Fire Resistant Cable (FRHF)

What sets fire resistant cable apart

Fire resistant cable, marked FRHF (fire resistant, halogen free), is designed to keep the conductor circuit intact and functioning while directly exposed to fire for a defined period, typically around 90 minutes at high temperature under the relevant test standard. That is a different requirement from ordinary flame-retardant cable, which only has to resist spreading fire along its own run; a flame-retardant cable is allowed to fail electrically the moment flame reaches it, it simply must not carry that flame to the next compartment. FRHF cable earns its rating through a mica or ceramic-forming tape wrapped directly around the conductor, underneath the insulation, which turns into a solid ceramic-like barrier when the polymer around it burns away, keeping the conductor path continuous. Halogen-free compounding on top of that keeps smoke non-corrosive and low in toxic gas if the cable does eventually fail, protecting escape routes and electronics elsewhere in the same space.

Main components

Conductor

Stranded copper, sized to current rating exactly as with standard power cable; fire performance sits in the layers around it, not the conductor itself.

Fire barrier layer

Mica glass tape or a ceramifiable silicone layer wound directly onto the conductor; this is what actually delivers the fire rating and is what the test standard is really certifying.

Insulation and bedding

Halogen-free, low-smoke compound (typically cross-linked polyolefin), chosen for low toxicity and low corrosivity of combustion products rather than for fire resistance, which is already provided by the barrier layer underneath.

Outer sheath and armour

Halogen-free sheath, often with braid or wire armour for mechanical protection where the cable is exposed rather than run in trunking or conduit.

Selection and sizing

• Circuit criticality - FRHF is specified for fire pumps, emergency lighting, steering gear, fire detection and public address, and any circuit required by SOLAS to keep functioning during a fire.
• Fire rating duration - matched to the survival time required for the connected equipment, commonly a 90-minute rating for essential services.
• Conductor cross-section - sized on normal current-carrying and voltage-drop rules, not affected by the fire rating itself.
• Route and segregation - main and backup feeds for the same essential service must run in physically separated routes so one fire cannot take out both.

Regulations and class

SOLAS Chapter II-2 requires cables for essential and emergency services to remain operational for a specified period during a fire, which is why FRHF is mandated on those circuits rather than being an owner's preference. Fire resistance is tested and type-approved against recognised standards (commonly referenced by class societies as IEC 60331), and cable for marine use additionally needs flame propagation testing under IEC 60332. Class surveys check both that the correct cable type is installed on essential circuits and that segregation of duplicated feeds has been maintained, since a correctly rated cable run alongside its own backup defeats the purpose.

Typical faults

• Wrong cable type installed on essential circuits - standard flame-retardant cable substituted for FRHF during a repair, discovered only at survey or, worse, in an actual fire.
• Mica tape damage during installation - excessive bend radius or crushing during pulling cracks the fire barrier layer, and the fault is invisible until the circuit is fire-tested or fails in service.
• Loss of segregation - main and emergency cable runs later re-routed through the same trunking during a refit, defeating the redundancy the original design intended.
• Termination not fire-rated to match the cable - a standard gland or terminal box downstream of an FRHF run breaks the fire survival chain at the weakest point.

What to look for in a supplier

• Type approval certificate referencing the actual fire test standard, not just a manufacturer datasheet claim.
• Confirmed minimum bend radius and installation guidance, since the fire barrier layer is more sensitive to installation damage than standard cable.
• Batch traceability, given how much depends on correct manufacture of the mica barrier layer that cannot be inspected once the cable is finished.

FRHF cable protects the circuit, not the installation around it - a fire-rated cable terminated in a non-rated gland or junction box is only as good as its weakest fitting.