by Jason Becker

Cable Size?

Selecting the right size welding cable for a job can be a very daunting task but it doesn’t have to be. I get this question a lot when I cover welding in the field.

I have seen many instances where the incorrect size cable was used and damage to the welding cable has been the result. Many times, the incorrect cable is selected to do the job simply due to the cost per linear foot of the cable. However, cost should not be the driving factor when selecting the right cable for the job.

In order to select the right size cable, we have to ask ourselves 3 very important questions.

  1. How far from the power source will I be welding?

  2. What is my anticipated amperage that I need to do the job correctly?

  3. What is the rated output and duty cycle of my machine?

In order to perform our task safely, we should ensure that the cable we intend to use will support the necessary current required to do the job. Welding cable is made up of fine strands of copper wire, the wire is coated with an insulator and an exterior coating of synthetic or natural rubber. The exterior jacket helps with flexibility, resists abrasions, and keeps the copper inner core from coming in contact with the workers and environment. The insulation of the cable is rated by the ability to with stand heat.

The typical ratings are 167°F (75°C), 194°F (90°C), and 221°F (105°C). The copper strands inside can withstand much higher temperatures but the coating would melt prior to this and could result in a fire. These cables are typically rated for an ambient temperature of 86°F (75°C). Higher temperatures can result in decreased current carrying capacity so a larger diameter may be needed for the job.

Additionally, welding cables should be spread apart to allow them to dissipate heat during use. Bundling the welding cables closely together can increase the heat to the cables. During use, it is normal for the welding cable to be slightly warm to the touch, but should never be “HOT”. If the cable is hot, it is a good indication that the welding cable is undersized for the amperage being used, or there is resistance built up due to damage to one or more components of the welding circuit. That is why it is a good practice to inspect the welding cable and components prior to welding.

The size of the cable is based off of its cross-sectional area and categorized by the American Wire Gauge (AWG). According to this diagram, smaller wire diameters have a larger number and larger diameter cables have a smaller number, for example a #5 cable would have a cross-sectional area of () where as a 1/0 (pronounce 1 aught) would have a cross-sectional area of (). See Table Below

How far from the power source will I be welding?

In order to determine the appropriate cable size, we must first determine the distance from the power source (welding machine). This will be the total linear feet of all welding cable needed, this include the work piece clamp and the electrode holder (external wire feeder, TIG Torch etc.). For instance, if the work will be taking place 100ft from the power source, you will most likely need 200ft. of welding cable to complete the electrical circuit.

What is my anticipated amperage that I need to do the job correctly?

This is a very crucial part of determining the appropriate cable size as selecting a size too small will not carry the anticipated current and could cause damage to the cable itself. Think of how a garden hose works. It can only deliver so much water at a time. If we tried to increase the amount of water in the garden hose, the hose would fail. This is the same concept when dealing with wire size and current. A given size will only be able to handle a certain amount of current before it absorbs too much heat and fails. This can result in melting the insulated jacket, damaging the cable and possibly starting a fire.

What is the rated output and duty cycle of my machine?

Machines are based off of their rated output and duty cycle. The rated output is the maximum amount of current that the machine can produce. The output rating is typically in the name of the machine such as Rebel 285. The maximum output would be 285 amps.

Duty cycle is a measure of output capacity expressed in percentage based on a 10-minute period. This is the allotted time the machine can perform at the given amperage before the windings of the machine overheat. For example, a machine rated for 250A at 30% would be able to produce 250 Amps for 3 minutes (30% of 10mins.) before the machine hits its duty cycle and shuts down. The machine should then cool down for the remaining 7 minutes before welding again. Generally speaking, the higher the output rating, the lower the duty cycle will be and vice versa, as output decreases, the duty cycle will increase. The outputs and duty cycle for your machine should be listed on the back of the machine or on the data plate.

Let’s try an exercise. If you needed to have 150 amps and your weldment was 220ft. from the power source, what size cable would be required?

Image from Lincoln Electric

If you said a #2 cable, you are correct.

Keep in mind that in order to ensure you are getting the set amperage in your cables to do the job, you need to keep your cables, attachments and accessories in good working order. All equipment should be inspected prior to use. If terminals on the power source are loose, connections and linkages are not securely connected, the cables are nicked, cut or damaged, you will not get the desired output. Damaged cables can cause additional resistance in the welding circuit and therefore restrict the welding current. These areas will also get hot due to the resistance and could cause additional issues. Always ensure the equipment is serviceable and in good working order.

Workpiece clamps are another item that is usually the culprit of amperage drop. Ensure that it is securely connected and not damaged, and make sure you get a good quality workpiece clamp, a lot of the clamps that come with power sources these days are rather cheap and flimsy and made from materials that do not conduct electricity as well as they should. Go ahead and spend the extra couple dollars on a solid copper/brass workpiece clamp. Your welding will be much easier if you make your setup as electrically efficient as possible. I hope you found the information in this article educational and would like to thank you for taking the time to read it. Until next time, Make Every Weld Better Than Your Last.

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