Know your conduit body and use it

Conduit bodies are used to access the inside of the raceway for pulling, inspection and maintenance when the raceway changes direction. Allows connection of straight conduit runs, branch conduit runs and 90° bends. Couplings for connecting conduit or conduit to enclosures or other equipment without rotating conduit, etc. Allows future access and removal of system components.

Comparison of Wiring Methods

Electrical conduit provides excellent protection for enclosed conductors from shock, moisture and chemical vapors. Different numbers, sizes and types of conductors can be pulled into conduit, which simplifies design and construction compared to the cost of multiple cables or custom composite cables. Wiring systems in buildings may change frequently. By using electrical conduit, frequent wiring changes are made easier and safer because existing conductors can be withdrawn and new ones installed with little interruption along the conduit path.

Conduit systems can be made waterproof or submersible. Metal conduit can be used to shield sensitive circuits from electromagnetic interference and also to prevent such interference from being emitted from closed power lines. Non-metallic conduit is corrosion resistant and lightweight, reducing installation labor costs.

When installed with proper sealing fittings, conduit will not allow the flow of flammable gases and vapors, providing protection from fire and explosion hazards in areas where volatile materials are handled.

Certain types of conduit are approved to be encased directly in concrete. This is often used in commercial buildings to allow electrical and communication outlets to be installed in the middle of large open areas. For example, retail display cases and open office areas use floor-mounted conduit boxes to connect power and communication cables.

Both metal and plastic conduit can be bent on the job site for a neat installation without the need for excessive fabricated fittings. This is especially beneficial when following irregular or curved building contours. Special bending equipment is used to bend conduit without kinking or denting it.

The cost of conduit installation is higher than other wiring methods due to material and labor costs. In applications such as residential construction, a high degree of physical damage protection may not be required, so the cost of conduit is not guaranteed. Conductors installed in conduit do not dissipate heat as easily as those installed in open wiring, so if multiple conductors are installed in a conduit, the current capacity of each conductor must be reduced (derated). Wiring regulations prohibiting total curvature of more than 360 degrees in conduit are impractical, so special outlet fittings must be provided so that conductors can be installed in such conduit without damage.

Certain types of metal conduit can also be used as useful connection conductors for grounding (earthing), but wiring codes may also specify workmanship standards or certain types of supplemental grounding methods. Although metal conduit can sometimes be used as a grounding conductor, the length of the circuit is limited. For example, long-term conduit used as a grounding conductor may have too high a resistance and not allow overcurrent equipment to operate properly in the event of a fault.

Fittings

Although similar to the conduit used in piping, electrical fittings are specifically designed to connect conduit.

A junction box connector connects conduit to a junction box or other electrical box. A typical box connector is inserted into the knock-down hole of the junction box and then a ring (called a lock nut) is used to secure the threaded end from inside the box, as the bolt will be held in place by the nut. The other end of the fitting usually has a screw or compression ring which is tightened down to the inserted conduit. Fittings for unthreaded conduit are either held in place with a set screw or with a compression nut that surrounds the conduit. Universal fittings for use with metal conduit can be made of die-cast zinc, but when stronger fittings are required, they are made of copper-free aluminum or cast iron.

A coupling connects the two conduits together.

Sometimes the fittings are considered conductive enough to connect (electrically connect) the metal conduit to the metal junction box (thus sharing the ground connection of the box); other times, a grounding sleeve is used, which has a jumper from the sleeve to a ground screw on the box.

Unlike plumbing, if the pipe is watertight, the idea is to prevent water from entering, not entering. In this case, gaskets are used with special fittings, such as the headers from the overhead power supply to the meter.

Flexible metal conduit is usually used with fittings with clips on the outside of the box, just like bare cable.

Conduit Bodies

Conduit bodies can be used to provide pull paths in a series of conduits to allow more bends in specific portions of the conduit to save space where full size bend radii are impractical or impossible, or to split conduit paths to multiple directions. Conduits shall not be spliced within the conduit body unless specifically listed for such use.

Conduit bodies differ from junction boxes in that they do not require separate support, which makes them useful in some practical applications.

Conduit bodies are available in a variety of types, moisture levels and materials, including galvanized steel, aluminum and PVC. depending on the material, they use different mechanical methods to hold the conduit in place. These include.

L-shaped bodies ("Ells") include LB, LL and LR, where the inlet is aligned with the access cover and the outlet is located on the back, left and right side, respectively. In addition to providing access for wire pulling, the "L" form allows for 90 degree turns in conduit where there is not enough room for a full radius 90 degree sweep (bent conduit section).

The T-shaped body ("Tee") features an inlet aligned with the access cover and an outlet located to the left and right of the access cover.

C-shaped bodies ("Cees") have identical openings above and below the service cover for straightening the conductors because they do not turn between the inlet and outlet.

"Service Ell" bodies ("SLBs") are shorter ell with an entrance flush with the service cover and are commonly used where circuits pass through the outside wall from the outside to the inside.