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An electrical ground system should have an appropriate current-carrying capability to serve as an adequate zero-voltage reference level. In electronic circuit theory, a "ground" is usually idealized as an infinite source or sink for charge, which can absorb an unlimited amount of current without changing its potential. Where a real ground ...
A ground connection that is missing or of inadequate capacity may not provide the protective functions as intended during a fault in the connected equipment. Extra connections between ground and circuit neutral may result in circulating current in the ground path, stray current introduced in the earth or in a structure, and stray voltage.
For power supplies, sometimes one of the supply rails is referred to as ground (abbreviated "GND") – positive and negative voltages are relative to the ground. In digital electronics, negative voltages are seldom present, and the ground nearly always is the lowest voltage level.
Electrical equipment may be designed with a floating ground for one of several reasons. One is safety. For example, a low-voltage DC power supply, such as a mobile phone charger, is connected to the mains through a transformer of one type or another, and there is no direct electrical connection between the current return path on the low-voltage side and physical ground (earth).
To save weight and wire, often the metal frame of the vehicle is connected to one pole of the battery and used as the return conductor in a circuit. Often the negative pole is the chassis "ground" connection, but positive ground may be used in some wheeled or marine vehicles. In a battery electric vehicle, there are usually two separate DC systems.
For the 12 volt systems, the center contact is the positive terminal and the shell is the negative terminal. Most automobiles connect the negative terminal to the frame of the vehicle (negative ground). 12 volt auto connectors are made to comply with a standard by Underwriters Laboratories for safety. UL2089 was developed to cover the ...
The reverse happens in a positive CG flash, where electrons travel upward along the lightning channel and a positive charge is transferred to the ground (conventionally the current flows from the cloud to the ground). Positive lightning is less common than negative lightning and on average makes up less than 5% of all lightning strikes. [73]
The symbol connected to the dot (usually the symbol found to the right) denotes the polarity of the center/tip, whereas the symbol connected to the broken circle denotes the polarity of the barrel/ring. When a device or adapter is described simply as having "positive polarity" or "negative polarity", this denotes the polarity of the center/tip.