The metal-enclosed knife switch is also a kind of hand switch, and it can be used in direct starting of the motor with small capacity and not frequently started. 

The metal-enclosed knife switch consists of blade, clip pedestal, operating handle, quick-break spring and fuse protector, etc. The metal-enclosed knife switch is also a knife-shaped switch. The difference is that the knife switch and the fuse protector are put into a metal box together, and it is equipped with quick-break spring which is mechanically connected with the rotating shaft, while the blade is fixed on the rotating shaft.. When the metal-enclosed knife switch switches on/off the circuit, due to very high voltage between switch blade and clip pedestal, large electric arc will be produced. If electric arc is not extinguished, it will burn out blade. 

The structure of metal-enclosed knife switch: 

There is a quick-break spring equipped between the hand shank spindle and pedestal of the metal-enclosed knife switch. During the process that hand shank shifts from switch-on location (hand shank is upward) to switch-off position (hand shank is downward), the quick-break spring is strained. When the pull of spring overcomes the force of friction between switch blade and clip pedestal, the switch blade will be separated from the clip pedestal quickly. At this moment, the electric arc will be lengthened quickly and extinguished. In order to ensure the safe use of electricity, the mechanical interlock device is equipped on the iron shell. Do not switch on when tank cove is open; after switch blade switches on, do not open the tank cover. 

In installation of the enclosed knife switch, pay attention to the following items:

The enclosed knife switch shall be installed vertically, its installation height shall take convenient operation as principle, generally it is about 1.3-1.5m away from ground. 

The grounding screw of shell of the enclosed knife switch shall be ground reliably or connected to Neutral. 

The incoming line and outgoing lines of both power line and motor shall pass through the inlet and outlet holes of the switch and the rubber collar shall be provided at the inlet and outlet holes. 

For the enclosed knife switch with 100A above, connect the incoming line of power supply to the upper chapiter of the switch, and connect outgoing line of motor to the lower chapiter of the switch. While for the enclosed knife switch with below 100A, connect the incoming line of power supply to the lower chapiter of the switch, and connect the outgoing line of motor to the upper chapiter. 

When connecting wire, make electric current pass the knife switch first, then pass fuse protector and then, enter into the electro-equipment for overhaul.