Building Wire – THHN and XHHW
Building wire is generally used to provide power in buildings and structures. The two main types of building wire found today are THHN and XHHW. This article helps explain both of these types of building wires as well as applications for each.
THHN Building Wire - THHN stands for “Thermoplastic High Heat-resistant Nylon coated”. THHN building wire can come in stranded or solid conductors in both copper and aluminum conductors depending on the size. Basically, THHN wire is copper or aluminum covered in a PVC (polyvinyl chloride) insulation with a nylon jacket. THHN wire is UL listed with a rated 90 degrees Celsius in dry locations or 75 degrees Celsius in wet applications with a THWN rating. The vast majority of THHN building wire these days’ carries a dual rating on the cable marked THHN/THWN for both the wet and dry temperature rating. It may also be used for wiring of machine tools, control circuits or on certain appliances.
XHHW Building Wire - stands for “XLP (cross linked polyethylene) High Heat-resistant and Water Resistant”. XHHW also can be found in stranded or solid conductors in both copper or aluminum conductors. XHHW is simply an extruded layer of XLP applied to the copper or aluminum condutor. The vast majority of XHHW today is rated XHHW-2 for both a wet/dry rating of 90 degrees Celsius.
Some key differences in THHN and XHHW building wire:
XHHW uses a thicker insulation than THHN. This can be advantageous in terms of its electrical properties. You will have less current leakage with a thicker insulation.
Also, XLP (the insulation used XHHW) can have better or worse characteristics than PVC (the insulation in THHN) in terms of chemical or environmental exposure. An example of this is how XLP is very resistant to nuclear radiation while PVC performs poorly against it.
Another difference or advantage to XHHW is its smoke and burn characteristics. It is a cross-linked polymer and doesn’t produce as much toxic smoke when burned like THHN. THHN burns off the conductor and XHHW burns more like rubber reducing the dangerous dripping during a fire.
XHHW is typically easier to handle, bend and install due to it not having the nylon coating like THHN. Many contractors or end users prefer to use a product that saves energy and time during installation so this is worth noting.
However, XHHW is more expensive than THHN. Many times paying the extra money for XHHW is not necessary as THHN can do the job required in your application.
Both XHHW and THHN building wires are manufactured in a variety of colors. The circuit sizes (14awg-10awg) offer the full rainbow of colors while the power sizes (8awg and larger) are most predominately offered in black or green. Almost any size can be dyed to any color since the insulation on both products will accept a dye.
While building wires are generally considered a commodity in the wire and cable industry, XHHW is considered more of a specialty item due to its infrequency of use compared to THHN. Many times building wires require striping per the specs of the job making it even more of a specialty wire item. The European three phase color code uses green with a yellow stripe and this is added by many wire and cable specialty distributors with a simple striping machine.
The key items to clarify when someone request THHN or XHHW building wire are:
1. Copper or aluminum?
2. Stranded or solid?
3. Color?
To learn more about the types of building wire, visit this link: Building Wire
Tags: Building Wire, colorado, denver, pvc, striped, striping, thhn, xhhw, xlp