earthing switch

[cpso]

how automatic earthing switch works?

[Hippy]

I think you might mean a Residual Current Circuit Breaker. This is a switch in line with an appliance that breaks the connection when it detects a small current leakage to the earth wire. It is a safety device, especially important when operating power tools at some distance from the main switch.

See http://www.federal.com.tr/eng/op/resopprinciple.ht
m for a more technical description.