THHN vs. TFFN: Everything That You Need To Know About Thermoplastic Building Wires
Today, we will educate you on the differences between thermoplastic building cables: THHN and TFFN. These wires are not dramatically different, but several ratings have a significant impact on their applications. Let's highlight their differences in an easy way.
What Is Special About Building Wires?
One of the most common cables on the wire and cable market, building wires, are construction cables used in the building of all types of a modern property, including homes, offices, and plans. These are the sturdy, powerful cables usually made with copper conductors that bring electricity to your homes and workplace.
Common types of building wire include service entrance cable, NM-B wire, USE-2 RHH RHW-2, UF-B, XHHW-2, and many others. THHN and TFFN are some of the most common building wires in the industry.
THHN Cable: The Definition and Applications
THHN wire is defined as Thermoplastic High Heat Nylon per its abbreviation. It is a thermoplastic wire with nylon covering and high-temperature resistance of 75 C for damp purposes and 90 C for dry ones. The most prevalent type of insulation found in THHN wire is PVC. Both THHN/ THWN and TFFN wires have a regular voltage rating of 600V.
Another variation of THHN, THWN is a water-resistant wire that works well in damp conditions and can be placed in conduit and in raceway anywhere. The majority of contemporary THHN cables are double-rated as THWN. However, it is best to check the rating of the before using near water or any kind of moisture.
There is also THWN-2, the cable that is virtually the same as THHN/THWN but has superior resistance to UV lights and an improved temperature grade of 90 C for both wet and dry environments.
As a rule, THHN/THWN is used in branch and control circuits, appliances, machine tools, and other building applications. The cable has an impressive size range of 4 AWG to 1,000 MCM, making it a perfect choice for most building applications that exist on the wire and cable market. The cable demonstrates an excellent ability to resist oil and gas across all performances. The wire is available in stranded or solid conductor varieties.
TFFN Cable: The Definition and Applications
TFFN means "Thermoplastic Flexible Fixture Nylon." This is the class of cable that can be used as a machine tool wire, an appliance wire, and a fixture wire. Unlike THHN, this wire is limited in sizing to 18 AWG and 16 AWG exclusively. The cable comes with a stranded conductor that makes it extremely flexible. If the conductor is solid, the variation, which is called TFN, is not actually flexible. This variation of the cable is only used in fixtures that do not require flexibility.
Like THHN/ THWN, TFFN is immune to oil and gas; however, it does not really perform well when it comes to water and moisture exposure. The heat grade for use in dry places is 90 C.
Unless double-rated as MTW, TFFN is not fit for use in wet and damp conditions, meaning that it is not designed to be placed in conduit outside. The ability to install TFFN in raceways is limited because the wire is flexible. It can only be used in extremely large raceways not affected by water or any kind of moisture.
The primary thing that makes TFFN different from THHN is that it is a fixture wire.
What Is A Fixture Wire?
Fixture wire is the term that indicates that a cable has a flexible conductor. This implies that the wire can be used in lighting fixtures, Class 1 fire alarm circuits, limited power circuits, and control circuits. However, fixture wire cannot be used for overall branch circuits because the National Electrical Code prohibits it due to the limited capacities of such wire in branch circuits.
Which Thermoplastic Building Wire Should I Use?
The discrepancies between THHN and THWN are quite subtle and you can use these types of cables interchangeably in many cases as long as the sizing and the temperature class is appropriate for you. However, there are several instances when strictly one type of wiring can be used.
These Include:
- Use only TFFN in applications that call for fixture wire per the National Electrical Code and flexible applications.
- Use only THHN or THWN in branch circuits.
- Use only THHN double-rated as THWN in wet and damp conditions unless TFFN is double-rated as MTW.
- Use only THWN in conduit and raceways outdoors.
- The resistance to heat is superior in THHN/ THWN than in TFFN.
- Neither THHN nor TFFN should be utilized for direct burial. Use UF-B for these applications instead.
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