Fire Growth Rate Index as a Key Fire Characteristic of Electrical Cables

This study deals with the Fire Growth Rate Index (FIGRA) as a key fire characteristic of electrical cables (determined by a cone calorimeter) that allows to estimate their reaction to fire class. Three power (supply) electrical cables (reaction to fire class B2_ca) were tested by a cone calorimeter using different heat fluxes of 20, 30, 40 a 50 kW·m⁻². The cables were three-wire (cross-section of each wire was 1.5 mm²) with a nominal voltage of 0.6 kV (alternating current), resp. 1 kV (direct current). The cable sheaths were made of an ethylene copolymer filled with aluminum hydroxide. The beddings were made of an ethylene copolymer filled with a mixture of aluminum hydroxide and calcium carbonate. The conductor insulations of one electrical cable were made of crosslinked polyethylene and the conductor insulations of the other two electrical cables were made of an ethylene copolymer filled with aluminum hydroxide. FIGRA was determined per unit length and unit area of electrical cables. FIGRA increased with increasing heat flux. At a heat flux of 50 kW·m⁻², all the electric cables examined showed a very similar FIGRA (from 0.19 to 0.21 kW·m⁻¹·s⁻¹ and 18.4 to 21.2 kW·m⁻¹·s⁻¹, respectively). Conversely, at a heat flux of 20 kW·m⁻², the investigated cables showed greater FIGRA variance (in the range of 0.11 to 0.16 kW·m⁻¹·s⁻¹ or 10.8 to 16.2 kW·m⁻¹·s⁻¹).