7 Types of Electrical Conduits and What You Need To Know
Here's what you need to know about electrical conduits and the purpose of each in electric wiring.
A simple electric wiring project can cost about $500. Depending on the installation needs, these costs can balloon up to $30,000 for large jobs. A key part of such an upgrade is the type of conduit needed.
Electrical conduit in an industrial setting. Image used courtesy of Adobe Stock
Electrical conduits are essential for a wiring job and depend on the wiring needs. You can choose from rigid metal, intermediate metal, and flexible metal conduits, electrical metallic and non-metallic tubing, liquid-tight flexible metal, and rigid PVC conduit.
What Is an Electrical Conduit?
An electrical conduit is a plastic or metallic pipe that routes electrical wires in an installation while protecting the electrical cables from damage in an exposed area. Therefore, electrical conduits are common in exposed locations such as exterior wall surfaces, crawlspaces, attics, basements, and the outdoors.
Electrical conduits can be rigid or flexible, typically installed with compatible fittings such as elbows, couplings, connectors, and electrical boxes made of similar material.
All electrical conduit installations must follow the National Electrical Code (NEC) guidelines and all applicable local code regulations.
Corrugated tube electric conduit pipe with copper power supply. Image used courtesy of Adobe Stock
The 7 Common Types of Electrical Conduits
There are seven common types of electrical conduit, each with a unique application. Typically, these conduits are divided into metal conduits and non-metal conduits.
Metal conduits include:
- Rigid metal conduit
- Flexible metal conduit
- Liquid-tight flexible metal conduit
- Intermediate metal conduit
- Electrical metallic tubing
Non-metal conduits include:
- Rigid PVC conduit
- Electrical non-metallic tubing
Here's a breakdown of each.
1. Rigid Metal Conduit
A rigid metal conduit (RMC) is a thick-walled threaded tubing typically made of stainless steel, coated steel, or aluminum. Screwing connectors connect the conduit to the main tubes. A rigid metal conduit is an excellent choice for protecting against impacts and severe damage due to its strong construction.
In short-run installations, RMC can also be used as a grounding conductor. However, the best practice is to use wiring with a grounding wire.
Rigid metal conduits also have thick walls to protect the cables from electromagnetic interference that can harm sensitive equipment.
Most RMCs have a PVC coating or are galvanized to prevent corrosion from water or other chemicals.
Galvanized rigid conduit is the most popular type of RMC, excellent for applications in industrial and commercial buildings.
PVC-coated aluminum is excellent for applications where chemical fumes can corrode the steel. Bronze alloy works well in chemical plants, coastal areas, underwater, and oil refineries.
PVC-coated rigid steel resists grease, oils, alkalis, acids, and moisture corrosion.
You must ensure that the fittings you use for an RMC use the same metal to avoid issues with galvanic corrosion.
2. Flexible Metal Conduit
A flexible metal conduit (FMC) is made by coiling self-interlocked steel or aluminum strips to form a hollow tube for electrical cables. This conduit is typically available in standard wall or reduced wall thickness.
Manufacturers also produce extra flexible FMC for tighter radii, though you have to confirm its UL certification.
Standard FMC is common in dry areas where installing a non-flexible conduit would be impractical, but the metallic strength is still needed. FMC is common in installations where you want to avoid passing vibrations from equipment, such as a motor, to another structure.
3. Intermediate Metal Conduit
Intermediate metal conduit (IMC) is a thinner, lighter version of rigid metal conduit. However, it can still be used in similar applications to RMC.
Intermediate metal conduits are commonly preferred in construction since they are easier to work with and lighter, offering the same level of protection as a rigid metal conduit. It is also a more economical alternative, thus suitable for projects with a tight budget.
4. Liquid-Tight Flexible Metal
Liquid-tight flexible metal conduit (LFMC) is a special type of flexible metal conduit with sealed fittings and plastic coating to make it watertight and corrosion-resistant. Therefore, it can be used in wet areas, unlike FMC, that's only suitable for dry locations.
LFMC is a common choice for outdoor equipment such as air conditioner units.
5. Electrical Metallic Tubing
Electrical metallic tubing (EMT) is a conduit commonly made with galvanized steel or aluminum. Unlike rigid metal conduits, it is lighter, thinner, strong, and bendable when used with a tube bender tool.
EMT is typically installed using fittings and couplings protected by compression-type fasteners or setscrew. It is also not threaded.
EMT is commonly used for indoor wiring for commercial and residential buildings. Any outdoor application must use watertight industrial fittings.
6. Electrical Non-Metallic Tubing
Electrical non-metallic tubing (ENT) is a flexible, plastic, corrugated tubing that's flame-retardant and moisture-resistant. It can be bent easily and installed using glued plastic fittings or a snap lock.
Unlike electrical metallic tubing, non-metallic tubing cannot be used in external applications. It is commonly used inside walls, especially standard metal-frame or wood walls. It can also be installed inside concrete block structures or covered with concrete.
7. Rigid PVC Conduit
Rigid polyvinyl chloride (PVC) conduit is similar to a plastic plumbing pipe. It is installed using plastic fittings glued together in place. It can also be bent easily using a heater box to fit various installations.
Rigid PVC conduit can be watertight since the tubing and fittings are glued together. Therefore, this conduit is excellent for outdoor applications where the electrical cables must be buried in the ground. It can also be used in various corrosive environments where code allows it.
Choosing the Right Conduit
Choosing an electrical conduit for your wiring project should be easy. You can refer to NEC, local, and engineering guidelines to identify the options that best suit your purpose.