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Can THHN Wire Be Buried in Conduit? (Quick Answers)

When choosing cables for making electrical bridges, we can think of many cables to use. THHN is a type of wire where they are preferred among the electricians for such purposes.

The THHN wire is a single node wire that we use commercially. They construct the wire with the coating of nylon that surrounds its core from the external elements. The THHN stands for Thermoplastic High Heat Nylon.

The THHN wires are an excellent cost-effective building wire that can be used for a multitude of reasons. If we were to give an example, the wires can be used for carrying electrical currents between external sources and buildings.

So, since we understand the use of the wires and their importance, we can understand why they need to bury them in the ground. We also know that having the nylon jacket for protection of the THHN is not enough for being underground.

This is where we can help you understand if the THHN cables are able to be buried inside a conduit. We will go in depth as well as explain the other things of relevance to this topic below, so keep reading to know more about THHN wires and conduits.

Can THHN wire be buried in conduit?

You can bury THHN wire in a conduit. This also goes without saying that the wire itself is not ready for direct burial. THHN wires are not designed for exposure like that, thus burying them in a conduit is the right way. Because this way the THHN wires will not be exposed to external damage.

THHN wires can be buried in a conduit. But if you want to bury it directly in the ground, that is not possible. This is because the wire will get damaged when it is buried directly.

Furthermore, the manufacturer of such wires does not condone buying them for such purposes. also does not approve of burying them without any conduit. They recommend that we bury THHN wires in a conduit, if we need to bury them.

It can get dangerous for us if the wire were to get damaged. That will happen if we do not use conduit to bury them. Moreover, not only will it be dangerous for us, it will also not be safe for animals, due to the wire being exposed to the ground.

Apart from being dangerous, there are other situations that might arise due to the wires buried without a conduit. Like unstable supply of electricity, which will be much worse of a headache then to just bury them in a conduit.

We can see there are multiple reasons as to why we should not bury THHN wires directly to the ground. The conduit acts as a safeguard that upon installing we will also follow the guidelines laid by the NEC (National Electric Code). 

If we assure that the THHN wire is buried in a conduit then whatever the conditions of the environment might be, the wires will not be exposed to the external elements. The temperature of the wire needs to be anywhere from 140° Fahrenheit and a maximum of 185° Fahrenheit. 

Because that temperature is the ideal temperature for the wires to be in workable condition.

Can you use Thhn wire underground?

THHN stands for Thermoplastic High Heat Nylon. This cable is designed to work in dry and damp environments. However, they are certainly not made to be directly buried in the ground.

THHN wires can reach temperatures of 90ºCelcius (194ºFahrenheit) for the maximum amount. That is a pretty high temperature and if they are laid out in the dirt without a conduit protecting them, there will be some collateral damage later on.

However, if we use the conduit, we can easily use the THHN wire underground. That way they will be safe from certain elements that might disrupt their power supply or even get exposed.

Although there are some other cables that are able to be used underground, like the UF-B and USE-2 cables. These wires are suited for direct burial where they can be laid without using conduits for protection.

3 reasons why thhn wire can be buried in conduit

THHN wires cannot be buried in the ground directly. However, here are some reasons why they can be buried in conduits.


We already established that the THHN wires will be vulnerable when we bury them directly in the ground. Conduits are designed for such purposes, where certain cables or wires that need protection. Thus, the THHN wire can be buried in a conduit.

Moreover, there are different types of conduits for such needs. The THHN wires preferably need metallic conduits, but the non-metallic conduits can also work. Being the conduit will keep the wires safe from exposure.

No Disruption: 

Whenever we install cables there will be electricity passing through them. THHN are building wires that serve the purpose of building electrical bridges between different electrical devices. 

When THHN cables are placed inside a conduit there is no risk for their safety. Moreover, the conduits keep the flow of electricity as stable as possible. 


In constructing a new house, people need to follow certain rules and regulations laid down by the authority. These rules and regulations need to be strictly followed by everyone.

NEC as discussed before has a code that states when making bridges of electricity, we cannot lay them directly in the ground without using a conduit. Thus, we have to bury THHN in a conduit.

How long will Thhn wire last underground?

THHN wire has a single node system which is protected by a nylon material on the outside. However, this small protection is not enough to keep it safe from exposure to the elements. Even if they seem fine when in direct burial, in time they will get damaged and cause accidents.

That will all change if we place the THHN cable in a conduit, preferably a metallic conduit. This will be enough protection for the cables and we will not need to worry about the exposure to the elements.

THHN cables that are placed in conduits will last as long as 30 years. You might think that this number is low when compared to the other cables, that is because the THHN wires do not have the required insulation that makes them last longer.

How to bury thhn wire in conduit?

There are many occasions where sometimes we ourselves will need to DIY cables and wires in our homestead. If you happen to work with THHN cables and need to bury them underground, you will need some insight before you actually start working on them.

Moreover, the process might seem too daunting but it is rather straightforward when you have the right tools.

Collect the tools: 

The first thing we need to make sure of is that we collect the main tools we need for this project. We would need 4-1 screwdriver, adjustable wrench, spade, and a corded drill.

Moreover, for the materials, we will need the THHN wire, any kind of conduit and fittings, preferably metal, and finally a service entrance well.

Start digging: 

Once we decide how deep we need the wires to be, we need to start digging. In this particular scenario let us say we need to dig 6 inches as a standard measurement.

Use a metal conduit: 

We dig 6 inches deep, then we use a rigid metal galvanized electrical conduit for the best protection. As a side note, we should make sure to check if the conduit has a “W” on the label to suggest it has waterproofing.

What wire can be buried in conduit?

Most of the wires or cables are approved for installation through a conduit. There are exclusive ones like the THWN wire.

However, cables like the nonmetallic NM or Romex cable may not be allowed in all jurisdictions, that is why we should not disapprove of the rules written by NEC and follow them faithfully for our safety. 

Either way here is a list of wires that are able to go through the conduit without hassle.

  • THHN Wire
  • THWN-2 Wire
  • THWN Wire
  • NM or Romex Wire
  • XHMW Wire

Final Thoughts

THHN wire is able to be buried in conduits. These wires might have a protective layer but regardless of that, they are not ideal for direct burial in the ground. Therefore, it is made a rule by the NEC, that we bury THHN cables in conduits instead of directly. This is for our safety.