Waterproof wire is wire that is designed to resist water intrusion. It may be labeled as water resistant or water repellent, depending on the manufacturer and its quality. There are some settings in which this type of wire is strongly recommended and sometimes actually required. However, it is important to note that different types of wiring are designed for burial and underwater applications. Unless a waterproof wire product specifically states that it can be used in these settings, it may not for these particular applications.
Water intrusion is an issue for wiring for a number of reasons. One obvious reason is that it can cause shorts which may damage the circuit or impair functionality. Shorts can also present a safety risk. In addition, water often carries salts which can have a corrosive effect, eroding the wire and its casing over time and presenting other safety and operational issues. Waterproof wire is designed to limit these problems by preventing water from reaching energized wiring.
Classically, wire is waterproofed by wrapping it in materials beyond the basic insulation used with all wiring. These materials are waterproofed and create a vapor barrier so that condensation cannot develop on the inside of the wrapping. When used with waterproof wire connectors, the wire can remain sealed so that water cannot intrude. It can be used in settings like bathrooms and kitchens where water intrusion may be a concern, and for outdoor wiring tasks such as porch lamps. In these settings, using waterproof wire is a safety measure so that in the event that water does get into the area with electrical wiring, it will be less likely to pose a risk.
For outdoor wiring locations such as setting up temporary lighting for a performance or seasonal display, using waterproof wire is critical. If the wiring is being left up for an extended period of time, even in the supposedly dry season, moisture can start to penetrate and cause problems. Waterproof wire and electrical cable for such applications is available from many stores which stock electrical supplies and related equipment.
For underground or underwater wiring, some additional insulation may be needed and a specialty cable or wire product may be necessary. People who are not sure about what kind of wire to use for a given application should ask for assistance or consider hiring an electrician for the installation to confirm that it is done properly and safely.