Fire Alarm Cable and Wiring
Explained
The cabling in a fire alarm system is often the last thing anyone thinks about — but it is one of the most important. A fire alarm system that loses its cabling in the early stages of a fire is a system that may fail precisely when it is needed most. BS 5839-1 sets specific requirements for cable survival in fire conditions.
MICC Cable — Mineral Insulated Copper Clad
MICC cable — commonly known as Pyro, from the Pyrotenax brand name — consists of one or more copper conductors surrounded by compacted magnesium oxide (MgO) mineral insulation, all enclosed within a seamless copper sheath. It is the most fire-resistant cable available and will survive fire conditions that would destroy any other cable type.
| Detail | |
|---|---|
| Construction | Copper conductors, magnesium oxide mineral insulation, copper outer sheath — all inorganic materials that do not burn |
| Fire performance | Will maintain circuit integrity at temperatures exceeding 1,000°C — the only cable type that can genuinely claim to survive the full duration of a severe building fire |
| Circuit integrity classification | PH 120 — maintains performance for at least 120 minutes under fire conditions |
| Typical applications | Critical fire alarm circuits in high-risk premises — hospital operating theatres, critical infrastructure, tunnels, applications where circuit survival for the full duration of firefighting operations is essential. Also widely used for emergency lighting circuits |
| Installation considerations | Requires specialised termination using compression pot fittings — installation is more skilled and time-consuming than conventional cable. The outer copper sheath must be earthed. Requires an outer PVC or LSF oversheath in most applications |
| Cost | Significantly more expensive than softskin alternatives — both in materials and installation labour. Justified only where the risk profile demands the highest level of circuit integrity |
| Standard | BS EN 60702 |
Softskin Fire-Resistant Cable — FP200 and Equivalents
Softskin fire-resistant cables — of which FP200 Gold is the most widely recognised trade name in the UK — are the standard choice for fire alarm wiring in the vast majority of commercial and residential installations. They consist of copper conductors insulated with a fire-resistant compound (typically mica tape or a similar mineral-based layer) surrounded by an outer sheath of Low Smoke and Fume (LSF) or Low Smoke Zero Halogen (LSZH) material.
| Detail | |
|---|---|
| Construction | Copper conductors, mica-based fire-resistant insulation layer, LSF or LSZH outer sheath |
| Fire performance | Maintains circuit integrity for a defined period under fire conditions — typically PH 30 or PH 60 depending on the specific product. FP200 Gold is rated to BS EN 50200 Category PH 30 as standard |
| Smoke and fume output | LSF and LSZH sheaths produce significantly less smoke and no halogen gases when burning — important for occupant escape and firefighter safety in enclosed spaces |
| Typical applications | The standard choice for virtually all fire alarm wiring in commercial buildings, schools, offices, hotels, retail premises, and residential blocks — wherever BS 5839-1 requires enhanced cable but MICC is not specified |
| Installation | Installed using conventional cable installation techniques — straightforward to terminate and handle. Standard cable clips and containment systems are used |
| Cost | Moderate — significantly cheaper than MICC but more expensive than standard PVC wiring. Widely available and competitively priced |
| Standard | BS EN 50200 (fire resistance of cables under fire conditions) |
Which Cable Does BS 5839-1 Require?
BS 5839-1 requires that fire alarm cables used in circuits that are critical to the operation of the system under fire conditions should be fire-resistant. For most installations, softskin fire-resistant cable such as FP200 satisfies this requirement. MICC is specified where the highest level of circuit integrity is required — typically determined by the fire risk assessment and the consequences of circuit failure during a fire. In practice, the vast majority of new commercial fire alarm installations use FP200 or an equivalent softskin fire-resistant cable throughout.
Containment and Segregation
Cable Containment and Segregation
How fire alarm cable is routed and contained is as important as the cable type itself. BS 5839-1 requires that fire alarm cables are segregated from other services to prevent damage from heat, mechanical impact, or electrical interference.
Segregation from Power Cables
Fire alarm cables should be run separately from mains power wiring wherever possible. Where this is not practicable, they should be separated by a minimum distance or contained within separate conduit or trunking to prevent electromagnetic interference and reduce the risk of damage from a power fault.
Physical Protection
In areas where cables are at risk of mechanical damage — plant rooms, areas with forklift traffic, external routes — cables should be protected by conduit, trunking, or armoured cable to reduce vulnerability to physical damage.
Colour Coding
BS 5839-1 recommends that fire alarm cables are identified — typically by using red outer sheathed cable or by applying red identification tape or cable ties at regular intervals. This makes identification straightforward during installation, maintenance, and future modifications.
Route Selection
Where possible, fire alarm cables should be routed away from areas of high fire risk. Running detection and sounder circuits through a high-risk kitchen or plant room creates a vulnerability — a fire in that area could disable the very system needed to warn occupants before the fire spreads.
A Common Cause of System Failure
In practice, one of the most frequent causes of fire alarm system unreliability is cabling that has been damaged, incorrectly installed, or routed without regard to fire-resistant requirements. A service engineer who finds evidence of non-fire-resistant cable in critical circuits, damage to containment, or inadequate segregation should record these as deficiencies requiring remedial action — not as minor housekeeping issues.
Concerned About Your System’s Cabling?
If you have received a service report flagging cable deficiencies, or if you are planning a system upgrade and want to understand what cable specification is appropriate, get in touch for independent advice.
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