By Dovydas Kersys · Chapter 9 of 58 in Machine Commissioning.
Before you begin: Follow the machine documentation, risk assessment, site procedures and lockout/tagout requirements. Commissioning can expose personnel to electrical energy, stored pressure and unexpected motion. Never defeat a safety function merely to make a test easier. Examples and diagrams are generic and must be checked against the actual machine.
Protective earth and bonding provide a low-impedance fault path and reduce dangerous touch voltages. They also influence EMC performance, shield behavior and drive reliability.
Protective earth is a parallel safety path through the machine, not just a green/yellow wire in the panel.
Why this matters during commissioning
A machine can appear functional with poor bonding until a fault or high-frequency noise event occurs. Commissioning must prove continuity before operation.
Commissioning procedure
- Inspect the main PE conductor and machine bonding network.
- Verify painted or insulated joints have proper bonding hardware or dedicated conductors.
- Check doors, subpanels, motor frames, drive enclosures and remote cabinets.
- Measure continuity using the method required by local rules/site procedure.
- Confirm shields and functional earth connections follow the machine design.
Common failure patterns
- Loose PE lug hidden behind wiring.
- Paint preventing metal-to-metal bond.
- Door earth strap missing after panel work.
- Cable shield connected to an unintended signal common.
Evidence to record
- Test points
- Measured resistance / continuity result
- Instrument used
- Corrective actions
- Final verification
FIELD RULE: Never use signal commons as a substitute for protective earth.
Continue the series
- Previous chapter: Electrical Panel Inspection: Commissioning Guide
- Next chapter: Power Supply and Phase Checks: Commissioning Guide
- Browse all Machine Commissioning chapters
Adapted from Machine Commissioning for Maintenance and Automation Technicians, by Dovydas Kersys. © 2026 Dovydas Kersys. Featured cover image is an AI-generated editorial illustration.