Why “low voltage” is the most dangerous phrase onboard
Introduction — LV hurts more people than HV
Most electrical injuries at sea occur on low-voltage systems, not HV. The reasons are simple:
- LV is accessed more often
- LV feels familiar
- LV work is rushed
- LV systems are rarely treated as energy-dense
On ships, 440 V can deliver enormous fault current due to low impedance and close-coupled generators. Treating LV casually is how routine jobs turn into fatalities.
The shipboard LV architecture (what feeds what)
A typical marine LV system is arranged as:
- Main LV switchboard (440 V AC)
- Distribution boards (440 V / 400 V / 230 V)
- Step-down transformers (for 230 V services)
- Emergency switchboard (segregated supply)
- Essential vs non-essential feeders
The key design principle is segregation by consequence, not convenience.
Voltage levels and why ships still use 440 V
- 440 V AC:
Primary shipboard LV distribution due to lower current for the same power → smaller cables, lower losses. - 400 V AC:
Increasingly common on newer builds to align with IEC industrial equipment. - 230 V AC:
Lighting, sockets, control power, hotel loads — where most human interaction occurs.
ETO judgement is required when multiple voltages coexist in the same space.
🔧 Regulatory anchors (explicit)
IEC 60092-201 (System design)
Defines:
- permissible LV system voltages
- segregation requirements
- earthing philosophy linkage
IEC 60092-401 / 402 (Installation & safety)
Requires:
- protection against shock
- appropriate protective devices
- discrimination between feeders
- safe maintenance access
SOLAS Chapter II-1, Regulation 45
“Electrical installations shall be arranged so as to minimize the risk of fire and electric shock.”
This applies fully to LV systems, not just HV.
Essential vs non-essential loads — not optional knowledge
Ships classify LV loads by consequence:
- Essential: steering gear, fire pumps, navigation, control systems
- Non-essential: HVAC, galley equipment, comfort loads
Protection and load shedding must ensure:
- essential loads survive faults
- non-essential loads drop first
- emergency systems remain powered
Misclassification causes blackouts and PSC findings.
Protection devices you will encounter
- MCCBs — adjustable, common on feeders
- ACBs — high-current main incomers
- Fuses — fast fault clearing, limited discrimination
- Earth-fault detection — especially critical on IT systems
Protection is a fire control system, not just a trip mechanism.
Real-world failure: LV feeder arc fault (Ro-Ro Vessel)
An AB suffered severe burns while working on a 440 V feeder believed to be “small load”. Investigation found:
- multiple generators online
- high prospective fault current
- no arc-rated PPE
- feeder protection time-delayed for coordination
The voltage didn’t injure him.
The fault energy did.
What ETOs must actively manage on LV systems
- Keep covers, shrouds, and barriers intact
- Control temporary modifications
- Verify feeder ratings after load changes
- Treat 440 V as high-energy equipment
- Enforce PPE during live diagnostics
Knowledge to Carry Forward
Low voltage on ships is high consequence electricity.
Its danger lies in familiarity, not magnitude.
If a system can deliver megawatts, it can deliver fatal energy — regardless of voltage label.
Tags
ETO, LV Distribution, 440V Ship Systems, Marine Switchboards, IEC 60092, Electrical Protection, Arc Flash, Marine Electrical Safety