This article is about DCS/ESD/PLC/SCADA Grounding Installation, Checklist & Requirements of Grounding Earthing System as per International Codes and standards for Commercial Buildings, Plants and Refinery Projects.
DCS/ESD/PLC/SCADA Grounding Installation | Grounding Earthing System
- Instrumentation systems (such as DCS, ESD, PLC & SCADA) shall contain two grounding systems:
a) Safety Ground for personnel safety.
b) Instrumentation Circuit Ground” - Requirements provided by manufacturers of instrumentation and control systems (e.g., distributed control systems and ESD Systems) shall also be taken into consideration.
- All exposed non-current-carrying metallic parts shall be connected to the equipment grounding circuits. Therefore, all metal equipment and enclosures within a panel or series of panels (i.e., instrument cases, hinged doors, racks, etc.) shall be bonded with bonding jumpers and connected to a safety ground bus with a minimum copper wire size of 4 mm2.
- Two copper conductors, 25 mm2 minimum, shall be connected from the safety ground bus to a single tie point on the safety ground grid in a closed loop configuration.
- Instrument circuit ground bus shall be isolated from the safety ground system except at a single tie point.
- Each instrument signal common shall be connected to the isolated instrument ground bus with copper wire sized to carry the expected fault current or 1.5 mm², whichever is larger.
- Two insulated copper conductors, 25 mm² minimum, shall be connected from the instrument circuit ground bus to a single tie point on the safety ground grid in a closed loop configuration.
- The resistance from the isolated instrument ground bus to the safety ground grid shall be less than 1 ohm.
- In control or process interface buildings, isolated instrument ground bars from all cabinets shall be consolidated into a Master Instrument Ground
- Bus located within that building. Similarly, safety ground bars shall be consolidated into a Master Safety Ground Bus. Bonding cabinet safety ground bus bars in a daisy-chain connection is not acceptable.
- The Master instrument circuit ground bus and safety grounds shall be both connected to the plant overall grounding grid, as mandated by IEEE 1100. The connection to the plant grid shall be in a loop configuration.
- Instrument cable shields shall be connected to the instrument circuit ground bus.
- Some equipment (data highways, computers, distributed control systems, etc.) may require special provisions for grounding. Manufacturers’ recommendations should be carefully evaluated at all times.
- When critical control systems, i.e., emergency shutdown (ESD) systems, utilize fully floating DC power where both positive and negative buses are isolated from earth ground, a selective ground fault detection system shall be incorporated to detect leakage current from field I/O wiring to ground.
- Due care must be taken to ensure that circuits from one ground fault selector switch will not be cross-connected to circuits from any other ground fault selector switch (e.g., at common annunciator points, lamp test connections)
- ESD grounds shall consist of separate, isolated ground buses to handle specific requirements for AC safety grounds, signal wiring shields, and/or DC reference ground signals from analog or digital electronic modules.
International Standard and Codes for UPS Static Switch
- Non-Hazardous Indoor Enclosures, Installation and Pre-Commissioning
- Boxes, Enclosures, and Accessories Materials Selection & Requirements
- SAES-J-902 — Electrical Systems for Instrumentation.
- SAES-J-601 — Emergency Shutdown and Isolation Systems.