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In this installment of our This vs.That series, we will be comparing TFFN and THHN building wires. These wires are built in accordance with the National Electrical Code for general purpose wiring for installation in conduits or recognized raceways. These wires are very similar, but the four letters in their name signify the different ratings that they meet.

What is THHN Wire?

THHN wire, or Thermoplastic High Heat Resistant Nylon wire, is a building wire ideal for use in machine tools, appliances, and control circuit wiring. This wire is made of thermoplastic material, specifically PVC insulation and a nylon jacket.

THHN wire is most commonly offered with stranded conductors but is also available with a solid conductor. Allied Wire and Cable offers this wire in 14 AWG to 1000 MCM. Most THHN wire is also dual-rated as THWN wire, making it water-resistant as well.

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What is TFFN Wire?

TFFN wire, or Thermoplastic Flexible Fixture Nylon wire, is a building wire with the same applications as THHN Wire. This wire is also made of thermoplastic materials. It is highly flexible but available in a smaller gauge range. TFFN wire is also classified as a fixture wire. It may also be rated as TFN wire. TFN wire features a solid conductor instead of stranded, which is why it doesn't have the second "F" for flexible.

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Max. Temperature Voltage Insulation Jacket Dual Rating
THHN Wire 90°C Dry, 75°C Wet 600V PVC Nylon THWN
TFFN Wire 90°C Dry 600V PVC Nylon TFN

What's the difference between THHN and TFFN Wires?

The main difference between these wires is their ratings. THHN wire may be used in both dry and wet locations, whereas TFFN wire is only suitable for use in dry locations. Nevertheless, both are suitable for installation in conduit and other approved raceways. However, since TFFN is a fixture wire, there are restrictions for its use in raceways. They must be large enough to permit the installation and removal of conductors without insulation damage.

While TFFN Wire is more flexible, THHN offers better heat resistance in wet locations. It can also be used in branch circuits. Another major difference is their insulation thickness and size availability. TFFN has thinner insulation and is only available in 16 and 18 AWG. Allied Wire and Cable has both THHN and TFFN Wire that is UL approved. Our TFFN Wire is also CSA approved and our THHN Wire is available with RoHS Compliance.

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