Home Electrical Wiring- Diagram and Installation Basics A diagram of a single-phase 120/240V service. HOME ELECTRICAL WIRING BASICS Whether you are considering a backup power system, want to add another electric circuit, or are going to install a new appliance, it is important to understand the home’s electrical wiring basics and applicable codes. How to Wire 120 V From 240 | eHow www››Home Repair & Maintenance›Electrical RepairsWiring a 120-volt circuit off of a 240-volt circuit can be useful where there is primarily 240 volts available. This could be the case at a water well or a workshop. A 240-volt circuit is comprised of two hot wires, a common neutral wire, and a ground wire.