Hi, I'm trying to wire a transformer which steps my mains voltage (240VAC) down. I just finished wiring the the primary to the plug, and thought I should test my connections by plugging it in. The coil was not inside the core or near the secondary, it was just lying on a piece of paper. I plugged it into an extension cord and then switched it on. Immediately, I heard the familiar mains hum coming from the coil, but I noticed its connection with the live wire sparking and switched it off within a second. I removed the plug from the extension and tried to switch it on again, which did not work. Upon further inspection, I found that the fuse had blown and I replaced it. I also touched the coil and found it was rather hot. My questions are the following: Firstly, why did the fuse on the extension cord blow, and not that of the plug which the coil was connected to? They were both 13A Bussmann fuses. If it makes any difference, the extension cord also had two chargers connected to it (Both of which are fine, by the way). Second, how do I know this won't happen again if I place the coil in the transformer with the secondary (which will still be disconnected)? It seems to me that the coil is causing a short circuit now, but what's gonna stop it from doing that if I place it into the transformer? Any help would be greatly appreciated.