Power distribution blocks shall be permitted in pull and junction boxes over ____

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, or www.charlesRmiller.com.

314.28 Pull and Junction Boxes

Article 314 of the National Electrical Code (NEC) covers the installation and use of all boxes and conduit bodies used as outlet, device, junction or pull boxes. This article also covers conduit bodies, handhole enclosures and installation requirements for fittings used to join raceways and to connect raceways and cables to boxes and conduit bodies. [314.1] Article 314 is divided into four parts: I. Scope and General, II. Installation, III. Construction Specifications, and IV. Pull and Junction Boxes for Use on Systems Over 600 Volts, Nominal.

Boxes and conduit bodies containing conductors 18 AWG through 6 AWG must meet the installation requirements in 314.16. Boxes and conduit bodies enclosing conductors 4 AWG or larger (under 600V) must be installed in accordance with the requirements in 314.28.

When determining the minimum size box for conductors 18 AWG through 6 AWG, the sizes and numbers of conductors are needed to calculate the minimum size box. Calculations are different for pull and junction boxes. Boxes containing conductors of 4 AWG or larger, under 600V, are calculated from the sizes and numbers of raceways (see Figure 1). Where pull and junction boxes are used on systems over 600V, the installation must comply with the provisions in Part IV of Article 314.

Specific provisions for calculating pull or junction boxes containing 4 AWG or larger conductors are covered in 314.28. For raceways containing conductors of 4 AWG or larger, and for cables containing conductors of 4 AWG or larger, the minimum dimensions of pull or junction boxes installed in a raceway or cable run must comply with 314.28(A)(1) through (A)(3). [314.28(A)]

These provisions apply to both metallic and nonmetallic boxes. The calculation for the minimum size box is based not only on the raceways, but where the conductors enter and exit the box. Will the conductors enter and exit the box on opposite walls? Will the conductors enter and exit on perpendicular walls? Or will the conductors enter and exit on the same wall? There are three types of pulls: straight pull, angle pull and U pull (see Figure 2).

Specifications for straight pulls are in 314.28(A)(1). Specifications for angle and U pulls are in 314.28(A)(2). Where an enclosure dimension is to be calculated based on the diameter of entering raceways, the diameter shall be the metric designator (trade size) expressed in the units of measurement employed. [314.28(A)]

When using the trade size of the raceway, the result of the calculation will be in inches. When using the metric designator of the raceway, the result of the calculation will be in millimeters.

314.28(A)(1) Straight Pulls

Boxes containing straight pulls are sized according to the largest single raceway entering the box. Only one calculation is needed for boxes having raceways entering two walls. Two calculations will be necessary for boxes with raceways entering four walls when all the pulls are straight pulls.

In straight pulls, the length of the box must not be less than eight times the trade size (metric designator) of the largest raceway. [314.28(A)(1)] The first step is to determine the type of pull. Installing a raceway in each end of a wireway (gutter) is one example of a straight pull. The ends of this pull box provide only enough room for one raceway each (see Figure 3).

Raceways directly opposite each other are one type of installation. To be considered a straight pull, it is not necessary for the raceways to be located straight across from each other. Boxes containing raceways on opposite walls, regardless of where they are located or the amount of offset, qualify as straight pulls (see Figure 4).

Calculating the minimum dimensions of a box containing straight pull(s) is quite simple: multiply the trade size (metric designator) of the largest raceway by eight. For example, calculate the minimum dimension for a pull box with two 2-inch conduits.

The conduits are directly across from each other in the ends of a 4-inch wireway. Since the conduits are the same size, multiply either by eight. The minimum length required for this box is 16 inches (see Figure 5).

The width and depth of the pull or junction box depends on the installed raceways. Unless a raceway enters the back of the box, no requirement specifies the width or depth. The box width and depth must be large enough to provide proper installation of the raceway (or cable), including locknuts and bushings (see Figure 6).

Use the largest raceway to size pull boxes containing different-size raceways. For example, a pull box contains two conduits located on opposite walls. While one conduit has a trade size of 2 inches, the other has a trade size of 3 inches. The minimum length of this box is the trade size of the largest raceway (3 inches) multiplied by eight. The length of this pull box must be at least 24 inches (see Figure 7).

Provided the box only contains straight pulls, boxes having more than two raceway entries are calculated exactly the same. For example, three raceways will enter the left side and three raceways will enter the right side. No raceways will enter the top or bottom. All of the pulls in this box will be straight pulls.

The raceways entering the left side include one 3-inch and two 2-inch conduits. The right side contains one 4-inch, one 3-inch and one 2-inch conduit. Since all the pulls are straight, the calculation for this box only requires the largest trade size conduit. The largest raceway is 4 inches and therefore the minimum length for this box is 32 inches (see Figure 8).

No added calculation is required for additional raceways when calculating the minimum length of a box containing straight pulls only.

Because there are no raceways entering the top and bottom, the minimum width will depend on the installed conduits on each side. The width and depth of this box must be large enough to provide proper installation of the raceways, including locknuts and bushings.

Next month's column continues the discussion of pull and junction box calculations. EC