THW Wire

Q: What is the temperature rating of THW?

THW 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)).

THW stands for Thermoplastic Heat-resistant Water-resistant. General purpose wire in raceway. Common in older installations. Listed in 75C column of Table 310.16.

Dry rating75°C

Wet rating75°C

Voltage600VV

LocationsDry, Wet

Specifications

Property	Value
Full name	Thermoplastic Heat-resistant Water-resistant
Insulation material	PVC
Outer covering	None
Temperature rating (dry)	75°C (167°F)
Temperature rating (wet)	75°C (167°F)
Voltage rating	600VV
Approved locations	Dry, Wet

Advantages and limitations

Advantages: ['Moisture resistant', 'Widely available']

Limitations: ['Only 75C (cannot use 90C column for derating)', 'Being replaced by THW-2 and THWN-2']

When to use THW wire

General purpose wire in raceway. Common in older installations. Listed in 75C column of Table 310.16.

Common applications for THW:

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

NEC code references for THW

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 THW 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 THW wire

Where can I use THW wire?

THW is approved for use in dry, 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 THW?

THW 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 75°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-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