12-Gauge Wire Meaning And Basics
“12-gauge” refers to the American Wire Gauge (AWG) size of the conductor. In this scale, a smaller number means a thicker wire. AWG 12 copper is a solid or stranded conductor with a bare diameter near 2.05 mm (0.0808 in) and a cross-section of about 3.31 mm². Thicker copper has lower resistance per unit length than thinner copper, so 12-gauge carries current more efficiently than 14-gauge and runs cooler at the same load.
Gauge describes the copper itself, not the insulation. Two 12-gauge conductors with different jackets may look different on the outside yet share the same copper area. Stranded 12-gauge packs many fine strands to equal the same copper cross-section as one solid wire; the strand bundle is more flexible and slightly larger overall because of tiny air gaps, while the electrical resistance is essentially the same for a given length.
12-Gauge Copper At A Glance
| Spec | Typical Value (Copper) | Why It Matters |
|---|---|---|
| Bare Diameter | ~2.05 mm (0.0808 in) | Relates to physical fit through connectors, lugs, and devices. |
| Area | ~3.31 mm² (≈ 6530 cmil) | Sets electrical capacity and resistance baseline. |
| DC Resistance @ 20 °C | ≈ 1.588 Ω per 1000 ft (≈ 5.21 Ω/km) | Drives voltage drop on long runs; lower is better. |
| Common Breaker Size | 20 A (copper branch circuits) | Matches standard overcurrent protection for general 120 V branch runs. |
| Typical Cable Types | NM-B, UF-B, THHN/THWN-2 | Different jackets and temperature ratings for different locations. |
What 12-Gauge Wire Is Used For
In homes and light commercial spaces, AWG 12 copper is the go-to size for 120 V 20-amp branch circuits that feed receptacles and small appliances. Many kitchens, garages, workshops, and utility areas run on 12-gauge to allow more headroom for tools and countertop loads. It’s also popular for longer speaker runs where lower resistance keeps the signal tight, and for low-voltage systems that pull more current and benefit from thicker copper.
Outdoors, 12-gauge shows up in UF-B direct-burial cable for yard circuits and shed feeds. In conduit, THHN/THWN-2 conductors make up services, feeders, and branch circuits; a 12-gauge THHN/THWN-2 is rated for high temperature limits and can be pulled easily through raceway thanks to its nylon jacket. The jacket type you pick depends on the location: dry interior walls, wet conduit, underground, or sunlight exposure.
Taking 12 Gauge Wire Amp Rating And Distance
Two ideas steer performance: ampacity and voltage drop. Ampacity is the continuous current a conductor can handle with a given insulation and installation method without overheating. In typical residential work, copper 12-gauge branch conductors pair with a 20 A breaker. The jacket rating (60 °C, 75 °C, or 90 °C) influences how many amps a conductor can carry in tables, yet small branch circuits still land on 20 A copper when protected per standard rules. When multiple current-carrying conductors share a raceway or cable bundle, de-rating may apply. That’s one more reason pros plan conduit fill and grouping carefully.
Voltage drop is the loss in voltage as current flows through wire resistance. Every foot adds a little resistance; longer runs and higher current raise the drop. Keeping drop modest improves equipment behavior and keeps motors happier on start-up. Many electricians aim to keep branch-circuit drop near 3 % to the farthest outlet and total feeder-plus-branch near 5 %. The thicker the copper and the shorter the run, the smaller the drop for a given load.
How To Think About Run Lengths
You can estimate run lengths from the resistance number in the table. For single-phase circuits, the round-trip path matters, so the formula uses twice the one-way length. A quick way to see what’s possible: pick a target drop, current, and the resistance per foot. Many contractors also keep a trusted voltage drop calculator handy to confirm numbers with precise distances and temperatures.
Quick Distance Guide For 3 % Drop
The table below shows approximate one-way runs for 12-gauge copper at room temperature. It’s a planning aid, not a substitute for a full calculation in your specific conditions.
| Load (Amps) | Max One-Way Run @ 120 V (~3 % drop) | Max One-Way Run @ 12 V (~3 % drop) |
|---|---|---|
| 5 A | ~227 ft | ~22.7 ft |
| 10 A | ~113 ft | ~11.3 ft |
| 15 A | ~75.6 ft | ~7.6 ft |
| 20 A | ~56.7 ft | ~5.7 ft |
12-Gauge vs. 14-Gauge vs. 10-Gauge
Compared with 14-gauge, 12-gauge has about 37 % less resistance per 1000 ft, which trims voltage drop and heat at the same current. That’s why many shops skip 14-gauge where portable tools or longer runs are common. Step up to 10-gauge when loads are fixed and heavy, or distances are long enough that a 20 A run would push drop too high. Think water-heater feeds, long garage circuits, or a far shed where you’d rather upsize than fight dim lights and weak motor starts.
Different metals change the story. Aluminum has lower conductivity than copper, so an aluminum conductor needs more cross-section to match a copper run. For small branch circuits, copper remains the standard pick because terminations are simpler, devices are built for it, and the wire size stays manageable in boxes.
Solid, Stranded, And Flexibility
Solid 12-gauge keeps its shape and holds form when you push it into receptacle clamps and device screws. It’s the common choice inside walls for NM-B cable. Stranded 12-gauge bends more easily and shines in conduit, machine panels, and places where frequent service loops or vibration demand flexibility. Both styles deliver the same copper area; device terminations must be listed for the construction you use.
Stranded construction varies. A coarse-strand cable might use fewer, thicker strands; fine-strand might use many hair-thin wires. Fine-strand needs fittings listed for that class so the connection captures all strands evenly. That prevents hot spots and loose terminations. Always match lugs and ferrules to the strand class listed by the manufacturer and the standard that applies in your region.
Common 12-Gauge Cable Types
NM-B (Nonmetallic Sheathed Cable)
NM-B carries multiple conductors under a nonmetallic jacket for dry, protected spaces like stud bays and ceiling cavities. It’s simple to strip and staple, and devices are designed to accept solid 12-gauge from NM-B. For attic or basement runs, keep bends gentle and protect the cable from sharp edges to preserve the jacket.
UF-B (Underground Feeder Cable)
UF-B uses a tougher, moisture-resistant jacket that bonds to the conductors. It can be direct-buried at the required depth or sleeved in conduit as it rises from grade. The construction resists sunlight and soil contact, making it a fit for yard lighting, shed circuits, and exterior receptacles served from a subpanel.
THHN/THWN-2 In Conduit
Single 12-gauge conductors marked THHN/THWN-2 are pulled through metallic or nonmetallic raceway. These conductors carry a PVC insulation with a nylon outer layer, which eases pulling and resists oil and moisture. Markings on the jacket spell out voltage rating and temperature limits. In wet or dry locations, THWN-2 support high temperature ratings that help in de-rating and in crowded raceways, while breakers on small copper branch circuits still land at 20 A.
Safety And Code Basics For 12-Gauge
- Protect copper 12-gauge branch conductors with a 20 A overcurrent device unless a specific allowance applies.
- Use connectors, wirenuts, and terminals that list 12 AWG on the label; don’t cram a wire into a clamp that’s listed for a smaller size.
- When multiple current-carrying conductors share a raceway or cable bundle, apply the de-rating rules and temperature column that match the jacket and installation.
- Splice boxes need volume for each conductor and device; 12-gauge takes more space than 14-gauge. Pick boxes with generous cubic-inch ratings so terminations stay tidy and cool.
- For long circuits feeding motors, compressors, EVSE, or shop tools, check voltage drop and upsize the wire or shorten the path to keep performance steady.
You can view the current NFPA 70 (NEC) online at no cost. That’s the fastest way to verify requirements in the edition your authority adopts. When you need a quick voltage drop check, use a reliable tool like Southwire’s voltage drop calculator and then size the conductors and raceway accordingly.
Working Tips That Pay Off
Keep Bends Smooth
Hard kinks stress insulation and the copper strands. Smooth sweeps ease pulling and make future service easier. In boxes, leave a loop that reaches the device twice; you’ll thank yourself when a device needs replacement.
Use Proper Stripping Depth
Strip just enough to land under the terminal and keep jacket support behind the clamp. On THHN/THWN-2, the nylon jacket can scuff during pulling; a clean strip leaves bright copper and undamaged insulation under the terminal.
Match Devices To The Circuit
On a 20 A branch run, use 15 A or 20 A receptacles as allowed. If a receptacle serves a single cord-and-plug appliance that needs a 20 A face, choose the correct device style. Always torque terminals to the manufacturer’s value so terminations stay tight.
Practical Takeaways
AWG 12 copper is a thick, versatile size with low resistance for its cost and footprint. It pairs well with 20 A overcurrent protection, tolerates longer runs than 14-gauge, and keeps drop in check for sensitive loads. In cable or in conduit, the right jacket and fittings keep the installation safe and durable. Measure the run, check the load, pick the jacket, and you’ll end up with a circuit that performs the way you expect.