A lightning protection system of an aircraft when it is electrically powered on the ground by a generator set is described. Such an aircraft consequently includes a fuselage and a connecting connector to allow the connection to the generator set. The connecting connector includes a frame, male electrical contacts protruding on either side of said frame, and a lightning protection system inserted between the male electrical contacts and electrical elements of the aircraft. The protection system includes peak-clipping devices for clipping an electrical signal and a printed circuit having conductive tracks linking the male electrical contacts to the peak-clipping devices.