NEC Commercial Electrical Practice Test

In multi-wire branch circuits, how many conductors must be disconnected simultaneously?

1. All grounded conductors

2. All ungrounded conductors

3. One conductor only

4. Two conductors

The correct answer is: All ungrounded conductors

In multi-wire branch circuits, it's essential that all ungrounded conductors be disconnected simultaneously. This requirement is in place to ensure safety during maintenance or troubleshooting. Since multi-wire branch circuits typically power two or more circuits from a single breaker using multiple ungrounded conductors sharing a common neutral, disconnecting only one ungrounded conductor could still leave other conductors energized. This poses a risk of electric shock or other hazards for anyone working on the circuit. By ensuring that all ungrounded conductors are disconnected together, the circuit is rendered safe, preventing potential backfeed from energized conductors. This is particularly crucial in multi-wire configurations, as it protects individuals from accidental engagement with live components while working on the overall system.