.png "Electrical Work in a Wet Construction Tunnel — Illustrated Reconstruction")
Illustrated reconstruction of the wet-tunnel work environment; this is not a photograph of the actual incident.
The most dangerous electrical mistake of my career began with one assumption: I believed I had switched off the correct breaker. Inside a dark, wet construction tunnel in South Korea, that unchecked belief left a 220 V pump cable energized while I worked on it alone.
I was not injured, but that outcome does not make the method acceptable. The incident taught me that operating a breaker is only one step. Safety depends on identifying every source, isolating it, preventing re-energization, and proving absence of voltage at the actual work point.
I switched off a breaker, but I did not verify the cable. The circuit remained live because I had isolated the wrong circuit.
Incident at a Glance
Accuracy note: The exact contact point was not identified after the event. The explanation below is based on the observed arc, momentary pump operation, and the fact that the breaker did not trip.
A Routine Task in a High-Risk Environment
Groundwater kept the concrete floor wet, and several submersible pumps operated continuously to control the water level. Temporary work lights provided limited illumination through the long underground passage. Other workers were present elsewhere in the tunnel, but I was performing this task alone.
Replacing and extending the pump cable felt routine. That familiarity reduced my sense of danger even though the surrounding conditions—water, darkness, temporary power, and isolation from coworkers—made the task unusually unforgiving.
The Breaker Was Off—or So I Thought
.png "Wrong Circuit Breaker Selected in a Temporary Distribution Panel — Illustrated Reconstruction")
Illustrated reconstruction of the mistaken breaker selection; this is not the actual panel.
Before touching the cable, I walked to the distribution panel and switched off what I believed was the correct breaker. I did not identify every source from drawings or labels, secure the breaker against operation, or test the cable at the work point.
I then returned to the pump cable and treated it as de-energized. The breaker handle position gave me confidence, but it gave me no proof about the cable in my hands.
A breaker may be mislabeled, incorrectly traced, supplied from another source, or re-energized by someone else. Absence of voltage must be verified at the conductors where the work will occur.
The Flash and the Pump Restart
.png "Contact Arc on an Energized 220 V Pump Cable — Illustrated Reconstruction")
Illustrated reconstruction of the contact arc and momentary pump operation; no actual accident photograph exists.
I cut and stripped the cable, then connected the protective conductor and neutral conductor. Nothing happened, which falsely reinforced my belief that the supply was isolated.
When I handled the remaining line conductor, a bright blue-white flash appeared. I immediately released the wires. At the same moment, the pump ran briefly and stopped as the conductors separated. The circuit breaker did not trip.
What Most Likely Happened Electrically
The most plausible interpretation is that the energized supply-side line conductor momentarily contacted the pump-side line conductor. Because the neutral and protective conductors had already been connected, that contact temporarily completed the motor’s normal supply path and the pump began to run.
Making and then breaking contact with a motor load can produce an electrical arc. Motor starting current and the load’s inductive characteristics can intensify that arc. This was not proven to be a line-to-neutral or line-to-earth short circuit, and it should not be described as a phase-to-phase fault on this single-phase circuit.
The lack of a breaker trip is also consistent with a momentary load-current path rather than a confirmed bolted short circuit. However, the exact current and contact geometry were not measured, so this remains a reasoned reconstruction—not a laboratory finding.
Why I Was Not Shocked
I was wearing insulating boots, but my gloves were ordinary half-coated work gloves, not voltage-rated insulating gloves. I did not receive an electric shock or physical injury.
I cannot determine which factor prevented current from passing through my body. The way the conductors touched, the brief contact time, my grip, and the insulating effect of equipment may all have influenced the outcome. None can be treated as a safety control after the fact.
Luck is not a safety procedure, and ordinary coated gloves are not a substitute for voltage-rated protective gloves.
The Hazards Beyond the Live Conductor
- Wet environment: Groundwater and damp surfaces increased the seriousness of any insulation or contact failure.
- Temporary power: Circuit identification and labeling may be less reliable as construction conditions change.
- Working alone: A collapse or severe shock might not have been discovered promptly.
- Limited lighting: Darkness made conductor identification and safe handling more difficult.
- Wrong gloves: Half-coated work gloves provided no verified electrical insulation rating.
The Missing Safety System: Isolation, LOTO, and Testing
The root cause was broader than choosing the wrong breaker. I had no complete safe-isolation process. The circuit was not positively identified, the breaker was not locked and tagged, and absence of voltage was not verified at the cable.
Lockout/tagout helps prevent a correctly isolated circuit from being switched on unexpectedly. It does not, by itself, prove that the correct circuit was selected. Identification, isolation, lockout/tagout, and testing are separate steps that must work together.
- Identify the correct circuit and every possible source of supply.
- Isolate the circuit at the appropriate disconnecting device.
- Apply a lock and warning tag where the work procedure requires it.
- Confirm the voltage tester operates on a known energized source.
- Test every relevant conductor at the actual work point.
- Recheck the tester on a known source before touching the conductors.
In South Korea, Article 319 of the Rules on Occupational Safety and Health Standards addresses electrical work on de-energized circuits. Its sequence includes identifying all supplies, isolating and confirming disconnecting devices, applying locks and tags, discharging stored energy where required, testing for voltage, and applying temporary grounding when voltage could reappear.
Official reference: Korean National Law Information Center — Article 319. Site-specific procedures and current legal requirements must always be followed.
Before and After This Incident
Frequently Asked Questions
Why did the pump run if the breaker was supposedly off?
The wrong breaker had been switched off. The pump circuit remained energized, and momentary contact between the supply-side and pump-side line conductors most likely completed the motor circuit briefly.
Why did the circuit breaker not trip?
The observed behavior is more consistent with momentary motor current than with a confirmed short circuit. The actual current was not measured, so the precise reason cannot be proven retrospectively.
Would lockout/tagout alone have prevented the mistake?
Not necessarily. Locking the wrong breaker would still leave the cable energized. Correct circuit identification and an absence-of-voltage test at the work point are essential parts of the process.
Were the half-coated gloves electrical protection?
No. Ordinary coated work gloves should not be represented as voltage-rated insulating gloves. Electrical PPE must be selected, rated, inspected, and used for the actual hazard.
Field Conclusion
What frightened me most was not the flash. It was realizing that, if I had collapsed in that tunnel, the nearest workers might not have found me for some time.
The incident permanently changed one habit: I no longer trust a breaker position, a label, silence, or previous experience as proof. I verify at the point where my hands will work.
Experience builds confidence. Verification is what keeps confidence from becoming a hazard.
Read Part 1
Part 1 records two earlier electrical shocks involving an energized kitchen faucet and an ungrounded metal outlet box.
Read Part 1: Two Electrical Shock Accidents That Changed How I Work →
Safety notice: This article records a real field incident for safety education. It is not a live-work procedure. Electrical work must be performed by qualified persons using site-specific isolation, testing, PPE, supervision, and emergency arrangements.
Published: July 26, 2026
Electric Korea
Korean Electrical Construction · Field Experience · Safety · Technical Education
Website: electrickorea.co.kr
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