Introduction
When it comes to electrical wiring for residential, commercial, or industrial projects, THWN and THHN wires are two of the most commonly used types. At first glance, they may look similar, but they have important differences in insulation, temperature rating, moisture resistance, and applications.
This article explains THWN vs THHN wire, helping you choose the right option for your electrical project.
THWN vs THHN Wire
1. What is THHN Wire?
THHN stands for Thermoplastic High Heat-Resistant Nylon-coated.
-
Insulation: PVC (Polyvinyl Chloride) insulation with a nylon jacket.
-
Temperature Rating: Up to 90°C (194°F) in dry locations.
-
Voltage Rating: Typically rated for 600V applications.
-
Environment: Designed mainly for dry locations.
Key Uses of THHN:
-
Building wiring and conduit systems.
-
Branch circuits and control wiring.
-
General-purpose indoor installations.
2. What is THWN Wire?
THWN stands for Thermoplastic Heat and Water-Resistant Nylon-coated.
-
Insulation: Similar PVC base insulation with nylon jacket.
-
Temperature Rating: 75°C (167°F) in wet locations, 90°C (194°F) in dry locations (for THWN-2, 90°C in both dry and wet).
-
Voltage Rating: Typically rated for 600V.
-
Environment: Specifically designed for both wet and dry locations.
Key Uses of THWN:
-
Outdoor or underground conduit wiring.
-
Applications exposed to moisture or damp environments.
-
Service entrance wiring.
3. Key Differences: THWN vs THHN
| Feature | THHN Wire | THWN Wire |
|---|---|---|
| Moisture Resistance | Dry locations only | Wet & dry locations |
| Temperature Rating | 90°C in dry | 75°C in wet, 90°C in dry (THWN-2 = 90°C both) |
| Outdoor Use | Not recommended | Suitable for outdoor/underground |
| Cost | Slightly cheaper | Slightly more expensive |
| Best For | Indoor conduit wiring | Outdoor or moisture-prone environments |
4. THWN-2 and Dual-Rated Wires
Today, many manufacturers produce dual-rated THHN/THWN-2 wires, meaning the same wire meets both THHN and THWN standards.
-
THWN-2 can handle 90°C in both wet and dry locations, making it a versatile choice.
-
If you see a wire marked “THHN/THWN-2”, it can be used for nearly all general electrical wiring needs.
5. How to Choose Between THHN and THWN?
When deciding, consider:
-
Installation Location: If the wire will be in wet or outdoor conditions (e.g., underground conduit), go with THWN or THHN/THWN-2.
-
Budget: THHN may be slightly cheaper for indoor-only applications.
-
Future Flexibility: Dual-rated THHN/THWN-2 is often the smartest option, as it works in both environments.
6. FAQs
Q1: Can THHN wire be used outdoors?
Only if it’s inside a watertight conduit and not directly exposed to moisture. THWN is better for outdoor conditions.
Q2: Is THHN or THWN better for underground conduit?
THWN or THWN-2 is the correct choice, as it’s rated for wet environments.
Q3: What does the “-2” mean in THWN-2?
The “-2” indicates a 90°C temperature rating in both wet and dry locations, making it more versatile.
Conclusion
The main difference between THWN and THHN wires is moisture resistance. While THHN is designed for dry locations, THWN (especially THWN-2) can handle wet and outdoor conditions, making it the preferred option for modern installations.
Looking for high-quality THHN/THWN-2 copper wires at competitive prices? Contact TOT Wire & Cable for bulk orders and expert advice.
2 comments
해운대한의원 09/07/2025
It's the best time to make some plans for the future and it is time to be happy. I've read this post and if I could I wish to suggest you few interesting things or suggestions. Perhaps you can write next articles referring to this article. I desire to read more things about it!
Totcables 09/09/2025
that's ok