Welding cable sizing: amps, lead length and voltage drop
Published Sep 30, 2026
Welding leads are sized differently from building wire. There is no NEC table for the electrode and work leads; the sizing comes from the welder's output current, the duty cycle and the total length of the circuit. Undersized leads run hot and waste voltage, which shows up as a weak, unstable arc.
What sets the size
Output current. Size for the maximum amperage you will actually weld at, not the input rating of the machine.
Total circuit length. Current flows out through the electrode lead and back through the work lead. Add both together. A 50 ft stinger and a 50 ft ground is a 100 ft circuit.
Duty cycle. A machine rated at 60 percent duty cycle welds for 6 minutes of every 10. Leads that carry current for most of the cycle need more copper than leads used in short bursts.
Voltage drop. Many lead charts published by welder makers are built around a drop of about 4 V in the leads. More than that and the arc voltage at the work falls noticeably.
Checking a size by voltage drop
Welding leads carry DC (or low-frequency AC), so the simple resistance formula works. Using the copper resistance values from NEC Chapter 9, Table 8 as an approximation (welding cable has much finer strands, but about the same copper area):
Drop = I x R x total length ÷ 1,000
Here the total length already includes both leads, so there is no factor of 2.
Example: 200 A, 100 ft total circuit.
| Size | Ohms per 1,000 ft (copper) | Drop at 200 A, 100 ft |
|---|---|---|
| 2 AWG | 0.194 | 3.9 V |
| 1 AWG | 0.154 | 3.1 V |
| 1/0 AWG | 0.122 | 2.4 V |
| 2/0 AWG | 0.0967 | 1.9 V |
2 AWG keeps the drop just under 4 V. At 150 ft total, 2 AWG would lose 5.8 V, so 1/0 (3.7 V) is the better choice. This is a check, not a replacement for the chart that came with your machine: always compare with the manufacturer's recommendation, which also accounts for heating at the rated duty cycle.
Class K or Class M
Welding cable is made with very fine strands so it stays flexible. The two common stranding classes are:
- Class K: fine stranding (30 AWG strands). Flexible and a little lower in cost.
- Class M: extra-fine stranding (34 AWG strands). Noticeably more flexible, easier on the welder's wrist, and a good choice for the stinger lead.
Both carry the same current for the same gauge. The choice is about handling, not capacity.
Jacket
Most welding cable has an EPDM, neoprene or similar rubber jacket made to take abrasion, oil and heat. Temperature and voltage ratings vary by maker, so check the product specifications and the jacket legend.
Welding cable is not building wire
Plain welding cable is not a listed building wire. Do not use it as a feeder or pull it through conduit in place of THHN or XHHW-2 unless the jacket also carries a building wire rating such as RHH or RHW-2. For battery banks and inverters, use a cable listed for that job; see our battery cable range.
Shop welding cable
- 2 AWG Class K and 2 AWG Class M
- 1/0 Class K and 1/0 Class M
- 2/0 Class K and 4/0 Class K
- All sizes in industrial cable
The sizing method above is general guidance. Your welder's manual and the lead chart from its manufacturer are the reference for your machine.