Figure 2. illustrates the principle of hot wire GTAW welding. Two separate power supplies are used: the GTAW torch with current from the GTA power supply establishes an arc which melts the area under the arc. The wire heating power supply sends current through a circuit from the contact tube through which the wire is fed to the tip of the wire as it contacts the weld pool. Resistance heating of the wire is provided by the power drop across the wire extension as I2R. The resistance is determined by the length of wire stick out and wire diameter with larger wire diameters providing less resistance