New York State Master Electrician Practice Exam

Which type of switch should not be opened under load for certain ratings?

1. Knife switches

2. Toggle switches

3. Rockers switches

4. Miniature circuit breakers

The correct answer is: Knife switches

Knife switches are designed for high-capacity applications and can be used in settings where equipment is energized. However, their construction poses a risk when opened under load—meaning while current is still flowing through them. Opening a knife switch while it is under load can create arcing, which can damage the switch and potentially lead to equipment failure or hazards such as fires. The design of knife switches often includes exposed contacts, which are more susceptible to maintaining a current path and generating arcs. Because of the potential for these dangerous situations, proper protocols dictate that such switches should only be opened when no load is present. In contrast, other types of switches, like toggle switches and rocker switches, are typically designed to handle load interruptions more safely. Miniature circuit breakers are engineered to trip and disconnect the circuit automatically when overload or short circuit conditions occur, making them more straightforward and safer to operate under load situations.