Mike Holt Newsletters

Boxes, conduit bodies, and handhole enclosures - Based on the 2011 NEC

By Mike Holt for EC&M

Article 314 contains installation requirements for outlet boxes, pull and junction boxes, conduit bodies, and handhole enclosures. The specific conditions of use will often determine the type of box and installation methods required.

If you install a box in a wet location, for example, you must use a box, fittings and installation methods that are acceptable for wet locations. Fortunately, Article 314 helps you select the right outlet, device, and junction boxes—and size them properly.

As with any other Article, Part I provides the scope and general information. In Part II, we find installation requirements. Many of those, such as the rule for repairing the surfaces of walls and floors around electrical boxes have changed.

Repairing noncombustible surfaces

The 2008 NEC changed 312.4 to require that noncombustible wall surfaces must be repaired if there are gaps or open spaces greater than 1⁄8 in. at the edge of a cabinet, cutout box, or meter socket enclosure. This differed from previous Code language, which mentioned only drywall, plasterboard, and plaster surfaces.

The 2011 revision changed 314.21 to mirror the language found in 312.4. Now 314.21 includes any noncombustible surface.

Gaps around boxes with flush-type covers that are recessed in noncombustible surfaces (e.g., plaster, drywall, or plasterboard) must be repaired so there’s no gap greater than 1⁄8 in. at the edge of the box [314.21].

Supported boxes

The allowance for a raceway-supported box or conduit body in 314.23(E) has been one of the more difficult rules for a Code user to read, due to the length of the rule and the number of technical requirements found in it. The exception for the support of conduit bodies has been equally difficult.

The 2011 revision to this section presents the exception in an easier to understand list format. It also names more types of raceways that can use this exception. For example, Type RTRC conduit has been added to the list in this exception [314.23(E) Ex].

Outlet boxes

The 2008 revision of the NEC significantly changed 314.27. Significant changes often bring numerous errors. The 2011 revision corrects an error in the previous NEC by requiring that boxes installed in a wall for luminaire support must be marked on the interior of the box to indicate the weight ratings of the box.

The 2011 revision also:

Breaks up the requirements into a list format, for easier reading.
Incorporates the provisions for lampholders into the title of the rule.
Revises the luminaire box ratings for clarity and ease of reading

Ceiling fan boxes

Outlet boxes used as the sole support of a ceiling-suspended (paddle) fan must be listed and must be marked as suitable for this purpose. If the maximum weight isn’t marked on the box, it is allowed to support a fan up to 35 lbs. If the box is marked with a weight, it can support a fan up to that weight, but not more than 70 lbs. Ceiling paddle fans over 70 lb must be supported independently of the outlet box [314.27(C)].

Occasionally an electrician may install an extra, unused switched conductor in a luminaire outlet box installed in the ceiling.While this may seem like a nice feature because it allows for a future ceiling fan, it’s a Code violation when the ceiling fan is finally installed unless the box is listed to support a ceiling fan. This change was accepted after initial reluctance, because the NEC isn’t in the habit of dealing with future violations, no matter how likely they might be.

The result of this change in 314.27(C) is that such an installation must incorporate a box that’s suitable for ceiling fan support, despite the fact that a ceiling fan isn’t installed. Considering the effort required to install the separate, independently switched conductor, this change doesn’t add much of a burden to the electrical community. It does add an enforceable requirement for AHJs who didn’t have one before.

Where spare, separately switched, ungrounded conductors are provided to a ceiling-mounted outlet box in a location acceptable for a ceiling-suspended (paddle) fan in a dwelling unit, the outlet box must be listed for the support of a ceiling-suspended (paddle) fan [314.27(C)].

Pull and Junction Boxes and Conduit Bodies

The title of 314.28(A) is “Pull and Junction Boxes and Conduit Bodies.” That title signifies that this section applies not only to pull and junction boxes, but also to conduit bodies. Unfortunately, the text didn’t seem to support this title in the 2008 NEC.

Nowhere in 314.28(A)(1) or (A)(2) did the reader see “conduit bodies.” This change makes it clear that the rule does apply to conduit bodies, not just to pull and junction boxes.

See the Sidebar for the minimum size rules in 314.28. Here are some other key requirements:

Boxes and conduit bodies containing conductors 4 AWG and larger that are required to be insulated must be sized so the conductor insulation won’t be damaged.

The requirements for sizing boxes and conduit bodies containing conductors 6 AWG and smaller are contained in 314.16.
If conductors 4 AWG and larger enter a box or other enclosure, a fitting that provides a smooth, rounded, insulating surface, such as a bushing or adapter, is required to protect the conductors from abrasion during and after installation [300.4(G)].

Power distribution blocks

Power distribution blocks have a history of being used in large pull and junction boxes, even though the NEC has been silent on these installations. The only requirements for power distribution blocks were in Article 376 (which applies only to metal wireways). This left uncertainty regarding the field installation requirements for these blocks in junction boxes. The NEC now addresses this practice and provides clear, concise rules.

Some key facts:

Only boxes exceeding 100 cu in. can contain power distribution blocks.
The power distribution blocks must be listed.
The values in Table 312.6 apply to the wire bending space at the terminals.
Live parts of the power distribution block must be covered, whether the box cover is installed or not.
Where the junction box has conductors that don’t terminate on the power distribution block(s), the through conductors must be arranged so the power distribution block terminals are unobstructed following installation.

Handhole enclosures

The 2008 Code rule in 314.30(D) required that covers of handhole enclosures containing service conductors be bonded per 250.92(A). While the bonding requirements for metallic equipment containing service conductors are indeed found in 250.92, they’re found in Subsection (B), not (A). This error has been corrected by referring to 250.92.

Saving time

The 2011 Code revisions eliminated many sources of confusion on the requirements for the boxes and similar raceway components. However, designing a code-compliant layout still has its challenges.

Because code violations can mean expensive rework, a good design review is obviously critical. This is no less true as you evaluate the requirements found in Article 314 and review the design in a cost-efficient manner. A methodical approach of reviewing each section of Article 314 against your design blends efficiency with compliance, and in the end, will save you money.

Sidebar. 314.28 Minimum size rules

For raceways containing conductors 4 AWG and larger, the minimum dimensions of boxes and conduit bodies must comply with the following:

Straight Pulls. The minimum distance from where the conductors enter the box or conduit body to the opposite wall must not be less than eight times the trade size of the largest raceway [314.28(A)(1)].
Angle Pulls. The distance from the raceway entry of the box or conduit body to the opposite wall must not be less than six times the trade size of the largest raceway, plus the sum of the trade sizes of the remaining raceways on the same wall and row [314.28(A)(2)].
U Pulls. When a conductor enters and leaves from the same wall of the box, the distance from where the raceways enter to the opposite wall must not be less than six times the trade size of the largest raceway, plus the sum of the trade sizes of the remaining raceways on the same wall and row.
Splices. When conductors are spliced, the distance from where the raceways enter to the opposite wall must not be less than six times the trade size of the largest raceway, plus the sum of the trade sizes of the remaining raceways on the same wall and row.
Rows. If there are multiple rows of raceway entries, each row is calculated individually and the row with the largest distance must be used.
Distance Between Raceways. The distance between raceways enclosing the same conductor must not be less than six times the trade size of the largest raceway, measured from the raceways’ nearest edge-to-nearest edge.

When conductors enter an enclosure with a removable cover, the distance from where the conductors enter to the removable cover must not be less than the bending distance as listed in Table 312.6(A) for one conductor per terminal [314.28(A)(2) Ex].

Boxes or conduit bodies smaller than those required in 314.28(A)(1) and 314.28(A)(2) are permitted, if the enclosure is permanently marked with the maximum number and maximum size of conductors [314.28(A)(3)].

Taken from Mike Holt’s 2011 Understanding the NEC Volume 1 Textbook. To order your copy, please click here, or call 888-632-2633