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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.

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  • \$\begingroup\$ Fusing current for AWG8 copper is well over 400 amps... \$\endgroup\$
    – PlasmaHH
    Commented Jan 15, 2016 at 9:07

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The AWG sizes in the table you posted is for electrical installations wires/cables buried in the walls. The wire itself can hold as much current until it melts down, the PVC insultation melts faster than copper, therefore special wires do exist that use silicone instead of PVC.
As for welding machine, the wire is not buried, it stays on floor, no fire hazard is present since the person is always present and trained what to do in case of fire.

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