Code Quandaries, May 2010

Code Quandaries, May 2010

Your most pressing National Electrical Code (NEC) questions answered. All questions and answers are based on the 2008 NEC

Q. What are the rules for the location of the service disconnect?

A. Section 230.70 contains the following rules:

  • The service disconnecting means must open all service-entrance conductors from the building or structure premises wiring.
  • The service disconnecting means must be placed at a readily accessible location either outside the building or structure — or inside nearest the point of service conductor entry.

Warning: Because service-entrance conductors don't have short circuit or ground-fault protection, they must be limited in length when installed inside a building. Some local jurisdictions have a specific requirement as to the maximum length permitted within a building.

  • The service disconnecting means is not permitted to be installed in a bathroom. Overcurrent devices must not be located in the bathrooms of dwelling units, or guest rooms/guest suites of hotels or motels [240.24(E)].
  • Where a remote-control device (such as a pushbutton for a shunt-trip breaker) is used to actuate the service disconnecting means, the service disconnecting means must still be at a readily accessible location either outside the building or structure — or nearest the point of entry of the service conductors as required by 230.70(A)(1). See the definition of "Remote Control" in Art. 100. The service disconnecting means must consist of either a manually operated switch, or a power-operated switch or circuit breaker also capable of being operated manually [230.76].
  • Each service disconnecting means must be permanently marked to identify it as part of the service disconnecting means. When a building or structure has multiple services and/or feeders, a plaque is required at each service or feeder disconnect location to show the location of the other service or feeder disconnect locations. See 230.2(E).

Q. In a commercial kitchen, does the 20A, 125V refrigerator receptacle outlet need to be GFCI protected?

A. All 15A and 20A, 125V receptacles installed in an area with a sink and permanent facilities for food preparation and cooking [Art. 100] — even those that don't supply the countertop surface — must be GFCI protected [210.8(B)(2)].

Q. Is there any requirement to install cages or lamp tubes on surface-mount fluorescent fixtures?

A. No, there is no such requirement in the NEC.

Q. I have equipment that draws 104A and runs for more than 3 hours continuously. The machine requires a neutral, with a load of 18A. The equipment has an integral panelboard in it, with a 125A main. How do I size the neutral conductor for this equipment?

A. The feeder neutral conductor must be sized to carry the maximum unbalanced load, in accordance with 220.61, and must not be smaller than the size listed in 250.122, based on the rating of the feeder overcurrent device [215.2(A)(1)]. In this application, a 12 AWG conductor would carry the load, but would not satisfy the requirement that the conductor be as large as indicated in 250.122. According to 250.122, a 6 AWG neutral conductor would be required, based on the rating of the feeder overcurrent device of 125A.

Q. Can I use SER cable in a 4-story multifamily dwelling?

A. NM and SE cables can only be used in multifamily dwellings permitted to be of Types III, IV, and V construction [334.10(A) and 338.10(B)(4)(a)]. The number of stories does not enter into the requirements. Types of construction are covered in the applicable building (such as the International Building Code), and are not covered in the NEC. Type of construction, in a nutshell, means the types of material a building can be constructed of, such as wood, concrete and steel. Because this is a difficult topic for electricians to deal with, your best bet is to consult the building official of the city/county you’re working in.

Q. Please explain the grounding requirements for a service that consist of up to six switches or six circuit breakers mounted in a group of separate enclosures.

A. A grounding electrode conductor is permitted from each service disconnecting means sized not smaller than specified in Table 250.66, based on the area of the ungrounded conductor for each service disconnecting means. Or, a single grounding electrode conductor is permitted from a common location, sized not smaller than specified in Table 250.66, based on the area of the ungrounded conductor at the location where the connection is made [250.64(D)].

Q. What are the bonding requirements for metal raceways?

A. For raceways containing conductors less than 250V, other than service conductors, the requirements of 250.96 apply. Metal parts intended to serve as equipment grounding conductors including raceways, cables, equipment, and enclosures must be bonded together to ensure they have the capacity to conduct safely any fault current likely to be imposed on them [110.10, 250.4(A)(5), and Note to Table 250.122]. Nonconductive coatings such as paint, lacquer, and enamel on equipment must be removed to ensure an effective ground-fault current path, or the termination fittings must be designed so as to make such removal unnecessary [250.12]. Author's comment: The practice of driving a locknut tight with a screwdriver and pliers is considered sufficient in removing paint and other nonconductive finishes to ensure an effective ground-fault current path.

In addition, for raceways containing conductors operating at over 250V, we must comply with 250.97. Metal raceways or cables containing 277V and/or 480V feeder or branch circuits terminating at ringed knockouts must be bonded to the metal enclosure with a bonding jumper sized in accordance with 250.122, based on the rating of the circuit overcurrent device [250.102(D)]. Author's comments: Bonding jumpers for raceways and cables containing 277V or 480V circuits are required at ringed knockout terminations to ensure the ground-fault current path has the capacity to safely conduct the maximum ground-fault current likely to be imposed [110.10, 250.4(A)(5), and 250.96(A)]. Ringed knockouts aren't listed to withstand the heat generated by a 277V ground fault, which generates five times as much heat as a 120V ground fault.

Exception: A bonding jumper isn't required where ringed knockouts aren't encountered, knockouts are totally punched out, or where the box is listed to provide a reliable bonding connection.

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