Should the DCS field distribution box be grounded?
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This post was last edited by cooldick on 2017-11-2 at 18:07. I’m facing a design issue related to DCS systems: the entire system consists of one main cable with 70 conductors, which is then divided into multiple sensor cables via a distribution box to supply the sensors on-site. The distribution box is located outdoors. At present, the signals from the main cable are fed into an isolation barrier. I have a question regarding the shielding layer of the signal cables – when the cables pass through the distribution box, should the shielding layer be connected to the body of the distribution box, or should it be connected to the shielding layer of the cables after they have been split off? Should it not be connected to the box? This relates to the selection of quick-connect connectors; do anyone have any suggestions regarding connector selection? If a housing is not used, then the core of the connector will have to be used to carry the shielding wire. Thank you all!
The shielding layer of the branch cable should be connected to that of the main cable; connecting it to the junction box creates an additional grounding point, which violates the principle of single-ended grounding.
The topic and content you’ve given are incorrect!
The junction box body is safely grounded; therefore, when selecting the model, grounding bolts are provided on the rear side of the outside of the junction box body. The terminals on the shield wire of the branch cable are connected to the branch shields of the main cable, e.g., 1/2/S/3/4/S/5/6/S…… Since the overall shield wire of the main cable is connected to all the branch shields, on the side of the junction box, the overall shield wire of the main cable remains unconnected, while on the side of the cabinet, the overall shield and the branch shields are both connected to the ground.
Thank you. I remember hearing that metals must be grounded in order to provide shielding, which is why I came up with this idea. It seems that if the metal wiring box isn’t grounded, electromagnetic interference can still get into the wires. I’m not sure if my understanding is correct
Metal grounding is to ensure personnel safety. Consider signal interference when using separate shield grounding.
The junction box is grounded; the shielding layer of the 20-core cable does not need to be grounded at the junction box – it is sufficient to ground the shielding layer at the DCS cabinet
This issue can be understood in this way: it is best to connect the shields of the individual cables to the shield of the main cable, with the DCS side being grounded at one end. If it seems troublesome, a two-stage single-ended grounding method can be used: ground one end of the cable on the junction box side, leaving the main cable ungrounded.
The shield wire is connected to the split box, which is not grounded; therefore, the shield wire can only be grounded at a single point, otherwise interference signals will be introduced due to level differences.
The junction box is grounded by itself, while the cable shielding layers are connected through the terminals of the junction box, occupying those terminals; overall, it is grounded in the control room.