The Different Types Of Romex Wires And What The Colors Mean
Today, we’re diving into the world of electrical wiring—specifically Romex wires. We’ll explore the different types, what they’re used for, and a bit of history to help put it all into perspective.
A Brief History of Wiring
Let’s go back in time to understand how far we’ve come in home electrical wiring.
Knob and Tube Wiring
In the 1940s and 50s, knob and tube wiring was the standard. It consisted of two separate wires—neutral on one side of the joist and hot on the other. These wires were suspended on porcelain knobs and passed through joists using ceramic tubes. Typically, one circuit would run from the basement up through the house, powering all lighting and outlets.
This wiring was usually 10-gauge copper-steel mix and coated in cloth. Over time, this cloth would become brittle and crack due to heat from light fixtures or exposure to moisture. Despite its age, knob and tube wiring is still technically legal—as long as it’s protected by a 15-amp fuse or breaker and GFCI protection. However, insurance companies strongly discourage it, often refusing coverage unless it’s removed.
Ungrounded Cloth Wiring
In the late 40s and 50s, wiring evolved. Electricians started using metallic dry wires that enclosed two cloth-covered conductors—still ungrounded. While it improved some safety aspects, this wiring was still prone to becoming brittle under heat and posed risks if overloaded.
The Introduction of Grounding
By the late 50s and into the 60s, electricians began using Romex (NMD7) wiring. This version often had rubber coatings and eventually transitioned into wax-coated cloth jackets containing higher-quality copper conductors. These were the first wires to include a ground wire, typically placed between the hot and neutral.
Despite these improvements, there was an unfortunate experiment in the 1970s with aluminum wiring, which quickly fell out of favor. Aluminum was too soft and had a tendency to melt at connection points. While aluminum is still used for large conductors today, anything 10, 12, or 14-gauge must be copper.
Modern Romex Wiring
Romex made a strong return in the late 70s and 80s. Early versions had paper inside and were often gray or green depending on their application. This new generation of wire was more mouse-resistant than current products—but once wet, it was ruined.
Modern Romex (or NMD90 in Canada) has a soy-based insulation jacket, which unfortunately tends to attract rodents. Despite that, it’s still the standard today, and we continue to use it in both residential and commercial construction.
The Different Types Of Romex Wires And What The Colors Mean
Let’s break down the different types of Romex/NMD90 wires and how they’re typically used.
14/2 White Romex
- Use: General-purpose residential wiring
- Components: Black (hot), White (neutral), and bare ground wire
- Voltage Rating: 300V
- Common Applications: Standard house wiring (lighting, basic outlets)
14/3 Romex
- Use: 3-way switches, 120/240V loads
- Components: Black, Red, White, and ground wire
- Common Applications: Multi-way light switches, split outlets
12/2 Yellow Romex
- Use: Heavier loads than 14-gauge
- Components: Black, White, and ground
- Common Applications: Kitchen counter receptacles (as per updated code), some commercial uses
10/2 or 10/3 Orange Romex
- Use: Large appliance circuits
- Common Applications: Wall ovens, cooktops, dryers, generators
Red 12-Gauge Romex (HeatX)
Note: If used for 120V (only in emergencies), the red wire must be clearly marked with white tape to indicate it’s neutral. However, this is not standard practice.
Use: Heating applications only (240V)
Components: Typically includes Black and Red wires
Common Applications: Electric baseboard heaters, mini-split heat pumps
Understanding Wire Types: From Romex to Service Wire
Today, we’re diving into different types of wires, focusing primarily on Romex (also known as NMD) wires and their history, construction, and applications.
Solid vs Stranded Wire
For wires over 10 gauge, like 6 gauge wire, you’ll find stranded conductors rather than solid ones. Under 10 gauge (such as 12 and 14 gauge), wires are typically solid. For example, this 6/2 Romex wire features stranded copper conductors for flexibility and durability.
Copper vs Aluminum Conductors
In Canada, any wire over 8 gauge can be either copper or aluminum. Aluminum conductors are much cheaper—roughly a quarter the price of copper—which makes them economical for large loads like stoves, subpanels, or subfeeds. When using aluminum wire, it’s important to apply antioxidant at connections and to double-check lug torque during inspections since aluminum can loosen over time.
Large Service Wires
For service entrances (like your main 200 amp service), we often use 250 kcmil (or 250 MCM in the US) aluminum stranded wire. Copper can be used one size smaller (3/0), but aluminum is more cost-effective for these applications. These wires come in black and white jackets (for neutral) and are used in both single-phase and three-phase systems.
Grounding Wire
For grounding, we use stranded copper wire in various sizes, often number six, which connects ground rods and equipment bonds to ensure safety.
Low Voltage Wiring
- Cat6 Wire: Blue Cat6 wire, rated for 300 volts, is common for high-speed internet, telephones, and doorbell wiring.
- Speaker Wire: Green stranded 14/2 wire is often used for home speaker or intercom systems and is also rated for 300 volts but typically runs low voltage.
Armored Cables and Protection
- AC90 (Armored Cable): This is a dry-location rated armored cable used to mechanically protect wires run along walls or under 5 feet high. It’s not meant for outdoor use.
- Tech Cable / ACWU: For outdoor and underground applications, we use armored cable with a rubber coating (ACWU), rated for wet and damp locations. It often uses aluminum conductors due to cost efficiency and is designed to be buried or run outside on poles.
Summary
Romex (NMD) wires have evolved over decades, with different coatings, conductor materials, and applications:
- Early wires were cloth-coated and prone to damage from heat and moisture.
- Modern Romex wires have a soy-based plastic jacket which rodents unfortunately find tasty.
- Aluminum conductors are used for larger sizes to save on cost.
- Armored cables protect wires in tough locations, with different types for indoors and outdoors.
This basic understanding of wiring types can help homeowners and electricians alike know what wire to use for each job and the reasons behind the choices.
