I saw on youtube some people performing arc welding with "consumable electrodes". At a first glance, I saw that the current flows through all the electrode and the workpiece and my question comes from this fact.
I think that the workpiece doesn't melt because it is usually a lot bigger than the electrode, therefore, it can dissipate the heat a lot faster.
The electrode is thinner though, and I don't understand why the whole electrode doesn't melt if the current that flows through it is high enough to melt the tip of the electrode.
I thought about it and my guess is that it has something to do with the contact resistance at the tip of the electrode being different from that of the electrode's material. The reason is that the power, which is somehow proportional to the heat generated, should be $$P=I^2R$$
But I don't think that the difference between the two resistors is high enough to explain this phenomenon, so I was wondering what part I'm missing!
Best Answer
The electrode's resistance isn't what's heating things up – it's the resistance of the ionized air in the arc!
Hence, things close to the arc get hot, and things farther away don't.