Life Safety Secondary Supply Routing: Technical Compliance with BS 7671 and BS 8519
Background and Scope
This guidance covers the routing of secondary supply cables from a life safety generator to the ATS (Automatic Transfer Switch), and the final equipment with reference to:
BS 7671:2018+A2:2022, specifically Section 560: Safety Services
BS 8519:2020, with emphasis on Clause 7 (Cable Routing) and Clause 11 (Cable Selection)
The goal: clarify requirements for the diverse cable routing and maintain circuit integrity under fire conditions for systems that support life safety and fire-fighting applications, such as sprinkler pumps, fire-fighting lifts, and smoke control systems.
Circuit Independence (BS 7671 Reg 560.7.1)
Requirement:
“Circuits of safety services shall be independent of other circuits.”
This mandates dedicated containment and routing. Safety circuits must not share cable trays, conduits, risers, or distribution routes with non-safety systems. Cross-contamination introduces unacceptable risk during fault conditions or maintenance interventions.
Design Implication:
Specify separate cable management systems
Route away from general LV distribution, lighting, and comms cabling
Physically segregate in risers and plant spaces unless barriers or fire-resistant separation are in place
Fire Risk and Explosion Zones (Reg 560.7.2)
Routing Restrictions:
“Circuits of safety services shall not pass through locations exposed to fire risk (BE2) unless they are fire-resistant. The circuits shall not, in any case, pass through zones exposed to explosion risk (BE3).”
Definitions:
BE2: Areas with a high probability of fire (e.g. plantrooms, kitchens, storage of combustibles)
BE3: Areas where explosive atmospheres may occur (e.g. battery rooms, fuel storage)
Design Implication:
Where BE2 zones cannot be avoided, specify cabling with a minimum 120 min fire survival rating
BE3 zones must be avoided entirely
Cable Separation (Reg 560.7.7)
Requirement:
“Safety circuit cables… shall be adequately and reliably separated by distance or by barriers from other circuit cables, including other safety circuit cables.”
Design Implication:
Implement route separation by duct, tray, or enclosure
If co-routing is unavoidable (e.g. entering the same panel), barriers or compartments must preserve independence
Avoid shared cable bundles, even among separate safety systems
Fire-Resistant Cabling Systems (Reg 560.8.1)
Permitted Systems:
“One or more of the following wiring systems shall be utilised for safety services required to operate in fire conditions…”
Permitted types include:
Mineral Insulated (MI): BS EN 60702-1, -2
Cables tested to BS 8491 (power circuits) or BS EN 50200 / BS 8434-2 (control circuits)
Systems in fire-protected enclosures or fire compartments
Design Implication:
Select cables based on the fire survival duration required for the system (see BS 8519 Clause 5)
Ensure terminations and fixings are tested as part of a complete system (cable + supports)
Dedicated Support Systems (BS 8519:2020 Clause 7.3)
Requirement:
“Cables should be installed on a dedicated cable support system, independent of other cable support systems and designed to maintain its circuit integrity…”
Design Implication:
Use fire-rated containment systems tested with the cable type selected
Avoid combined trays or baskets — this invalidates fire certification
Support fixings must withstand fire temperatures and mechanical stress
Diverse Routes and Fire Compartmentation (BS 8519 Clause 7.3)
Requirement:
“Where the diverse routes come together… they should be separated by fire compartmentation with a fire resistance period of at least the fire survival time…”
Design Implication:
If primary and secondary cables converge (e.g. entering the same room), their routes must be separated by minimum 120 min fire-rated construction
Consider routing one through a separate riser or service shaft
Cable Selection: Category 3 (BS 8519 Clause 11)
Definition:
“Category 3: fire-fighting (120 min fire survival time)… power cables meeting the 120 min survival time when tested in accordance with BS 8491…”
Design Implication:
Specify Category 3 cables for life safety loads: sprinkler pumps, smoke control, fire-fighting lifts
Include fire survival test evidence from manufacturers, including for joints and terminations
Ensure mechanical protection (e.g. armoured or in steel conduit) for small power circuits
Additional Notes
Fire-fighting lifts: also reference BS EN 81-72:2020, which mandates ATS placement, response times, and fire compartmentation of switchgear
Escape routes: wiring must comply with Regulation 521.10.202, which now applies throughout, not just in escape routes
Low smoke zero halogen (LSZH) cables are preferred in all occupied areas
Cross Check
For life safety systems, both cables and their containment must be designed to survive fire conditions for no less than 120 minutes, as required for Category 3 circuits under BS 8519 Clause 5. This means routing must be through dedicated, fire-resisting cable support systems – no sharing trays.
Where routes converge or pass through risk-prone areas (BE2), enclose them within a fire-compartmented construction with equal or greater resistance. And to limit smoke toxicity and flame spread (BE3), all cabling must be specified as LSZH (Low Smoke Zero Halogen) or demonstrably equivalent.
This isn’t belt and braces – it’s basic life safety compliance.
