What Type of Wire Is Romex and When to Use It

What Type of Wire Is Romex?

Romex is a type of electrical wire that is commonly used as residential branch wiring.

It is categorized as either underground feeder (UF) or non-metallic sheathed cable (NM and NMC).

NM and NMC conductors have insulated conductors contained in a non-metallic sheath, with NMC cable having a non-conducting, flame-resistant, and moisture-resistant coating.

Romex is permitted in damp environments and must be protected, secured, and clamped to device boxes, junction boxes, and fixtures.

It should not be used as a substitute for appliance wiring or extension cords.

Armored cables, such as BX, provide extra protection and have similar rules for protection and support as Romex.

Knob-and-tube wiring, an obsolete method, is considered a fire hazard and should be evaluated by a qualified electrician.

Key Points:

  • Romex is commonly used as residential branch wiring.
  • Romex can be categorized as either underground feeder (UF) or non-metallic sheathed cable (NM and NMC).
  • NM and NMC conductors have insulated conductors contained in a non-metallic sheath, with NMC cable having additional flame and moisture resistance.
  • Romex is permitted in damp environments but needs to be protected, secured, and clamped to device boxes, junction boxes, and fixtures.
  • Romex should not be used as a substitute for appliance wiring or extension cords.
  • Armored cables, like BX, have similar rules for protection and support as Romex.
  • Knob-and-tube wiring is outdated and considered a fire hazard, needing evaluation by a qualified electrician.

Did You Know?

1. Romex wire, also known as Nonmetallic Sheathed Cable (NM), was first introduced in the United States in the 1920s and quickly gained popularity due to its ease of installation and cost-effectiveness.

2. The name “Romex” is actually a brand name held by Southwire Company LLC, one of the largest manufacturers of electrical cables in North America. However, over time, the term “Romex” has become a genericized trademark and is commonly used to refer to any nonmetallic sheathed cable.

3. Romex wire is typically made up of three main components: a set of copper conductors for electrical current transmission, a polyethylene insulation layer to protect the conductors, and a PVC jacket for mechanical protection.

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4. While Romex wire is most commonly used for residential electrical wiring, it is also approved for use in commercial and industrial applications. Its 600-volt rating and various gauge sizes make it versatile for a wide range of electrical installations.

5. Romex wire is available in different colors, each indicating its specific purpose. For example, standard Romex cables usually come in white or yellow, indicating they are used for general-purpose electrical installations. However, there are also specialized Romex cables available in different colors, such as orange for outdoor use or red for dedicated circuits.

Romex: An Overview Of A Common Residential Electrical Conductor

Romex is a commonly used electrical conductor in residential branch wiring. It is renowned for its versatility, ease of installation, and cost-effectiveness. This cable, developed by the Romex brand, falls into two main categories: underground feeder (UF) and non-metallic sheathed cable (NM and NMC).

Understanding The Different Categories Of Romex: UF And NM/NMC

Romex cables serve different purposes and requirements, categorizing them accordingly. Underground feeder (UF) conductors are ideal for underground installations, featuring a solid plastic core that provides insulation and environmental protection. Notably, UF cables have a rigid structure and cannot be rolled between fingers.

In contrast, non-metallic sheathed cable (NM and NMC) conductors find common application in indoor wiring installations. These cables consist of two or more insulated conductors enclosed in a non-metallic sheath. The sheath acts as extra protection, safeguarding the conductors against accidental damage.

Features And Benefits Of NM And NMC Conductors

NM and NMC cables offer several advantageous features that make them a popular choice for residential wiring. One notable feature is the non-conducting, flame-resistant, and moisture-resistant coating found on NMC cables. This coating provides an extra layer of safety and protection, making them suitable for use in damp environments such as basements.

Along with their protective coating, NM and NMC cables are designed to be secured, protected, and clamped to device boxes, junction boxes, and fixtures. This ensures proper installation and adherence to electrical safety codes. It is important to avoid using support devices that may damage the cables, such as bent nails and overdriven staples.

Romex And Its Uses In Damp Environments

One of the notable advantages of Romex is its suitability for use in damp environments. The moisture-resistant coating found in NMC cables allows them to function effectively in areas such as basements, where water presence may be a concern. This feature provides homeowners with peace of mind, knowing that their electrical wiring is adequately protected even in potentially wet conditions.

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Romex And Its Limitations: Not Suitable For Certain Construction Projects And Appliances

While Romex is a versatile and widely used electrical conductor, it does have limitations. It is crucial to be aware of these limitations to ensure the proper and safe use of Romex cables.

One limitation is that Romex is not permitted for use in residential construction higher than three stories or in any commercial construction. This restriction is in place to ensure that the wiring used in larger buildings meets specific safety and regulatory standards.

Another important point to highlight is that Romex should not be used as a substitute for appliance wiring or extension cords. Romex is intended for permanent wiring in homes and is not designed to handle the load and flexibility required by appliances or the temporary nature of extension cords.

In conclusion, Romex is a widely used and reliable electrical conductor in residential branch wiring. It offers various advantages, such as ease of installation and cost-effectiveness. Understanding the different categories of Romex, such as UF and NM/NMC, allows for appropriate selection and installation based on specific needs.

Furthermore, it is important to be aware of its limitations to ensure the compliant and safe use of Romex in different construction projects and appliance installations.


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Frequently Asked Questions

What is the real name for Romex wire?

The real name for Romex wire is Non-Metallic Sheathed Cable (NM cable) or Non-Metallic Cable (NMC). It has gained popularity over the last four decades and is distinguishable by the trademarked jacketing known as SIMpull, developed by Southwire. This type of electrical cable has been widely used for residential applications and is widely recognized by its official name, NM cable or NMC.

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Why is wire called Romex?

The term “Romex” is derived from Rome Cable Corp., a prominent manufacturer based in Rome, New York. This company was known for producing the type of cable commonly referred to as Romex. However, the exact origin of the letter “x” in Romex remains shrouded in mystery. Rome Cable Corp. experienced a significant decline in its fortunes, ultimately leading to its bankruptcy filing in 2003. Unfortunately, the company’s factory faced demolition in 2010, marking an end to its era as an industry leader.

What are the 4 wires in Romex?

The 4 wires in Romex include a white wire for the neutral connection, a black wire and a red wire for the hot connections, and a green wire for equipment grounding. However, it is important to note that only three of these wires actually carry current for the circuit. The neutral wire provides the return path for the current, while the hot wires (black and red) carry the actual electrical current. The green wire, on the other hand, serves as a safety measure, providing a path for any potential electrical faults or excess current to safely dissipate.

What material is Romex?

Romex is a type of electrical cable that is commonly used for indoor applications. It is composed of multiple THHN wires that are bundled together and protected by a sheath made of polyvinyl chloride (PVC). This makes Romex cables durable and suitable for various purposes, such as connecting electrical panels to appliances and lighting fixtures. Thanks to its design, Romex is a reliable and efficient choice for wiring projects in areas like garages, interior walls, and surface wiring above ground.

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