The field problem
Rail / LRT Station — Complex Architecture
Parapets, roof edges and a metallic bridge/cladding envelope created conflicts over air-terminal mounting, down-conductor routing and whether metallic elements should be isolated or bonded.
why the obvious answer can be misleading
The key issue is not simply 'metal must be isolated' or 'metal must be bonded'. The designer must determine whether the metal is a natural LPS component, an equipotentially bonded part, or an item requiring separation, and then manage touch/side-flash risk accordingly.
Why it failed
The key issue is not simply 'metal must be isolated' or 'metal must be bonded'.
The designer must determine whether the metal is a natural LPS component, an equipotentially bonded part, or an item requiring separation, and then manage touch/side-flash risk accordingly.
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
Calculate protection zones; coordinate air terminals with architecture; route conductors directly; use supports for mechanical/electrical separation where required; and define bonding of the metallic bridge/envelope within the overall LPS concept.
Correction & verification
Calculate protection zones; coordinate air terminals with architecture; route conductors directly; use supports for mechanical/electrical separation where required; and define bonding of the metallic bridge/envelope within the overall LPS concept.
Verification recorded in the case
- Inspect continuity, separation, protection geometry and interfaces to the earth-termination system.
- 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 62305-3; NFPA 780 where specified; listed/approved connection components as applicable.
PIS reviewed field handbook · PIS-CS-039
View the original social cardThe engineering lesson
The steel bridge was not the problem. The engineering decision about its role in the LPS was.
Take the lesson into your next design review.