Earthing switch

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Earthing switch is a mechanical switching device for earthing parts of a circuit, capable of withstanding for a specified time short-circuits currents, but not required to carry normal rated currents of the circuit. 

Earth switch is also connected on the isolator to ground residual current. The tubular arm of earthing switch is permanently connected with the earthed frame by a flexible connection. In the open position, the contact arm is located along the base frame.
Fig. Earthing switch at open position

During closing operation, the arm rotates in the vertical plane and reach the fix contact. In the  end position, the earthing blade moves up along its axis and is inserted into earthing contact.

 Arcing horns are connected to contacts of earth switch. An arc can establish between the switch contacts when contact arm and fix contact connects during a short circuit fault.The horns are designed to endure the arc rather than the contact surfaces of the earth switch.

In isolator, mechanical interlock is provided between isolator and earth switch. Isolator cannot be closed unless earth switch is in the open position and vice-verse. In normal operation, the isolator and circuit breaker are close and earth switch is open. Once the circuit breaker operates, isolator can be opened and then earth switch can be closed. After maintenance, first earth switch is opened, then isolator and circuit breaker are closed.

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