THHN, THWN and TFFN Wire
When it comes to electrical wire there are a lot of options for customers out there. The three most popular kinds of electrical wire are THHN, THWN, and TFFN wires. These are most commonly referred to as building wire. They are all single conductor copper wires that can be used both indoors and sometimes outdoors.
THHN
THHN wire is the most common kind of electrical wire used today. Now a days you can find that most THHN wire is dual rated and can also be called THWN. This kind of dual rated wire is known more commonly as the universal building wire. THHN stands for thermoplastic insulation, heat resistant, high heat resistant, and nylon coating. The temperature rating on the THHN wire is up to 75°C for heat resistance and 90°C for high heat resistance. These wires are also approved to handle up to 600 volts of electricity.
THWN
There is only one difference between the THHN wire and the THWN wire. That difference is that the THWN wire is water, gas and oil resistance. This wire still has the same insulation, nylon coating, and the same heat resistance. The THWN wire is temperature rated to be able to handle heat as high as 75°C. But again most of the THHN and THWN wires are made to be dual rated and are considered to be universal building wire.
TFFN
The TFFN wire is a little bit different than both the THHN and the THWN wires. This wire does however still have the same thermoplastic insulation and the same nylon coating. The only differences are that the TFFN wire is flexible and fixture. This kind of wire does not have the same heat resistance as the THHN and THWN; it also is not a good wire to use in wet conditions. The TFFN wire also only comes in sizes 16 AWG and 18 AWG. Anything bigger in size than the 18 gauge wire will become a THHN or THWN dual rated wire.
A very common question a lot of wire and cable distributors get it whether or not this kind of wire can be used for electric dog fencing. It cannot. It is not approved for underground use even in conduit. Typically most of the applications for this wire are running power from the electrical box up to a light switch or outlets throughout the home. All these variations of wire are UL approved, RoHS and REACH compliant.
Written by: WesBell Electronics Inc.