When is a switch described as "normally open"?

A switch is described as "normally open" when it does not allow current to flow through it in its default state. In this configuration, the switch is open until it is manually or automatically closed, which then allows current to flow. This means that in its resting state, there is no continuity in the circuit, effectively preventing the flow of electricity until the switch is actuated.

The term "normally open" is key in various applications, particularly in control systems, where a device will only operate when the switch is activated. This functionality supports safety protocols, ensuring that devices do not operate unintentionally. Following this logic, the description aligns with the understanding of a switch that remains non-conductive until engaged.

The other choices describe different states that do not align with the function of a normally open switch. For instance, describing a switch as allowing current to flow by default misrepresents how normally open switches operate, as that description applies to switches that are "normally closed."