Single‑phase power—often called split‑phase—is delivered via two hot conductors and one neutral. Each hot carries 120 V relative to neutral, giving 240 V across the two hots for appliances that require it. The conductors are typically black and red for the hots, white for neutral, and green for the grounding conductor.
Three‑phase power uses four conductors: three hot wires and a neutral. Each hot is 120 V to neutral, but 208 V between any two hots. This arrangement delivers power more smoothly and efficiently, making it ideal for motors and heavy‑load equipment. The hot conductors are usually black, blue, and red; the neutral is white, and green is the ground.
Residential homes normally receive single‑phase service from the utility. Commercial buildings, factories, and data centers are wired for three‑phase to run motors, HVAC systems, and other high‑power loads. Even 240‑V household appliances—water heaters, dryers, ovens—use the split‑phase portion of a single‑phase service.
Inspect the cable: a single‑phase cable will show two insulated conductors (hot) and a separate neutral. A three‑phase cable will contain three insulated conductors plus a neutral. Voltage tests are also reliable: a single‑phase system measures 120 V between a hot and neutral, 240 V between the two hots; a three‑phase system measures 120 V hot‑to‑neutral and 208 V between any two hots.
