New York State Master Electrician Practice Exam

The choice to open knife switches rated over 1200 amps without load is correct due to the significant safety risks associated with high-current systems. When a knife switch is under load, opening it creates an arcing hazard due to the high current flowing through the switch contacts. This arcing can damage the switch and potentially cause injuries or fires.

Opening the switch without load minimizes the risk of arcing. It ensures that there is no electrical current present when the switch is being opened, making it safer for the operator and reducing the chance of equipment damage. Understanding this safety procedure is critical for adhering to electrical safety standards and practices, especially when dealing with high-capacity switches.

Other options would lead to unsafe practices; for example, opening under load increases the risk of arcing, while only opening during maintenance or not opening at all does not address situations where the switch needs to be operated safely. Ultimately, the correct procedure is always to ensure the switch is free of load before opening.