New York State Master Electrician Practice Exam

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What is the permitted use for a knife switch rated for more than 1200 Amps at 250 Volts or less?

Can be used for load switching
Can be used as an isolate switch only
Can be used for emergency shut-off
Can be used for circuit protection

The correct answer is: Can be used as an isolate switch only

A knife switch rated for more than 1200 Amps at 250 Volts or less is specifically designed for isolating electrical circuits. This is due to its ability to provide a secure, visible means of disconnecting power. An isolating switch operates by physically interrupting the current flow, ensuring that maintenance and service work can be performed safely on the connected equipment. In this context, the switch is not intended for load switching or managing fluctuating electrical loads, as its primary function is to serve as a disconnecting means. Unlike circuit protection devices, which are designed to protect circuits from overload or short circuit conditions, the knife switch does not offer this protection inherently. Moreover, while it may be involved in emergency shut-off scenarios, its primary designation in this rated capacity is for isolation, making it crucial for safety protocols in electrical installations.