Connection from MCC electrical cabinet to DCS cabinet
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Dear experts, in the wiring diagrams prepared by the design institute, from the MCC to the DCS, no intermediate relays are used at the DI and DO points. I would like to ask whether this is safe; I just feel it’s not safe. I hope those who have experience with this can provide some guidance
The signal between MCC and DCS must be isolated by relays, and these must be separate relays; relay boards cannot be used
When there are digital signal transmissions between high-voltage and low-voltage systems, an intermediate relay is necessary for isolation; otherwise, the DCS circuit boards will be damaged. An independent relay cabinet is an excellent solution
For this, you need to check whether the circuit diagram of the electrical cabinet already uses an intermediate relay, and whether there are fuses on the DI/DO card side. Everyone is worried that 220V might burn out the fuse. I’d like to ask: if only the live wire at 220VAC is connected to 24VDC, and no complete circuit is formed, will it still damage the card?
Theoretically, it should be added. Didn’t you ask the design institute why it wasn’t included in the design?
I agree with the opinion from the fifth floor. First, it is necessary to check the control circuit of the electrical cabinet – whether an intermediate relay is already being used with the AC contactor, or whether the auxiliary contacts of the AC contactor themselves provide a 24V signal. There is also a need to check whether there is a fuse on terminal block D of the DCS cabinet; if there is one, then there is no need for additional design work
It is best to add relay isolation; if the wires in the MCC are connected incorrectly, it may damage the equipment, which would be a costly mistake
This must be added. You can include these relay points in the negotiations with the DCS supplier; it shouldn’t increase the cost significantly