Metal conduits are hollow tubes that protect electrical wires from mechanical and chemical damage while providing an organized route for the cables. Due to the enhanced strength, the metal conduits are suitable for demanding applications and environments.
Running the cables through the tubes protects them from abrasion, vibrations, corrosion, high temperatures, chemicals, UV rays and other harsh conditions with the potential to cause damage. In addition, the conduits support and direct the conductors to respective parts of the building or structure.
A single type or a combination of coatings increases the capabilities of the metal conduits to provide protection. For example, adding metallic coatings, such as zinc, and a non-metallic coating, like a PVC, or an organic coating greatly enhances the corrosion resistance.
To meet the different application requirements, there is a wide range of conduits. These differ on the type of metal, flexibility of rigidity, wall thickness, corrosion resistance, chemical resistance, and other factors as we can see below.
Basic types of metal conduits
There are both rigid and flexible options, and these may have different designs to meet varying application needs and budgets. These will have variations such as the wall thickness, coating, how much it can bend, and more. The properties influence where to use the conduit and which method to use when installing, bending, and joining the different parts.
Metal conduits are mostly made of aluminum, stainless or galvanized steel. Some for certain applications have additional coatings or other materials to protect them and the cables from corrosive, high temperature and other harsh conditions. Of these, galvanized steel is the most common due to its high corrosion resistance and favorable cost.
Although there several types of conduits, the four basic categories are;
- Rigid Metal Conduit (RMC)
- Intermediate Metal Conduit (IMC)
- Flexible Metal Conduit (FMC)
- Electrical Metallic Tubing (EMT)
The Rigid Metal Conduit (RMC)
This is the heaviest and thickest metal conduit that is often used for the most demanding applications. The thick walls allow the conduit to withstand impacts and pressure from heavy weight, and accommodate threading which makes it easy to install in any custom or standard length.
The rigid metal conduits are suitable for both exposed and concealed indoor and outdoor applications, such as underground power cables. It can also be used in heavy traffic areas like driveways, across the roads, and more.
Other applications include the service entrance since the conduits great strength helps in withstanding the rough conditions caused by heavy weights, powerful winds, falling trees or branches, storms, and others.
One point to note is that the RMC provides the best protection, but is the most expensive option due to its cost. It is also more complicated to install as it requires special tools.
Intermediate metal conduit (IMC)
This is usually a galvanized metal conduit which is lighter, thinner and less costly than the rigid type, but heavier than the Electrical metal tubing (EMT). Although it is lighter than the RMS, the IMC provides adequate protection for a majority of applications and is a great choice for the many installers due to its lower cost and ease of handling.
The IMC is an ideal choice for outdoor applications, like basements, garages, and other exposed walls.
Electrical Metallic Tubing (EMT)
This has thinner walls, making it the lightest and most affordable among the three types of metal conduits. It is easy to handle, alter, bend, or redirect using simple tools. However, you cannot add threads due to the light walls. Technicians usually use clamps to fit them together and hold them in place.
But despite the light walls, the conduit provides adequate protection to the cables. It is typically used within building’s walls and for lighting fixtures
Flexible metal conduits
The flexible metal conduit, just like the rigid types, has a hollow tube where wires can pass. It easy to take any shape and does not maintain permanent bends, making it suitable for applications that require flexibility or where the cables are subjected to regular movements.
The flexible conduit has a corrugated spiral rib form that allows it to flex and bend easily. This makes it perfect for applications prone to vibrations or regular movements of the electrical cable during machine operation and where the use of the rigid conduit is impossible or would require too many bends.
Typical applications include water heaters, can lights, motors, attic vents, etc.
One of the benefits is its ability to protect the wiring without necessarily confining the installation to straight lines. Furthermore, it has the ability to withstand vibrations and movements without straining itself or the cable inside.
The general flexible type is not ideal for wet conditions. But there are some, for example the liquid-tight flexible metal conduit that has a coating of a waterproof material, which allows them to work in both dry and wet conditions.
Benefits of metal conduits
- The conduits provide a strong mechanical protection for the electrical cables. Besides protecting the cables against mechanical or chemical damage, some types, just as the galvanized steel conduits, whether rigid or flexible, are more durable, have better corrosion resistance and longer service life.
- For the steel conduit, it protect the cables from electromagnetic interference (EMI). This EMI-shielding capability makes the steel conduits suitable for sensitive wirings, e.g. power and data cables for computers, communication or security systems.
- If properly installed, the conduits can be used as grounding conductors.
Metal conduits provide the best protection to electrical cables. In addition to preventing damage from mechanical and chemical conditions, they provide a route and support for the wires, hence, ensuring an organized and flexible installation. Other than preventing physical damage, the metal conduits can also be used as a corrosion protection, EMI shielding, and electrical grounding.