Multiwire branch circuits can be dangerous. Section 210.4(B) specifically requires simultaneous disconnection of all ungrounded conductors and requires that it take place at the panelboard of origin. The reason for this requirement is to reduce the risk of shock should a worker fail to disconnect all of the ungrounded circuits to the equipment mounted on a single yoke or strap of a device. Most commonly, receptacles are the focus of this requirement. However, equipment mounted on a yoke can include devices such as receptacles, switches, and lampholders, as well as other items such as dimmers, pilot lights, and home automation controls.
Many 125-volt, 15- and 20-ampere duplex receptacles have a break-off tab that permits each of the two receptacles to be supplied from different circuits or a 3-wire (multiwire) branch circuit. This arrangement is commonly called a split-wired receptacle (i.e., one circuit supplies half the duplex receptacle and another circuit supplies the other half). The simultaneous opening of both ?hot? conductors at the panelboard effectively protects personnel from inadvertent contact during servicing with an energized conductor or device terminal. The simultaneous disconnection can be achieved by a 2-pole circuit breaker or by two single-pole circuit breakers with an approved handle tie, as shown in Exhibit 210.1 (bottom). If fuses are used, a 2-pole disconnect switch is required.
Most be slow in da Heat, Be Safe !