Published In January 2002
CODE CITATIONS Article 110—Requirements for Electrical Installations Article 210—Branch Circuits Article 230—Services Article 250—Grounding Article 408—Switchboards and Panelboards Article 430—Motors, Motor Circuits, and Controllers Article 695—Fire Pumps NFPA 20—1999 Standard for the Installation of Stationary Pumps for Fire Protection Power supply for a fire pump Q: Is a legally required standby generator an acceptable power source for an electric motor-driven fire pump? The generator has adequate capacity to start and run the motor. Load shedding of nonessential loads allows the generator to deliver locked-rotor current to the motor. Item 2 in 695.3(A)(2) allows an “On-Site Power Production Facility” to serve as a reliable power supply (the only power source) for a fire pump, but there is no explanation or definition for an “On-Site Power Production Facility.” Is a legally required standby generator that meets the requirements for delivering locked-rotor current and voltage drop acceptable as the sole supply for a fire pump? A: Because there was confusion in the field about the meaning of the words “On-Site Power Production Facility,” a definition now appears in 695.2: “On-Site Power Production Facility. The normal supply of electric power for the site that is expected to be constantly producing power.” There is also a definition for “On-Site Standby Generator. A facility producing electric power on site as the alternate supply of electric power. It differs from an on-site power production facility in that it is not constantly producing power.” This information appears in Appendix A of the 1999 edition of NFPA 20 Standard for the Installation of Stationary Pumps for Fire Protection: “A-6-2.2 An on-site electric power production facility located on the premises served by the fire pump is considered an acceptable facility if it is in a separate powerhouse or cut off from the main buildings.” Although a legally required standby generator is not acceptable as a reliable power source for a fire pump motor, it can be used as an alternate power source. Actually, if a utility service is used and determined to be reliable, the generator supplying legally required loads could serve as back-up power for the fire pump, and would not have to be capable of supplying locked-rotor current continuously or be limited to a voltage drop of not more than 15 percent for motor starting or 5 percent while the motor is running. Stranded conductors on receptacles Q: Are Nos. 12 and 14 copper stranded conductors permitted to be connected to 15- and 20-ampere, 125-volt receptacles that have wire binding screw terminals? On some of these receptacles it is difficult to capture all of the strands under the wire binding screws with upturned back plates. A: I am not aware of any rules in the NEC that limit terminations on 15- and 20-ampere, 125-volt receptacles to solid conductors. Also, there are no limitations in the UL standard. There should not be any problem terminating seven-strand Nos. 12 and 14 on these wiring devices. However, flexible wire with many small strands is much harder to terminate properly. To make sure that all strands remain under the screw head on the terminal, the strands must be tightly twisted together, or twisted together and soldered before wrapping the wire around the screw. If an inspection reveals that some strands of wire are not in contact with the terminals, 110.2 can be used to reject the installation. This section requires a neat and workmanlike installation of electrical equipment. Lighting switches for kitchens Q: In a single-story, one-family dwelling, there are three doors in the kitchen. One is the entrance from the carport, and the other two lead into other rooms. I installed a wall switch to control the lighting in the kitchen at the entrance door from the carport. The homeowner does not want any more switches, but the Inspector is insisting on switches at each door. Where will I find this requirement in the NEC? A: There is no requirement for more than one wall switch, regardless of the number of doors. Additional switches that may be provided is a design consideration that may be exercised by the owner. The requirement for a wall switch-controlled lighting outlet in the kitchen of a dwelling unit is found in 210.70(A)(1). This part reads: “At least one wall switch controlled lighting outlet shall be installed in every habitable room and bathroom.” There is no change in the wording between the 1999 and 2002 editions of the NEC. Grounding electrode system Q: A small commercial building is supplied by a three-phase, four-wire, 208Y/120-volt service that has No. 4/0 copper service-entrance conductors. The grounding electrode conductor that runs to the buried metal water pipe is No. 2 copper. Is it permissible to connect a No. 6 copper grounding conductor from two driven rods to the water pipe within 5 feet of its entrance into the building? Is a concrete-encased electrode a suitable supplementary grounding electrode? If the answer is “yes,” may the No. 4 copper grounding electrode conductor be connected to the water pipe? A: The sizes of the grounding electrode conductors meet the requirements of Table 250.66, 250.66(A), and 250.52(A)(3). Although 250.53(D)(2), which deals with supplemental electrodes, does not mention the water pipe as a suitable electrode for connection of the grounding electrode conductor, 250.52(A)(1) allows the first 5 feet of metal water pipe that enters a building to be used for interconnection of other grounding electrode conductors. Here is the sentence in 250.52(A)(1) that seems to indicate that the first 5 feet of metal water pipe in the building is acceptable as a connection point for other grounding electrodes: “Interior metal water piping located more than 1.52 m. (5 ft.) from the point of entrance to the building shall not be used as a part of the grounding electrode system or as a conductor to interconnect electrodes that are part of the grounding electrode system.” The title of 250.52 (D)(2) is “Supplemental Electrode Required.” Part of this paragraph contains this sentence: “The supplemental electrode shall be permitted to be bonded to the grounding electrode conductor, the grounded service-entrance conductor, the nonflexible grounded service raceway, or any grounded service enclosure.” Notice that water pipe is not mentioned. To be safe and ensure compliance with the NEC, I would not connect the grounding electrode conductor from the supplemental grounding electrode to the metal water pipe. A concrete-encased electrode meeting the requirements of 250.52(A)(3) may be used to supplement a metal water pipe grounding electrode. Panelboard classification Q: A 120/240-volt, single-phase panelboard is used as service equipment for a one-family dwelling. It contains the following overcurrent devices: 2—100 ampere, two-pole circuit breakers feeding 120/240-volt sub-panels; 1—90 ampere, two-pole circuit breaker that supplies electric heating; 1—40 ampere, two-pole circuit breaker for an air conditioning unit; 1—40 ampere, two-pole circuit breaker that supplies an electric range; and 1—20 ampere, two-pole circuit breaker that feeds a 240-volt water pump. Is this a lighting and appliance branch circuit panelboard that requires one or not more than two mains? Or is this a power panelboard that requires a single main? A: Definitions for these two types of panelboards can be found in 408.18(A) and (B). Because this panelboard does not supply any lighting and appliance branch circuits that are defined as circuits with neutrals, and overcurrent protection not exceeding 30 amperes, it is classified as a power panelboard. Therefore, overcurrent protection must satisfy the requirements in 408.16(B). Although this section requires overcurrent protection for the panelboard that does not exceed the ampere rating of the panelboard, the exception permits elimination of the overcurrent protection ahead of the panelboard where it is used as service equipment. However, the panelboard must be marked “Suitable for Use as Service Equipment” and cannot have more than six disconnecting means. Also, all of the circuit breakers must have current interrupting ratings that are equal to or greater than the maximum available fault current at the line terminals of the panelboard. The six- disconnect rule is in 230.71, and the requirement for interrupting rating is in 110.9. If the panelboard meets these requirements, overcurrent protection ahead of the panelboard is not required. Wye-delta start motor circuit conductors Q: What are the minimum sizes of branch circuit conductors to supply a 50-horsepower, 480-volt, three-phase, Wye-Start Delta-Run motor? According to Table 430.150, the full-load current for this motor is 65 amperes. Therefore, minimum branch circuit conductor ampacity between the disconnecting means and line terminals of the motor controller cannot be less than (1.25 x 65) 81 amperes. No. 3 copper conductors with 60 degrees Celsius insulation or No. 4 copper conductors with 75 degrees Celsius insulation are adequate. Between the motor controller and motor, conductor sizes are based on 58 percent of motor full-load current. This reduction in wire size is permitted by 430.22(c). Doing the multiplication results in a minimum conductor ampacity of 47, and according to Table 310.16, No. 6 copper with 60 degrees Celsius insulation or No. 8 copper with 75 degrees insulation may be used. In selecting these wire sizes, it is assumed that a maximum of three current-carrying conductors are in a single raceway. FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at (504) 254-2132.