The work clamp must be the correct size for the current being used, and it must clamp tightly to the material. Heat can build up in the work clamp, reducing welding efficiency.
Power losses in the work clamp are often overlooked. The clamp should be touched occasionally to find out if it is getting hot.
In addition to power losses due to poor work lead clamping, a loose clamp may cause arcing that can damage apart.
If the part is to be moved during welding, a swivel-type work clamp may be needed, It may be necessary to weld a tab to thick parts so that the work lead can be clamped to the tab.
It is important that the work clamp be securely connected to the work. GMA welding is very sensitive to changes in arc voltage. A loose or poor connection results in increased circuit resistance and a decrease in the arc’s voltage. Voltage changes affect GMA weld quality. A more significant welding problem occurs when this resistance varies during the course of a weld.
Such variations can dramatically adversely affect your ability to maintain weld bead control. GMA welding is more significantly affected by changes in the arc voltage than is SMAW (stick) welding. To be sure that you have a good work connection, remove any paint, dirt, rust, oil, or other surface contamination at the point where the work clamp is connected to the weldment.
Further reference on how arc voltage affecting to arc length: