I've recently seen a homemade AC stick welder that was using 8 AWG wire for the stinger (the electrode holder) and the ground clamp. The voltage and amperage was around 30V at 200A. According to various websites, the maximum capacity for 8 AWG wire is around 40A to 55A (Source: http://www.cerrowire.com/ampacity-charts)
Granted, he only used it for a single weld, but how did it not burn up almost instantly? The video later showed him using it at 200A for an electric arc furnace and he was drawing current for over a minute.