Why the same spanner mistake ashore becomes an explosion at sea
Introduction — fault energy is what kills and burns, not voltage
Most people fear voltage because it’s easy to picture. But in switchboards, the severity of an event is driven by available fault current and fault clearing time — the energy that turns copper into plasma and panels into shrapnel.
On ships, short-circuit levels can be brutally high because:
- generators are close to switchboards
- impedances are low
- busbars are compact
- parallel operation multiplies available fault current
This is why “it’s only 440 V” is one of the most dangerous phrases onboard.
The regulatory reality: you must know and respect prospective fault levels
SOLAS requires precautions against shock and fire hazards of electrical origin, and administrations/class interpret this through compliance, ratings, segregation, and appropriate protective devices.
Class/IACS then makes it practical: equipment and installations must be designed and tested to withstand expected electrical stresses, and IACS requirements harmonize testing expectations with IEC ship standards.
So when you assess short-circuit risk, you’re not doing “engineering for interest” — you’re verifying the ship is still inside its certified design envelope.
How ships calculate short-circuit current (and why it differs from shore)
Shipboard short-circuit calculation is commonly done using IEC 61363 methodologies for AC systems (and related approaches for DC systems). Academic and applied marine power literature explicitly references IEC 61363 as the standard basis for shipboard short-circuit current calculations.
The key difference from shore plants is the source model:
- you’re dealing with generator subtransient reactance and decaying current contributions
- motor contributions can be significant in the first cycles
- bus-tie status and PMS logic change the fault level in real time
ETO judgement: you don’t just ask “what’s the fault level?”
You ask “what’s the fault level in this configuration — right now?”
What “fault energy” means in practice (why arc flash happens)
Short-circuit current is only half the story. The hazard is the energy released before clearing:
- high fault current + slow clearing = extreme arc energy
- lower fault current + very slow clearing can still be severe
This is why coordination and breaker settings are safety devices, not reliability tweaks.
Real-world case: arc flash from a tool-induced short circuit
A UK MAIB-summarised incident (shared by IMCA) describes an electrician injured in an explosion when a short-circuit occurred between phases on a switchboard. The report notes the high current vaporised copper and part of a spanner, producing an arc flash with extreme heat and blinding light, followed by an explosive burst of hot gas and molten metal.
This isn’t a “bad luck” story. It’s a direct demonstration of fault energy:
- the board had enough prospective fault current to instantly plasma-form copper
- the enclosure released pressure violently
- the injury mechanism was thermal + blast + molten metal
This is why “quick job, no PPE” kills.
Practical ETO controls that actually reduce short-circuit risk
1) Maintain switchboard integrity (loose parts become projectiles and ignition points)
- tightness and torque of busbar joints matters
- contamination tracking reduces insulation strength and promotes arcing paths
- missing barriers change arc behaviour inside compartments
2) Never ignore “configuration risk”
PMS decisions and operator actions change fault levels:
- running 1 generator vs 3 in parallel is not the same fault energy
- closed bus-tie vs split bus changes prospective current and selectivity margins
3) Protection coordination is a life-safety function
Coordination isn’t just “avoid nuisance trips”. It is:
- limiting arc duration
- preventing busbar damage
- preventing cascade blackouts
Bad coordination can create:
- a fault that should isolate a feeder instead trips a generator
- a fault that should clear quickly instead persists as a sustained arc
4) Verify ratings after modifications
Any time someone adds:
- bigger transformers
- new VFD banks
- shore power converters
- ESS systems
…your fault levels and protection assumptions change. That’s when “original certificates” stop being trustworthy unless revalidated.
A quiet SOLAS-class trap: cables and fire behaviour
Even if you clear faults correctly, cable routing and properties affect fire spread. SOLAS-aligned requirements include expectations around cable flame-retarding characteristics and proper installation, which flag administrations publish and enforce.
Short-circuit events can ignite insulation; poor cable selection turns one panel incident into a space-wide casualty.
Knowledge to Carry Forward
Short-circuit levels define whether your switchboard incident is a “trip” or an “explosion”. Ships can have very high prospective fault current at LV, and the real hazard is fault energy — current multiplied by clearing time. Use IEC-based calculation approaches (commonly IEC 61363 in marine practice), treat bus configuration as a variable, and remember that coordination settings are part of your life-safety controls.
Tags
ETO, Short Circuit, Fault Current, Arc Flash, Switchboards, Protection Coordination, IEC 61363, SOLAS II-1, Class Compliance, Marine Electrical Safety