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Can THHN Wire Be Buried in Conduit? (Read This First!)

There are multiple types of wires available in the market for various kinds of wiring. THHN is one of them. It is a single node wire which is known as Thermoplastic Hight Heat Nylon.

You might ask can THHN wire be buried in conduit. Well, let us help you get the answer you are looking for and provide you with some additional information related to this.

Can THHN wire be buried in conduit?

THHN wire can be buried in a conduit. If using the wire buried in a conduit, then the conduit must have to be metallic or non-metallic. The temperature of the wire has to be around 185 degrees Fahrenheit. The conduit can be in dry or wet conditions and will not affect the THHN wire buried in it.

THHN wire is a single-phase wire. It is made for residential and commercial use. It uses a Nylon jacket to protect the internal core of the wire.

This is the only protection of the wire. Therefore, it has to be buried in conduit to provide it the necessary protection that it needs.

THHN cannot be directly buried. As THHN comes with only one outer protection which is known as a Nylon jacket, the wire can be damaged easily while buried. It may not be suitable enough to overcome the dry, wet or corrosive environment.

So, THHN wire cannot be buried directly rather than it has to be in a conduit while buried.

THHN can be used in underground conduits. In the underground, it can be buried in a PVC conduit. PVC conduit is one of the most common non-metallic conduits available in the market. Moreover, there are metallic conduits available in the market.

You can use THHN wire underground in these conduits and use these wires without any problem.

Why can’t THHN be buried?

There are multiple reasons why your THHN cannot be buried. Here are some ideal reasons why you cannot do it:

It uses a simple protective layer:

THHN wire uses a simple one layer protective layer. It is known as a PVC coating with Nylon shielding.

This protective layer is enough for basic everyday protection. But it cannot keep the wire protected while it is buried because it may be dry, wet or corrosive. These conditions may damage the wire.

The manufacturer does not approve it for that use:

All wire manufacturers test and check if their wires are appropriate for certain uses. THHN wires are also tested by manufacturers as well.

But manufacturers do not test it for using it while buried. Therefore, you cannot use it while buried as the manufacturers do not approve it for such use.

It can get damaged:

THHN wires are vulnerable to getting damaged. As they use a simple protective layer, it can get damaged without noticing.

If it gets damaged, the core of the wire will be exposed to humans and animals and that is dangerous for everyone. It can cause risks.

Voltage and wattage supply may get disrupted:

Wires have a certain voltage and wattage while in use. But the wires are not in a suitable condition, it may not supply an adequate amount of voltage and wattage. The same goes for THHN.

If it is buried, there is a possibility that it may not be able to provide the necessary voltage and wattage required for the appliances that it is connected to.

What happens if you bury THHN in conduit?

THHN wires have a simple protective layer. So, it cannot be directly buried. Using a conduit and taking the wire through the conduit, is the ideal way to bury THHN wire.

Certain things happen if you bury THHN in a conduit. Here are the ones that we think you should know about:

THHN wires will be more protected:

As THHN wires come with a simple protective layer which is known as PVC based Nylon shielding, conduit adds an extra layer of protection to it. You may use metallic or non-metallic conduits according to your needs and requirements.

Can bury the wires deeper than usual:

You could say that you can use UF type cables that can be directly buried. But if you use conduit to bury your THHN wire, you can bury the wire deeper than usual.

Maintaining the NEC:

The National Electric Code is an important rule book that has to be maintained by all. According to the NEC, if any wire has to be buried then it has to be taken through a conduit for better safety and reliability.

What type of wire can be buried in conduit?

There are various types of wires that are available in the market. All of these wires have a different use cases. Based on that all wires have a different set of safety features and protections to make them ideal for the use case that it is in.

You may ask which wires can be buried in the conduit. Here are the wires that we think are best for this case for you:

THHN wire:

This wire is a commonly used single phase wire. Famous for its availability in the market as well as low cost. It uses a simple protection layer which makes it much flexible and easy to work on. This wire is suitable for underground conduit wiring.

THWN wire:

THWN is simply a different version of THHN but a much better and more reliable option if you are opting for a wire that can be buried in a conduit. This wire has a better water resistance capability than THHN.

Therefore, as wires underground may get wet in course of time, THWN is the best possible wire for burying it in a conduit.

NM wire:

This wire is a Romex wire but with a better protection layer. Where Romex wires tend to have a single PVC layer as protection, NM wire has multiple layers of protection.

This makes the wire much reliable and sustainable for the underground conditions. So, NM wire can be used for burying in conduit.

XHHW wire:

This wire is a heavy-duty wire that is designed for higher voltage and wattage power distribution in residential and commercial buildings.

This cable is manufactured using copper and aluminum which makes this cable much more reliable for electricity supply. Moreover, it has a better heat resistance capability so it can be used in a conduit while buried.

Can THHN be used in wet locations?

No, THHN can not be used in wet locations. THHN is a wire that can sustain high temperatures. It can take around up to 194 degrees Fahrenheit. It is an ideal wire for high-temperature locations.

But this wire is not made for wet environments. THWN is suitable for these kinds of places which is a type of THHN wire. But THHN cannot be used in locations that are wet.

Can THHN be used outdoors?

THHN can be used outdoors. THHN is a wire which is made both for indoor and outdoor use. As it has higher temperature protection, it can prevent damages made by temperatures up to 194 degrees Fahrenheit.

So, the sun and the heat of the environment will not be a problem for this wire. But, the wire uses a single Nylon jacket to protect itself. Therefore, you will have to use the wire through a conduit in order to ensure the safety of the cable.

Can THHN wire be used without conduit?

According to the National Electric Code (NEC), you cannot use THHN wire without a conduit. THHN wire is a popular wire choice in the community for its flexibility and availability.

But to make this wire less costly, there is only a single layer Nylon jacket on it. This makes this wire vulnerable to external damages. Thus, the NEC prohibits THHN wire from being used without conduit.

What use is THHN wire suitable for?

THHN is used for various uses. Here are some highlighted uses that are suitable for it by us:

Carrying electrical currents in buildings and external power sources:

This wire is ideal for electrical current transmission. It is used in residential and commercial buildings. As multiple phases are required, multiple THHN wires are used.

Automation systems:

There is various automation system that is available in the market. People use them in their daily. THHN is the perfect wire for these systems due to its lower price.

Machine Tools:

You may use various machine tools in your everyday life. All of these require various kinds of wires to do various works. Therefore, THHN is perfect for these machines.

Final thoughts

THHN wire can be buried in conduit. As this wire is used for electricity distribution, it is common to run a wire underground using conduit. Moreover, the wires can be buried deeper in the ground if required due to the protection of the conduit. So, THHN is perfect for underground conduits.