Branch Circuit, Feeder, and Service Calculations; Overcurrent Protection; Grounding; IT Equipment; and Water-intensive Installations

CODE CITATIONS Article 210—Branch Circuits; Article 220—Branch-Circuit, Feeder, and Service Calculations; Article 240—Overcurrent Protection; Article 250—Grounding; Article 645—Information Technology Equipment; and Article 680—Swimming Pools, Fountains, and Similar Installations Arc-fault circuit-interrupters Q: Were there any proposals to delete the requirement for arc-fault circuit-interrupters (AFCIs) for receptacles in bedrooms of dwelling units? This requirement is in Section 210-12 of the 1999 National Electrical Code (NEC) and has an enforcement date of January 1, 2002. What action did the Code Panel take in response to this and possibly other proposals? A: There were 16 proposals to expand the use of AFCIs and three to delete Section 210-12. Code Making Panel No. 2 accepted a revision to delete the word “receptacle” and remove the enforcement date of January 1, 2002. There was one negative vote by a panel member. By deleting the word “receptacle,” all of the wiring that supplies electricity to dwelling unit bedrooms will have to be protected by arc-fault circuit-interrupters. This will simplify the wiring for bedrooms, but may result in more complex and time-consuming troubleshooting should an arcing fault develop somewhere in the branch circuit. With this change, it may be possible to wire three bedrooms with one 20-ampere, 125-volt branch circuit protected by an AFCI circuit breaker, thereby reducing the installation cost. Underwriters Laboratories Inc. has developed Standard 1699 “Arc-Fault Circuit-Interrupters.” This standard defines these types of AFCIs as: Branch/Feeder AFCIs intended for installation and protection of branch circuits and feeders; Outlet Circuit AFCIs that provide protection of power supply cords connected to appliances (lamps, TVs, clocks, etc.) and cord sets; and combination AFCIs that provide both Branch/Feeder and Outlet Circuit protection. Because the Branch/Feeder AFCI does not provide a high level of protection against arcing faults in flexible cords or appliances plugged into a receptacle, some proposals that were submitted recommended that both types (Branch/Feeder and Outlet Circuit AFCIs) be used on the same branch circuit. The State of Vermont has adopted an amendment to Section 210-12(b) in the 1999 NEC. This amendment requires AFCI protection for branch circuits that supply receptacle outlets in dwelling unit living areas and bedrooms. The effective date for this change was January 1, 2001. This advanced enforcement date should give us a good field test and an unbiased opinion on the value of AFCIs. Wiring and grounding data processing equipment Q: Is there any requirement in the NEC that limits the number of receptacles on a 15- or 20-ampere, 125-volt branch circuit to four in a data processing room? Also, is there a requirement for isolated ground receptacles that supply electronic computers? A: The answer to both questions is “no.” Requirements for data processing and computer equipment are found in Article 645—Information Technology Equipment, and there is nothing in this Article that limits the number of receptacles on branch circuits. Insulated ground receptacles are also not required. It is up to the engineer who designs the electrical system to specify the maximum number of receptacles permitted on each branch circuit and to indicate on the electrical plans which receptacles are to be isolated ground type. In the absence of a specific number of receptacles on a branch circuit, Section 220-3(b)(9) can be used to determine the maximum number of receptacles allowed on 15- or 20-ampere, 125-volt branch circuits. This Section requires that a load of 180 volt-amperes be figured for each receptacle outlet that has three or less receptacles on the same strap. This calculation allows 10 receptacles on a 15-ampere circuit and 13 receptacles on a 20-ampere branch circuit. However, I would not wire a data processing room with this many receptacles on a circuit without prior written approval from the design engineer. The data processing equipment manufacturer’s installation instructions should be thoroughly reviewed before making the wiring installation. Their instructions could require dedicated circuits for some types of equipment, isolated ground receptacles, and a maximum number of receptacles on a branch circuit for different types of data processing equipment. These are all design issues that do not impact electrical safety, and are therefore not covered by the NEC. Article 645 of the NEC, the “Standard for the Protection of Electronic Comput-er/Data Processing Equipment” and NFPA 75-1999 should be completely reviewed before starting to wire the computer room. Sizing service-entrance conductors Q: A single set of service-entrance conductors supplies a six-unit apartment building. The service-entrance conductors enter a wireway and supply six meters, disconnects, and overcurrent devices. Can I size the conductors supplying each meter from the Special Ampacity Table shown in 310-15(b)(6) or must I use the conductor ampacities given in Table 310-16? A The higher ampacities in Table 310-15(b)(6) can be used for sizing the service-entrance conductors for each apartment. The service to the multifamily building must be 120/240 volts, three wire, single phase. The main power feeder to each dwelling unit may also be sized according to this Table. Single-pole and multipole circuit breakers Q: Under what conditions am I allowed to use single-pole circuit breakers with or without handle ties on multiwire branch circuits? A: Single-pole circuit breakers without handle ties are permitted on most multiwire branch circuits that supply line to neutral loads. Single-pole circuit breakers are not allowed to supply multiwire branch circuits in a dwelling unit where the multiwire circuit supplies devices or equipment secured to the same mounting yoke. Single-pole circuit breakers with approved handle ties are allowed to supply single-phase line-to-line loads. On three-phase, four-wire systems, line-to-line loads are permitted to be supplied by single-pole circuit breakers with approved handle ties. These rules appear in Sections 210-4(b) and 240-20. Code Making Panel No. 10 has accepted Proposal 10-26 to require common trip circuit breakers that supply line-to-line loads. Nine voted for this proposal and three voted against it. For example, a 240-volt, single-phase space heater protected by two single-pole circuit breakers with a handle tie could develop a phase-to-ground fault in the resistance element close to a line terminal, which would cause one of the single-pole circuit breakers to trip; however, current would continue to flow through the remaining circuit breaker and the equipment grounding conductor without tripping the circuit breaker. Now the reduced-size equipment grounding conductor is acting as a circuit conductor, and this condition would not exist with a two-pole common trip circuit breaker. Therefore, two-pole common trip circuit breakers provide a better level of protection than two single-pole circuit breakers with a tie handle for line-to-line connected appliances. Is a neutral conductor necessary? Q: A 208Y/120 service to a factory includes a neutral conductor, which is grounded in the service disconnection means. Recently, an electrical contractor installed a 200-ampere, three-wire, three-phase feeder to supply a new machine. The feeder is about 100 feet long and terminates in a panel that contains eight three-pole circuit breakers. The electrical contractor did not include a neutral conductor in the feeder. When questioned about the absence of a neutral conductor, the contractor stated that there was no need for a neutral conductor because there was no neutral load. Isn’t this a violation? I always thought that the neutral had to be included with the phase conductors in all feeders that supply panelboards. Does Section 250-24(b) apply to feeders or to services only? A: The electrical contractor is correct. Section 250-24(b) applies to services and requires that the grounded system conductor (in this case the neutral) be brought in with the ungrounded service conductors and grounded to the grounding electrode system. Where there are no loads that require a grounded circuit conductor, this conductor does not have to go any further than the service equipment. Ungrounded feeder conductors are permitted to be connected to a grounded system by Section 215-7. This is what part of this Section says: “Two-wire dc circuits and ac circuits of two or more ungrounded conductors shall be permitted to be tapped from the ungrounded conductors of circuits having a grounded neutral conductor.” An equipment grounding conductor must be included with the feeder conductors. The equipment grounding conductor must be a wire or any of the wiring methods mentioned in Section 250-118. Wall switch location for a bathroom with a hot tub Q: There is a hot tub in the bathroom of a residence. The room is small and the walls are less than 5 feet from the hot tub. Am I allowed to install the ceiling lighting fixture switch on the wall to comply with Section 210-70(a)(1)? A: The wall switch control for the ceiling light in the bathroom may be located on a wall outside of the bathroom at least 5 feet from the hot tub. The emergency shut off switch mentioned in Section 680-38 does not apply to single-family dwellings. If an emergency switch is required, it must be located within sight of the hot tub and at least 5 feet away from it. There is also a requirement for wall switches that control lighting fixtures or paddle fans or both. These switches must be located at least 5 feet horizontally from the inside walls of this hot tub. This requirement appears in Section 680-41(b). FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at (504) 254-2132.

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