Electrical wiring relies on conduit for protection, while pull-out boxes and junction boxes simplify circuit handling. However, these elements must be firmly fixed together for a safe electrical installation. Furthermore, they must also be equipped with structural support. These functions are performed by electrical connections, and there are several types on the market.
This article will provide an overview of the most common types of electrical accessories, along with their applications and some general guidelines for correct use. Keep in mind that connections are different for metallic and non-metallic conduit – this article will focus on those designed for metallic conduit . Note that some electrical connections may be available in different versions, and each has advantages and disadvantages, as with any engineering decision.
Our experienced electrical engineers can help you meet NEC and local codes.
Using fixtures incorrectly is not only dangerous, but it goes against building codes and can lead to modification requests and legal action from the New York City Department of Buildings. By working with qualified electrical design engineers, you can ensure that all electrical materials and equipment are specified correctly.
The range of commercially available electrical accessories goes far beyond those described in this article. We'll focus on the most common ones, but this is not an exhaustive list.
Couplings: Joining Conduit to Conduit
Couplings are used when you need to connect separate segments of metallic conduit into the same circuit. There are three main mechanisms by which couplings perform their function:
- Threaded couplings simply have internal threads, as implied by their name, and are used to easily join threaded conduits (e.g. threaded RMC). Typically, this type of coupling is a single piece.
- Set screw couplings achieve a union with adjustable screws, to lock the conduit in place once inserted. Although the main body of a set screw coupling is a single piece, the screws are typically removable.
- Compression couplings are typically three-piece fittings. The coupling has external threads and locknuts to insert the conduit and secure it by compression. Note that the threads are used by the locknuts, not the conduit.
Because set screw and compression couplings are intended for non-threaded conduit, electrical design engineers must often choose between them. Compression couplings are more expensive, but they secure the conduit across its entire diameter, rather than at a single point like set screws. However, threaded connections are cheaper and easier to install, adapting to more locations because they are adjusted with a screwdriver – compression couplings require a wrench and can be difficult to install when space is limited. . Keep in mind that couplings must be rated for the conduit type; for example, EMT couplings are for EMT conduit only, even though other types of conduit will fit.
FMC and LFMC use a special type of bolted coupling, similar to the center portion of a compression fitting, but without the locknuts. Note that there are also combined couplings, where each end is intended for a different type of track. For example, you can find couplings that join RMC and LFMC.
Oversized conduit can make your installation much more expensive than necessary. Keep in mind that the diameter of the conduit determines the size of the fixtures, so you also end up with oversized fixtures.
Connectors: Joining Conduits with Electrical Boxes
Connectors are used to join metal conduits with junction boxes, junction boxes, and other electrical enclosures. Metal cases typically come with holes, which are designed to insert connectors. The connector is attached to the electrical box with a thread and locknut, while the conduit is connected with methods similar to those used for connectors:
- For EMT, IMC, and RMC conduit types, there are clamping and compression screw connectors.
- FMC and LFMC conduit types use a special type of threaded connector that has a compression locknut.
- Multipurpose connectors use a pair of screws to adjust the metal handle and can be used with flexible conduits of smaller diameters, as well as shielded and coated cables.
If you need to change the position of a connector in an electrical box and you have already cut a knockout hole, there are seals available. As in the case of couplings, compression connectors offer a higher cost, but offer a more rigid connection, while fixing screw connectors have a lower cost and are easier to install in reduced spaces.
Support Straps and Clamps: Securing Conduit to Fixed Surfaces
Straps are used to secure conduit to surfaces. They have a U-shaped body that allows them to be attached around the conduit and have one or two extensions with holes for screws. Because conduit comes in a wide variety of diameters, typically ranging from ½” to 6”, strips are also available in corresponding sizes.
Support clamps achieve a similar purpose by securing conduit to surfaces, but the design is different. A C-shaped bracket is attached to a surface with screws and clamps are then inserted into the bracket, held in place by hooked legs. Each clamp is made of two identical halves that are joined together with a screw at their intersection, holding the conduit in place.
When dealing with a single run of conduit, strapping is the most practical solution. However, support clamps are very useful when there are parallel conduit runs, as the same support segment can contain multiple clamps.
Elbows: Change conduit direction
Elbows are short segments of conduit manufactured to a specified turning angle, typically 90° or 45°. Being conduits themselves, they are typically connected to straight conduits using couplings – threaded, set screw or compression. Just keep in mind that threaded elbows require threaded couplings, otherwise there is a choice between set screw and compression.
Metal conduit can be bent, so elbows can be avoided in many cases. Smaller diameter EMTs tend to be easy to bend, so elbows are rarely needed. The difficulty of bending increases as the diameter of the conduit increases, or if you are dealing with the stiffer types: IMC and RMC. A manual bender is generally useful for small diameter EMT.
Conduit bodies: combined drive and direction change box
Conduit bodies are among the most versatile and useful electrical accessories, as they can be opened to serve as a pull box while allowing a change of direction if necessary. There are also T-shaped conduit boxes with two openings on the same axis, plus another opening at a 90° angle if two circuits are to run in different directions. Electrical engineers can specify conduit bodies to eliminate junction boxes near bends or bent elbows, since conduit bodies can perform the function of both.
General Recommendations
Electrical accessories offer choice and versatility, but that also means there's a lot of room for error when dealing with them. Working with a qualified MEP engineering firm ensures your electrical installations are up to code while minimizing material requirements. MEP engineers use software to simulate the electrical installation layout prior to actual construction, allowing for a reduction in the total length of conduit in the project, which also reduces the number of accessories.
