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ABB 64844-004 3-064843-002接口过程编程板
在供电系统中，接地系统定义导体的相对电势地球导电表面。接地的选择
系统对安全和电磁有影响电源的兼容性。请注意，法规对于接地系统不同的国家。
保护接地（PE）连接确保导电表面的电位与地面，以避免电击风险如果有人接触到绝缘故障的设备发生。它确保在绝缘故障（“短路电路”），电流非常大，将触发过电压
断开电源的电流保护装置（保险丝、断路器）。功能性接地连接的用途不同于提供防电击保护。相比之下保护接地连接，功能性接地连接在设备正常运行期间可能携带电流。
设备可能需要功能性接地连接如浪涌抑制和电磁干扰滤波器、某些类型的天线和各种测量仪器。通常，保护接地也用作功能性地球，尽管在某些情况下需要小心。国际标准IEC 60364区分了三个使用双字母代码的接地装置系列TN、TT和IT。
第一个字母表示接地和电源设备（发电机或变压器）：
T： 点与地面的直接连接（拉丁语：terra）；
一： 没有任何点与接地（绝缘）相连，除非也许是通过高阻抗。
第二个字母表示接地和所提供的电气设备：T： 点与地的直接连接N： 直接连接至安装起点的中性点，连接到接地TN系统在TN接地系统中，发电机中的一个点或变压器接地，通常为星点在三相系统中。电气设备主体为通过变压器处的接地连接与大地相连。基本上有三种不同类型的TN系统区别：TN-S、TN-C、TNCS。
TN系统可由MCB（微型电路）保护断路器）。系统中的任何短路都会产生足够的使MCB跳闸的能量。
TT系统在TT接地系统中耗电元件由本地接地连接提供，独立于发电机的任何接地连接。如果发生接地故障，则故障路径的电阻会返回电源电压过高，分支电路电流过大操作保护（熔断保险丝或使断路器跳闸）。
在这种情况下，安装剩余电流检测器（RCD）检测泄漏到地面的电流并中断电路
In electricity supply systems, an earthing system defines
the electrical potential of the conductors relative to that
of the Earth’s conductive surface. The choice of earthing
system has implications for the safety and electromagnetic
compatibility of the power supply. Note that regulations
for earthing (grounding) systems vary considerably among
different countries.
A protective earth (PE) connection ensures that all exposed
conductive surfaces are at the same electrical potential as
the surface of the earth, to avoid the risk of electrical shock
if a person touches a device in which an insulation fault has
occurred. It ensures in case of an insulation fault (a “short
circuit”), a very high current flows, which will trigger an over
current protection device (fuse, circuit breaker) that disconnects the power supply.
A functional earth connection serves a purpose other than
providing protection against electrical shock. In contrast to a
protective earth connection, a functional earth connection
may carry a current during the normal operation of a device.
Functional earth connections may be required by devices
such as surge suppression and electromagnetic interference
filters, some types of antennas and various measurement
instruments. Generally the protective earth is also used as a
functional earth, though this requires care in some situations.The international standard IEC 60364 distinguishes three
families of earthing arrangements, using the two-letter codes
TN, TT and IT.
The first letter indicates the connection between earth and
the power-supply equipment (generator or transformer):
T: direct connection of a point with earth (Latin: terra);
I: no point is connected with earth (insulation), except
perhaps via a high impedance.
The second letter indicates the connection between earth and
the electrical device being supplied:
T: direct connection of a point with earth
N: direct connection to neutral at the origin of installation,
which is connected to the earth
TN-system In a TN earthing system, one of the points in the generator or transformer is connected with earth, usually the star point in a three-phase system. The body of the electrical device is connected with earth via this earth connection at the transformer. Basically three different types of TN systems are distinguished: TN-S, TN-C, TN-C-S. TN systems can be protected by a MCB (miniature circuit breaker). Any short circuit in the system will create sufficient energy to trip the MCB. TT-system In a TT earthing system, the protective earth connection of the consumer is provided by a local connection to earth, independent of any earth connection at the generator. In case of an earth fault the resistance of the fault path back to the supply is too high for the branch circuit over current protection to operate (blow a fuse or trip a circuit breaker). In such case a residual current detector (RCD) is installed to detect the current leaking to ground and interrupt the circuit
