Published In November 2000
Herewith, various 1999 National Electrical Code (NEC) issues that do not warrant a whole page of discussion. This is an example of why it is wrong to follow a “remove exceptions” edict without first examining the consequences. The 1996 NEC, Section 410-12 reads as follows: “410-12. Outlet Boxes to Be Covered. In a completed installation, each outlet box shall be provided with a cover unless covered by means of a fixture canopy, lamp holder, receptacle, or similar device. Exception: As provided in Section 410-14(b).” In the 1999 NEC, the Exception has been deleted. Sec. 410-14(b) reads: “(b) Access to Boxes. Electric-discharge lighting fixtures surface mounted over concealed outlet, pull, or junction boxes shall be installed with suitable openings in back of the fixture to provide access to the boxes.” Removing the Exception from Sec. 410-12 created a new conflict. But Exceptions were properly removed in Sec. 450-13, Accessibility of Transform-ers. Two former Exceptions have been reworded into positive language as subsections (a) and (b), and (b) has further been amended to read as follows: “(b) Hollow Space Installations. Dry-type transformers 600 volts, nominal, or less and not exceeding 50 kVA shall be permitted in hollow spaces of buildings not permanently closed in by structure, and provided they meet the ventilation requirements of Section 450-9 and separation from combustible materials requirements of Section 450-21(a). Transformers so installed shall not be required to be readily accessible.” The 1996 version spoke of “fire resistant” hollow spaces, but since a hollow space cannot have a fire rating, that phrase has been replaced by a reference to the requirements for separation from combustible materials in Sec. 450-21. The location in the circuit of overcurrent protection for conductors is covered in Sec. 240-21, where subsection (c) covers Transformer Secondary Conduct-ors, and (c)(3) reads as follows: “(3) Secondary Conductors Not Over 25 ft (7.62 m) Long. For industrial installations only, where the length of the secondary conductors does not exceed 25 feet (7.62 m) and complies with all of the following. a. The ampacity of the secondary conductors is not less than the secondary current rating of the transformer, and the sum of the ratings of the overcurrent devices does not exceed the ampacity of the secondary conductors. b. All overcurrent devices are grouped. c. The secondary conductors are suitably protected from physical damage.” People are so used to the six-disconnect limit (Sec. 225-33 for a second building on a property, and Sec. 230-71 for services) that some assume the number of overcurrent devices in this application is limited to six. (Circuit breakers serve as both overcurrent and disconnect. If the overcurrent protection is by fuses, Sec. 240-40 requires a disconnect for each set of fuses.) However, the number of overcurrent devices isn’t limited, provided the conductor ampacity is at least equal to the sum of the ratings of the overcurrent devices. Remember that this rule pertains to the overcurrent protection of the conductors. If the transformer requires both primary and secondary protection, then Sec. 450-3 requires that the number of overcurrent devices on the secondary be limited to not more than six. Sec. 370-23 covers support for boxes and conduit bodies. “(e) Raceway Supported Enclosure, Without Devices or Fixtures. An enclosure that does not contain a device(s) or support a fixture(s) or other equipment, and is supported by entering raceways shall not exceed 100 in.3 (1640 cm3) in size. It shall have threaded entries or have hubs identified for the purpose. It shall be supported by two or more conduits threaded wrenchtight into the enclosure or hubs. Each conduit shall be secured within three feet (914 mm) of the enclosure, or within 18 in. (457 mm) of the enclosure if all entries are on the same side. Exception: Rigid metal, intermediate metal, or rigid nonmetallic conduit or electrical metallic tubing shall be permitted to support a conduit body of any size, including a conduit body constructed with only one conduit entry, provided the conduit body is not larger than the largest trade size of the conduit or electrical metallic tubing.” The only use of an “E” conduit fitting that does not contain a receptacle, lamp holder, or support other equipment is to enclose the taped ends of a discontinued circuit. The phrase “of any size” in the Exception removes the 100-square-inch limitation of the basic rule. Big deal: the largest “E” conduit body available at my local source (1 inch) has an internal volume of less than 20 cubic inches. The basic rule requires two or more threaded conduits supported within three feet of the enclosure (or within 18 inches if the entries are on the same side), while the Exception permits a single raceway, which can now be rigid nonmetallic conduit or electrical metallic tubing supported within 18 inches of the conduit body. The intended application is difficult to recognize. SCHWAN is an electrical code consultant in Hayward, Calif. He can be reached via e-mail at email@example.com.