When it comes to interpreting the National Electrical Code (NEC), Chapter 3 addresses the building stage of electrical construction projects, outlining general installation requirements for tasks completed by electricians daily. Article 314 is one of the essential articles in the NEC for electricians; it contains basic guidelines like box [fill] volume calculations for conductors, devices, and equipment.
Why do we use Art. 314?
Improperly sized junction or device boxes can cause damage to conductors and create unintentional arcs between those damaged conductors. Table 314.16(A) and (B) is one of the most important guides in the NEC; we use it for sizing and selecting the proper metallic (sheet metal) device or junction boxes used in dry location, residential, commercial, and light industrial applications necessary to:
- Protect combustible building materials from arcs.
- Make splices for branch-circuit conductors and feeders.
- Transition raceways or wiring methods from one method to another.
- Support and protect electrical equipment and devices or utilization equipment.
Section 314.15 also covers installation requirements and design specifications for electrical junction boxes and fittings. For example, device or junction boxes used outdoors shall be listed for wet or damp locations; in other words, they must be constructed for the application and environment in which they are installed. The NEC does not contain a table for conductor fill for plastic or nonmetallic boxes and junction boxes. Manufacturers must durably and legibly mark the volume of the box on the device. Typically, you find this information stamped on the back of the device or box. Plaster rings and extension rings can be used to expand the volume of a box.
Pull and junction boxes
In commercial and industrial applications, FS and FD boxes (typically used in non-hazardous or wet locations with a gasket), cast-iron junction boxes (typically used in hazardous, damp, or wet locations with a sealant), and junction boxes are used to simplify the circuit design and installation of long conductor runs. They provide a way to:
- Pull, splice, or change the direction of conductors.
- Reduce excessive strain on the wire and the installer(s).
- Allow long wiring runs to be installed in shorter intervals.
Pull and junction boxes can be used for both straight and angled pulls. They are mandatory in conduit runs where the total number of bends between outlets exceeds 360 degrees, which is the maximum permitted by the NEC. In addition, Sec. 314.71 provides guidelines for pull box sizing based on the size (diameter) of the connecting raceways and the direction the raceway enters the box.
Harold Deloach, a master electrician and electrical trainer/instructor, is the founder of The Academy of Industrial Arts (www.taia-school.com) in Philadelphia. With more than 30 years of experience in the field, he will be writing regular exclusive content for E-Train and can be reached at [email protected].
