Square Peg, Round Hole

Where raceways and cables contain No. 4 AWG or larger conductors and connect to conduit bodies, do these conduit bodies have to meet the same dimension requirements as pull and junction boxes? Does the 2008 National Electrical Code (NEC) provide clear and concise text covering this situation, or is an interpretation of the text necessary? Studying the definition of a conduit body, as well as the in-depth analysis of the text in 314.28, will help you understand the issues and answer these two questions.

Part I of Article 100 provides the definition of a conduit body as “a separate portion of a conduit or tubing system that provides access through a removable cover(s) to the interior of the system at a junction of two or more sections of the system or at a terminal point of the system.” It further states that boxes, such as FS and FD or larger cast or sheet metal boxes, are not classified as conduit bodies. This definition makes it clear that a conduit body is not a box and that boxes are not conduit bodies.

Section 314.5 recognizes short-radius conduit bodies that enclose No. 6 AWG or smaller conductors, such as capped elbows and service-entrance elbows, are not intended to contain splices, taps or devices; therefore, these conduit bodies are not part of the discussion of this issue. In addition, 314.16(C)(1) requires regular conduit bodies enclosing No. 6 AWG conductors and smaller to have a cross-sectional area of not less than twice the cross-sectional area of the largest conduit or tubing, which could be attached to the conduit body.

The maximum number of conductors that can be installed in the conduit body is the same as the number that is permitted for the conduit or tubing in Table 1 of Chapter 9. Since the conduit or tubing is required to contain not more than the appropriate amount of fill and the conduit body is part of the conduit or tubing, it just makes sense that both must contain the same amount of conductors.

Section 314.16(C)(2) permits splices, taps and devices within the conduit body but only where these conduit bodies are durably and legibly marked by the manufacturer with the volume of the conduit body since splices, taps and devices will take up more space than just the conductors. For the maximum number of conductors in the conduit body, including taps, splices and devices, 314.16(B) must be used, and the marked volume of the conduit body would then be used to ensure enough space is provided within the conduit body.

Section 314.28 provides additional requirements for pull and junction boxes, as well as conduit bodies, and states that boxes and conduit bodies used as pull or junction boxes must comply with 314.28(A) through (D). The text in 314.28 is not as clear and concise as it should be since the definition of conduit body clearly indicates that a conduit body is not a box, and a box is not a conduit body. If the conduit body contains insulated conductors larger than No. 6 AWG, then sufficient distance, just like the distance requirements for boxes, must be provided for the conductors to be installed without the possibility of damage to the insulation. For a straight pull on a Type C conduit body, the length or distance from the entrance side of the conduit body to the exit side of the conduit body must not be less than eight times the trade size of the largest raceway.

For an angle or U-pull, an LB (a cover located on back side of conduit body with the exit opposite the cover), LR (a cover located on back with exit on the right side), or LL (a cover located on the back with the exit on the left side), the distance between each raceway entrance must not be less than six times the trade size of the largest raceway. An exception in 314.28(A)(2) states, “where a raceway or cable entry is in the wall of the conduit body opposite the removable cover, the distance from that wall to the cover is permitted to comply with the distance required for one wire per terminal in Table 312.6(A),” which is the bending radius of the conductor. Section 314.28(A)(3) permits conduit bodies of a lesser size than required in (A)(1) or (A)(2) for installations of combinations of conductors that are less than the maximum conduit or tubing fill if the conduit body has been listed for and permanently marked with the maximum number and size of conductors permitted.

As can be seen from this discussion, the text in 314.28 requires some interpretation for use where dealing with conduit bodies and could be clarified in future editions of the NEC.

ODE is a staff engineering associate at Underwriters Laboratories Inc., based in Peoria, Ariz. He can be reached at 919.949.2576 and mark.c.ode@us.ul.com.

About the Author

Mark C. Ode

Fire/Life Safety Columnist and Code Contributor
Mark C. Ode is a lead engineering associate for Energy & Power Technologies at Underwriters Laboratories Inc. and can be reached at 919.949.2576 and Mark.C.Ode@ul.com .

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