For a three-wire control circuit to operate properly, the initiating device must have what type of contact?

In a three-wire control circuit, the initiating device, such as a push button or a switch, must typically use a momentary contact that is normally open. This type of contact allows the circuit to remain in a de-energized state until the initiating device is activated. When the button is pressed, the normally open contact closes momentarily, allowing current to flow and energizing the control circuit.

This design is advantageous because it ensures that the circuit only operates while the button is being held down, effectively preventing unintended prolonged operation. Once the button is released, the contact returns to its normal state, opening the circuit and stopping the flow of current. This makes momentary, normally open contacts ideal for applications such as start buttons in machinery and systems where user control is essential.

In contrast, other types of contacts, such as normally closed or continuous contacts, would not provide the same level of control needed for a three-wire circuit to function correctly. Normally closed contacts would energize the circuit as long as the contact is intact, while continuous contacts would hold the circuit in an energized state until power is removed, which is not desired for momentary activation scenarios.