Wiring a house is not a simple task. There are many requirements and considerations in a residential installation. Copper wires must run in parallel, but not touch one another. This presents a challenge when they’re in a tightly packed bundle, which is where Romex wire and cable solve this problem.

What Is Romex Wire?

Romex® is a brand name for cable and wire products made by Southwire. It generally refers to nonmetallic (NM) sheath wire used in branch (B) applications (hence the common name Romex NM-B wire). A Romex cable usually has multiple thermoplastic high-heat-resistant, nylon-coated (THHN) wires bundled and sheathed in polyvinyl chloride (PVC). These wires and cables are often used in interior walls, and garages, and to connect home electrical panels to lights and appliances. However, they’re not adequately protected from the elements, so aren’t well-suited for outdoor applications.

The NM cable used in Romex wire has a non-conducting coating. This coating is also moisture-resistant and flame-resistant. These properties make Romex cables different than other types of home wiring in that they can be used in basements and other damp environments. They also feature nylon jacketing, bare copper grounding, and annealed soft copper conductors. For wires used as underground feeder conductors, a solid plastic core is used.

Specifications of Romex NM-B Wire

The design and construction of this type of wire support a rating of up to 600 volts. They have an ampacity limit of 140℉. In a dry environment, Romex NM-B wire has a tolerance for temperatures up to 194℉.

Romex wire is supplied with two or three conductors, in sizes from 14 American Wire Gauge (AWG) to 2 AWG. Its suitability for many applications is due to compliance with specifications such as ASTM International B-3 and B-8, Restriction of Hazardous Substances (RoHS), and National Fire Protection Agency (NFPA) 70. Romex also complies with UL Standard 83 and 719 as well as the Registration, Evaluation, Authorization, and Restriction of Chemicals (REACH) regulation.

National Electric Code (NEC) Requirements

The NEC requires Romex conductors to be protected, secured, and clamped to other electrical equipment. This applies to connections to device boxes, junction boxes, and fixtures. Intended as permanent wiring, Romex wires cannot be used as substitutes for extension cords or appliance wiring. They also cannot be placed more than 4½ feet apart and should be secured within 12 inches of panels and junction boxes to prevent sagging and damage. Nails and staples are not permitted for support, as they can cause damage.

Selecting/Installing Romex Wire

When choosing a wire type, it’s important to understand how it is labeled. The label on Romex cable is designated using the gauge of the wire and how many conductors are included. For example, 12-3 means that the product is a 12-gauge wire with three conductors (two hot, one neutral, and bare copper), while a 12-2 Romex has a black (hot) and white (neutral) wire. The most common sizes are 10, 12, or 14 AWG wire.

A 12-gauge Romex wire is rated for 20 amps and has a yellow jacket. Thinner 14 AWG wire is rated for 15 amps and has a gray coating, while 10 AWG Romex is suited for higher-power clothes dryers and water heaters and has an orange jacket. But 12 and 14 AWG wires are suited for most home lighting and outlet circuits.

Is Romex NM Cable Superior to Other Types of NM Wiring?

While other brands of NM cable may be cheaper, there’s no difference in quality or safety if the wiring is installed correctly. NM wiring in general has benefits such as:

  • Can be installed in an ungrounded plastic box.
  • Lighter and less costly than metal-sheathed wiring.
  • Pliable PVC sheathing makes it easier to unspool and straighten.
  • Smooth sheathing for pulling wire through holes in studs. Romex is coated to make this even easier.
  • Can be cut with side-cutting pliers. Smaller gauges can be cut with a wire stripper.
  • Easier to attach to framing members, using special plastic cable staples.

Schedule Wiring Installation/Repair with Over the Moon

We strongly recommend Romex wire for its versatility and durability. Electrical repair is also complex and risky, especially if you don’t have experience, so if you need a wiring inspection or your home rewired, you can count on Over the Moon. We serve customers throughout Oconomowoc and the Milwaukee area. To schedule electrical services, contact us online or call 262-218-2881 today.