Which type of ground should be connected to the shield wire of the DO signal cable between MCC and DCS?
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I would like to ask everyone: For the DO signal cable between the electrical MCC and the DCS, to which type of ground should the shielding wire (which has only a single shield layer, no separate shield sections) be connected? A protected area or a workplace?
Is no one answering me?
DO is a 220VAC circuit. The workplace for 220 is Line N.
You have to be patient!
This problem is tricky. Experts from the design institute, why are the DO points and the 220V electrical supply circuits connected to the DCS cabinets? In my opinion, this approach is not very reasonable and is unsafe. Why isn’t an additional circuit added for the DO that has been unified by MCC, with a relay on the DCS side used to drive it, instead making use of the 220V voltage circuit in the electrical secondary circuit? 220V is connected to the earth ground, while other signals are connected to the shield ground (explosion-proof).
The ground wire of the 220VAC power cable is connected to the protective ground. A shielded ground is a type of working ground. The DO signal from the DCS to the MCC should be considered a type of signal circuit; according to the 2019 draft guidelines for grounding design in the petrochemical industry, its shielding wire still needs to be connected to the working ground. Some DCS manufacturers and experienced professionals say that the shielding wires for these DOs can either not be grounded or connected to the protective ground. Confused.
Is it a DO for controlling the high-voltage motor or 220VDC?
It’s one thing to form a circuit, but connecting 220V to the DCS cabinet is very unsafe. What I mean is to consider adding a cabinet at MCC, including relays, and changing the DCS system to use 24V circuits, so that 220V is not fed into the DCS. (If it is added on the DCS side with relay isolation, I think the power consumption in the 220V circuit, given all those DO cables between the MCCs and the DCS, is wasteful.)
Work experience generally involves single-ended grounding, connected to the shielded ground copper bar in the DCS cabinet
In that case, the DO output from the DCS would need to change from a dry contact to a wet contact, with 24VDC being output to drive the relay coils on the electrical side; this seems feasible. I’ve just never seen it done in reality. . Could it be that the addition of a relay has increased the number of fault points in the circuit?
Is that connected to the ground shield of the AI/AO/DI/DO signals from the field?