When an electric current flows through a conductor, a certain amount of heat is generated due to the current having to overcome the electrical resistance of the conductor. This is called resistance heating and it is proportional to I2 x R where I is the current and R is conductor resistance. The resistance, R, increases with the length of the conductor and decreases as the diameter increases.
In continuous wire consumable electrode welding, the electrode extension (Figure 1.5) represents an electrical conductor through which a fairly high welding current passes. When the electrode extension is increased, its resistance increases and therefore the magnitude of resistance heating also increases. As a result, for the same welding current, the consumable wire melts at a faster rate and thus increases the deposition rate for the same arc energy. However, this heating effect means that less heat is available to heat and melt the workpiece. Consequently, penetration is reduced and the risk of incomplete fusion type of flaws is increased. Also, due to an increase in voltage drop over a longer electrode extension, a higher voltage setting is usually needed to maintain a constant arc length as with the shorter electrode extension.
The effect of electrode extension for individual arc welding processes is addressed later.