10/2 Romex Wire: The Complete 30-Amp Circuit Guide
10/2 Romex (NM-B) is the go-to cable for 30-amp, 240-volt residential circuits. If you are wiring an electric dryer, electric water heater, a 30-amp Level 2 EV charger, a window air conditioner disconnect, or a hot tub sub-feed, 10/2 NM-B is almost certainly the correct cable. Here is everything you need to know about 10 gauge wire, including what the numbers mean, where it is required by code, and how much to buy for your project.
What the Numbers Mean
The “10” in 10/2 refers to the wire gauge: 10 AWG copper conductors. 10 AWG is rated for a maximum of 30 amps of continuous current, which is why 10/2 cable is paired exclusively with 30-amp circuit breakers in residential wiring. The “2” indicates two insulated current-carrying conductors inside the jacket: one black (hot) and one white (neutral). A bare copper ground wire is also included, so the cable physically contains three wires despite the “2” designation. The NM-B jacket is thermoplastic, rated for dry indoor locations, with 90-degree Celsius conductor insulation.
Where 10/2 Romex Is Used
Electric Dryer
A standard residential electric dryer requires a dedicated 240-volt, 30-amp circuit. The NEC requires a 4-wire connection on dryer circuits in new construction (two hots, neutral, and ground), but for a basic 30-amp supply circuit from the panel to the dryer outlet box, 10/2 NM-B is the correct cable. Pair it with a 30-amp double-pole breaker and a NEMA 14-30 dryer outlet. The dryer circuit is one of the most common applications for 10/2 Romex in residential construction.
Electric Water Heater
Most residential electric water heaters draw 18.75 to 25 amps at 240 volts, which falls within the 30-amp capacity of 10/2 NM-B. The NEC requires a dedicated circuit for the water heater. A 30-amp double-pole breaker with 10/2 NM-B running from the panel to the water heater is the standard residential installation. Some larger water heaters (80-gallon or larger, or high-recovery models) may require 40-amp circuits with 8 AWG wire, so confirm the heater nameplate data before selecting wire size.
Level 2 EV Charger (30-Amp)
A 30-amp Level 2 EV charger (7,200 watts) requires a dedicated 240-volt, 30-amp circuit with 10/2 NM-B from the panel to the charger location. This is a growing application as EV adoption increases in residential settings. Many popular EV chargers including Tesla and Lectron are available in 30-amp and 40-amp configurations, with the 30-amp version pairing directly with 10/2 wire and a NEMA 14-30 outlet or hardwired connection.
Air Conditioner Disconnect and Sub-Feed
Window air conditioning units rated above 20 amps and many mini-split systems require dedicated 240-volt circuits with 10 AWG wire. The disconnect box installed outside near central AC and heat pump equipment is often fed with 10/2 NM-B from the panel. Confirm the equipment nameplate amperage rating before selecting wire size, as some larger units require 8 AWG or 6 AWG wire.
Hot Tub and Spa Sub-Feed
Smaller hot tubs and portable spas rated at 240 volts and 30 amps or less can be fed with 10/2 NM-B inside the home to a GFCI disconnect box. However, the outdoor portion of a hot tub circuit typically requires UF-B or conduit with individual conductors rather than NM-B, since NM-B is rated for dry indoor locations only. Confirm with a licensed electrician for the complete hot tub wiring requirements in your jurisdiction.
10/2 vs 10/3: When to Use Each
10/2 NM-B contains one black hot conductor, one white neutral, and one bare ground. It is correct for standard 240-volt circuits where both hots share a single neutral return path (such as water heaters and single-motor appliances). 10/3 NM-B adds a red second hot conductor (black, white, red, and bare ground), making it the correct choice for appliance circuits requiring two separate hots plus a neutral plus ground, such as ranges, cooktops, and newer 4-wire dryer circuits where a separate neutral is required. Using 10/2 on a circuit that requires 10/3 will result in a failed inspection. Confirm the appliance wiring diagram before ordering cable.
10/2 vs 12/2: The Gauge Decision
12/2 NM-B handles 20 amps. 10/2 NM-B handles 30 amps. You must match the wire gauge to the breaker size: 12 AWG on a 20-amp breaker, 10 AWG on a 30-amp breaker. Never use 12/2 on a 30-amp breaker. The larger conductors in 10/2 Romex are noticeably stiffer and thicker than 12/2, which affects how it pulls through conduit or studs and how it terminates in outlet boxes. Budget slightly more time for 10/2 terminations than for 12/2 work.
Available Lengths and Packaging
10/2 NM-B Romex is sold in 25-foot, 50-foot, 100-foot, 250-foot, and 500-foot spools. For single appliance circuits, a 50 to 100-foot spool typically covers the panel-to-outlet run with enough spare length for box terminations. For multiple circuits or larger projects, 250-foot spools offer better per-foot pricing and reduce the number of spool changes during installation.
IB Lighting carries 10/2 Romex NM-B in standard spool sizes from Southwire with nationwide shipping and free freight insurance. Browse our electrical wire and cable selection or call (800) 674-9019 for contractor pricing. We also carry the full Southwire product line including all NM-B gauges and specialty cables.