You're on the right track, but let's clarify: 120/240V Single Phase, 3-Wire

This is a standard residential service. It means you have two "hot" legs, a neutral, and a ground. The voltage between each hot leg and neutral is 120V. The voltage between the two hot legs is 240V.

Breaker Requirement

A 120/240V panel requires a

2-pole breaker to feed it, not a 1-pole. Here's why: Both Hot Legs

To utilize the full 120/240V capability, the panel needs to be fed with both hot legs. A 2-pole breaker provides protection for both of these legs simultaneously. If one leg experiences a fault (short circuit or overload), the 2-pole breaker trips and shuts off both hot legs, preventing a potentially dangerous imbalance.

1-Pole Breaker

A single-pole breaker can only provide 120V from one of the hot legs. While you could theoretically wire only one leg, you would not have 240V available for larger appliances like water heaters, stoves, or AC units. And it would be a misapplication of the panel's capabilities.

"3-Wire" Explanation

The "3-wire" designation refers to the conductors coming into the panel: Two "hot" wires (typically black and red) One neutral wire (typically white) (The ground wire is usually separate but is often counted as the third connection for the neutral)

In summary:

Even though the panel is single-phase, you must use a 2-pole breaker to feed it properly. This is because it needs both hot legs of the 120/240V service to provide both 120V and 240V circuits. Flag for review