Protective Earth (PE) and Clean Ground (CG) bars serve distinct roles in control panels to ensure safety and signal integrity. PE handles fault currents for personnel protection, while CG provides a low-noise reference for sensitive instrumentation.
Purpose and Function
PE bar connects all exposed conductive parts to the earth system, diverting fault currents safely to prevent shock hazards during short circuits or insulation failures.
CG bar (also called instrument ground) offers a quiet, low-impedance path for signal returns in analog loops, PLCs, and transmitters, isolated from PE to avoid noise coupling from power faults.
Key Differences
| Aspect | PE Bar | CG Bar |
|---|---|---|
| Primary Role | Safety grounding (fault current) | Signal reference (low noise) |
| Connections | Chassis, enclosures, equipment grounds | Shields, analog returns, I/O commons |
| Impedance | Low (for fault clearing) | Very low (<1Ω), dedicated path |
| Separation | Direct to earth electrode | Isolated or single-point to PE |
| Standards | IEC 60364, NEC 250 | ISA 5.1, manufacturer specs |
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