Ignition behavior of overloaded electric wire is investigated under various gravitational conditions to know the impact of surrounding flow field on the ignition process. The experimental parameters are oxygen concentration, supplied electric current value and the applied time. The result shows that the ignition phenomenon easily occurs in non-convective flow field (in microgravity), which is characterized by lower limit of electric current to attain ignition. Moreover, as a result of the observation by Mach-Zehnder interferometry, due to a distinguished difference of pyrolysis gas motions in convective and non-convective flow field, ignition delay time and a minimum electric current leading to ignition occurrence are influenced considerably.