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Most electrical circuits have a ground which is electrically connected to the Earth, hence the name "ground". The ground is said to be ''floating'' when this connection does not exist. Conductors are also described as having a floating voltage if they are not connected electrically to another non-floating conductor. Without such a connection voltage and current flows are induced by electromagnetic fields or charge accumulation within the conductor rather than being due to the usual external potential difference of a power source. == Applications == 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. Ensuring that there is no electrical connection between mains voltage and the low-voltage plug makes it much easier to guarantee safety of the supply. It also allows the charger to safely only connect to live and neutral, which allows a two-prong plug in countries where this is relevant. Indeed, any home appliance with a two-prong plug must have a floating ground. Another application is in electronic test equipment. Suppose you wish to measure a single-volt potential difference between two wires that are both 100V above Earth ground. If your measuring device has to connect to Earth, some of its electronic components will have to deal with a 100V potential difference across their terminals. If the whole device floats, then its electronics will only see the 1V difference, allowing more delicate components to be used which can make more precise measurements. Such devices are often battery powered. Thirdly, a floating ground can help eliminate ground loops, which reduces the noise coupled to the system. An example of such a configuration is shown in the image on the right. Systems isolated in this manner can and do drift in potential and if the transformer is capable of supplying much power, they can be dangerous. This is particularly likely if the floated system is near high voltage power lines. To reduce the danger of electric shocks, the chassis of the instruments are usually connected separately to Earth ground. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「floating ground」の詳細全文を読む スポンサード リンク
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