What Is 12/2 Electrical Wire? | Decoding The Yellow Jacket

12/2 NM-B cable contains two 12-gauge insulated conductors plus a bare copper ground, with a 20-amp rating for indoor branch circuits.

The “2” in 12/2 confuses more homeowners than the “12.” When you buy 12/2 electrical wire as NM-B cable — the familiar yellow-jacketed Romex — the “2” counts two insulated conductors: a black hot and a white neutral, with a bare copper ground running alongside them. That ground wire is always present; it just isn’t part of the number.

12/2 Electrical Wire: What The Numbers On The Jacket Say

The name gives you two independent facts. The 12 is the conductor size in American Wire Gauge (AWG). Smaller numbers mean thicker wire, so 12 AWG is heavier than the 14 AWG found in basic lighting circuits but lighter than 10 AWG range-cable. In practice, 12 AWG is the standard size for 20-amp residential branch circuits.

The 2 tells you how many insulated current-carrying conductors are inside the jacket. In standard NM-B cable, those two conductors are color-coded black (hot) and white (neutral). A bare copper equipment grounding conductor rides alongside them, and almost all NM-B sold for residential work is labeled “with ground.”

Southwire’s spec page for Romex SIMpull Type NM-B cable lays out the construction: solid copper conductors, PVC insulation with a nylon outer sheath, and a yellow PVC jacket so 12 AWG is easy to spot on a shelf. The cable carries a 600V insulation rating, and its listed allowable ampacity is 20 amps.

What Can 12/2 Wire Run?

12/2 NM-B is built for indoor branch circuits feeding outlets, switches, lighting, and similar 120V loads in normally dry locations. You’ll most often see it on 20-amp household circuits — kitchens, garages, workshops, and bathroom receptacle circuits — though 12 AWG is also permitted on 15-amp circuits when a thicker conductor is wanted for lower voltage drop.

Three limits matter before you buy:

• Dry locations only. NM-B cannot be used outdoors, in damp or wet areas, or buried directly in the ground. Those jobs need a wet-rated cable type such as UF-B, or individual conductors in conduit.
• The conductors stay in the jacket. Southwire states that individual conductors inside NM-B are not listed or marked as THHN and are not permitted to be installed apart from the complete cable — the only exception is routing them inside a panelboard or box to make terminations. Don’t strip NM-B and run the wires separately.
• 20 amps is a ceiling, not a mandate. The cable’s allowable ampacity is 20 amps, but the actual breaker size depends on the complete circuit design, the connected loads, and the electrical code that applies where you live. A licensed electrician or local inspection authority makes the final call.

Southwire’s Romex SIMpull Type NM-B product page confirms these ratings and the dry-location limitation.

How Much Does 12/2 Wire Cost?

Pricing follows a simple pattern: the longer the spool you buy, the less you pay per foot. Home Depot’s current listings for Southwire 12/2 Romex SIMpull NM-B with ground look like this:

Copper prices move, so these figures shift over time. If you’re planning a bigger project and comparing spool options, our tested best 12/2 electrical wire picks break down what’s worth paying for.

FAQs

How Many Wires Are Actually Inside 12/2 Cable?

Three physical wires: a black insulated hot conductor, a white insulated neutral, and a bare copper equipment grounding conductor. The “2” in the name counts only the two insulated current-carrying conductors, which is why the cable is described as “12/2 with ground.”

Can 12/2 Wire Be Used Outdoors?

No. Standard 12/2 NM-B cable is approved only for normally dry indoor locations. Outdoor runs, damp areas, and direct burial require a cable rated for wet locations, such as UF-B, or individual conductors installed in conduit with the proper wet-rated insulation.

Does 12/2 Wire Require A 20-Amp Breaker?

Not automatically. The cable has a 20-amp allowable ampacity, but breaker sizing depends on the whole circuit — conductor length, connected loads, and the applicable electrical code. A 20-amp breaker is common with 12/2, and 12 AWG can also serve 15-amp circuits where the installation allows it.