I am extending a residential 15 amp circuit from my house to my greenhouse. I have installed PVC conduit that runs from an existing GFCI receptacle on the exterior of the house and then underground where it comes up inside my greenhouse. The run is about 100' and I am intending to pull individual 12 gauge wires (to help minimize voltage drop). To save money, can I buy a single roll of, say, white-jacketed wire, run three wires, and then tape the ends so that I have a white, black, and green? Or do I have to buy individual lengths of white, black, and green?