Stand in front of the wire aisle at any home center and the choices are overwhelming: spools of black THHN, yellow rolls of Romex, bare copper, stranded versus solid, a dozen gauges. Knowing the different types of wires and where each one belongs keeps your projects safe and your inspections clean. Using the wrong gauge or the wrong cable for an application is not just a code violation; it is a genuine fire hazard. This guide explains the common wire and cable types found in U.S. homes, what the color codes mean, and how to read a gauge so you buy the right product the first time.
Cable vs. Wire: Knowing the Difference
People use the terms interchangeably, but they are not the same. A wire is a single conductor, usually a strand or solid piece of copper or aluminum. A cable is two or more wires bundled together inside a single jacket. The yellow Romex you pull through walls is a cable; the individual black, white, and bare conductors inside it are wires.
Understanding that distinction makes the product labels far easier to read once you know what each type does.
Common Residential Cable Types
Most home wiring uses just a handful of cable types, each with a specific job.
- NM-B (non-metallic, “Romex”): the standard for dry, indoor residential wiring. The jacket color signals gauge: white is 14-gauge, yellow is 12-gauge, orange is 10-gauge.
- UF (underground feeder): a gray, moisture-resistant cable rated for direct burial and damp locations.
- THHN/THWN: individual insulated conductors pulled through conduit. THWN is rated for wet locations.
- Armored cable (AC/MC): conductors wrapped in a flexible metal sheath, common in exposed or commercial runs.
- Low-voltage wire: thin conductors for doorbells, thermostats, and landscape lighting.
For typical indoor circuits in finished spaces, NM-B is what you will reach for most often.
Understanding Wire Gauge
Wire is sized by the American Wire Gauge (AWG) system, and the number works backward from intuition: the smaller the number, the thicker the wire and the more current it carries. Matching gauge to the circuit’s amperage is the single most important safety rule in wiring.
- 14-gauge: rated for 15-amp circuits, such as general lighting.
- 12-gauge: rated for 20-amp circuits, common for kitchen and bathroom receptacles.
- 10-gauge: rated for 30-amp circuits, such as water heaters and some dryers.
- 8-gauge: rated for 40-amp circuits, such as ranges.
- 6-gauge: rated for 50- to 55-amp circuits, such as large ovens and some EV chargers.
Never protect a 14-gauge wire with a 20-amp breaker. The breaker would allow more current than the wire can safely carry, overheating it before the breaker trips.
Solid vs. Stranded Wire
Within a given gauge you will find both solid and stranded conductors. Solid wire is a single piece of copper; it is stiffer, holds its shape, and is preferred for the permanent NM-B runs inside walls. Stranded wire is many thin strands twisted together, making it more flexible and better for connections that move or vibrate, such as appliance cords and conduit pulls in tight bends.
For most home rough-in wiring, solid conductors are the norm. Reach for stranded when flexibility matters.
Wire Color Codes
Color tells you a wire’s role, and following the convention keeps your work readable for the next person.
- Black: hot (line) conductor.
- Red: a second hot, used in 240-volt circuits and three-way switches.
- White: neutral (return). When taped black or red, it is being used as a hot.
- Bare copper or green: ground.
- Blue and yellow: typically travelers in switch legs or hots in conduit.
Always treat any wire as live until you verify it is dead with a tester. Colors are a guide, not a guarantee, especially in older homes wired before modern conventions.
Specialty and Low-Voltage Wiring
Beyond standard power wiring, a modern home contains a web of specialty cables, and knowing them helps you avoid mixing things up. Low-voltage wiring runs your doorbell, thermostat, and HVAC controls, typically using 18- to 22-gauge thermostat wire with multiple color-coded conductors. Landscape lighting uses heavier low-voltage cable, often 12- or 14-gauge, rated for direct burial.
- Coaxial cable: carries cable TV and internet signals; RG-6 is the current standard.
- Ethernet (Cat5e/Cat6): twisted-pair data cable for hardwired networking.
- Speaker wire: typically 14- to 16-gauge stranded for home audio.
- Thermostat wire: multi-conductor 18-gauge for HVAC and doorbells.
These low-voltage cables carry little or no shock hazard, but they should still be run neatly and kept away from running parallel to high-voltage lines to avoid signal interference. Many jurisdictions have separate rules for low-voltage versus line-voltage wiring, and they are often run by different trades.
Copper vs. Aluminum
Most branch circuits use copper because it conducts well and connects reliably. Aluminum, lighter and cheaper, is still used for large service-entrance and feeder cables. Older homes wired with aluminum branch circuits in the 1960s and 70s can develop loose, overheating connections; if you have it, use CO/ALR-rated devices or AlumiConn connectors and have an electrician inspect it.
Reading the Markings on a Cable
Every cable carries printed markings along its jacket, and learning to read them tells you exactly what you are holding. A roll of NM-B might read something like “12-2 WITH GROUND 600V.” The first number is the gauge (12-gauge), the second is the number of insulated conductors (2, plus a bare ground), and the voltage rating is the maximum it is rated to carry. So “14-3 with ground” means 14-gauge cable with a black, red, and white conductor plus a bare ground, the configuration used for three-way switches and some 240-volt circuits.
The jacket also lists the cable type (NM-B, UF-B, etc.) and any wet- or sun-resistance ratings. Individual conductors carry their own letter codes: THHN, for example, means thermoplastic, high heat-resistant, nylon-coated. The “W” in THWN adds a wet-location rating. These letters matter when you are pulling wire through conduit in a damp or outdoor location, because using an indoor-only conductor where moisture is present is a code violation and a safety risk. When in doubt, take a photo of the printing and ask the pro at the electrical counter.
Choosing the Right Wire for the Job
When you sort through the different types of wires at the store, work backward from the circuit. Identify the amperage, choose the matching gauge, pick the cable type rated for the location (dry, damp, or buried), and follow the color code. When a project involves your main panel, new circuits, or anything you are unsure about, hire a licensed electrician and pull a permit. Electricity is unforgiving of guesswork, but with the right wire correctly sized, your home stays safe for decades.
