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, Art. 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 also 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].
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 NEC revision to this section presents the exception in an easier-to-understand list format. In addition, it 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].
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; and 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 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 lb. If the box is marked with a weight, it can support a fan up to that weight, but not more than 70 lb. Ceiling paddle fans more than 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 is not installed. Considering the effort required to install the separate, independently switched conductor, this change does not add much of a burden to the electrical community. However, it does add an enforceable requirement for AHJs who did not 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)] (click here to see Fig. 1).
Pull and Junction Boxes and Conduit Bodies
The title of 314.28(A), “Pull and Junction Boxes and Conduit Bodies,” 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 below 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/other enclosure, a fitting that provides a smooth, rounded, insulating surface, such as a bushing or adapter, is required to protect conductors from abrasion during/ 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 Art. 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 (click here to see Fig. 2).
- 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.
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.
The 2011 Code revisions eliminated many sources of confusion on the requirements for the boxes and similar raceway components. However, designing a NEC-compliant layout still has its challenges. Because Code violations can mean expensive rework, a good design review is critical. This is no less true as you evaluate the requirements found in Art. 314 and review the design in a cost-efficient manner. A methodical approach of reviewing each section of Art. 314 against your design blends efficiency with compliance. In the end, it will also save you money.
SIDEBAR: Minimum Size Rules in 314.28
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 (click here to see Fig. A) .
- 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] (click here to see Fig. B) .
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)].