PLC控制系统的地线包括系统地、屏蔽地、交流地和保护地等。接地系统混乱对PLC系统的干扰主要是各个接地点电位分布不均，不同接地点间存在地电位差，引起地环路电流，影响系统正常工作。例如电缆屏蔽层必须一点接地，如果电缆屏蔽层两端A、B都接地，就存在地电位差，有电流流过屏蔽层，当发生异常状态如雷击时，地线电流将大。

　　此外，屏蔽层、接地线和大地有可能构成闭合环路，在变化磁场的作用下，屏蔽层内有会出现感应电流，通过屏蔽层与芯线之间的耦合，干扰信号回路。若系统地与其它接地处理混乱，所产生的地环流就可能在地线上产生不等电位分布，影响PLC内逻辑电路和模拟电路的正常工作。PLC工作的逻辑电压干扰容限较低，逻辑地电位的分布干扰容易影响PLC的逻辑运算和数据存贮，造成数据混乱、程序跑飞或死机。模拟地电位的分布将导致测量精度下降，引起对信号测控的严重失真和误动作。

The ground wire of the PLC control system includes system ground, shielding ground, AC ground, and protection ground. The interference of chaotic grounding system on PLC system is mainly due to uneven potential distribution at various grounding points, and the existence of ground potential differences between different grounding points, which causes ground loop current and affects the normal operation of the system. For example, the cable shielding layer must be grounded at one point. If both ends A and B of the cable shielding layer are grounded, there is a ground potential difference, and current flows through the shielding layer. When an abnormal state occurs, such as a lightning strike, the ground wire current will be high.
In addition, the shielding layer, grounding wire, and ground may form a closed loop. Under the action of changing magnetic fields, induced currents may appear inside the shielding layer, which can interfere with the signal loop through coupling between the shielding layer and the core wire. If the grounding of the system is chaotic with other grounding methods, the generated ground current may generate unequal potential distribution on the ground wire, affecting the normal operation of the logic and analog circuits in the PLC. The logic voltage interference tolerance of PLC operation is relatively low, and the distribution interference of logic ground potential can easily affect the logic operation and data storage of PLC, causing data confusion, program runaway or crash. Simulating the distribution of ground potential will lead to a decrease in measurement accuracy, causing serious distortion and misoperation of signal measurement and control.