Power Cable (0.6/1 kV)

Bedding and armour

An inner bedding layer separates the insulated cores from a steel wire braid or tape armour, which gives the cable mechanical protection and, earthed correctly, a return path for fault current.

Outer sheath

Marine cable sheathing is specified for low smoke and zero halogen performance so that, in a fire, it does not add toxic or corrosive smoke to spaces that may already be hard to evacuate.

Selection and sizing

Current-carrying capacity, derated for the number of cables run together in a bundle and for the ambient temperature of the space they pass through, sets the minimum cross-section. Voltage drop over the run length is checked separately, since a cable that is rated for the current can still be too small if the run is long enough to drop voltage below what the load needs at start-up.

• Cross-sectional area sized to derated current capacity, not the nameplate rating alone
• Number of cores and whether a separate earth core or the armour itself provides the earth return
• Armour type suited to the routing, since exposed deck runs need more mechanical protection than a protected trunk
• Fire performance class matching the space: flame-retardant as standard, fire-resistant where the circuit must keep working during a fire, such as emergency lighting or fire pumps

Regulations and class

Marine power cable construction and testing follows the IEC 60092 series, which covers conductor sizing, insulation and sheath materials and fire performance for shipboard use. SOLAS Chapter II-2 requires that cable routed through machinery spaces and other fire risk areas meet flame-retardant standards as a minimum, with fire-resistant cable required for circuits that must stay live during a fire, such as emergency power, fire pumps and emergency lighting. Class societies check routing and segregation as part of the electrical survey, since running the main and emergency feed for the same system through one trunk defeats the redundancy the rules are meant to provide.

Typical faults

What to look for in a supplier

• Type approval to IEC 60092 with test certificates for the specific fire performance class ordered
• Consistent core colour coding and marking that matches the ship's existing cable schedule
• Batch traceability, since a cable fault investigation needs to trace back to a specific manufacturing lot
• Stock of the specific armour and sheath combination the ship's routing standard calls for, not just the nearest equivalent

Check derating for bundled cable runs before assuming a cable is oversized on paper - a cable that is comfortably rated on its own can still run hot once it is one of a dozen in the same tray.