THWN Wire

Q: What is the temperature rating of THWN?

THWN is rated 75°C in dry locations and 75°C in wet locations. The ampacity values in NEC Table 310.16 use the 90°C column for conductors rated at or above 90°C, but actual usable ampacity is limited by the termination temperature (typically 75°C per 110.14(C)).

THWN stands for Thermoplastic Heat-resistant Water-resistant Nylon-coated. Wet location version of THHN. Rarely sold standalone - see THWN-2.

Dry rating75°C

Wet rating75°C

Voltage600V

Locationsdry, damp, wet

Specifications

Property	Value
Full name	Thermoplastic Heat-resistant Water-resistant Nylon-coated
Insulation material	PVC (thermoplastic)
Outer covering	Nylon jacket
Temperature rating (dry)	75°C (167°F)
Temperature rating (wet)	75°C (167°F)
Voltage rating	600V
Approved locations	dry, damp, wet

Ampacity by gauge

The table below shows NEC Table 310.16 ampacity for THWN conductors. Values shown reflect the 110.14(C) termination temperature limit, which determines the real-world usable ampacity - not just the insulation rating. Click any gauge to see the full derating chain.

Gauge	Copper	Aluminum
14 AWG	See page	-
12 AWG	See page	See page
10 AWG	See page	See page
8 AWG	See page	See page
6 AWG	See page	See page
4 AWG	See page	See page
3 AWG	See page	See page
2 AWG	See page	See page
1 AWG	See page	See page
1/0 AWG	See page	See page
2/0 AWG	See page	See page
3/0 AWG	See page	See page
4/0 AWG	See page	See page

When to use THWN wire

Wet location version of THHN. Rarely sold standalone - see THWN-2.

Common applications for THWN:

Specialized applications - THWN is used where its specific temperature and environment ratings are required
See manufacturer specifications for approved installation methods

NEC code references for THWN

The NEC defines wire insulation types in Table 310.4(1) (formerly Table 310.104(A)). Key sections that apply:

Table 310.4(1) - lists THWN with its temperature rating, insulation material, and approved locations
Table 310.16 - ampacity values for conductors in raceway, cable, or earth (the values shown in our ampacity table above)
Section 110.14(C) - termination temperature limits that determine real-world usable ampacity
Section 310.15(C)(1) - adjustment factors for more than 3 current-carrying conductors in a raceway

Frequently asked questions about THWN wire

Where can I use THWN wire?

THWN is approved for use in dry, damp, wet per NEC Table 310.4(1). It has a dry temperature rating of 75°C and a wet rating of 75°C. Always verify that your specific installation meets the approved location requirements.

What is the temperature rating of THWN?

THWN is rated 75°C in dry locations and 75°C in wet locations. The ampacity values in NEC Table 310.16 use the 90°C column for conductors rated at or above 90°C, but actual usable ampacity is limited by the termination temperature (typically 75°C per 110.14(C)).

Other wire insulation types

THHN 90°C THWN-2 90°C XHHW 90°C XHHW-2 90°C RHH 90°C RHW-2 90°C USE-2TW 60°C NM-B 60°C UF-B 60°C MC Cable 90°C AC Cable (BX) 90°C SER/SEU 75°C PV Wire 90°C THHW 90°C THW 75°C THW-2 90°C RHW 75°C MI 90°C UF 60°C XHH 90°C FEP 90°C SIS 90°C

Requirements vary by state. NEC edition, licensing, permits, and GFCI rules differ by jurisdiction. Check your state or pick it below for personalized info across WireRef.

Important: For reference only. Not a substitute for a licensed electrician. Electrical work can cause serious injury, death, fire, or property damage if performed incorrectly. Always hire a licensed electrician for electrical work, especially for service upgrades, panel work, and 240V circuits. Values are derived from NFPA 70 (NEC) for educational purposes. Always verify against your locally adopted NEC edition and amendments - local jurisdictions may enforce stricter requirements. WireRef provides reference information only and is not responsible for work performed based on this content. NEC® is a registered trademark of the National Fire Protection Association. Free NEC access via NFPA · OSHA Electrical Safety · Terms of use.

NEC 2023 references verified April 2026