In a 120/240V single-phase, 3-wire system, a subpanel is fed with which configuration?

In a 120/240V single-phase, 3-wire system, a subpanel is fed with which configuration?

• A. 120/240V 1-phase, 3-wire
• B. 240V 1-phase, 2-wire
• C. 277/480V
• D. 3-phase 4-wire

Answer: (A)

In a 120/240V single-phase system, power comes from two hot legs that are 180 degrees apart, with a center-tapped neutral. That means you get 240V between the two hot conductors and 120V from either hot to neutral. A subpanel fed from this system uses a feeder that carries both hot legs plus the neutral, which is three conductors in a single-phase configuration. That’s why the correct description is a 120/240V 1-phase, 3-wire feeder to the subpanel. The other options describe different systems: a 240V 1-phase, 2-wire setup has no neutral for 120V loads; a 277/480V setup refers to a higher-voltage three-phase system with a different voltage to neutral; and a 3-phase 4-wire system involves three hot legs plus a neutral, not the simple split-phase 120/240V arrangement.

In a 120/240V single-phase system, power comes from two hot legs that are 180 degrees apart, with a center-tapped neutral. That means you get 240V between the two hot conductors and 120V from either hot to neutral. A subpanel fed from this system uses a feeder that carries both hot legs plus the neutral, which is three conductors in a single-phase configuration. That’s why the correct description is a 120/240V 1-phase, 3-wire feeder to the subpanel.

The other options describe different systems: a 240V 1-phase, 2-wire setup has no neutral for 120V loads; a 277/480V setup refers to a higher-voltage three-phase system with a different voltage to neutral; and a 3-phase 4-wire system involves three hot legs plus a neutral, not the simple split-phase 120/240V arrangement.