconnect switches to be connected on the supply side of the service disconnect. Therefore, a 400-ampere circuit breaker in a panelboard is not a violation of 230.91, which requires service overcurrent protection devices to be an integral part of the service disconnecting means or the overcurrent protection and disconnecting means must be located immediately adjacent to each other.
Lighting Fixtures above Bathtubs
Q: Are recessed lighting fixtures installed in the ceiling above a bathtub in a dwelling unit required to be protected by a ground-fault circuit-interrupter (GFCI)? The fixtures are marked "Suitable for Damp Locations."
A: These (lighting fixtures) luminaries are not required to be protected by a GFCI to comply with the NEC. The requirement for GFCI protection in dwelling units applies only to 15- and 20-ampere, 125-volt receptacles. However, some manufacturers of damp location lighting fixtures require they be protected by a GFCI as part of the installation instructions. Where this requirement is included with the product, GFCI protection must be provided to comply with 110.3(B), which requires that listed or labeled equipment be installed and used in accordance with instructions furnished with the product.
Branch Circuit for Microwave Oven
Q: I installed a dedicated 20-ampere branch circuit in a kitchen for a microwave oven. This circuit supplies a 15-ampere duplex receptacle. The only load is the oven. The inspector has requested that I install a single 20-ampere receptacle in place of the 15-ampere duplex receptacle. Am I in violation of any requirements in the National Electrical Code?
A: Not that I know of. A duplex receptacle is actually two receptacles on a single yoke and a 15-ampere duplex receptacle is permitted on a 20-ampere branch circuit. In fact, part of 210.21(B)(3) says branch circuits supplying two or more receptacles are allowed to have ratings listed in Table 210.24. And the ampere ratings of receptacles on 20-ampere branch circuits are shown to be 15 or 20 amperes. A branch circuit that supplies a single receptacle is called an individual branch circuit, and the receptacle ampere rating cannot be lower than the ampere rating of the branch circuit. This information is found in 210.21(B)(1). EC
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.