What Is THW Wire And What Is The Difference Between THW And THWN Wire?

As I mentioned earlier, THW stands for, Thermoplastic Heat and Water-resistant wire. The THW electrical wire is specifically designed for use in dry locations up to 750 Celsius dry or wet. That being said, the National Fire Protection Association (NFPA)  limits the wire’s ampacity to 750 Celsius conductor temperature. Like most electrical wires, this type of wire occurs in two forms namely, solid or stranded. Its conductor is made of soft galvanized copper and is insulated using Polyvinyl Chloride (PVC).

As I indicated earlier, the THW wire is suitable for universal wiring, machine tool wiring and internal wiring of various electrical appliances. Still, for general ground wiring, it is always advisable to use a solid THW wire. What are some of those ground wiring situations? Well, some common general ground wiring situations that call for the use of solid THWs include CATV installations and swimming pool pumps.

Also, it is important to note that like most electrical wires and cables THW wires are not one-fits-all. For instance, the THW- 2 wire is specifically suited for general wiring applications associated with feeders, conduits or any other raceway services and branch circuits. The image below will give you a comprehensive overview of everything you need to know including THW wire sizes and the insulation thickness of any THW copper wire that you might want to buy;

Most people often find it difficult to differentiate between a THW wire and a THWN-type Wire. The difficultly in differentiating the two electrical wires is quite understandable considering that they share a lot of similarities. Basically, THWN stands for, Thermoplastic Heat and Water-resistant Nylon-coated wire. As you can see, the difference between THW and THWN is the ‘N’ which stands for Nylon-coated.  So, logically, the only difference between THW and THWN is the nylon coating. To put it simply a THW Wire does not have a nylon coating whereas; a THWN is reinforced with a nylon coating. The difference between the two is pretty straightforward, right?

Regardless of the fact that a THWN wire is an additional jacket of extruded nylon, its uses are significantly similar to those of a THW. It is rated 750 Celsius wet or dry and is normally used in conduit installations, machine tools, regulated electrical circuits and any other general-purpose wiring needs. For new buildings and rewiring for 60-volt applications, the National Electrical Code (NEC) permits the use of THWN-2 electrical wires.

Do you intend to carry out some outdoor installations? If the answer is yes you should definitely go for a THWN-type wire. Why is it advisable to use this type of wire for outdoor wiring purposes? Well without the nylon coating, wire type THW provides minimal protection against various environmental adversities. That being said, if you wiring needs are limited to an indoor environment, you should go for a THW building wire especially because it is less costly compared to THWN-type wires and suits your specific needs.