What is the main limitation of knife switches rated above 1200 amp?

The main limitation of knife switches rated above 1200 amps is that they shall not be opened under load. This is because, at higher ampere ratings, the risk of electric arcing becomes significantly greater when a switch is operated while current is flowing. Arcing can cause damage to the switch contacts, leading to potential equipment failure and safety hazards such as fires or explosions.

Therefore, knife switches of this rating are designed to be opened only when no load is present, ensuring the contacts are not subjected to the destructive effects of arcing. This operational guideline is crucial for maintaining safety and reliability in high-current applications, especially in industrial settings where large amounts of current must be managed.

In contrast, the other options reflect misunderstandings of the functionality and safety protocols associated with high-amperage knife switches.