什麼是earthing?

In simple words, earthing means the conductive connection to the ground so that electrons can be carried away quickly as a safety measure.





The term ground or earth usually means a common return path in electrical circuits.

Meanings
In electrical engineering, the term ground or earth has the following meanings:

An electrical connection to earth. The part directly in contact with the earth (the earth electrode) can be as simple as a metal (usually copper) rod or stake driven into the earth, or a connection to buried metal water piping (though this carries the risk of the water pipe being later replaced with plastic). Or it can be a complex system of buried rods and wires. The resistance of the electrode-to-earth connection determines its quality, and is improved by increasing the surface area of the electrode in contact with the earth, increasing the depth to which it is driven, using several connected ground rods, increasing the moisture of the soil, improving the conductive mineral content of the soil, and increasing the land area covered by the ground system. This type of ground applies to radio antennas and to lightning protection systems.

In a mains (AC power) wiring installation, the ground is the wire that carries currents away under fault conditions. This power ground grounding wire is (directly or indirectly) connected to one or more earth electrodes. These may be located locally, be far away in the suppliers network or in many cases both.

In an electrical circuit operating at signal voltages (usually less than 50 V or so), a common return path that is the zero voltage reference level for the equipment or system. A system where the system ground is not actually connected to earth is often referred to as a floating ground.

An electrical connection to the inside surface of a Faraday cage. Any excess charges deposited on the inner surface of a Faraday cage will migrate to the outer surface of the cage, where they can produce no electric fields within the enclosure. For this reason, the inside surface of a Faraday cage behaves like an infinite sink for electrical charge from the perspective of objects within. Even if the Faraday cage itself is not connected to the Earth, the inner surface of the cage can be used in place of an earth connection.
A ground conductor on a lightning protection system used to dissipate the strike into the earth.


Uses
A power ground NEC (Article 250 ) You need to establish an effective ground-fault current path and the earth shall not be considered as an effective ground-fault current path. Ground serves to provide a return path for fault currents and therefore allow the fuse or breaker to disconnect the circuit. The power ground is also often bonded to the house's incoming pipework, and pipes and cables entering the bathroom are sometimes cross-bonded. This is done to try to reduce the voltage between objects that can be touched simultaneously. Filters also connect to the power ground, but this is mainly to stop the power ground carrying noise into the systems the filters protect, rather than a direct use of the power ground.

Grounding is primarily used for safety to prevent electric shock or fires caused by a voltage potential between the earth and a conductor such as an appliance cabinet or chassis. Grounding is often used to conduct lightning strikes harmlessly to earth rather than starting fires and damaging equipment. It is also used to control electrical noise in computer, audio and video, and communications circuits. This illustrates that an electrical ground should have an appropriate current-carrying capability in order to serve as an adequate zero-voltage reference level.

電磁學的確很難，但是會考範圍的電磁學只是入門知識，非常簡單。大學課程的電磁學就相當艱深，原因有三：一、電與磁並非肉眼能見的物理現象，比較抽象，需要多些想象力才可理解；二、電磁學需要使用高等數學來作陳述，學生的數學根底要好，才可學好電磁學；三、電磁學可引申至相對論、波動力學、量子力學、固體力學和統計力學等等近代物理，可以算是古典和近代物理的一門過渡學科。

好像冇earthing(不知道)我找到有earth,是地球,(電器的)地線

earthing

n.接地