# Box-Fill Calculations, Part XII

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

The scope of Article 314 is covered in 314.1 and covers requirements pertaining to the installation and use of all boxes and conduit bodies used as outlet, device, junction or pull boxes, depending on their use, and handhole enclosures.

In the 2005 edition of the National Electrical Code (NEC), a new section (314.30) covering “handhole enclosures” was added to Article 314. Another change in the 2005 edition was the part titled, “Manholes and Other Electric Enclosures Intended for Personnel Entry.”

All of the provisions in Part IV of Article 314 have been relocated to Part V in Article 110. The middle sentence of Article 314's scope states that cast, sheet-metal, nonmetallic and other boxes such as FS, FD and larger boxes are not classified as conduit bodies.

Provisions for boxes and conduit bodies enclosing conductors 6 AWG or smaller are in 314.16. Boxes and conduit bodies enclosing conductors 4 AWG or larger must also meet the provisions in 314.28. Box-volume calculations are in 314.16(A) and box-fill calculations are in 314.16(B). Requirements for the maximum numbers and sizes of conductors in conduit bodies are in 314.16(C).

Last month's Code in Focus concluded with a discussion of general provisions for conduit bodies in 314.16(C)(1). This month will conclude the series titled, Outlet, Device, Pull and Junction Boxes; Conduit Bodies; Fittings; and Handhole Enclosures.

314.16(C)(2) Conduit Bodies with Splices, Taps and Devices

A common misconception is that conduit bodies cannot contain splices or taps. Where meeting the specifications in 314.16(C)(2) and 314.16(B), conduit bodies can contain splices, taps or devices.

Only those conduit bodies that are durably and legibly marked by the manufacturer with their volume shall be permitted to contain splices, taps or devices. [314.16(C)(2)] If the cubic inch (or cubic centimeter) volume is not marked on the conduit body, no splices, taps or devices can be installed.

For example, a Type LB conduit body with 1-inch raceway entries has been installed. There are no volume markings in or on the conduit body. Three 12 AWG conductors will enter the conduit body through one raceway and will exit through the other raceway.

For this particular installation, the conductors must be cut and spliced. Because the volume is not marked on this conduit body, the conductors must not be spliced. Although it may be of sufficient size, it is a Code violation to splice conductors in this conduit body (see Figure 1).

A marking indicating the volume is not the only requirement that must be met before a conduit body can contain splices, taps or devices. The maximum number of conductors must be calculated in accordance with 314.16(B).[314.16(C)(2)] Since a conduit body can function as a junction box, the volume allowance required for the conductors must not exceed the volume of the conduit body. If the volume is marked on the conduit body and the conductors are calculated in accordance with 314.16(B), the conduit body can contain splices, taps or devices.

For example, a Type LB conduit body with 1-inch raceway entries has been installed. A marking inside shows the volume of the conduit body is 12.5 cubic inches. Three 12 AWG conductors will enter the conduit body through one raceway and will exit through the other raceway. Each raceway contains three 12 AWG conductors: one black, one white and one green conductor. For this installation, the conductors must be cut and spliced. As per Table 314.16(B), the volume required for each 12 AWG conductor is 2.25 cubic inches.

The two black 12 AWG conductors and the two white 12 AWG conductors must be counted. In accordance with 314.16(B)(5), the two green equipment-grounding conductors count as one 12 AWG conductor. The total volume required for all six 12 AWG conductors is 11.25 cubic inches (5 x 2.25). No volume allowance is required for the wire connectors. Since this conduit body has a volume of 12.5 cubic inches, this installation is permissible (see Figure 2).

Where different sizes of conductors will be installed in a conduit body containing splices, taps or devices, treat the conduit body like a junction (or device) box and perform a box-fill calculation.

For example, a Type T conduit body with 1_-inch raceway entries has been installed. A marking inside shows the volume of the conduit body is 30 cubic inches. Two 12 AWG conductors will enter one end and will exit the conduit body at the opposite end. The colors of these two conductors are black and white. These two conductors will not be cut or spliced.

A green 12 AWG conductor will exit the conduit body along with the black and white conductors. (This green conductor will be spliced to other green conductors.) Six more conductors will enter one end of the conduit body and will exit through the raceway in the middle of the conduit body. All six of these conductors will be cut and spliced. Entering the end raceway (along with the two 12 AWG conductors) will be four 10 AWG conductors and two 14 AWG conductors. The colors of the 10 AWG conductors are black, red, blue and green. The colors of the 14 AWG conductors are black and red. Six conductors, of the same size and color as the six 10s and 14s, will exit through the raceway in the middle of the conduit body. All the green conductors (one 12 AWG and two 10 AWG conductors) will be spliced together.

The volume required for the six 10 AWG conductors (not counting the green conductors) is 15 cubic inches (6 x 2.5). The volume required for the four 14 AWG conductors is 8 cubic inches (4 x 2). Since the black and white 12 AWG conductors pass through the box without splice or termination, the volume required is only 4.5 cubic inches (2 x 2.25).

There are three green conductors (equipment-grounding conductors), but only the largest one is counted. The volume required for one green 10 AWG conductor is 2.5 cubic inches (1 x 2.5). The total volume required for all these conductors is 30 cubic inches (15 + 8 + 4.5 + 2.5). Because this conduit body has a marked volume of 30 cubic inches, this installation complies with the Code (see Figure 3).

Where splices are made in conduit bodies, the length of free conductors must meet 300.14's provisions. At least 6 inches (150 mm) of free conductor, measured from the point in the conduit body where it emerges from its raceway must be left for splices or the connection of devices (see Figure 4).

The last sentence in 314.16(C)(2) states that conduit bodies must be supported in a rigid and secure manner. This support may be effectively achieved by the use of any of the following: rigid metal conduit, intermediate metal conduit, rigid nonmetallic conduit, or electrical metallic tubing. [314.23(E) Exception]

Box-fill calculations, summary

The table above (courtesy of NFPA's Electrical References) is a quick reference of box-fill calculation specifications. The left column describes items within the box. The center column shows the volume allowance for the items in the box. The right column shows how the items in the box are -counted.

For example, two 12-2 with ground nonmetallic sheathed cables enter a device box. The device box will also contain a single-pole switch and an equipment-bonding jumper. The box contains two internal cable clamps. The two white conductors will be spliced together with a wire connector. The two black conductors will be connected to the single pole switch.

Since the two white and two black conductors originate outside the box and terminate in the box, they count as four 12 AWG conductors total. The two internal cable clamps count as one 12 AWG conductor. The switch counts as two 12 AWG conductors. The two equipment-grounding conductors count as one 12 AWG conductor. The equipment-bonding jumper is not counted. The wire connectors are not counted. For box-fill purposes, this box contains eight 12 AWG conductors. 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.