NEC 314: Outlet, Device, Pull, and Junction Boxes
What This Article Covers
NEC Article 314 covers the installation and use of outlet boxes, device boxes, pull boxes, and junction boxes. It includes the box fill calculation rules in 314.16 that every electrician needs to size a box correctly.
Key Requirements
- Box fill: count conductors, devices, clamps, and ground wires per 314.16
- Conductor volume allowances from Table 314.16(B)
- Internal cable clamps count as one conductor of the largest size in the box
- Each yoke (device) counts as two conductors of the largest size connected to it
- All grounding conductors together count as one conductor of the largest grounding conductor present
Common Field Applications
- Determining whether a single-gang box has enough cubic-inch capacity
- Sizing a pull box for a 4 inch conduit
- Sizing a junction box for splices on a feeder
Common Mistakes & Inspection Failures
- Counting all ground wires individually instead of as one largest
- Forgetting to add device fill
- Stuffing more conductors than the box's cubic-inch rating allows
Related NEC Articles
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What does NEC 314 cover?
NEC Article 314 covers the installation and use of outlet boxes, device boxes, pull boxes, and junction boxes. It includes the box fill calculation rules in 314.16 that every electrician needs to size a box correctly.
What are the key requirements of NEC 314?
Key requirements include: Box fill: count conductors, devices, clamps, and ground wires per 314.16; Conductor volume allowances from Table 314.16(B); Internal cable clamps count as one conductor of the largest size in the box. See the full requirements list on this page.
What are common mistakes with NEC 314?
Counting all ground wires individually instead of as one largest Forgetting to add device fill Stuffing more conductors than the box's cubic-inch rating allows
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Michael B.
IBEW Local 134 Journeyman Electrician · Licensed Electrical Contractor
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