Conduit body
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A conduit body (North American terminology, an "ELL") is used in electrical wiring to enable the splicing of conductors being placed within a conduit. The devices also include a fastening system to secure the conduit to the body which can be used to splice two runs of wire of a single circuit, as if a junction type of wiring box.
They are also used to enable a 90 degree corner in the conduit where there is insufficient space to mount a full-radius 90 degree sweep (curved conduit section). "Ells" are frequently used external to a building where a circuit passes through the wall either to underground conduit or up a wall via exterior wiring.
Conduit bodies come in various types and moisture ratings, using different mechanical methods of securing the pipe like conduit to the body: LB, LL, LR are types where the opening is on the back, left and right, respectively. A type T ("Tee") conduit body is like the capital letter of the alphabet— a combination of an LL and LR. The type C (coaxial) conduit body is used to splice conductors in a straight run of conduit or tubing, as it makes no turn between inlet and outlet conduit clamping opening.
Three main types of conduit are in common use:
- Plastic -- PVC conduit is now in common use and except for threaded fastenings, combines the best attributes of the other two types, allowing construction of a water proof conduit as well as one easy to assemble and shape.
- Thick wall galvanized-- The oldest type of conduit, conduit bodies are threaded female pipe receptacles for the male threaded conduit pipe ends. (Plumbing pipe threads and those for conduits are made mutually incompatible so they cannot be intermixed by accident). Joints between sections use a similarly threaded Coupling. An intermediate wiring pull point or splice uses the 'C' body in a similar manner.
- Thin wall galvanized -- called EMT in North America, EMT can be cut with a tubing cutter and bent with a pipe bender to make complex curves. (Heating PVC conduit allows the same shaping.) Couplings and fasteners are usually secured using a single compression screw at each joint flange. It is rated as water resistant, but will let flowing water into the system if it encounters immersion or a hose pipe stream. It is most commonly found in crawl spaces, basements, and garages where moisture is not a concern. A compression adapter can be used with the EMT and heavy walled (threaded) bodies, to achieve a water proof branch circuit, such as an exterior conduit run to a spot light.
The electrical code requires that conduit bodies used to contain conductor splices be marked with cubic-inch capacity. (Reference: 2003 International Residential Code, Chapter 34, p 34-5) (Also see: 2005 NFPA 70: National Electrical Code, code 300.15)
