New York State Master Electrician Practice Exam

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Knife switches rated for over what amperage can only be used as isolating switches?

600 amps
800 amps
1200 amps
1500 amps

The correct answer is: 1200 amps

Knife switches rated for over 1200 amps are specifically designated for use as isolating switches due to safety and operational standards in electrical systems. Isolating switches are designed to safely disconnect a portion of a system from the power source, providing a clear indication that the circuit is de-energized and ensuring that maintenance personnel can work safely. The reason knife switches above this amperage are restricted to isolating functions pertains to the considerable electrical load they must handle. At such high amperage ratings, the potential for arcing and sparking during operation increases significantly. This can result in dangerous situations if the switch is used in a manner other than intended. Utilizing a knife switch as an isolating switch ensures a clear distinction: it will primarily be used to cut off power, rather than regularly switching circuits on and off. This limitation emphasizes the need for appropriate equipment that can handle daily switching tasks while also encompassing the robust safety protocols necessary for high amperage applications. In summary, the requirement for knife switches rated over 1200 amps to be used only as isolating switches underscores the importance placed on safety and functionality in high-power electrical systems.