Calculate a suitable welding return cable size from welding current, cable length, duty cycle and allowable voltage drop.
The welding return cable completes the electrical circuit between the workpiece and the welding power source. Welding current flows through this return path just as it flows through the welding lead.
An undersized, excessively long or poorly connected return cable can introduce unnecessary resistance and voltage drop. The result can include cable heating, connection heating and reduced electrical performance.
The ground cable should therefore be treated as an important part of the welding circuit rather than simply as a connection to ground.
The calculator checks the return cable against current-carrying capacity and voltage drop.
Cable resistance decreases as conductor cross-sectional area increases. A larger cable therefore produces less voltage drop for the same current and length.
The calculator selects the smallest reference copper cable size that satisfies the entered current and voltage-drop requirements.
The return cable has its own resistance. Increasing the distance between the workpiece and welding machine increases the length of the current path.
For example, a 15 metre return cable has approximately twice the conductor length of a 7.5 metre return cable.
Longer return cables can therefore require a larger conductor to maintain a similar voltage drop.
The calculator uses the following approximate reference values for flexible copper welding cable. Actual cable ratings vary by product and operating conditions.
| Cable Size | Reference 100% Capacity | Approx. Copper Resistance |
|---|---|---|
| 10 mm² | 60 A | 1.83 Ω/km |
| 16 mm² | 80 A | 1.15 Ω/km |
| 25 mm² | 110 A | 0.727 Ω/km |
| 35 mm² | 135 A | 0.524 Ω/km |
| 50 mm² | 170 A | 0.387 Ω/km |
| 70 mm² | 215 A | 0.268 Ω/km |
| 95 mm² | 260 A | 0.193 Ω/km |
| 120 mm² | 300 A | 0.153 Ω/km |
| 150 mm² | 340 A | 0.124 Ω/km |
| 185 mm² | 385 A | 0.0991 Ω/km |
| 240 mm² | 450 A | 0.0754 Ω/km |
Using the same cable size for the welding lead and return cable is a simple and conservative approach because both conductors carry the welding current.
In some systems, cable sizing may be determined separately based on the actual return path, duty cycle, cable length and applicable specifications. However, reducing the return-cable size without verifying its current rating can introduce unnecessary heating and voltage drop.
For demanding welding applications, matching the return cable to the welding lead is often the straightforward choice.
The cable is only one part of the return circuit. The ground clamp, cable lug, quick connector, workpiece connection and other terminals must also be capable of carrying the welding current.
A high-current cable connected to an undersized clamp can create a localized hot spot at the connection even though the cable itself is adequately sized.
Keep the contact area clean and secure, and ensure the clamp is firmly attached to suitable conductive material on the workpiece or work table.
A welding machine may operate at a particular current intermittently rather than continuously. Duty cycle describes the proportion of time during which welding current is flowing.
Higher duty cycles create greater thermal loading. Cable selection should therefore consider the applicable duty-cycle rating of the actual welding cable.
The calculator applies a conservative screening factor to the reference current capacity, but this does not replace the manufacturer's duty-cycle rating.
Voltage drop occurs because every conductor has electrical resistance. At high welding currents, even relatively small resistance can produce a measurable voltage loss.
For example, if a return cable has 0.01 Ω of resistance and carries 250 A:
At a 25 V welding voltage, that represents:
Increasing cable cross-sectional area reduces resistance and therefore reduces the voltage lost in the return conductor.
The welding return cable carries welding current back to the welding power source. A protective grounding conductor has a different electrical safety function.
They should not automatically be treated as interchangeable conductors.
This calculator is specifically for the welding work-return cable between the workpiece and welding machine.
What size cable should a welding ground clamp use? The return cable should be adequately rated for the welding current, duty cycle, length and installation conditions. Matching the welding lead size is a straightforward conservative approach.
Can the ground cable be smaller than the welding cable? It can be possible in some applications, but the return conductor must still safely carry the required welding current. The actual cable manufacturer's rating should be checked.
Does return cable length affect voltage drop? Yes. Longer cable produces greater resistance and therefore greater voltage drop at the same welding current.
Should the work clamp have the same current rating as the cable? The clamp and connection system should be suitable for the actual welding current and duty cycle. The weakest component should not limit a properly sized cable.
Why does the welding return cable get hot? Excessive current for the cable size, high duty cycle, damaged cable strands, poor connections or excessive resistance can cause heating.
Is the welding ground cable actually a ground wire? It is normally a welding work-return conductor. It carries welding current back to the power source and is different from a protective grounding conductor.
Does a longer return cable require a thicker cable? Often yes, particularly when voltage drop must be kept low. Increasing conductor size reduces resistance.
Can I use the same size cable for the welding lead and return lead? Yes. Using the same size is a common straightforward approach when both leads carry the same welding current.
Does duty cycle affect return cable size? Yes. Higher duty cycle increases thermal loading and can require greater current-carrying capacity.
Can this calculator size a protective earth cable? No. It is specifically intended for the welding work-return cable. Protective grounding conductors require separate code-based sizing.