Electrical wiring to be run in conduit comes in individual strands, encased in insulation to protect the wire and insulate it from other wires and the conduit. Wires come in ither solid or stranded, depending on the wire size. Bare conductors are available for ground wires only. The insulation is made to take on some rather extreme conditions. Heat-, oil-, gasoline- and water-resistant coatings are all available to help your electrical wire survive.
The labeling on a wire's insulating jacket tells the story of the wires ruggedness. You'll likely see labels like THHN or THWN written on the wire. THHN wire stands for thermoplastic high heat-resistant nylon coated wire. THWN stands for thermoplastic heat- and moisture-resistant nylon coated wire.
The "T" stands for themoplastic, the type of insulation covering the wire itself. The "H" stands for a heat resistance of up to 167°F. Likewise, the "HH" stands for a heat resistance, only it increases the rating to 194°F. The "W" stands for moisture resistance. The "N" stands for an additional nylon coating that makes the wire both oil and gasoline resistant. As you can see, these wires are built to take on many different conditions.
The labeling on the wire also tells the conductor size and what the wire is made of, either aluminum or copper.
And don't forget, the color of the wire tells a story of its own. It indicates whether the wire is used for a hot, neutral, or a ground wire.