Why not?

THHN wire is usually made with PVC insulation and it is not approved for outdoor use. This wire does not have the nylon coating that would make it acceptable for outdoor use. The wire is not water or moisture resistant and will be ruined quickly if it is put outside. The only way it would work is if you used the wire in conduit above ground; however it still cannot be buried. Most wires or cables that can be buried have additional layers of insulation or jackets to withstand the environmental conditions.

Underground Cable

Cables that are intended for use underground have a special insulation around them that allows for this kind of use. These wires are generally resistant to sunlight, water, moisture, and fungus.  Some of the wires that are approved for burial have an extra layer of PVC insulation on top of their nylon jacket. The PVC and the nylon jackets work together to make the wire better resistant to extreme weather conditions as well.

It is suggested that you ask the pet shop to make sure that you buy the correct wire for the job. The wire or cable needs to have an insulation that is strong enough to withstand direct burial. You want a wire that is going to last for a long time; these kinds of long lasting heavily insulated wires are going to cost more money than a THHN wire. Some of your underground cable options are UF-B cable, USE-2 wire, and Tray cable. Each is approved for outdoor and underground use because of the stronger insulation they have.

Written by: WesBell Electronics, Inc.

Conductors and Insulation

This specific kind of UF-B cable is made with either 2 or 3 conductors, and customers have the option of ordering the cable with or without a ground wire. The conductors of the UF-B cable can be made with three variations of copper, annealed, solid, or compressed stranded copper. Each of the conductors of the UF-B cable has a PVC insulation wrapped around them. The cable also has a nylon jacket and the wire is color coded for identification purposes. The grey PVC jacket on these wires is resistant to sunlight, moisture, and fungus making this wire acceptable for use both outdoors and underground.

Applications

The UF-B cables are used for outdoor electrical applications. They can go directly in the ground with or without conduit. The wires come in sizes 14, 12, 10, 8, and 6 AWG. The wire is built tough to be able to withstand the difficult outdoor weather. If you need an underground electrical cable this is generally your best option. You can use it in conduit underground but that is not necessary seeing as how the PVC insulation is resistant to water, sunlight, and fungus.

UF-B cable is made to be used underground. It is a direct burial cable and there is no need to use conduit when installing this wire. The UF-B cable only comes in the one color. That PVC insulation is resistant to a number of things such as moisture, fungus, and sunlight.  The Southwire UF-B cable meets all UL standards and the requirements of the National Electric Code as well so customers can be assured they are getting a quality product.

Written by: WesBell Electronics Inc.