THWN is a code for thermoplastic heat and water resistant which is suitable for use in both dry and wet locations with a maximum temperature rating of 75ºC (167ºF).
The main difference between THHN and THWN wires are their maximum recommended operating temperatures in wet locations. While THHN wire is rated to be used in wet locations with ambient temperatures up to 75°C, THWN wire has a higher maximum recommended operating temperature of 90°C in both wet and dry environments.
THWN-2 (and therefore THHN/THWN-2 dual-rated) wires are suitable for use in temperatures up to 90°C or 194°F in wet or dry environments.
Use THHN/THWN wire for outdoor purposes; THWN is the same as THNN, but it is also water resistant. When we produce this wire we make a dual purpose wire that is clearly labeled on the outer coating.
Most THHN building wire comes with the dual rating THHN/THWN, meaning it is usable in both wet and dry conditions, as well as both indoor and outdoor use. THHN carries a UL rating of 90 degrees Celsius in dry environments and 75 degrees Celsius in wet environments.
THWN is a code for thermoplastic heat and water resistant which is suitable for use in both dry and wet locations with a maximum temperature rating of 75ºC (167ºF).
If you want to install THHN wires underground, you must first insert them in conduit, but they don't require any additional protection.
XHHW vs THHN Wire
'The “X” in XHHW (generally abbreviated as XPLE) is an insulation material that is more resistant to wet environments than THHN (90°C vs 75°C). It's also a thicker insulation that can better protect against breakdown when exposed to extreme environments.
One key reason why Romex can't be used outdoors is that if it gets wet with water, gas, oil, or another solvent, these liquids could penetrate the jacket and ruin the connection by touching the bare copper ground wire. Understanding this limitation is crucial for ensuring wiring safety in outdoor environments.
Things to Look out for When Wiring THHN Electrical Wire
Thinner THHN wires can leak or break down.
Can I directly bury a THHN wire? The short answer is no. THHN and THWN-2 Copper Building Wire is only approved to be buried in conduct, as it lacks the characteristics that would make it eligible for direct burial.
Wire and cable manufacturers at NEMA and Underwriters Laboratories (UL), state that Type NM-B cable (which includes Southwire's Romex® Brand) needs to be removed if the cable has been submerged in flood waters.
For longer runs, solid wires are the better choice because they feature less current dissipation. Stranded wire will perform well over shorter distances.
Stranded copper is easier for installers to handle in tight areas and inside buildings because it is more flexible and faster to manually manipulate.
American Wire Gauge (AWG) is the standard way to denote wire size in North America. In AWG, the larger the number, the smaller the wire diameter and thickness.
Noting that Romex is the name of a popular brand of Non Metallic cable, of the type specified in the NEC (US National Electrical Code) as type NM. (Like “Kleenex” is a brand of facial tissue.) Romex is not permitted anywhere that it is exposed to risk of damage, to water (dampness), and/or to sunlight.
Gray-colored sheathing is used to designate cable intended for underground installation. It has excellent water resistance and may also be rated for resistance to oil and sunlight. In this cable, the conductors are embedded in solid vinyl rather than running loosely inside the jacket.
Running NM cable in conduits in exterior environments, or any location considered damp, is strictly prohibited.
Note that Type NM cable, also known as Romex, is not one of the permitted wiring methods for service-entrance conductors. Type MC cable and ENT are also not permitted for this use. These wiring methods are usually only used for branch circuits within a building or premises.
XHHW Wire Overview
XHHW is an alphabetism or initialism which stands for "XLPE (cross-linked polyethylene) High Heat-resistant Water-resistant." XHHW is a designation for a specific insulation material, temperature rating, and condition of use (suitable for wet locations) for electrical wire and cable.
THHN wire is approved for up to 600V and is listed by Underwriters Laboratory (UL), as rated for 90° C (194° F) in dry and 75° C (167° F) in wet environments. THHN wire comes with a dual rating: THHN / THWN, which means it's appropriate for both dry and wet applications.
You may use THHN wire indoors and outdoors in dry and damp applications.
Number of wires: This number follows gauge. For example, 14/2 indicates that there are two 14-gauge wires (a ground wire, if part of the cable, is not included in this number) within the cable. Grounding: The word “GROUND” or the letter “G” indicates the presence of a ground wire.
Does 240v wiring need to be in a conduit? When running individual 240v wires, they must be placed in conduit for the entire length of the run. Non-metallic conduit is preferred due to its easier installation compared to rigid or EMT.