In this episode of “EC&M Tech Talk,” Randy Barnett, a journeyman electrician, electrical instructor, inspector, author, trainer, and electrical safety expert, takes viewers through the background and requirements for typical boxes used in the electrical trade.
A box, which can be metallic or nonmetallic, is used to enclose conductors and oftentimes devices such as switches and receptacles. Article 314 of the National Electrical Code “Outlet, Device, Pull & Junction Boxes, Conduit Bodies, Fittings & Handholes” addresses the specific boxes listed in Sec. 314.1 Scope.
Information in the video is also taken from the UL White Book, a periodic guide providing information about electrical equipment regarding listing or labeling requirements. For example, all metal boxes except for those constructed of aluminum alloys have corrosion protection that allows them to be installed in concrete. An explanation is provided for the term “Extra Duty” as required by the NEC. Markings on cable clamps used inside of a box provide the installer specifics about the type of cables that can be used with the clamp. The UL White Book can be a valuable tool for those specifying electrical boxes and clamps as well as the installer.
Sizing a box for a particular application requires use of tables in the Code. Tables 310.16(A) and (B) are discussed, including how they are used to size boxes. Standard size metal boxes appear in the first table, giving users the volume in cubic inches of these boxes. The second table provides the volume allowed in the box for given AWG sizes of conductors. The total volume allowance for conductors cannot exceed the total volume of the box – or a larger size box must be chosen. New requirements in the 2020 NEC regarding volume allowances for equipment grounding conductors are also explained in the video.
Whether used as a review for experienced electrical workers or information for those just entering the trade, this Tech Talk episode can provide sound basic information on boxes used in electrical installations.
