What must be provided for multiwire branch circuits used in temporary wiring?

For multiwire branch circuits utilized in temporary wiring, it is essential to provide a means to disconnect all ungrounded conductors simultaneously. This requirement is crucial because multiwire branch circuits consist of two or more ungrounded conductors that share a common neutral conductor. If one of the ungrounded conductors were to be disconnected while the others remained connected, it could lead to improper operation of connected devices or create a safety hazard.

Simultaneous disconnection of all ungrounded conductors ensures that when the circuit is de-energized for maintenance or safety purposes, all components connected to the circuit are completely shut off. This is particularly important in temporary wiring scenarios, where the risk of accidental energization might be higher due to the nature of the installation.

The necessity of this safety measure prevents shock hazards and ensures that maintenance personnel can work safely without the concern of energy still being present in any part of the circuit. It is a standard safety precaution outlined in the National Electrical Code to ensure that the temporary wiring systems are as safe as possible.