#12 THHN wire is 12 AWG copper building wire with a nylon-jacketed insulation rated 600 volts and up to 194°F (90°C) in dry locations.
Two spools of 12 AWG wire can sit side by side on a shelf, look identical, and still carry different limits — because the letters printed after the gauge, not the gauge itself, set the heat, moisture, and current ratings. What #12 THHN wire is comes down to four things: the copper conductor, the nylon-jacketed PVC insulation, the 600-volt rating, and the exact listing stamped on the jacket. Nail those four and the rest of the spool label reads like plain English.
12 Gauge THHN Wire: Copper Core, Nylon Jacket, 600 Volts
Every 12 AWG THHN product is a copper conductor wrapped in PVC insulation with a thin nylon jacket over it, and current listings rate the wire at 600 volts with a 194°F (90°C) dry-location limit.
Southwire sells 12 AWG THHN/THWN in both solid and 19-strand constructions. Insulation thickness runs about 0.015 to 0.016 inches, and the overall outside diameter lands near 0.122 to 0.133 inches depending on the variant. Standard insulation colors include black, white, red, blue, and a green jacket with a yellow stripe for grounding. Southwire’s 12 AWG THHN/THWN product page lists those same construction and color options.
The jacket stamping is where wires stop being interchangeable. Current listings carry markings such as UL 83, UL 1063, cULus, and AWM, and many products are dual-marked THHN/THWN-2 or THHN/THWN-AWM. A plain search for 12 THHN returns four different product families, and each one has its own temperature and moisture limits.
| Wire Variant | Voltage And Temperature | Where It Fits |
|---|---|---|
| THHN | 600 V; 194°F (90°C) dry | Dry indoor runs inside conduit |
| THHN/THWN | 600 V; 90°C dry, 167°F (75°C) wet | Conduit that may see moisture |
| THHN/THWN-2 | 600 V; 194°F (90°C) dry and wet | Damp, wet, or hotter locations |
| THHN-THWN-MTW-AWM | 600 V; rating varies by listing | Machine tool and appliance leads |
| Solid 12 AWG THHN | 600 V; 194°F (90°C) dry | Panels, switches, short straight pulls |
| 19-strand 12 AWG THHN | 600 V; 194°F (90°C) dry | Long pulls through bends and conduit |
| Green/yellow 12 AWG THHN | 600 V; 194°F (90°C) dry | Equipment grounding conductors |
Does 12 AWG THHN Carry 20 Amps Or 30 Amps?
Both numbers turn up on live product pages: pure THHN listings commonly show 20 amps, while some THHN/THWN-2 listings show 30 amps at their higher temperature rating. Neither figure is the whole code answer.
Gauge and ampacity are separate questions. The 12 AWG label fixes conductor size; the current a wire may carry comes from the insulation rating on the jacket, the temperature rating of the terminals it lands on, how many current-carrying conductors share the conduit, the ambient temperature, and the installation conditions in the NEC. Standard ampacity tables put 12 AWG copper at 20 amps in the 60°C column, 25 amps at 75°C, and 30 amps at 90°C — which is exactly why the same gauge shows two different numbers depending on what a listing claims.
On a typical 20-amp household branch circuit, 12 AWG copper lands right where it belongs. Anything more ambitious belongs against the actual product listing and your local electrical code, not a product page alone.
THHN, THWN, And THWN-2: Why The Letters Matter
The suffix letters describe a wire’s moisture and heat ratings, so treating THHN, THWN, and THWN-2 as one product means guessing at limits the code already set.
Plain THHN is dry-location wire rated 194°F (90°C). THWN adds a 167°F (75°C) wet rating. THWN-2 holds 194°F (90°C) in dry and wet conditions both. Current product pages also describe the jacket as resistant to heat, moisture, oil, gasoline, and sunlight.
The costly mistake is grabbing a bare THHN coil for a run that sits in a wet location. Read the jacket print before you cut, match the marking to where the wire actually goes, and size the breaker to the weakest link in the chain — usually the terminal rating, not the wire.
If narrowing down spools is the step you’re stuck on, our tested best 12 gauge THHN wire roundup compares them by marking, length, and price.
FAQs
Can 12 AWG THHN Go Outside?
Only if the jacket marking allows wet locations. Plain THHN is dry-rated, so an outdoor conduit run needs a wet-rated product such as THWN or THWN-2. Dual-marked spools cover both, and the marking is printed right on the insulation. Check it before cutting, and confirm the run against your local code.
What Does The 19-Strand Version Change?
Stranded 12 AWG uses 19 fine copper strands instead of one solid core, which makes the wire easier to pull through conduit with bends. Ampacity and termination are unchanged. Solid 12 AWG is stiffer but simpler to land under a terminal screw inside a panel.
Is 12 AWG The Same As 20-Amp Wire?
No. The 12 AWG number describes conductor size, not the current it may carry. Allowable amps come from the insulation’s temperature rating, terminal ratings, conduit fill, ambient heat, and the code rules that apply to the install. That is why 12 AWG copper appears as 20 amps in one column and 30 in another.
References & Sources
- Southwire. “12 AWG THHN/THWN Copper Building Wire.” Confirms conductor construction, insulation colors, and the 600-volt rating.
- AutomationDirect. “THHN/THWN-2 Wire Specifications.” Source for temperature ratings and the 500 ft reel pricing.
- AutomationDirect. “THHN Wire Specifications, Earlier Revision.” Shows how markings and temperature ratings vary across product families.
