MC Electrical Wire or Romex: A Guide to These Cables


About MC Electrical Wire or Romex, Electrical wires are available in many types and designs. Each model has unique aspects based on the purpose and usage environment. Metal-clad (MC) electrical cables and Romex are among the most common types. You can find an MC electrical wire in many residential buildings. Electricians also use them on feeders and branch circuits.

Here is more information on MC cables and a comparison with Romex.

Table of Contents

MC Electrical Wire Definition and Types

MC electrical wires are cables with a metallic coating. Edwin Greenfield developed the original design in the early 1900s. The models currently in the market slightly differ from the first type.

MC wires have several aspects that make them unique. First, they feature metallic sheathing around the insulated wires. Besides that, they contain at least three wires.

One is typically a ground wire, while the others are hot and neutral conductors.

Another unique feature is the inner coating. Manufacturers often use THHN nylon to cover individual cables. This material withstands heat and is water resistant.

An MC cable

An MC cable

MC electrical wire Types

MC cables come in various types to suit different applications. Some common ones are:

  • Continuously corrugated weld (CLW)
  • Galvanized armor
  • Steel wire armor (SWA)
  • Aluminum interlocked armor (AIA)

CLW is a medium-voltage cable. Electricians use it for control instrumentation. The corrugated metal sheath in CLW cables is usually aluminum. Still, some types contain copper, bronze, or steel.

CLW cables have a wavy look. Additionally, they are water resistant, making them ideal for specific fields. Such are transportation and petrochemicals.

Galvanized armor wires have a steel coating. They also come with a PVC roll jacket. These features make the wires ideal for oily and wet areas. You will likely find galvanized armor cables in the mining and petroleum industries.

Galvanized steel wires

Galvanized steel wires

SWA cables contain strands of galvanized steel wire. They are popular in underground applications. Electricians also use them for auxiliary cable control.

AIA wires are spirally wound designs common in many industrial applications. Such are pulp and paper, mining, and power. AIA cables that contain PVC jacketing are water and flame resistant. They can also withstand the sunlight for an extended period.

The Pros of MC Electrical Wire

Metal-covered electrical wire is popular due to its pros. Here are some of them.

1. Reliability in harsh conditions

MC wires can endure piercing, unlike non-metallic cables. This aspect makes them perfect for environments with a lot of machine movement. Besides, they are ideal for areas frequently under construction.

Damaged cable

Damaged cable

2. Flexibility

MC cables have a flexible casing. Hence, they can easily fit into tight spaces and bend around corners.

3. Easy and cheap installation

Many electrical cables need conduit and lubrication to pass through pathways. MC electrical wire doesn’t need tubing since it has durable material. When using it, you enjoy easy installation while saving time and money.

4. Approval by IEEE

The Institute of Electrical and Electronics Engineers (IEEE) approves MC cables for most uses. This is because they meet many specifications. Such are:

  • UL 1685
  • A-A59544
  • UL 1569

What Is a Romex Cable?

Romex is a brand name for an electrical cable produced by Southwire. This type of wire has a non-metallic (NM) sheathing. It’s also among the most popular for residential uses.

While Romex is a brand name, many consumers use the term when referring to all NM sheathing wires.

Romex cables consist of PVC material. Due to this, they are flexible and can fit into tiny spaces. The wires have one ground and at least two conductor wires.

One is typically a neutral conductor, while the rest are hot ones. Every wire in a Romex cable has individual insulation. There is also an added coating on the strands.

NM sheathing cable

NM sheathing cable

You can find various types of Romex cables in the market. The wires cables come in different sizes based on the power they can run. The most common types are 10AWG, 12AWG, and 14AWG.

Romex Cable Pros

Romex cables have many advantages due to their design. For example, they can handle up to 600 volts. Further, you can install them in plastic boxes. This aspect eliminates the need for grounding.

Installing NM wires in some environments can be tricky. If the cable encounters an obstacle, it won’t move. Additionally, the PVC thermal insulation coating may tear, leading to losses.

Romex cables are easy to install in most environments. When using them, you can save time and not worry about damage.

Other pros of Romex electrical wires are:

  • They are easy to cut
  • You can easily unspool and straighten the cable
  • The cables are light
 Pliers cutting an electrical cable

 Pliers cutting an electrical cable

Romex Wires Vs. MC Cables

After learning about Romex electrical wire and MC cable, you may wonder which one is suitable. You might also ask –’ When is MC cable required?’

Understanding the differences between these options can help you identify the best one for your needs.

MC cables have metal armor protecting the strands. On the other hand, Romex wires feature PVC sheathing. This one is more delicate, especially for outdoor uses.

Romex wires may need conduits in some environments. While this improves protection, installation requires more time. It also increases the total cost of your project.

Running Romex in piping is a debatable topic among electricians. While some experts prefer it, others oppose it due to the high cost. Metal electric wire doesn’t require a conduit. Hence, its installation process is pretty cheap and quick.

Electrical lines in conduit pipes

Electrical lines in conduit pipes

Romex cables offer limited PVC jacket protection. Due to this, they are only ideal for indoor applications. Using the wires outside will lead to frequent damages and repairs. It can also affect the integrity of your entire electrical system.

MC cable vs. Romex cost is another critical difference. Romex is cheaper to buy since it requires fewer resources to make. Still, it will be more expensive for areas that need conduits.

PVC insulated cables


Is an MC cable better than Romex?

MC cable is better than Romex if you are looking for durability. You can also consider it if you want to run the wire in a wet area or one highly prone to fires.

Romex cables are preferable only for indoor applications. They are also the best choice if your project requires a lot of cutting.

Can I use Mc cables for residential applications?

Yes. While MC electrical wire is popular in hazardous applications, it’s also great for residential use. NEC approves its usage for over 12 general indoor and outdoor applications. 

Why is Romex not allowed in conduit?

The NEC doesn’t ban consumers from using conduits with Romex cables. Still, many electricians are against the idea for several reasons.

First, running Romex in conduit leads to heat accumulation. This problem will most likely occur when using metal ducts. Besides, placing Romex in tubes isn’t cost-effective.


MC electrical wire is a perfect choice for almost any use. It meets the requirements for most environments. Likewise, it offers reliable protection against elements.

While MC cables are great, they aren’t cost-effective for residential use. If you don’t need conduits, consider Romex electrical wires.

The sheathing is less durable, but you might not need to worry about corrosion and high temperatures indoors.

Contact us if you need help choosing between MC electrical wire and Romex.