The field problem
Critical Government Facility — NAC
Sensitive systems showed disturbances during testing.
Multiple earthing systems were installed without a coordinated equipotential-bonding concept.
why the obvious answer can be misleading
Physically separate electrodes can still become electrically interconnected through PE conductors, cable screens, metallic services and equipment. Uncontrolled interconnection can create potential differences and unwanted current paths.
Why it failed
Physically separate electrodes can still become electrically interconnected through PE conductors, cable screens, metallic services and equipment.
Uncontrolled interconnection can create potential differences and unwanted current paths.
Follow the engineering
Switch between the field condition and the engineering concept. Trace the path and examine what changes.
Inspect the engineering detail
What changes
Develop a coordinated bonding architecture.
Correction & verification
Develop a coordinated bonding architecture.
Where systems are intentionally interconnected, size the bonding path for the governing electrical duty and coordinate the final performance target with the most demanding connected system, while respecting functional/EMC requirements.
Verification recorded in the case
- Verify continuity, potential differences and current paths before and after corrective bonding.
- Record as-built topology and connection points.
- Repeat the measurement or functional test under a defined condition.
- Confirm continuity and mechanical integrity of the corrected path.
- Document instrument/setup, environmental condition and test method.
- Close the NCR/case only when evidence supports the conclusion.
References & project context
References are reproduced from the PIS casebook. Select the governing edition and project acceptance criteria before using them for a design. The diagrams explain the concept, rather than define construction dimensions.
IEC 60364-5-54; IEC 62305 bonding concepts; application-specific EMC requirements.
PIS reviewed field handbook · PIS-CS-008
View the original social cardThe engineering lesson
Isolation by drawing does not guarantee electrical isolation in the completed facility.
Take the lesson into your next design review.