What type of receptacle must have a means to simultaneously disconnect all ungrounded conductors?

The requirement for a receptacle to have a means to simultaneously disconnect all ungrounded conductors is a safety measure that is particularly relevant in specific applications, such as when dealing with certain types of circuits or installations where maintenance or service might expose an individual to electrical hazards. A duplex receptacle, which consists of two outlets in a single housing, typically requires a way to ensure that both outlets can be disconnected together in some circumstances.

In practice, this means that duplex receptacles are often designed to be part of circuits where a local disconnecting means is needed, ensuring that the entire receptacle is de-energized. This is especially important in settings where multiple devices might be plugged in, as it enhances safety by providing a singular control point for cutting off power.

Other types of receptacles, like single or non-grounded ones, may not necessarily adhere to the same requirement due to their limited scope of use or their specific design limitations. GFCI receptacles play a different role, focusing primarily on ground fault protection rather than the simultaneous disconnection of all ungrounded conductors. Thus, the design and code standards for duplex receptacles make them the correct answer in this context.