Which of the following is a manual control device?

A manual control device is one that requires direct human intervention to operate. The momentary contact normally closed (NC) pushbutton switch fits this definition perfectly, as it is designed to be physically pressed by a user to create a temporary circuit connection. This type of switch relies on the action of a person to either complete or interrupt the electrical circuit, making it a clear example of a manual control device.

In contrast, limit switches, pressure switches, and float switches operate automatically based on specific conditions. Limit switches are activated by the position of an object, pressure switches react to changes in fluid pressure, and float switches respond to liquid levels. These devices do not require manual action for regular operation, which sets them apart from the momentary contact NC pushbutton switch. Thus, the momentary contact NC pushbutton switch is the only option that strictly qualifies as a manual control device.