ROOTING OUT RESISTANCE: ELIMINATING THE HIDDEN VARIABLE

“Mill scale is an oxide, which is a poor conductor of electricity,” adds Erpelding. “So you really need to be sure that both the weld joint and the area where the work clamp is placed are free of mill scale and other contaminants.”

Another source of work clamp resistance is a tension spring that is too loose. If the work clamp’s spring tension is insufficient to ensure close contact with the work piece, the result can be increased resistance and poor welding performance. Crackling or popping while you’re welding, as well as sparks coming from the work clamp, are both signs of a clamp that is too loose. In some cases, the work clamp can actually arc to the base metal, which will also create increased resistance.

Although more common in the work lead, the work clamp cable can also become frayed and lead to increased resistance. Areas along the cable that are unusually hot or that are much easier to bend than the rest of the cable are common signs that the cable is creating resistance. Here are some signs and/or reasons that your clamp/work connection may be the cause of trouble:

• Damaged clamp spring
• Insufficient clamp spring tension, causing cracking and popping sounds or sparks coming from clamp
• Rounded clamp ends on both jaws
• Clamp welded to work piece
• Excess spatter on clamp
• Work connection is hot to the touch
• Excessive flexibility in cable
• Lugs at front of machine are not tightened down

TROUBLESHOOTING: THE WORK LEAD
The work lead (MIG gun, TIG torch and Stick stinger) is the other part of the circuit where excessive resistance occurs. Most commonly, the work lead becomes damaged over time as the individual copper strands in the cable stretch and compress and eventually break – gradually lowering the voltage that can flow through the welding circuit.

“Your work lead constantly flexes, stretches and compresses; it’s simply what is demanded of the welding equipment, but it also causes the components to become brittle and break over time,” explains Erpelding. “As the individual strands within the cable break, less electricity is able to flow through the cable and resistance increases. That resistance creates heat, which further damages the remaining strands and makes them less resilient to the continued flexing of the cable.”

Broken strands within the cable also reduce output at the arc, and as welders notice the gradual lessening of welding performance, they will turn up the voltage to compensate. Pushing more power through a narrower channel increases electrical resistance, heating up the remaining work lead strands. “If it seems like you’re continually having to increase your current at the power source, the best way to determine if it is being caused by resistance is to use a volt meter to confirm that the power at the output stud of the machine is the same that is being delivered at the point of the arc,” says Erpelding.

One frustrating phenomenon that welders should be aware of is that flexing a damaged cable in a certain direction (e.g., clockwise) can make the problem of poor welding performance seem to disappear. When the welder rotates the cable counterclockwise, however, the problem returns. This intermittent problem is caused when the torsion of the cable (clockwise in this instance) actually improves the connection of the broken cable strands by “squashing” them together. Counterclockwise torsion does the opposite, drawing strands apart and interrupting the connection.

The couplings between the power source, cable, gun and consumables can also loosen and degrade as the repeated bending and twisting can loosen these connections and create increased resistance. In the case of gas-shielded processes, resistance-caused heat in the cable can also melt the rubber shielding of the gas tube, within which is contained the welding wire and liner. If this occurs, the cable will deliver the current to the gun liner and electrode, causing them to arc and fuse together.

Another common root cause of resistance-related issues is the use of cables, both work lead and ground clamp, that are undersized for the duty cycle of the application – for instance, 150 amp cables for work that consistently requires 180 amp output. Here are some signs and/or reasons that your work lead may be the cause of trouble:

• Welding lead cable is hot to the touch
• Loose output studs
• Welding gun is too hot to handle
• Gas tube breaks
• Intermittent wire feeding and welding performance
• Poor arc starting

MENTAL CHECKLIST
When faced with seemingly random interruptions in good welding performance, searching for sources of resistance in the welding circuit should be any welder’s first course of action. To check for resistance-related problems, visually inspect the entire welding circuit beginning and ending at the power source. Is the work clamp located close enough to the weld joint? Is it clamped securely to an area free of paint, mill scale and other contaminants?

Then move on to physically checking that all connections are clean and tight, that the power cables are not excessively soft and spongy or hard and brittle and that there are no areas that are unusually hot to the touch. With experience, pinpointing and rooting out resistance is a straightforward task that can be accomplished by carefully checking the areas where it can occur. Then, getting back to the job at hand is usually as simple as replacing the malfunctioning part. Sometimes the simplest things are the cause of the most frustrating problems.