|
As the neutral point of an electrical supply system is often connected to earth ground, ground and neutral are closely related. Under certain conditions, a conductor used to connect to a system neutral is also used for grounding (earthing) of equipment and structures. Current carried on a grounding conductor can result in objectionable or dangerous voltages appearing on equipment enclosures, so the installation of grounding conductors and neutral conductors is carefully defined in electrical regulations. Where a neutral conductor is used also to connect equipment enclosures to earth, care must be taken that the neutral conductor never rises to a high voltage with respect to local ground. ==Definitions== Ground or earth in a mains (AC power) electrical wiring system is a conductor that provides a low-impedance path back to the source to prevent hazardous voltages from appearing on equipment. (The terms "ground" and "earth" are used synonymously here. "Ground" is more common in North American English, and "earth" is more common in British English.) Under normal conditions, a grounding conductor does not carry current. Neutral is a circuit conductor that normally carries current, and is connected to ground (earth) at the main electrical panel. In the electrical trade, the conductor of a 2-wire circuit connected to the supply neutral point and earth ground is referred to as the "neutral. 〔"Neutral Conductor" in Article 100 - Definitions, NFPA 70 ''National Electrical Code'', 2011 Edition, International Electrical Code Series. The requirement to ground the neutral point begins at Article 250.4.〕 In a polyphase (usually three-phase) AC system, the neutral conductor is intended to have similar voltages to each of the other circuit conductors, but may carry very little current if the phases are balanced. The United States' National Electrical Code and Canadian electrical code only define neutral as the grounded, not the polyphase common connection. In North American use, the polyphase definition is used in less formal language but not in official specifications. In the United Kingdom the Institution of Engineering and Technology defines a neutral conductor as one connected to the supply system neutral point, which includes both these uses. All neutral wires of the same earthed electrical system should have the same electrical potential, because they are all connected through the system ground. Neutral conductors are usually insulated for the same voltage as the line conductors, with interesting exceptions.〔For example, in North American practice an overhead service-entrance cable has two insulated conductors which are wrapped around and supported by the bare neutral conductor〕 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「Ground and neutral」の詳細全文を読む スポンサード リンク
|