Knife switches rated for more than 1200A at 250V or less are restricted to which usage?

Knife switches rated for more than 1200A at 250V or less are specifically restricted to isolating switch usage. This is primarily due to safety and operational considerations in electrical systems. Isolating switches are designed to disconnect a part of the electrical circuit from the power source, providing a means of safety to allow maintenance or repairs to be performed safely.

Using a knife switch in this manner ensures that maintenance personnel have a secure means to isolate equipment without risking inadvertent electrical contact. The switch is not intended for regular operation under load conditions, as this could pose dangers such as arcing or damage to the switch contacts.

The other options would not be appropriate applications for such high-capacity knife switches due to their design and operational characteristics. Load currents typically require devices rated for frequent switching and are not suitable for high-capacity knife switches which are meant for isolating rather than switching loads during operation. Additionally, while overhead line applications and multiple load connections may utilize different types of switches and gear optimized for their specific conditions, they fall outside the defined purpose of these high-capacity knife switches focused on isolation.