370-23(f) Exception No. 2
This is the second exception to the main rule in 370-23(f). Last month’s In Focus covered the main rule and the first exception. Essentially, rigid metal or intermediate metal conduit can support an enclosure that is supporting a fixture where the conduit is secured within 18 inches of the enclosure. However, if the conditions of this second exception are met, the support distance can be lengthened to 36 inches. This exception also permits a single conduit to support a box used for fixture support or a wiring enclosure used in lieu of a box.
Where meeting all of the conditions in this exception, unbroken length(s) of rigid metal or intermediate metal conduit can support a box used for fixture support, or support a wiring enclosure within a fixture and used in lieu of a box in accordance with Section 300-15(b). This exception does not stipulate that the fixture must be supported by two or more conduits. In fact, two of the conditions [(d) and (e)] are only applicable for a fixture supported by a single conduit.
Before looking at the six conditions, we must look at this exception’s first sentence. As with the main rule, only two conduit types are permitted-rigid metal and intermediate metal conduit. (This requirement is reemphasized in the last condition.)
Another important part of the first sentence states that the conduit must be unbroken. Unbroken does not mean that the conduit must have a length of 10 feet. The length depends on the conduit’s last point of support.
The length of conduit extending beyond the last support must not exceed 3 feet. [370- 23(f) Exception No. 2 (a)] This is the same length permitted for raceways supporting enclosures not containing fixtures or devices. So what is this difference between this exception and Section 370-23(e)? The main difference is each supporting conduit. Conduit supporting a fixture must remain unbroken within a certain distance from the enclosure. In last month’s In Focus, a violation was depicted in Figure 3, because a light fixture was added to an existing code-compliant installation. Conduits, secured within 3 feet of the enclosure, were used to support an enclosure that did not contain a device or support a fixture. Since the conduits supporting an enclosure containing a fixture must be secured within 18 inches, a violation occurred.
Notice the threaded coupling in each conduit—they are approximately 2 feet from the enclosure. If the conduits were unbroken lengths, no additional supports would be required.
The term “unbroken conduit length” is not just referring to a conduit that has been cut, threaded, and coupled with another conduit. It also refers to a conduit that terminates into a box, conduit body, enclosure, etc.
The unbroken conduit before the last point of support must be 12 inches or greater, and that portion of the conduit must be securely fastened not less than 12 inches from its last point of support. [370-23(f) Exception No. 2 (b)] This one sentence contains two specific provisions. First, The conduit must be unbroken from the enclosure, to a point at least 12 inches past the last support. For example, if the support for the conduit is 36 inches from the enclosure, the unbroken conduit length must be at least 48 inches (36 + 12). If the support is 20 inches from the enclosure, the unbroken conduit length must be at least 32 inches (20 + 12).
The second part of this requirement states that the unbroken conduit must be securely fastened not less than 12 inches from its last point of support. This means that the unbroken conduit must have two means of support, and they must be at least 12 inches apart. A threaded coupling is between the two enclosures. The unbroken conduit is supported by two straps that are not less than 12 inches apart. If there was no coupling and the first support remained at 20 inches, the enclosure secured to the wall could serve as the second support. This condition does not stipulate that the second support be exactly 12 inches from its last point of support.
Do not exceed the support requirements for rigid metal and intermediate metal conduit. Each conduit must be securely fastened within 3 feet of each termination (outlet box, junction box, device box, cabinet, conduit body, etc.). [345-12(a) and 346-12(a)]
Where accessible to unqualified persons, the fixture’s lowest point must be at least 8 feet above grade (or standing area) and at least 3 feet (measured horizontally to the 8-foot elevation) from windows, doors, porches, fire escapes, or similar locations. [370-23(f) Exception No. 2 (c)]
More often than not, installations will be accessible to unqualified persons. Although “unqualified person” is not defined, Article 100-Definitions does define “qualified person.” A qualified person is one familiar with the construction and operation of the equipment and the hazards involved. Therefore, an unqualified person is neither familiar with the construction and operation of the equipment, nor the hazards involved.
The next two requirements, within this exception, are for enclosures or fixtures supported from a single conduit. A fixture supported by a single conduit must not exceed 12 inches in any direction from the point of conduit entry. [370-23(f) Exception No. 2 (d)] This is not saying that the fixture’s size is limited to 12 inches; rather, it means that, measured from where the conduit enters, the fixture cannot exceed 12 inches in any direction.
The weight supported by any single conduit must not exceed 20 pounds. [370-23(f) Exception No. 2 (e)] This 20-pound limit not only includes fixture(s), it also includes the box, cover, lamp(s), etc.
At the fixture end, the conduit(s) must be threaded wrenchtight into the box or wiring enclosure, or into hubs identified for the purpose. [370-23(f) Exception No. 2 (f)] Simply hand tightening the conduit(s) will not comply with this provision—some type of wrench must be employed. The previous two requirements [(d) and (e)] specify rules for enclosures or fixtures supported with a single conduit. This provision, along with (a), (b), and (c), applies to enclosures or fixtures supported by any number of conduits, not just one.
Next month’s In Focus, beginning with Section 370-28, will cover pull and junction box sizing requirements. While boxes within the scope of 370-16 are calculated from the sizes and numbers of conductors, boxes in 370-28 are calculated from the sizes and numbers of conduits.
MILLER, owner of Lighthouse Educational Services and author of the Illustrated Guide to the National Electrical Code, can be reached by phone at (615) 333-3336, or via e-mail at charles@charlesRmiller.com.