# Box-Fill Calculations, Part IX

314.16 Number of Conductors in Outlet, Device, and Junction Boxes and Conduit Bodies

Section 314.1 covers the scope of Article 314. This article covers the installation and use of all boxes and conduit bodies used as outlet, device, junction or pull boxes, depending on their use. In the 2002 edition of the National Electrical Code, manholes and other electric enclosures intended for personnel entry were in Article 314. In the 2005 edition, provisions pertaining to manholes and other electric enclosures intended for personnel entry were moved to Article 110, Part V. New specifications for handhole enclosures, an addition to Article 314 in the 2005 Code, are in 314.30. The last sentence in the scope of Article 314 states that the article also includes installation requirements for fittings used to join raceways and to connect raceways and cables to boxes and conduit bodies.

Specifications for calculating the number of conductors in outlet, device and junction boxes and conduit bodies are in 314.16. While box-volume calculations are in 314.16(A), box-fill calculations are 314.16(B). Last month's “Code in Focus” concluded with equipment-grounding conductor fill in 314.16(B)(5). This month, the discussion begins with conduit bodies in 314.16(C).

314.16(C) Conduit Bodies

Numbers of conductors in conduit bodies (also referred to as condulets) are specified in 314.16(C). A conduit body, as defined in Article 100, is 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 (see Figure 1). Conduit bodies can be useful in many ways. They can be installed to change the direction of the conduit or tubing; they can be installed in long runs, thereby making it easier to pull the conductors; they can be installed when the number of raceway bends exceeds the equivalent of four quarter bends (360 degrees); and conduit bodies can contain splices, taps or devices under certain conditions.

The letter type associated with a conduit body indicates the number of raceway entries and where they are located. Examples of conduit-body types include C, E, LB, LL, LR, L, T, TA, TB and X. Some configurations include an LB that has a raceway entry in one end and another in the back of the opposite end, an LL that has a raceway entry in one end and another in the left side of the opposite end, an LR that has a raceway entry in one end and another in the right side of the opposite end, and a C that has one raceway entry in each end of the conduit body. While several conduit bodies have more than two raceway entries (T, TA, TB and X), only one has a single entry (E) (see Figure 2).

The last sentence in the definition and the middle sentence in the scope of Article 314 (314.1) state that cast, sheet metal, nonmetallic and other boxes such as FS, FD and larger boxes are not classified as conduit bodies. Type FS and FD boxes are also known as cast-device boxes and can be used as outlet, device, junction and pull boxes. Both FS and FD boxes are cast-device boxes with a single conduit entry. While the “S” in FS stands for shallow, the “D” in FD stands for deep (see Figure 3).

Like conduit bodies, the letters associated with cast-device boxes indicate the number and location of raceway entries. For example, an FS box is a shallow-cast box with one conduit entry. An FSS is a shallow-cast box with two entries on the same end. Other examples include an FSC that has one conduit entry on each end, an FSL that has one entry on the top and another on the left side, an FSR with one entry on the top and another on the right side, and an FSX that has one raceway entry on each end and on each side (see Figure 4). Most cast boxes are manufactured in both shallow and deep versions. For other configurations, check with your electrical-supply house or online at each manufacturer's Web site.

Conduit bodies enclosing conductors no larger than 6 AWG must have a cross-sectional area at least twice the cross-sectional area of the largest conduit or tubing to which it is attached. [314.16(C)(1)] While this requirement seems more like design criterion for manufacturers, it does have practical installation applications. This rule prohibits using a conduit body (enclosing 6 AWG or smaller conductors) that is smaller than the largest raceway to which it is attached. Installing coupling and reducer fittings onto the raceway in order to install a smaller conduit body is a violation. For example, installing a 1-in. rigid-metal conduit with a coupling and reducer fittings into a _-in. conduit body is a violation (see Figure 5).

This rule does not prohibit using a conduit body that is larger than the largest raceway to which it is attached. Installing a reducing fitting into a conduit body and attaching the conduit body to a smaller conduit or tubing is not a violation. For example, a conduit body will contain conductors that will be spliced. Since additional volume allowance is needed, an oversized conduit body will be installed. Although the raceway system is _-in. rigid-metal conduit, the conduit body will be sized for 1-in. raceway entries. Since the conduit body is larger than the attached raceway, there is no violation (see Figure 6).

Compliance with the first sentence of 314.16(C)(1) is not required for short radius conduit bodies as stipulated in 314.5. Conduit bodies, such as capped elbows and service-entrance elbows enclosing conductors 6 AWG or smaller and that are only intended to enable the installation of the raceway and the contained conductors, shall not contain splices, taps or devices. Although standard conduit bodies are permitted to contain splices, taps or devices under specified conditions, short-radius conduit bodies cannot. Short-radius conduit bodies must also be of sufficient size to provide free space for all conductors enclosed in the conduit body. [314.5] Boxes and conduit bodies enclosing conductors 4 AWG or larger must also comply with the provisions of 314.28.

Next month's “Code in Focus” continues the discussion of box-fill calculations. EC

MILLER, owner of Lighthouse Educational Services, teaches classes and seminars on the electrical industry. He is the author of “Illustrated Guide to the National Electrical Code” and NFPA’s “Electrical Reference.” He can be reached at 615.333-3336, charles@charlesRmiller.com or www.charlesRmiller.com.