The NEC requires simultaneous disconnect of ungrounded conductors for multiwire branch circuits that supply more than one device on the same yoke. Which device satisfies this requirement when disconnecting at the panelboard?

• A. two single-pole breakers
• B. one two-pole breaker
• C. either a or b
• D. neither a nor b

Answer: (B)

When a multiwire branch circuit uses two ungrounded conductors sharing a neutral, both hot conductors must be disconnected at the same time at the panelboard. A two-pole breaker is designed with a common trip (or a handle-tied pair in a unit) so both poles open together. This guarantees that neither hot remains energized and prevents any backfeed through the neutral, which protects anyone servicing the circuit.

Two single-pole breakers do not inherently guarantee simultaneous disconnection unless they are a listed, properly tied pair with a handle tie or a common-trip feature. Since the requirement is for a single, reliable disconnecting means at the panelboard, using one two-pole breaker is the correct choice.