TW Wire

Q: What is the temperature rating of TW?

TW is rated 60°C in dry locations and 60°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)).

NEC Quick Answer

Conductors with Type TW insulation have a temperature rating of 60C (140F). TW is a moisture-resistant thermoplastic insulation rated for dry and wet locations. Its ampacity values are found in the 60C column of NEC Table 310.16.

NEC 2023: Table 310.16, Section 310.4(A)

TW stands for Thermoplastic moisture-resistant. Basic low-temp wire. Rarely used today - THWN-2 is preferred.

Dry rating60°C

Wet rating60°C

Voltage600V

Locationsdry, wet

Specifications

Property	Value
Full name	Thermoplastic moisture-resistant
Insulation material	PVC
Outer covering	None
Temperature rating (dry)	60°C (140°F)
Temperature rating (wet)	60°C (140°F)
Voltage rating	600V
Approved locations	dry, wet

When to use TW wire

Basic low-temp wire. Rarely used today - THWN-2 is preferred.

Common applications for TW:

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

NEC code references for TW

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 TW 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 TW wire

Where can I use TW wire?

TW is approved for use in dry, wet per NEC Table 310.4(1). It has a dry temperature rating of 60°C and a wet rating of 60°C. Always verify that your specific installation meets the approved location requirements.

What is the temperature rating of TW?

TW is rated 60°C in dry locations and 60°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-2NM-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

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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