What is the common residential single-family service voltage?

• A. 120/240 V split-phase system
• B. 208 V single-phase
• C. 240 V single-phase
• D. 277/480 V three-phase

Answer: (A)

The important idea is that most typical single-family homes in the U.S. use a 120/240 V split‑phase service. In this setup, a center-tapped transformer provides two hot legs that are 180 degrees out of phase. Each hot leg to neutral delivers about 120 V, which powers the common lighting and outlets. The voltage between the two hot legs is 240 V, which is used for high-power appliances like dryers and ranges. This arrangement gives you both 120 V circuits for everyday devices and 240 V for heavier loads without needing a separate transformer.

The other voltages describe systems used in different settings. 208 V single-phase comes from a 120/208Y three-phase system and is common in some commercial or multifamily buildings. 277/480 V is typical for large commercial or industrial power distribution. 240 V single-phase can occur in some contexts, but it isn’t the standard residential service for single-family homes.