The fire performances of small telecom halogen-free cables were measured using cone calorimeter by changing several test conditions (heat flux, number and spacing of cables) and cable properties (sheath thickness and insulation mass). An analytical phenomenological fitting was proposed to predict accurately main fire performances (time-to-ignition, peaks of heat release rate and time to peak of heat release rate) from a set of 42 tests. The phenomenological model also assesses quantitatively the influence of different test conditions and cable properties. It appears that time-to-ignition is only dependent on heat flux. Moreover the influence of sheath is pointed out to delay the occurrence of the main peak of heat release rate corresponding to the decomposition of non-flame retarded insulation. The fitting allows better predicting the fire hazard in case of cables burning.