An insulated conductor, usually copper, that carries electric current from the welding power supply to the torch and then from the workpiece back to the power supply. Cables should be inspected periodically to assure that insulation is not cracked or damaged and that fittings are tight.
The diameter or size of cable required for a given application depends on the welding or cutting current and the distance from the power supply to the work site.
The use of the steel frame of a building in place of a copper workpiece cable is a widespread but poor practice. This is especially true if the frame of the building is riveted. In this case there is likely to be a considerable voltage drop across riveted joints, and this drop will vary as the riveted connections warm up due to 12R heating. Weld quality is almost certain to suffer from this practice; it is far better to use a copper cable as the workpiece lead.