Welding cable is a 600 V, 105°C single conductor with an EPDM or neoprene jacket over extremely fine copper stranding. The stranding is the whole point: it is built to be dragged across a shop floor and coiled thousands of times without work hardening. What it is not is NEC building wire — it carries no THHN, XHHW or USE listing and may not be used as a branch circuit or feeder conductor.
| Property | Value |
|---|---|
| Voltage rating | 600 V |
| Temperature rating | Typically 105°C |
| Insulation | EPDM rubber or neoprene, oil and abrasion resistant |
| Conductor | Fine-stranded annealed bare copper |
| Class K | 30 AWG individual strands — flexible, the common shop grade |
| Class M | 34 AWG individual strands — extra flexible, more expensive |
| Sizes | 6 AWG through 4/0 typically; 8 AWG to 500 kcmil available |
| NEC article | Article 630 covers welder circuits, not the cable itself |
| Building wire use | Not permitted — no NEC conductor listing |
| Typical use | Welding leads, battery cables, inverter DC runs, portable power |
The class describes the stranding, which determines flexibility. Class K uses 30 AWG individual strands and is the standard shop welding cable. Class M uses 34 AWG strands — many more of them, finer — and is noticeably more supple, at a meaningful price premium.
For comparison, ordinary stranded THHN building wire is Class B, with far coarser and fewer strands. A 2/0 Class B conductor has 133 strands; a 2/0 Class M welding cable has over 2000. That is why welding cable coils like rope and building wire does not.
Fine stranding has a practical consequence at the terminals: standard set-screw lugs listed for Class B stranding can crush or fail to grip fine-stranded conductors. Use lugs and terminals specifically listed for fine-stranded cable, or crimp on a proper compression lug.
NEC 310.3(A) requires conductors to be of a type listed in Table 310.4(A) — THHN, THWN-2, XHHW-2, USE-2 and the rest. Welding cable is not in that table. It carries no NEC conductor type letter, so there is no ampacity column that applies to it and no legal basis for installing it as a branch circuit, feeder or service conductor. An inspector will fail it.
The confusion arises because Article 630 governs welder circuits and sets special rules for sizing the supply conductors by duty cycle. Those supply conductors still have to be listed building wire. The welding cable is the flexible lead from the machine to the work, which is equipment wiring, not premises wiring.
The other common use — battery and inverter cables in vehicles, boats and off-grid systems — sits outside NEC premises wiring entirely, or under a different standard such as ABYC for boats. There, welding cable is often a reasonable choice, though marine work should use tinned, ABYC-listed cable rather than bare copper welding cable.
Welding cable ampacity is published by the manufacturer rather than by the NEC, and it is always quoted against a duty cycle. A welder at 60% duty cycle draws its rated current for six minutes in every ten, and the cable cools in between — so the same conductor carries a far higher nameplate current than a continuously loaded building conductor of the same size.
This is why welding cable ampacity charts show numbers that look implausible next to Table 310.16. They are not comparable figures. For a continuous DC load such as an inverter, use the manufacturer's 100% duty cycle column, and size for voltage drop as well — low-voltage DC runs are almost always voltage-drop limited rather than ampacity limited.
For sizing the supply circuit to a welder, see NEC 630.11, which applies a duty-cycle multiplier to the rated primary current, and our welder wiring guide.