Which of the ladder diagrams shown best illustrates the use of a holding circuit that will allow the control relay to stay energized when the start button is pressed and released?

The answer is based on the function of a holding circuit, which is designed to maintain the energized state of a control relay after the start button is pressed and subsequently released. In a properly configured ladder diagram illustrating this concept, the holding circuit typically includes a normally open contact associated with the control relay itself in parallel with the start button.

When the start button is pressed, the control relay energizes, closing its contacts. These contacts then form a new parallel path for the current, allowing the relay to remain energized even after the start button is released. This self-latching action is the hallmark of a holding circuit.

The ladder diagram identified as the correct option effectively demonstrates this self-holding feature, accordingly illustrating the connection that allows for continued relay energization after the initial action. Thus, it is vital that the design integrates both the start button and the normally open contact of the relay in a way that provides this functionality, which is captured in only that particular diagram.

Other options may not correctly or effectively show the mechanism necessary for the holding circuit, lacking the combination of components needed to ensure that the relay remains energized post-operation of the start button. Therefore, the third option stands out as the best representation of the holding circuit in use.