Why HV systems forgive nothing — and why procedure is the control
Introduction — HV doesn’t fail often, but when it does it ends careers
High-voltage systems (typically 3.3–11 kV AC onboard) are designed to be robust and rarely operated. That reliability creates a dangerous illusion: because HV equipment “never causes trouble,” crews assume it is inherently safe.
It isn’t.
HV systems are safe only when interlocks, permits, and earthing procedures are followed exactly. Deviate once, and the system will punish you without warning.
What makes HV fundamentally different from LV at sea
HV introduces hazards that do not exist — or are negligible — at LV:
- Induced voltage on isolated cables
- Capacitive charge retained after isolation
- Stored energy in long cable runs
- Arc propagation across larger air gaps
- Human error amplification (mistakes scale with energy)
This is why HV work is governed by procedure first, tools second.
🔧 Regulatory anchors (explicit and enforceable)
IEC 60092-503 (Special features — HV installations)
Requires:
- restricted access to HV spaces
- mechanical and electrical interlocking
- means to earth and short-circuit conductors before work
- visible indication of earthing applied
This is not guidance; it is a design and operational requirement.
IACS E11 (Electrical Installations)
Class expectations include:
- permit-to-work mandatory for HV
- two-person rule (authorised HV personnel)
- earthing devices approved for fault level
- procedures posted at HV access points
Class surveyors routinely verify practice, not just documents.
SOLAS Chapter II-1, Regulation 45
“Precautions shall be taken to minimize the risk of electric shock and fire.”
HV permits and earthing are the accepted method of compliance.
HV permits: what they must contain to be valid
A legitimate HV permit-to-work must explicitly state:
- Exact equipment identification (feeder name, section, cable ID)
- Isolation points (upstream and downstream)
- Interlocks verified (what prevents re-energisation)
- Earthing method applied (where, how, and by whom)
- Test-before-touch confirmation
- Control of access (who is allowed inside the HV space)
- Hand-back procedure
If any of these are missing, the permit is incomplete — regardless of signatures.
Interlocks: safety devices, not inconveniences
HV interlocks exist to prevent three fatal actions:
- opening live compartments
- removing breakers under load
- applying earths to live conductors
Common (and deadly) failures:
- interlocks defeated “temporarily”
- mechanical linkages worn or misaligned
- false assumptions that interlocks equal isolation
An interlock prevents one specific error.
It does not make the system safe by itself.
Earthing HV systems: the step people rush
HV earthing must:
- be applied after isolation
- be rated for full prospective fault current
- be applied visibly (not assumed)
- remain in place until work is complete
Using:
- undersized earthing leads
- uncertified clamps
- makeshift bonds
…turns the earthing step into a false sense of security.
🔻 Real-World Case: Fatality During HV Cable Work (Offshore Vessel)
An offshore vessel ETO was fatally injured while working on an HV feeder believed to be isolated. Investigation found:
- feeder breaker opened
- earthing switch not applied
- cable retained induced voltage from adjacent live circuits
The voltage was invisible.
The outcome was immediate.
The system behaved exactly as HV physics dictates.
Knowledge to Carry Forward
HV safety is procedural engineering.
If the permit is unclear — stop.
If earthing is not visible — do not enter.
If interlocks don’t align — do not force.
HV systems only forgive one thing: strict discipline.
Tags
ETO, High Voltage, HV Permit to Work, Interlocks, Earthing Procedures, IEC 60092-503, IACS E11, Marine Electrical Safety