The problem of upward leader inception from transmission lines has not been thoroughly discussed, largely because of the difficulty to obtain experimental data under natural circumstances. Previous studies have primarily examined reduced-scale experiments or single-phase test lines. In this context, a real-size experimental system aimed at studying upward leader characteristics on both the phase conductor and ground wire is designed in this study. The results associated with real-size experiments corresponding to 110 kV, 220 kV, 500 kV and 1000 kV AC transmission lines, including the phase conductor and ground wire, are presented and discussed. It is shown that as the triggering voltage on the phase conductor increases, the streamer and leader incept earlier for a leader emerging from the phase conductor, and incept later for a leader emerging from the ground wire. The increase of the triggering phase angle corresponds to a higher voltage on the phase conductor, thereby increasing the strike probability on the phase conductor. The leader velocity and charge density present, in general, an increasing trend for the phase conductor as a function of the phase angle, while an opposite trend is observed for the leader emerging from the ground wire except for some special occasions. It is also determined that the phase conductor leader velocity is larger for a higher voltage class, while the charge density associated with the leader emerging from the phase conductor is smaller for a higher voltage class. (C) 2015 Elsevier B.V. All rights reserved.