Romex is a type of electrical wire used in various applications. While Romex wiring is useful for many indoor applications, it is unsuitable for outdoor use. This article explores why Romex can’t be used outdoors, compares Romex vs THHN for outdoor use, and discusses safer alternatives for outdoor wiring projects. While THHN and THWN wires can be used outdoors, they cannot be put directly underground.
Romex features a bare copper ground wire inside the cable that is not fully protected by the polyvinyl chloride (PVC) jacket that covers the conductors. One key reason why Romex can’t be used outdoors is that if it gets wet with water, gas, oil, or another solvent, these liquids could penetrate the jacket and ruin the connection by touching the bare copper ground wire. Understanding this limitation is crucial for ensuring wiring safety in outdoor environments.