Cable Wires: Complete Guide for Homeowners

Walk into the wire aisle of a Home Depot and you’re looking at 60 different products that all look superficially similar. Picking the wrong cable wires for your project costs money in best case and starts fires in worst case. After running miles of low-voltage and line-voltage cable in residential remodels, here’s the practical guide to which wires do what, when each is required by code, and what to avoid.

The Basic Categories of Cable Wires

Residential wiring breaks into three main categories. Line-voltage power cables (NM-B, UF-B, MC) carry 120 or 240 volts to outlets, switches, and fixtures. Low-voltage cables (Cat 5e/6, RG6, speaker wire) carry data, video, and audio signals. Specialty cables (THHN/THWN single conductors, service entrance, doorbell) cover everything else.

Each category has its own gauge requirements, insulation ratings, and code requirements. Mixing them up — running Cat6 inside a wall stuffed with NM cable, or using indoor speaker wire outside — causes performance problems or code failures.

NM-B (Romex): The Workhorse of Home Wiring

NM-B cable, commonly called Romex, is the standard wiring for indoor residential branch circuits. It’s a sheathed cable with two or three insulated conductors plus a bare ground wire wrapped in plastic jacket. The most common gauges are 14/2 (yellow jacket, 15-amp circuits), 12/2 (yellow until 2014, now yellow with markings, 20-amp circuits), and 10/2 (orange, 30-amp circuits like dryers).

NM-B is rated only for dry indoor locations. Don’t use it in damp basements, exterior walls below grade, conduit runs, or anywhere the jacket might be exposed to moisture or physical damage. National Electrical Code (NEC) limits NM-B to permitted residential and similar occupancies — it’s prohibited in commercial buildings.

UF-B: When You Need to Go Outside or Underground

UF-B (Underground Feeder) cable looks similar to NM-B but uses a solid plastic encasement around the conductors that resists moisture. UF-B is rated for direct burial, exterior locations, and damp environments. It’s the right cable for running power to a detached garage, well pump, post light, or shed.

The NEC requires direct-buried UF-B cable to be at least 24 inches deep, or 18 inches deep if protected by 2 inches of concrete, or 12 inches deep if installed in conduit. GFCI protection is required at the source for any UF-B circuit feeding outdoor outlets.

MC and AC Cable for Special Applications

Metal-clad (MC) cable wraps the conductors in interlocked metal armor instead of plastic. It’s required in some commercial settings and used in residential where physical protection matters — exposed runs in unfinished basements, garages, or anywhere the cable might be subject to damage.

Armored cable (AC, often called BX) is similar but uses the metal armor itself as the equipment ground rather than a separate green wire. AC has been replaced by MC in most modern installations because MC offers better grounding and is easier to work with. Older homes still have AC in their walls.

THHN/THWN Single Conductors

Single-conductor THHN (or THWN-2 for wet-rated) wires pull through conduit when the run requires it. Common gauges are 12 AWG and 14 AWG for residential branch circuits, scaling up to 4 AWG, 2 AWG, and beyond for service feeders.

THHN is the right wire for runs through conduit in basements, panel feeders, sub-panel installations, and anywhere flexibility or future-proofing matters. Buy by the spool from electrical supply houses for any large project — by-the-foot pricing at big-box stores doubles the cost.

Low-Voltage Data Cables

Cat 5e is the minimum for new home networking and supports gigabit Ethernet up to 100 meters. Cat 6 is the current best practice and handles 10-gigabit speeds up to 55 meters. Cat 6A handles 10 gigabit at the full 100 meters with thicker insulation that resists crosstalk.

For a typical home, run Cat 6 to every TV location, every potential office space, and one drop in each main living area. Pull cables to a central network closet (usually a basement or utility area). Plenum-rated cable (CMP) is required when running through return-air spaces; standard riser-rated (CMR) cable is fine in walls and accessible attics.

Coaxial Cable for Cable TV and Internet

RG6 quad-shield is the standard residential coax for cable internet, satellite, and over-the-air antenna distribution. Older homes often have RG59, which is thinner and not rated for the higher frequencies used in modern cable systems. Replace RG59 if you’re upgrading to gigabit cable internet.

For a single-family home, run RG6 to every TV location and to the basement utility area where the modem typically lives. Use compression-style F-connectors with a quality crimp tool — twist-on F-connectors work loose over time and degrade signal quality.

Speaker Wire and Audio Cables

For in-wall speaker wire, use 16-gauge or 14-gauge CL2- or CL3-rated cable. The CL rating means the cable is approved for in-wall installation per UL standards — non-rated cable is not legal to bury inside finished walls. Monoprice, Mediabridge, and Belkin all sell quality CL-rated speaker wire by the 50- and 100-foot reel.

For runs over 50 feet or when using 4-ohm speakers, step up to 12-gauge to minimize signal loss. Subwoofer cable (typically a thicker single-conductor coax) handles low-frequency runs for powered subs.

Doorbell and Thermostat Wire

Standard doorbell circuits run on 18 AWG, 2- or 3-conductor wire. Modern smart thermostats need 18/5 or 18/8 cable (5 or 8 conductors) to handle the C-wire (common) and additional control wires for heat pumps or zoned systems.

If you’re remodeling and the walls are open, pull 18/8 cable to every thermostat location even if you only have a basic 4-wire need today. The marginal cost is $30 and you future-proof for any thermostat upgrade.

Common Mistakes With Cable Wires

Mixing voltage classes in the same hole through a stud is a top failure. NEC requires line-voltage and low-voltage cables to be separated. Drilling separate holes 6 inches apart through framing keeps the install code-compliant and prevents interference between data and power lines.

The other common error is using indoor cable in outdoor or damp locations. NM-B in a wet basement deteriorates within years. Cat 5e UV exposure outdoors fails in months. Buy the right rating for the location — outdoor-rated, direct-burial-rated, or wet-rated as the situation demands.

Buying Tips

For projects under 100 feet, the orange-box stores are fine for pricing. For larger projects, electrical supply houses (Rexel, Graybar, City Electric Supply) sell by the spool at significantly better prices and stock professional-grade cable that often outperforms big-box options. Open an account if you’re remodeling for several months — most distributors accept residential customers without a contractor license, you just pay cash or credit.

Choose cable wires based on the application, location, and code requirements. NM-B for indoor branch circuits, UF-B for outdoor and underground, Cat 6 for data, RG6 for coax. Pull more than you think you need while walls are open, and label every cable at both ends. Good wiring lasts 50 years and costs less than fixing bad wiring once.