THHN Vs NM B Wire – Which One To Choose?

When it comes to renovating your newly built home, office, or factory, one of the prime factors you have to decide on is the electrical wiring.

Both THHN and NM B wires are currently the best electrical wires in the market.

You need to determine which type of project you are planning to get the right set of wires. If you are working on your house or a small office, you should pick NM B wires. But if you are planning to carry electricity between buildings and an external power source, THHN is your bet.

But that’s not all. In this article, you will get a vivid knowledge of THHN vs NM B wires so that you can choose the suitable one for your project.

6 Comparison Factors Between THHN And NM B Wire

Apart from being similar in multiple factors, there are still some significant differences between THHN and NM B regarding their applications.

THHN cable contains a single thermoplastic high heat-resistant nylon wire, while the former conductors of NM B are basically THHN wires.

This is what creates the most confusion between the types of cables.

FactorTHHNNM BWinner
Voltage Rating600 Volts600 VoltsBoth
Heat-Resistance90º Celsius90º CelsiusBoth
ConductorSingleMultipleNM B
ComponentThermoplastic InsulationPVC InsulationTHHN
Size1, 2, 4, 6, 8, 10, 12, 14 AWG2, 4, 6, 8, 10, 12, 14 AWGTHHN
PriceCheck the priceCheck the price

No, it’s time that I take you through a detailed tour of both of these wires.

Voltage Rating

The first quality comparison between electrical wires should be their voltage ratings. It means the wire’s capacity to carry the highest voltage continuously in cable construction.

Both THHN and NM B have a voltage rating of 600 volts.

This is because NM B cables are basically created by bundling THHN wires and sheathing them in PVC.


Since NM B cables are actually made of THHN wires and their voltage ratings are the same, both of them serve equally when it comes to this factor.

Heat-Resistance & Components

Another major quality of electrical wires is their heat resistance.

THHN wires are made through thermoplastic insulation. Their heat resistance in dry conditions is up to 90º Celsius, and for moist conditions, it is 75º Celsius.

On the other hand, NM B cables can never be used in moist conditions. Their heat resistance is also up to 90º Celsius in dry conditions.

However, NM B cables are coated in PVC, which makes their use not recommended around high heating situations.


Considering the versatility, I will give this round to THHN cables as they are capable of functioning in any environment.


Conductor is the inside material of the wire that performs the task of carrying electricity. Most contractors prefer multi-conductor cables, with all the necessary wires under a single jacket.

THHN wires use just one single conductor. Though their performance is high, still using single-conductor cables on a construction site increases the labor time and cost.

On the contrary, NM B cables have multiple conductors since they are created by combining multiple THHN wires.

This not only reduces labor expenses but also speeds up the installation process and reduces the chances of on-site risks.


If we take the performance into account for both these wires, I will have to pick NM B over THHN.

No matter how durable THHN cables are, NM B will always be one step ahead because of having multiple conductors.


As I have mentioned before, THHN wires are mainly made for industrial use. Whereas, NM B cables are mostly used in households and small offices.

Nevertheless, let’s see their brief application areas.

THHN Wire Application

  • Carrying electricity between buildings.
  • Carrying electricity from external power sources for commercial purposes.
  • Controlling wiring and signaling.
  • Connecting machine tools and automation systems.

NM B Wire Application

  • Residential building wiring.
  • Connecting devices and outlets.
  • Connecting home appliances like washing machines.
  • Used for lighting, switches, and wall tiles.


Both of these wires are used for different purposes under different requirements. But they serve their best which is why both of them are winners under this condition.


Both THHN and NM B wires come in multiple sizes, from 14 AWG to 2 AWG. But for THHN cables, the case is a bit extended.

THHN cables also come in 1 AWG size. On the other hand, you can select if you want a 2-conductor NM B wire or a 3-conductor one.


The less the size of THHN and NM B cables, the more electricity they can carry. This means 2 AWG-sized wires can carry more electricity than 14 AWG-sized wires.

THHN has the lowest sized wires, which is 1 AWG.

Now that you know all the specifics and features of both THHN and NM B wires, let’s get into which one is more suitable for your project.

NM B Wire

When Should You Go For THHN Wire?

Whether you are working on your house outlets, or maybe building a complete electrical grid, it is always best to know which wires to use for which condition.

You should use THHN wires if

  • You want to run power inside buildings and between various outlets.
  • Your application has exposure to high heat.
  • You are dealing with both dry and moist situations.
  • You are using cables for outdoor home applications.

When Should You Go For NM B Wire?

As you already know, NM B cables are more suited for your residential purposes. You should go with NM B wires if

  • Your project includes regular branch wiring.
  • You need a stable and steady connection inside your walls.
  • Your project requires multi-conductor cables.

Final Verdict

Despite having so many similar functions, THHN and NM B cables have extra different benefits to add.

As NM B wires have PVC coating, they are suitable for any interior walls, garages, and above-ground surfaces.

They are also color-coded according to sizes, so it is really convenient to pick out.

On the other hand, THHN cables are compatible with almost any building code. Also, their nylon coating offers superior protection against any chemical or water damage.

Well, now that we have reached the end of this article, I hope I have managed to help you with your decision on the THHN vs NM B wire dilemma for your project.

Hey, if you have any inquiries about more wiring systems for your other home appliances like air conditioning, you can check out our article 10 2 or 10 3 wire for air conditioner.


What does type NM-B mean?

Residential wiring of lighting systems, gadgets, and appliances frequently uses Type NM B (Non-Metallic Sheathed Cable).

The Type NM B ampacity limit must adhere to the National Electrical Code, which is a 60º Celcius conductor temperature rating.

Can I run nm-B through conduit?

The answer to this question is Yes, NM B wires can be run through conduit or any other type of protection.

Can nm-b wire be used outdoors?

The most widely used construction electrical wire is THHN. Per the National Electric Code, the THHN wire is made to be used in building construction.

Engineers do, however, frequently include it in control circuits, machine tools, and for carrying electricity between buildings.