Electrical Fittings for Metallic Conduit: Types and Their ...

Electrical Fittings for Metallic Conduit: Types and Their Applications

Electrical wiring depends on conduits for protection, while pull boxes and junction boxes simplify circuit handling. However, these elements must be firmly attached to each other to ensure a safe electrical installation. Furthermore, they must also be provided with structural support. These functions are carried out by electrical fittings, and a variety of types are available in the market.

To explore a range of fittings, you may refer to rotating type conduit fitting suppliers.

This article will provide insights into the most common types of electrical fittings, their applications, and general guidelines for correct use. Remember, fittings differ for metallic and nonmetallic conduit—this article focuses on those designed for metallic conduit. Some electrical fittings may be available in different versions, each with its own advantages and disadvantages, depending on the engineering scenario.

Our experienced electrical engineers can help you meet the NEC and local codes.

Using fittings incorrectly is dangerous, violates construction codes, and may lead to modification requests and legal action from the NYC Department of Buildings. By working with qualified electrical design engineers, you ensure that all electrical materials and equipment are properly specified.

The range of commercially available electrical fittings goes far beyond those described in this article. We will focus on the most common ones, but this is not an exhaustive list.

Couplings: Joining Conduit with Conduit

Couplings connect separate metallic conduit segments in the same circuit. There are three main mechanisms by which couplings perform their function:

• Threaded couplings: These have internal threads and are used to join threaded conduit with ease (e.g., threaded RMC). Normally, this type of coupling is a single-piece fitting.
• Set-screw couplings: These achieve a union with adjustable screws to lock the conduit in place. The main body of a set-screw coupling is a single piece, though the screws are usually removable.
• Compression couplings: These are usually three-piece fittings. They have external threads and locknuts to insert conduit and fix it in place by compression. Note that the threads are used by the locknuts, not the conduit.

Since set-screw and compression couplings are both intended for unthreaded conduit, electrical design engineers must often choose between them. Compression couplings are more expensive but grip the conduit around its diameter. Set-screw fittings are less expensive and easier to install, adapting to more locations with a screwdriver. Keep in mind that couplings must be rated for the type of conduit; for example, EMT couplings are for EMT conduit only, even if other types of conduit fit.

FMC and LFMC use a special type of screw-in coupling, similar to the central portion of a compression fitting but without the locknuts. There are also combination couplings where each end is intended for a different type of raceway. For example, you can find couplings that join RMC and LFMC.

Oversized conduit can make your installation more expensive than necessary. Conduit diameter determines the size of fittings, so you end up with oversized fittings as well.

Connectors: Joining Conduit with Electrical Boxes

Connectors join metallic conduit with pull boxes, junction boxes, and other electrical enclosures. Metallic boxes typically come with knockout holes designed to insert connectors. The connector attaches to the electrical box with a thread and locknut, while the conduit is attached using similar methods:

• For conduit types EMT, IMC, and RMC, there are both set-screw and compression connectors.

• Conduit types FMC and LFMC use a special type of screw-in connector with a compression locknut.

• All-purpose connectors use a pair of screws to adjust a metallic grip and can be used with flexible conduit of smaller diameters, as well as armored and sheathed cable.

If the position of a connector in an electrical box needs to change and a knock-out hole has already been opened, seals are available. Like couplings, compression connectors offer a more rigid connection but at a higher cost, while set-screw connectors are less expensive and easier to install in limited spaces.

Straps and Strut Clamps: Attaching Conduit to Fixed Surfaces

Straps fix conduit to surfaces and have a U-shaped body that clips around the conduit with extensions for screws. With conduit diameters usually ranging from ½” to 6”, straps are also available in corresponding sizes.

Strut clamps serve a similar purpose but have a different design. A c-shaped strut is connected to a surface with screws, and clamps are inserted into the strut, held in place by hook-shaped legs. Each clamp is made of two identical halves joined with a screw, holding the conduit in place.

For single conduit runs, straps are practical. Strut clamps are useful for parallel conduit runs, as the same strut can hold several clamps.

Elbows: Conduit Direction Change

Elbows are short conduit segments manufactured with a specified turn angle, typically 90° or 45°. They are normally connected to straight conduit runs using couplings—threaded, set-screw, or compression.

Smaller diameter EMT is easy to bend, so elbows are rarely needed. Larger conduit diameters or more rigid types like IMC and RMC are more challenging to bend. A hand bender is generally useful for small diameter EMT.

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Conduit Bodies: Combined Pull Box and Direction Change

Conduit bodies are versatile electrical fittings that can be opened to serve as a pull box while allowing a directional change if needed. T-shaped conduit boxes have two openings along the same axis with another opening at a 90° angle for circuits running in different directions. Electrical engineers can specify conduit bodies to eliminate junction boxes near bent turns or elbows, as they can perform both functions.

General Recommendations

Electrical fittings offer choice and versatility, but they also leave room for error. Working with a qualified MEP engineering firm ensures your electrical installations are code-compliant while minimizing material requirements. MEP engineers use software to simulate the electrical installation layout before construction, reducing the total conduit length and, subsequently, the number of fittings in the project.

For more information about different kinds of conduits, visit our website Flexible Conduit.