Why “isolated” is meaningless until you prove zero energy
Introduction — the most dangerous voltage is the one you don’t expect
Electrical fatalities at sea often share a common phrase in investigation reports:
“The circuit was believed to be dead.”
Belief has no electrical value.
Only measured absence of energy matters.
What “test-before-touch” really means
Testing is not a ritual. It is a three-step verification:
- Prove the tester works (on a known live source)
- Test the circuit (all phases, to earth and between phases)
- Prove the tester again
Skipping step 1 or 3 invalidates the result.
Induced voltage: the killer on ships
Shipboard cabling often runs:
- in parallel trays
- through steel structures
- near live HV feeders
This creates electromagnetic induction. Even isolated conductors can carry dangerous voltage.
Induced voltage:
- cannot be seen
- may disappear when tested lightly
- reappears when touched or grounded
Only proper earthing and short-circuiting neutralises it.
Capacitive charge: stored energy that waits
Long HV cables behave like capacitors. After isolation:
- they remain charged
- voltage decays slowly
- re-energises when disconnected from measurement devices
This is why IEC requires:
- discharge before work
- earthing maintained throughout the task
🔧 Regulatory anchors (clear and specific)
IEC 60092-503
Requires:
- testing for absence of voltage
- discharge of capacitive systems
- earthing before and during work
Class / Flag guidance
Expect:
- approved voltage detectors
- documented test-before-touch procedures
- training evidence for personnel performing tests
Using a multimeter alone is often not acceptable for HV verification.
Tools that are acceptable — and those that aren’t
Acceptable (when rated and approved):
- HV voltage detectors (rated above system voltage)
- earthing switches with visible position
- discharge resistors
Not acceptable:
- low-rated multimeters
- test lamps
- “it didn’t spark” logic
🔻 Real-World Case: Serious Injury from Capacitive Discharge (Cable Termination)
An electrician suffered severe burns when terminating an HV cable thought to be discharged. Investigation found:
- voltage tested once, not re-proven
- cable not earthed during work
- capacitive charge reappeared after testing
The injury occurred minutes after isolation.
Why ETOs rush this step — and shouldn’t
Testing feels repetitive.
Pressure exists to “get on with it”.
But testing is the last barrier between procedure and physics. Once you touch the conductor, there is no recovery window.
Knowledge to Carry Forward
Isolation removes supply.
Testing proves absence.
Earthing removes stored and induced energy.
Miss any one of those, and the system remains dangerous.
Professional ETOs treat test-before-touch as non-negotiable, even when it slows the job.
Tags
ETO, Test Before Touch, Induced Voltage, Capacitive Charge, HV Safety, IEC 60092, Electrical Testing, Marine Electrical Hazards