Understanding the fire behavior of the calibration cable for assessing the reaction to fire of cables

The EN 50399 standard for large-scale cable fire testing requires the use of a single, mandatory calibration cable—a non-electrical dummy whose sole purpose is to verify the test chamber before any cable campaign. This cable is the only one accepted by the standard worldwide, and its large-scale fire performance (damage length 1.4 ± 0.4 m) is well documented through extensive round-robin testing. However, its ignition and burning behavior at the bench scale has never been systematically characterized. This study fills that gap by testing the EN 50399 reference cable using simultaneous thermal analysis (STA) and the fire propagation apparatus (FPA). STA characterized the thermal decomposition of the outer sheath under inert and oxidative conditions. FPA provided ignition, combustion, and flame propagation data under varying heat fluxes (25–50 kW/m²) and oxygen concentrations (21%–40%). The derived thermal response parameter (TRP = 292 kW·s⁰·⁵/m²) and fire propagation index (FPI ≈ 10.6) are consistent with the cable’s known non-propagating large-scale behavior. The resulting small-scale dataset provides a reliable benchmark for early-stage cable design and for predicting EN 50399 outcomes without resorting to costly full-scale tests.