Question: For the DI and DO signal cables in the PLC cabinet, is it necessary to ground the cable shielding layer?
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As the title suggests, some people say that it is sufficient to ground the cable shielding layer for analog (AI, AO) signals only, and that it is not necessary to do so for digital (DI, DO) signals. I would like to know if this is indeed the case. Also, where should the power grounding bars and signal grounding bars inside the PLC cabinet be connected? Can they be connected to the same electrical grounding bus? Or do them separately. Thank you
In some places, digital signals are transmitted without shielded cables, and yet everything works fine there; however, this is not standard practice and should not be adopted as a model to follow. Since a shielded cable is being used, its shielding layer must be properly grounded; otherwise, the shielding layer is wasted and ineffective. For signal and power grounding, it is preferable to have two separate grounding bars inside the cabinet; when connecting to the indoor grounding main, they can be connected to the same main.
The working area and the protective area are separated; both ends of the outer screen are grounded, while one end of the inner screen (current discharge line) is grounded, usually at the panel cabinet
In general, signals follow the principle of single-ended grounding. If the other end of the PLC is connected to instruments or control devices, the cable shield should be grounded on the PLC side. If the other end of the PLC is connected to the plant’s DCS or something else, grounding is usually done on the DCS side.
For digital signal cables, SH 3019 only requires overall shielding; even for 4–20 mA signals, separate shielding is not required……