Is it permissible to use THHN/THWN cable instead of USE-2 cable in underground conduits?

[Rory Choicllroy]

I am an electrical engineer working on a construction site for an educational facility.

We are installing streetlights in the exterior spaces of the building, and the power will be supplied from the electrical panel board inside the building.

I have heard discussions about using USE-2 cable for the underground conduit to the exterior lights, but there's also mention that THHN/THWN cable could be used.

I am curious to know if there are any issues according to the NEC (National Electrical Code).

 

[LarryFine]

Welcome to the forum.

THHN/THWN is a single conductor, not a cable. Yes, it can be used outdoors and underground as long as it is completely enclosed in a complete conduit assembly.

 

[don_resqcapt19]

If you are using USE, note the requirements in 338.12(B).

 

[Strathead]

I am an electrical engineer working on a construction site for an educational facility.

We are installing streetlights in the exterior spaces of the building, and the power will be supplied from the electrical panel board inside the building.

I have heard discussions about using USE-2 cable for the underground conduit to the exterior lights, but there's also mention that THHN/THWN cable could be used.

I am curious to know if there are any issues according to the NEC (National Electrical Code).

For the record your entire question is backwards. You can use THWN in conduit in most situations, but you can't use USE-2 to any interior location. It isn't allowed inside a building, period. And that includes in conduit.

 

[Strathead]

In general you would use the USE without conduit. Not that this is required, but it is allowed.

 

[Rory Choicllroy]

Thank you for answer.