Control & Signal Cables

What sets this cable apart

A power feeder cable is built around one or a few large conductors sized for ampacity and voltage drop. Control and signal cable does the opposite job: many small conductors, often 0.5 to 2.5 square millimetres, grouped as pairs, triads or multicore bundles, screened to keep electromagnetic interference from generators, thrusters and variable frequency drives off the signal. Losing a control cable rarely trips a breaker the way a faulted power cable does; instead it produces a false alarm, a stuck valve position indication, or a drifting instrument loop, faults that are harder to spot and easier to ignore.

Main components

Conductor

Tinned or bare stranded copper, flexible enough for the tight bend radii typical of control panels and junction boxes.

Insulation

EPR or XLPE for higher fire and thermal duty, PVC for less demanding, lower-cost runs.

Screen

Individual pair or triad screening for instrumentation loops that are sensitive to crosstalk, plus an overall braid or foil screen with a drain wire for the whole cable.

Armour

Galvanised steel wire braid or tape, fitted where the run is exposed to mechanical damage rather than protected in trunking.

Outer sheath

Low smoke, zero halogen (LSZH) compound is standard on modern newbuildings so a cable fire does not add toxic, corrosive smoke to an already dangerous situation.

Selection and sizing

Core count and pair/triad grouping follow the number of signals in the loop. Conductor gauge is set less by current than by loop resistance over the run length, which matters directly for 4-20 mA current loops and RTD circuits where a few extra ohms shift the reading. Screening choice, foil, braid or both, follows how noisy the routing is: a cable run alongside a thruster feeder needs better screening than one in a quiet accommodation trunk. Fire performance class is chosen against where the cable is routed relative to fire zones and escape routes.

Regulations and class

Shipboard cable construction and testing follow the IEC 60092 series. Flame retardance is verified to IEC 60332 and smoke emission to IEC 61034; class societies require type approval certificates covering both before a cable can be used. Cables routed through fire zone boundaries or serving essential and emergency services need a fire-resistant type able to keep circuit integrity during a fire, not just flame-retardant sheathing.

Typical faults

• Screen grounded at both ends -- creates a ground loop; the consequence is induced noise on the signal that looks like an unstable process rather than a wiring fault.
• Gland moisture ingress -- a poorly sealed cable gland lets condensation or wash-down water track along the conductors; the consequence is falling insulation resistance and eventual earth faults.
• Chafing against structure -- unsecured runs rub against steelwork with vessel motion; the consequence is intermittent signal loss that is hard to reproduce during troubleshooting.
• Undersized conductor on a long loop -- voltage drop on a 4-20 mA loop over a long run; the consequence is a measurement offset that reads as instrument drift.

What to look for in a supplier

• Type approval certificates matching the exact construction being supplied, not a similar catalogue item.
• LSZH compliance documentation if the vessel's fire safety design specifies it.
• Screening effectiveness data relevant to the electrical noise environment the cable will run through.
• Consistent core colour coding and print legend across the full delivered length, which saves real time during termination.

Megger the insulation resistance of every control cable run before it goes into service, not after a fault appears -- a marginal reading found during commissioning is a five-minute fix, the same fault found after installation is a day of tracing.