A multiwire branch circuit must have a means to disconnect all un-grounded conductors in what manner?

In a multi-wire branch circuit, having a means to disconnect all un-grounded conductors simultaneously is essential for safety. This requirement is rooted in the need to ensure that if maintenance or repair is being conducted on the circuit, all power sources are eliminated at once. This prevents any possibility of accidental re-energization of any part of the circuit while work is underway, which is critical for protecting both the workers and the system itself.

When all un-grounded conductors are disconnected simultaneously, it minimizes the risk of electric shock or fire that could occur if only one conductor were to be disconnected. This is particularly important in scenarios where multiple circuits feed different loads from a single source, and they may be interdependent.

Other methods, such as disconnecting conductors individually or manually, do not offer the same level of safety as they leave the possibility of a technician working on a circuit while other circuits remain energized. Thus, the simultaneous disconnection of all un-grounded conductors is the preferred practice and aligns with electrical safety codes and standards.