THHN Vs TFFN Wire – Busting The Myths

Building wires are the most common type of construction wires in the cable market. This is why it is very important to determine your project requirements and understand the functionalities of different wires.

For building wires, it is very easy to get confused since a major number of wires serve the same purpose, however, under different conditions. THHN vs TFFN creates the same conflict.

Thermoplastic High Heat Nylon (THHN) and Thermoplastic Flexible Fixture Nylon (TFFN) are two construction wires commonly used for commercial, residential, and industrial buildings. THHN wire has a solid copper conductor, which makes it perfect for branch wiring, but TFFN has a stranded copper conductor, which gives the wire great flexibility.

But that’s not everything. When planning a project as crucial as electrical wiring, you must know every detail of the equipment you will use.

This article will give you a complete idea of which wire to choose between THHN and TFFN under different circumstances.

8 Comparison Factors Between THHN And TFFN Wire

The key difference between THHN and TFFN wire is that THHN wire is perfectly capable of functioning under dry and wet conditions. On the other hand, TFFN cables are only suitable for dry conditions.

Let’s dig deeper.

Voltage Rating600 Volts600 VoltsBoth
Heat-Resistance90° Degrees on dry condition
75° Degrees on moist condition
90° Degrees on dry conditionTHHN
ApplicationResidential and Commercial wiringFlexible fixtureBoth
Gauge Range4 AWG to 1000 MCM18 AWG and 16 AWGTHHN

Comparison Factor 1: Voltage Rating

When it comes to wiring, the voltage rating is a very serious factor for taking into account. This indicates how much voltage can be applied through a wire or cable.

If the voltage rating of any construction cable is significantly lower, it has more chance of failing and creating a fire hazard.

THHN and TFFN wires have a voltage rating of 600 Volts, making them equally reliable and safe for cable construction.


Since THHN and TFFN cables have the same voltage rating capacity, both function identically under dry conditions.

Comparison Factor 2: Heat-Resistance

Installing a wiring system for industrial or residential purposes isn’t just a piece of cake.

Alongside the amount of passing electricity, the voltage applied, and the wire quality, the surrounding impacts a lot in terms of proper functioning.

Both THHN and TFFN wire can resist up to 90° Celcius heat under dry conditions. However, THHN can also tolerate up to 75° Celcius temperature under wet conditions, which TFFN can’t.


It is not recommended to use TFFN under wet conditions because although it can resist gas, oil, and heat just like THHN wires, TFFN is not water-resistant like THHN.

So this round goes to THHN wires.

Comparison Factor 3: Conductor

Both THHN and TFFN wires have a single copper conductor in them for carrying the electricity.

However, THHN wires have a solid conductor, for which you can run a large amount of electricity through them without worry.

TFFN cables, on this matter, have a stranded conductor. This makes TFFN wires highly flexible for branch circuits and other flexible fixture applications.


The single conductor in both THHN and TFFN wires makes them perfectly able to carry electricity in residential and industrial cable constructions.

They can also be run through conduits and transfer the electricity to electrical appliances. So there is actually no superior when it comes down to the conductor.

Comparison Factor 4: Application

THHN has a solid copper conductor installed inside, making it capable of carrying high-voltage electricity in control circuits.

On the contrary, TFFN wires have stranded copper conductors inside. For this, TFFN wires are recommended by National Electrical Code for situations where fixture wires are needed.


THHN wire offers great versatility, while TFFN wires offer fixture flexibility. This only happens due to their different conductor types.

That’s why in terms of application, both wires hold separate grounds.

Comparison Factor 5: Insulation

THHN and TFFN wires have nylon jacket around their conductors wrapped in PVC insulation.

This protects the wires from heat and grease and allows them to run through conduits behind walls.

The PVC also increases the durability of the wires, making them last for a really long period of time.


As both the THHN and TFFN wires have the same PVC insulation, they dominate the area regarding protection.

Comparison Factor 6: Gauge Range

The gauge range indicates the wire sizes and how much electricity can pass through them.

Let me explain it a bit more. The lesser the gauge size, the more electricity it can transfer.

The gauge range of THHN wires can be between 4 AWG and 1000 MCM, while TFFN wires range from 18 AWG to 16 AWG.


The sizes of both wires clearly show that THHN wires have the lowest-sized cables and are thus able to convey more electricity than TFFN cables.

So, undoubtedly, THHN wire is the winner.

Comparison Factor 7: Jacket

A jacket is the first line of mechanical defense that protects the conductors from external pressure or force like flame and chemicals.

THHN and TFFN wires have nylon jacket coating, making them impenetrable to any damaging chemicals or heat that may occur on the construction site.


This round is a tie as THHN and TFFN both wires have the same nylon-coated jacket.

Comparison Factor 8: Dual Rating

Dual-rated cables can have two different voltage ratings on their jacket.

THWN is the dual-rated version of THHN, whereas TFN is the dual-rated version of TFFN wires.


THWN is a completely water-resistant wire, while TFN is an extended flexible version of TFFN cable, which may have a single or stranded conductor.

Although TFN offers you great flexibility, THWN wires can resist water completely, making them the grand champion of electrical wires.

Now that we have reached the article’s end, you should know how to differentiate between the THHN and TFFN wires.

Now it’s time we learn where to use them.

THHN Vs TFFN: Which One To Choose?

Let’s check out which situations demand which type of wiring systems.

  • If your project requires fixture wire according to the National Electrical Code, go with TFFN wires.
  • If your project includes branch circuits, you can use both THHN or TFFN wire.
  • If your construction site is damp and wet, always use THHN wires. Better with the THWN wire.
  • For carrying wires through a conduit or outdoor raceways, always use THHN wires.
  • If the cable construction area has a high temperature, go with THHN wires.


Is TFFN the same as Thhn?

In reality, the TFFN and THHN wires are the same. Their individual assessments are the only thing that differs. These wires’ names contain letters that represent the clearances they have received.

As a result, even in the letters used to identify them, their slight variances may be seen.

What is TFFN and Thhn wire?

Electrical wires used in the building wiring category include THHN and TFFN wires. The National Electrical Code for general-purpose wiring specifies the construction of TFFN and THHN wire for installation in conduits or other approved raceways.