During the maintenance of electrical equipment, the power supply must be disconnected, separated from the live parts, and kept at an effective isolation distance. The voltage withstand level should be capable of withstanding the overvoltage between its open ends. The knife switch is a switch electrical appliance used for isolating the power supply. The knife switch for isolating the power supply is also known as an isolation switch.

Knife switches used for isolation are generally considered as no-load circuit breakers, capable only of connecting or disconnecting "negligible currents" (referring to the capacitive current of busbars with voltage, or the current from short cables or voltage transformers). Some knife switches possess a certain level of switching capability, and when this capability matches the required switching current, they can connect or disconnect certain electrical equipment or complete sets under non-fault conditions.

The knife switch used as an isolation switch must meet the isolation function, i.e., the switch has a clear break and the break distance is qualified.

A knife switch and fuse are connected in series to form a unit known as a knife switch-fuse assembly; when the movable part (moving contact) of the knife switch is composed of a fuse carrier with a fuse element, it is called a fuse-type knife switch.

Combination of fuse links for circuit breakers and auxiliary components such as operating rods, springs, and arc cutters. These can be assembled into load switches. Load switches have the ability to connect or disconnect load current under non-fault conditions and offer certain short-circuit protection functions.

Maintenance of Knife Switches

Check if the load current exceeds the rated value on the knife switch.

2) Inspect for poor contact between static and moving contacts, overheating, burned contacts, and wire (body) connections on the conductive part of the switch disconnector. In case of any of the above, repair promptly.

3) Inspect insulating rods, bases, and other insulating components for signs of burn and discharge.

4) Inspect that all components of the switch operating mechanism are intact and flexible, and ensure that the opening and closing of the three phases are synchronized and accurately positioned.