Most articles about Article 630 spend their length on the supply side — the duty cycle multipliers, the 200 percent overcurrent allowance, the group arithmetic. That is where the arithmetic is. It is not where the cable is.
The cable gets Part IV. Part IV is two sections long, and one of them is a single sentence. That is not a sign the code does not care about welding cable. It is a sign that the code treats it as a component that does one job in one place, and writes the rule for that job and that place. Here is the whole of it, plus the supply-side provisions that decide what size the cable has to be.
The two rules of Article 630 Part IV
Part IV contains two rules
Article 630 is organized in four parts: general, arc welders, resistance welders, and welding cable. The first three are about apparatus. Part IV is the only part that is about the cable itself.
Section | What it requires |
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630.41 Conductors | Insulation of conductors intended for use in the secondary circuit of electric welders shall be flame retardant |
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630.42 Installation | Cables shall be permitted to be installed in a dedicated cable tray, as provided in (A), (B) and (C) |
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630.42(A) Cable support | The cable tray shall provide support at not greater than 150-mm (6-in.) intervals |
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630.42(B) Spread of fire | The installation shall comply with 300.21 |
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630.42(C) Signs | A permanent sign at intervals not greater than 6.0 m (20 ft), reading CABLE TRAY FOR WELDING CABLES ONLY |
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Notice what is not there: no ampacity table, no temperature rating, no size, and no cable type. All of that arrives from Article 400, where Types W, G, G-GC and the rest are defined and their ampacities set. Article 630 Part IV tells you what the cable must be able to do and where it may be put; Article 400 tells you what it is.
And Part IV is not optional or self-contained. The cable tray article reaches in and pulls it forward. 392.10(B)(1)(b) reads, in full: "Welding cables shall comply with the provisions of Article 630, Part IV." So a welding cable in a tray under Article 392 is governed by Part IV.
The insulation rule is the entire conductor requirement
630.41 is one sentence: "Insulation of conductors intended for use in the secondary circuit of electric welders shall be flame retardant."
That is the whole conductor requirement in Article 630. Not a temperature rating, not a voltage class, not a wall thickness. Flame retardant, for the secondary circuit specifically — the welding side, the electrode conductor and the work conductor, carrying low voltage at very high current.
Notice also what the sentence does not say. It does not say "listed." It says flame retardant, a material property rather than a listing status. In practice the two travel together, because a cable that gets dragged, coiled and stepped on in a shop is going to be listed anyway. But the requirement is the property.
A dedicated tray, and the sign that has to be on it
630.42 opens with permission, not prohibition: "Cables shall be permitted to be installed in a dedicated cable tray as provided in 630.42(A), (B), and (C)."
The word that matters is dedicated. The code makes sure nobody has to guess, requiring a permanent sign at intervals not greater than 6.0 m (20 ft), carrying this legend:
CABLE TRAY FOR WELDING CABLES ONLY
The dedicated welding cable tray rules
The legend is given as words to be reproduced, not a topic to be paraphrased, and the 20-foot interval is the requirement: a single sign at the end of a long run does not meet it.
630.42(B) then sends you to 300.21 for spread of fire and products of combustion. That is the general requirement about openings in fire-rated assemblies, and it means the tray does not get an exemption just because it holds welding cable.
Support at six-inch intervals
630.42(A) is the provision that most often surprises people: "The cable tray shall provide support at not greater than 150-mm (6-in.) intervals."
Six inches, for a cable that gets dragged across a shop floor and coiled by hand. The interval is set for the cable, not for the tray.
The reason sits in the construction, and I am flagging that as my reading rather than a quotation. Welding cable is fine-stranded and very flexible — it has to be — so it has a great many small strands and comparatively little resistance to sagging between supports. Tight spacing keeps it from sagging into a shape it will keep.
Practically, this is a tray specification, not a cable specification. When a customer asks for a welding cable to run in a tray, the question worth asking back is the rung spacing. At 150 mm, 630.42(A) is satisfied. Anything greater, and the installation has a problem no cable choice fixes.
The secondary circuit is not premises wiring
630.15 takes the welder’s secondary circuit out of the grounding and bonding article: "The secondary circuit conductors of an arc welder, consisting of the electrode conductor and the work conductor, shall not be considered as premises wiring for the purpose of applying Article 250."
The informational note explains why, and the explanation is the useful part: "Connecting welder secondary circuits to grounded objects can create parallel paths and can cause objectionable current over equipment grounding conductors." Bond the work lead to a grounded steel bench and you have built a parallel return path through the building’s grounding system, carrying current nobody designed for. The answer is to keep the secondary out of the premises grounding scheme rather than to ground it harder.
For a cable supplier the consequence is concrete: the two secondary leads are a pair of single-conductor cables, not a multiconductor assembly with a grounding conductor. They are bought and coiled that way, and the second conductor in the pair is the return path, not a ground.
Ampacity follows the duty cycle, not the load
This is where Article 630 earns its reputation.
For arc welders, 630.11(A) starts with the rating plate: supply conductor ampacity shall be not less than the I_eff value. If I_eff is not given, you take the rated primary current and multiply it by a factor from Table 630.11(A) chosen by the welder’s duty cycle.
Duty cycle (%) | Nonmotor generator | Motor generator |
|---|
100 | 1.00 | 1.00 |
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90 | 0.95 | 0.96 |
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80 | 0.89 | 0.91 |
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70 | 0.84 | 0.86 |
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60 | 0.78 | 0.81 |
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50 | 0.71 | 0.75 |
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40 | 0.63 | 0.69 |
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30 | 0.55 | 0.62 |
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20 or less | 0.45 | 0.55 |
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Duty cycle multipliers for arc welders
Read the first row and the last: at 100 percent duty cycle the multiplier is 1.00, and it falls from there. The multiplier never exceeds one. That single fact is the difference between this article and the one that governs EV charging cable, where the continuous-load rule pushes the other way and you size at 125 percent. Same trade, opposite arithmetic. A welding circuit is sized on the assumption that the welder is not welding most of the time; a charging circuit is sized on the assumption that it is charging all of the time.
The duty cycle is a computed quantity, not a label you can look up, and the informational note after 630.31 shows the arithmetic. A spot welder on a 60 Hz system — 216,000 cycles per hour — making 400 fifteen-cycle welds per hour has a duty cycle of 2.8 percent: 400 times 15, divided by 216,000, times 100. A seam welder running 2 cycles on and 2 cycles off has a duty cycle of 50 percent. Same machine class, two different multipliers, and the difference is the process, not the box.
Groups of welders are added up differently
630.11(B) handles a shop with several arc welders on one set of conductors, and it does not simply add them.
Welder | Arc welders, 630.11(B) | Resistance welders, 630.31(B) |
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Largest | 100% | 100% of the largest |
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Second largest | 100% | 60% of each of all others |
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Third largest | 85% | — |
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Fourth largest | 70% | — |
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All remaining | 60% | — |
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The arc welder rule counts the two largest at full value, then steps down: 85 percent for the third, 70 percent for the fourth, 60 percent for everything after. The resistance welder rule is blunter — the largest at full value, and 60 percent of all the rest, with no step at all.
Both rest on the same assumption, which the informational note after 630.11(B) states plainly: the calculation considers both the magnitude and the duration of the load while each welder is in use, and how many will be in use at the same time. 630.11(B) also carries an exception permitting lower percentages where the work makes a high duty cycle on an individual welder impossible.
For resistance welders, 630.31(A)(1) takes a different route for machines that run at different settings: not less than 70 percent of rated primary current for seam and automatically fed welders, and 50 percent for manually operated nonautomatic welders. Where the welder is wired for one specific operation with a known, unchanging current and duty cycle, 630.31(A)(2) applies its own multiplier table instead, running from 0.71 at 50 percent duty down to 0.22 at 5 percent or less.
The overcurrent allowance is unusually wide
| Arc welders, 630.12 | Resistance welders, 630.32 |
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Protection for the welder | Not more than 200% of I_max, or 200% of rated primary current where I_max is not given | Not more than 300% of rated primary current |
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Protection for conductors | Not more than 200% of conductor ampacity | Not more than 300% of conductor ampacity |
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Step up to a standard size | Permitted, per 240.6, where the calculation lands between sizes or the setting causes nuisance opening | Permitted, not exceeding the next higher standard rating |
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Two hundred and three hundred percent read as generous against the 125 percent that governs a continuous load, and they are. It is the same arithmetic decision as the multiplier table, taken one step further: if a welder draws its rated current for 3 percent of the hour, the protection can be set for the welder rather than for a current it will never sustain.
FAQ
Does Article 630 name a cable type for welding?
No. Article 630 Part IV gives the insulation property and the installation rules. The cable types and their ampacities come from Article 400.
Can a welding cable share a tray with other cables?
630.42 permits a dedicated cable tray, and 630.42(C) requires a permanent sign at intervals not greater than 6.0 m (20 ft) reading CABLE TRAY FOR WELDING CABLES ONLY.
What support spacing does a welding cable tray need?
Not greater than 150 mm (6 in.), per 630.42(A).
Must the welder’s work lead be bonded to ground?
630.15 says the secondary circuit conductors — electrode conductor and work conductor — are not premises wiring for the purpose of Article 250, and the informational note explains that bonding them to grounded objects can create parallel paths and objectionable current.
Welding cable for a hard-use shop
Everything above is a floor, and it says very little about the cable itself. What fills that gap is the jacket and the stranding.
Welding cable lives in the worst environment in the building: dragged over concrete, coiled wet, left under a bench, stepped on by people wearing steel toecaps. A flame-retardant insulation satisfies 630.41. What survives five years of that treatment is a different question, and it is decided by the jacket compound, the strand count and the strand diameter, and how the assembly handles being flexed at the same point a few thousand times.
Those are the three things worth specifying, and they are also the three things a quotation usually leaves out. Our flexible cable range covers the fine-strand constructions this duty needs, and OEM and ODM projects are where a custom jacket compound or a specific strand configuration gets built.
Two related subjects sit either side of this one. Flame-retardant insulation and how it is listed is covered in our guide to cable listing, and the fire-rated assembly side of 630.42(B) is in the firestop guide. Support spacing outside a welding tray is a separate subject, covered in the pathway support guide.
Sources
- NFPA 70, National Electrical Code, 2011 edition — Article 630 (Electric Welders): 630.11(A) and (B) with Table 630.11(A), 630.12(A) and (B), 630.15, 630.31(A)(1) and (B) with Table 630.31(A)(2), 630.32(A) and (B), 630.41, and 630.42(A) through (C). These are the sections the article quotes or cites. Article 392: 392.10(B)(1)(b). Article 300: 300.21. Article 240: 240.6. Public-domain copy consulted at Internet Archive, gov.law.nfpa.nec.2011.
- Same edition, Article 400 (Flexible Cords and Cables), Table 400.4 and Table 400.5(A)(2), where the cable types used in welding service and their ampacities are set out.
