Residential Wiring: Types of Romex Wires
Romex is a type of electrical cable that is a non-metallic cable (NM). Electricians and homeowners often use it in residential wiring. People have used it in older homes as well as modern homes.
Romex is easy to identify as it uses a color coding system. This helps electricians, home owners and inspectors quickly see if the wire is the right size for the circuit. They can check this based on the circuit's amps.
Manufacturers will write the date of production on the side of recently produced Romex. This allows people to easily check the age of the Romex.
You can identify Romex in two different ways. First by the wire gauge. next by the number of insulated wires that are inside of it/inside the jacket.
For example, a yellow 12/2 wire is a 12 gauge wire with two insulated wires inside of the jacket. The manufacturer prints numbers such as 14/3 or 12/2 on the outside jacket of the Romex for easy identification.
Romex & NM Wire Ampacity
You determine the ampacity of Romex and NM wire by using the 60-degree column in Table 310.16. unless meeting certain exceptions. The National Electrical Code (NEC) specifically states:
“334.80 Ampacity. The ampacity of types NM and NMC cable shall be determined in accordance with 310.14. The ampacity shall not exceed that of a 60 degree Celsius (140 degree Fahrenheit) rated conductor. The 90 degree Celcius (194 degree Fahrenheit) rating shall be permitted to be used for ampacity adjustment and correction calculations, provided the final calculated ampacity does not exceed that of a 60 degree celsius (140 degree Fahrenheit) rated conductor. The ampacity of Types NM and NMC cable installed in cable trays shall be determined in accordance with 392.80 (A).
Where more than two NM cables containing two or more current-carrying conductors are installed, without maintaining spacing between the cables, through the same opening in wood framing that is to be sealed with thermal insulation, caulk, or sealing foam, the ampacity of each conductor shall be adjusted in accordance with Table 310.15 (C) (1) and the provisions of 310.44 (A) (2). Exception, shall not apply.
Where more than two NM cables containing two or more current-carrying conductors are installed in contact with thermal insulation without maintaining spacing between cables, the ampacity of each conductor shall be adjusted in accordance with Table 310.15 (C) (1).” (Austin, Coache, Hannahs, Hohengasser, and Sargent, 2023)
Note: Table 310.16 in the National Electrical Code: 2020 Edition, pg. 161. Copyright 2019 by National Fire Protection Association. (Reference #2)
Electricians must understand the amperage rating for Romex wire and use its application correctly. Otherwise, you may end up with a fire hazard and/or short circuits.
Existing Romex wire may not support the minimum amperage needed for new equipment. We see this often with new HVAC installations. In this case, our electricians determine the needed size of Romex and size up accordingly.
Common Types of Romex & NM(Non-Metallic) Wire
White:
It has a white jacket and has a maximum rating of 15 amps. The size of the wire is a 14-gauge wire, which is about as thick as a dime.
14/2 romex wire: It has a black(hot wire), white (neutral wire) and ground wire (non-insulated copper) within the wire. Common uses: 15 amp circuits for lighting and receptacles.
14/3 wire: It has a black(hot), white (neutral), ground wire (non-insulated copper) and red(travel wire) within the wire. Common uses: 15 amp/220 circuits that need a neutral.
14/2/2 wire: It has black(hot), white(neutral), ground (non-insulated copper), red (travel) and an additional neutral that is striped white. Common uses: Branch off power from a main run in a residential home/application. People often use it for general lighting circuits.
Yellow:
Rated for maximum 20 amps. Yellow on the outside. 12-gauge wire. About as thick as nickel.
12/2 romex wire: It has black(hot), white (neutral) and ground (non-insulated copper). Common uses: Household outlets, often for plug in appliances such as kitchen appliances. Also, used for some light fixtures. Dedicated appliance circuits.
Orange:
Rated for maximum 30 amps. Orange on the outside. 10 gauge wire.
10/2 romex wire: It has a black(hot), white (neutral) and brown on the inside. Common uses: 30 amp circuits. AC lines, air compressors.
10/3 wire: It has black (hot), white (neutral), red(travel), and ground(non-insulated copper) in the wire. Common uses: Supply loads larger residential appliance loads such as water heaters, air conditioners and clothing dryers.
Black, 8 Gauge:
Rated for a maximum 40 amps. Black on the outside. 8-gauge wire.
8/2 romex wire: It has a black(hot), white(neutral) and ground (non-insulated copper) in the wire.
8/3 wire: It has a black (hot), white (neutral), red and ground (non-insulated copper). Common Uses: Wiring up ovens when they need a neutral, two powers and a ground.
Black, 6 Gauge:
Rated for a maximum 55 amps. Black on the outside. 6-gauge wire.
6/2 romex wire: It has black (hot), white(neutral) and ground (non-insulated copper) inside the wire.
6/3 wire: It has black (hot), white (neutral), ground (non-insulated copper) and two red(travel). Common Uses: Feeding a subpanel, double oven and electric range
Grey:
Manufacturers design a grey Romex cable for outdoor and/or underground burial use. People call it an Underground Feeder cable or UF. It comes in a variety of sizes including 14/2, 14/3, 12/2, 10/2, 10/3, 8/2, 8/3, 6/2 and 6/3. This type of Romex is extremely expensive because of its heavy-duty and UV protection coatings.
Common Uses: Outdoor use. You can bury it underground. It has UV coating as well so it’s “sun resistant”.
Miller's Electric: Your Local Residential Electrical Experts
Do you need to get some electrical work done in Clark County or the surrounding areas? Our professional team of experts are ready to help with the following electrical services:
Install electric car charger
Replace or upgrade electrical panel
Repair electrical panel
Install a generator
Install outlets or switches
Repair outlets or switches
Install light fixtures
Repair light fixtures
Install fan
Repair fan
Home remodels
Power issues
Whole home safety check
References
Austin, D.; Coache C; Hannahs, C.; Hohengasser, E.; and Sargent, J. (eds) (2023) National Electrical Code Handbook. 16th edition. Quincy, Massachusetts: National Fire Protection Association.
(2019) National Electrical Code. 20th edition. Quincy, Massachusetts: National Fire Protection Association.
