what is a earth system in electric?how its work?

Answer 1

Your question is not clear, but "earth" in electric systems ("ground" in the USA) is a base reference potential that circuits have in common. In home electric wiring, the earth potential is connected to the "neutral" wire, and is actually connected to the earth with a long electrode. In electronic systems, earth potential can be arbitrary, but is usually established by the power supply. The earth of an electronic device is not necessarily the same as the earth of electical wiring (mains). However, if circuits are to be connected together, there must be a reference potential that is common between them. That is called the earth (ground) potential.