Electrical cables are extensively used in nuclear power plants. Therefore, the fire-retardant performance of electrical cables is generally verified according to the Institute of Electrical and Electronics Engineers (IEEE) 383 standard, which describes the requirements for flame testing of cables. However, the IEEE 383 standard only stipulates one requirement for the minimum ambient temperature (5°C) surrounding the facilities for the flame test. To analyze the influence of the ambient temperature on the fire-retardant performance of 5cables, flame test experiments were conducted on two types of non–Class 1E cables under several conditions with respect to the seasonal ambient temperatures surrounding the experimental facilities. According to the results, the burning lengths of the cables did not increase in proportion to the increase in the ambient temperature. The longest burning lengths of the cables were obtained from experiments conducted in the autumn season, and not the summer season (with the highest ambient temperature). To investigate these experimental trends, we analyzed the influence of the ambient temperature on the flammability of the cables in terms of the consumption rate of the propane fuel used for the flame tests and the evaporation rate of volatile cable materials. Consequently, it was found that the highest flammability of the cables was observed under autumn conditions, similar to the standard temperature conditions in accordance with the IEEE 1202 standard and in which the volatile materials in the cables did not evaporate more than in the summer condition.