What type of switch is intended for isolating an electric circuit from the power source?

The type of switch that is designed specifically for isolating an electric circuit from the power source is known as an isolating switch. This switch plays a crucial role in ensuring the safety of electrical systems by providing a means to disconnect the electrical supply when maintenance or repairs are required. Isolating switches are typically used in situations where it is essential to ensure that a circuit is completely de-energized, allowing maintenance personnel to work safely.

They are distinct from general-use switches, which are typically meant for everyday operation of electrical devices, and control switches, which can be used to operate motors or lighting but are not specifically designed for isolation purposes. The term "isolation device" may also imply a broader category, but the specific nomenclature in the context of NEC typically refers to isolating switches. Thus, "Switch, Isolating" is the most accurate choice here, as it directly aligns with the intended function of completely severing electrical connection from the power source when needed.