Instrument reading
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What does the “S” in the on-site junction box in the diagram represent, and what does the arc on the left side mean?
This post was last edited by ZhiGE on 2021-5-12 at 11:27; S=Shield, meaning to block. The arc on the left represents the shield wire.
It means the same thing on both sides; it’s for connecting to the shielding layer
Just a side note: there’s something wrong with the diagram of this junction box. I’ve marked it in green; what should be written in that position is the terminal number of the corresponding cabinet. It’s a problem that you’ve assigned a number to this shielding as well – who is shielding the terminals at the top of the cabinet?
This post was last edited by ZhiGE on 2021-5-12 at 16:16. In accordance with the SHT 3081-2019 Standard for Grounding Design of Petrochemical Instruments: the main cable’s main panel is connected to the protective ground via a grounding bus bar on the side of the cabinet room； The branch cables of the main cable are connected to the ground at the cabinet side via grounding busbars; therefore, as mentioned above, there is no need to label the terminal numbers (since there are no terminals to connect to). It is possible to consider marking E=Earthing (grounding).
Yes, you have just answered this question: why does the shielding wire still occupy a terminal? The design is incorrect.
Yes, your reply is quite accurate and detailed; thank you.