Electrical splice box sizing11/4/2023 NEC 314.28 establishes certain minimum dimensions for pull and junction boxes and conduit bodies to ensure adherence to wire fill requirements and protection for electrical conductors during pulling. Minimum Size of Conduit Bodies Used as Pull and Junction Boxes Three hub configurations are referred to as “T” bodies, and four hub configurations as “X” bodies (see photo 3). Two hub configurations are often referred to as straight, LB, or LL or LR, to designate the direction the raceway will be diverted. Other conduit body configurations may have two, three or even four raceway attachment hubs of the same size or different sizes. Be sure, however, to look for the internal volume marked in the conduit body for verification. ![]() These conduit bodies typically are designed to contain wire splices or a wiring device so most often they will be listed for this purpose. The obvious use for this conduit body is at a termination point of a wiring system. The simplest conduit body has only one raceway attachment hub. Example largest hub size 21 (3/4): Measurements expressed as multiples of trade sizes are to be determined by converting the trade size of the raceway (not the metric designator) to a value expressed in millimeters. According to NEC 314.5, “Conduit bodies such as capped elbows and service-entrance elbows that enclose conductors 6 AWG or smaller, and are only intended to enable installation of the raceway and the contained conductors, shall not contain splices, taps, or devices and shall be of sufficient size to provide free space for all conductors enclosed in the conduit body.”įigure 3. Since a conduit body does not typically contain screw holes for wiring device mounting, specially designed and listed covers, for this purpose, are provided by the manufacturer of the conduit body. These same rules apply for determining the minimum size of the conduit body used as a box. The simplest way to determine if a listed conduit body is suitable for use as a splice box or as an outlet or device box is to look for the internal volume marking required by NEC 314.16 in the conduit body. When intended for such use, a conduit body is subject to the requirements for a box. NEC 300.15 also recognizes a conduit body as equivalent to a box for containing wire splices and wiring devices, such as a switch or receptacle. ![]() It has also been common practice to connect a wide variety of approved raceways, cables and cord to internally threaded hubs in conduit bodies using listed fittings.Ĭonduit Bodies Used As a Box for Housing Splices or Wiring Devices Nonmetallic conduit bodies may have unthreaded hubs (sockets) into which rigid PVC conduit is to be glued or internally threaded hubs to accept threaded adapters that are listed for use with raceways. Metallic conduit bodies are provided with means for securing rigid or intermediate metal conduit by threading into internally threaded hubs or electrical metallic tubing (EMT) by unthreaded hubs having set-screws. ![]() In addition, it is anticipated that a conduit body will be used as a pull box, and therefore they are subject to either specific dimensional or performance requirements to ensure adherence to wire fill requirements and protection for electrical conductors during pulling according to NEC 314.28. A listed conduit body is always subject to the construction and performance requirements for a conduit fitting for direct attachment to conduit or tubing. First and foremost, a conduit body is part of the raceway system to which it is attached.
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