Why do some manufacturers offer fire resistant cable rated at up to 125ºC?
There is no obvious advantage offering a fire alarm cable that claims to be rated above 70°C: a) Temperature limitation of connectors and accessories is usually 70ºC. See BS 7671:1992 IEE Wiring Regulations 17th Edition clause 512 – 02 – 1. b) Effect of cable temperature on adjacent components since the surface temperature of the cable is only likely to be 10ºC less than the conductor. If laid next to a PVC cable then the surface temperature of the cable must not exceed 70ºC. [Ref: BS7671: 1992 /IEE Wiring Regulations 17th Edition section 422 “Protection Against Fire And Harmful Effects”.] c) Touch temperature should be less than 90ºC. [ Ref BS7671: 1992 /IEE Wiring Regulations 17th Edition section 423 “Protection Against Burns”.] d) Fire alarm cables are normally sized on volt drop considerations rather than current ratings.
