Key takeaways
- Lincoln's answer is a 50 A super lag fuse or time-delay breaker on each hot line, a NEMA 6-50R receptacle, and #10 or larger copper in conduit. Over 100 ft (31 m), use #8.
- The AC225 draws 50 A at 230 V at its rated 225 A output, at a 20 percent duty cycle. NEC Table 630.11(A) multiplies a 20 percent welder's input current by 0.45, so the wire needs 50 x 0.45 = 22.5 A. #10 copper is 30 A even in the 60 C column.
- NEC 630.12 lets the breaker go up to 200 percent of the welder's input current and up to 200 percent of the wire's ampacity. On #10 at 30 A that ceiling is 60 A, so Lincoln's 50 A sits inside it.
- "50 A on #6" passes every rule but is heavier wire than Lincoln asks for. "30 A on a dryer circuit" carries the wire fine but puts a 50 A welder on a breaker rated for 60 percent of its draw.
- Lincoln's newer Precision TIG 225 makes the same point in writing. Use a super lag fuse or delay-type breaker, 50 A or up to 70 A if dedicated, because smaller breakers cause nuisance trips from inrush current.
Three answers circulate for this welder: 30 A on a dryer circuit, 50 A on #6 wire, and Lincoln's own 50 A on #10. Only the last is what the maker prints. It is also the one that looks wrong to anyone who sizes wire to the breaker.
It is not wrong. The National Electrical Code (NEC) has a separate article for welders, Article 630. Below, Lincoln's figures are set beside that article's arithmetic, and each answer is checked against both.
The terms this answer turns on
Input current is what the welder draws from the wall, not what it puts into the arc. Lincoln's spec sheet for the AC225 (product K1170) lists "Input Current @ Rated Output" as 50 A at 230 V. The code calls this the rated primary current.
Rated output is the welding current the machine is rated to deliver. For the AC225 it is 225 A at 25 V. The input current of 50 A goes with that top setting.
Duty cycle is how long the arc can run before the welder needs to cool. Lincoln's manual bases it on a ten minute period. The 60 Hz welders are rated at 20 percent. That "means that the arc can be drawn for 2 minutes out of each ten minute period" without danger of overheating.
Ampacity is how much current a wire can carry all the time without overheating. It depends on wire size and on the insulation's temperature rating. That is why wire tables have 60 C and 75 C columns.
A super lag fuse is a fuse built to carry a short surge without blowing. Lincoln's Precision TIG manual names the breaker version too. It is a breaker with "a delay in tripping action that decreases as the magnitude of the current increases," also called inverse time or thermal-magnetic.
Inrush is the surge a welder pulls in the instant it is switched on, before it settles. No Lincoln document checked here gives its size for the AC225.
What Lincoln's manual says
Lincoln's operator's manual for the AC-225-S and AC/DC 225/125 (IMT237-P, May 2022) has a short installation section. This is everything in it that sets the circuit.
| Item | Lincoln's instruction |
|---|---|
| Receptacle | NEMA Type 6-50R, within reach of the welder's plug |
| Wire | "Three #10 or larger copper wires are required if conduit is used" |
| Long runs | Over 100 ft (31 m), "#8 or larger wire in conduit will be needed to prevent excessive voltage drops" |
| Protection | "Fuse the two hot lines with 50 ampere super lag type fuses" |
| Disconnect | If one is used, two poles, "both should be fused for 50 amperes" |
| Grounding | Center contact of the receptacle; a green wire in the cord bonds the frame |
The manual also says the installation must "meet the United States National Electrical Code and local code requirements." So Lincoln does not claim to override the code. The code agrees with it, through Article 630.
The spec sheet adds that the 60 Hz AC225 runs on 230 V single phase and ships with a NEMA 6-50P plug.
Why a welder can have a small wire and a big breaker
Most circuits size the wire on the full current, and the breaker protects the wire. A welder is treated differently because it works in bursts.
The wire: Table 630.11(A)
NEC 630.11(A), as printed in the 2008 edition, says the wire must carry at least the welder's I1eff, if the rating plate gives one. I1eff is the effective input current, already averaged over the duty cycle. If the plate does not give it, take "the rated primary current in amperes given on the welder rating plate." Multiply it by the factor in Table 630.11(A), "based on the duty cycle of the welder."
For welders that are not motor-generator sets, which includes the AC225, the table reads:
| Duty cycle | Multiplier |
|---|---|
| 100% | 1.00 |
| 80% | 0.89 |
| 60% | 0.78 |
| 50% | 0.71 |
| 40% | 0.63 |
| 30% | 0.55 |
| 20% or less | 0.45 |
The table rests on the fact that wire heats slowly. A load that runs 2 minutes in 10 heats it less than the same load running all the time.
Mike Holt's Code Q&A for EC&M (September 2011) works the same method on a different welder. Take a 40 A input at 50 percent duty: 40 A x 0.71 = 28.4 A, so the wire must be good for at least that. His answer is 10 AWG.
This is not a new rule. Wisconsin's electrical code of 1964, chapter E 630, prints the same 0.45 for a duty cycle of "20 or less". Its E 630.12 sets the same two 200 percent limits described next. The method is more than sixty years old.
The breaker: 630.12 and its 200 percent
NEC 630.12(A), in the same 2008 text, sets the welder's protection at "not more than 200 percent of I1max." I1max is the highest input current at full output. If the plate does not give it, the limit is "not more than 200 percent of the rated primary current of the welder."
630.12(B) adds a second limit for the wire itself. Conductors that feed a welder "shall be protected by an overcurrent device rated or set at not more than 200 percent of the conductor ampacity."
Both limits apply, and the lower one wins. The section also allows "the next higher standard rating" in two cases. One is where the figure is not a standard breaker size. The other is where the specified one "results in unnecessary opening of the overcurrent device." That phrase is the reason for the whole section: a breaker sized to the averaged wire current would open on the welder's peaks.
Worked through: the AC225 at 230 V
Take the AC225 on a 230 V supply, as the spec sheet lists it, and walk it through the code.
Step 1, the input current. The spec sheet prints one figure: 50 A at 230 V at rated output. It gives no I1eff, so the walkthrough uses the multiplier. If your own machine's rating plate prints an I1eff, use that instead.
Step 2, the wire. The AC225 is a 20 percent duty welder, so the factor is 0.45.
50 A x 0.45 = 22.5 A
Cerrowire's ampacity chart is built on the 2017 NEC, with no corrections applied. For copper it gives:
| Copper | 60 C (NM-B, UF-B) | 75 C (THW, THWN) | Clears 22.5 A? |
|---|---|---|---|
| 12 AWG | 20 A | 25 A | Not at 60 C |
| 10 AWG | 30 A | 35 A | Yes, in both columns |
| 8 AWG | 40 A | 50 A | Yes |
| 6 AWG | 55 A | 65 A | Yes |
#10 at 30 A clears 22.5 A with 7.5 A to spare, even in the lowest column. That is why Lincoln can ask for #10.
Step 3, the breaker ceiling. Work both 630.12 limits:
| Limit | Arithmetic | Ceiling |
|---|---|---|
| 630.12(A), welder | 50 A x 2.00 | 100 A |
| 630.12(B), #10 wire at 30 A | 30 A x 2.00 | 60 A |
| 630.12(B), #8 wire at 40 A | 40 A x 2.00 | 80 A |
On #10 the wire limit is the lower one, 60 A. Lincoln's 50 A is under it, and so is the 100 A welder limit.
Step 4, the floor. The code sets a ceiling, not a floor. The floor comes from the welder. Lincoln asks for 50 A, which is 100 percent of the input current at full output, on a time-delay device that rides through the start.
So the walkthrough lands where the manual does: 50 A super lag protection on #10 copper, with a 6-50R receptacle. A 60 A breaker on #10 also passes the code arithmetic, but it is not what Lincoln asks for. Lincoln pairs the 6-50R with 50 A. Use 50 A.
The three answers, settled
50 A on #10: right, and it is Lincoln's
This is the manual's instruction, and it passes 630.11 and 630.12 with room left over. It looks wrong only through the habit of matching wire to breaker, which Article 630 sets aside for welders.
50 A on #6: safe, but more than Lincoln asks for
#6 copper is 55 A in the 60 C column, so it carries a 50 A breaker without leaning on Article 630 at all. That is why it gets recommended. It is the wire you get when you size the wire to the breaker, as on an ordinary circuit.
It is not wrong. It costs more copper than the welder needs. It does make sense if the circuit may later feed something other than a welder, since 630.12 applies only to welders.
30 A on a dryer circuit: not what Lincoln specifies
Take a 30 A dryer circuit wired in #10. The wire is fine, since #10 clears the 22.5 A the code asks for. The breaker is the problem.
At rated output the AC225 draws 50 A. That is what the breaker sees while the arc is lit:
50 A / 30 A = 1.67, or 167 percent of the breaker's rating.
A breaker does not trip the instant it passes its rating. It trips on heat and time, as our table saw and dust collector circuit guide explains. So a 30 A breaker may hold for a short weld at low settings. That is why people report it working. But at 167 percent it is carrying far more than its rating, and nothing in Lincoln's documents or the code supports running the welder there.
The surge on switch-on is the other half. Lincoln's Precision TIG 225 manual says it plainly. "Using fuses or circuit breakers smaller than recommended may result in 'nuisance' shut-offs from welder inrush currents even if not welding at high currents." That warning is printed for the TIG, not the AC225, and no Lincoln document here puts a number on the AC225's inrush. But it is Lincoln explaining why it asks for 50 A on a delay-type device.
So the dryer circuit can carry the AC225 only at reduced output, at best. Lincoln prints no input current for settings below 225 A. No published figure says which setting a 30 A breaker will hold.
There is a fitting problem too. Lincoln's manual names a 6-50R receptacle for the welder's plug. Running on a dryer outlet means an adapter or a plug change, and Lincoln's manual describes neither.
Lincoln's newer machine says the same thing in plainer words
The Precision TIG 225 manual (IM895, May 2022) prints more detail than the AC225 manual.
| Figure | Precision TIG 225 at 230 V | AC225 at 230 V |
|---|---|---|
| Input current, effective (I1eff) | 39 A | not printed |
| Input current at full output | 85 A (I1max) | 50 A |
| Duty cycle | 225 A at 10%, 180 A at 20% | 225 A at 20% |
| Protection Lincoln asks for | Super lag fuse or delay breaker, 50 A, up to 70 A if dedicated | 50 A super lag fuses |
| Receptacle | 6-50R | 6-50R |
Lincoln's note on the TIG reads: "Use a Super Lag type fuse or circuit breaker with a delay in tripping action. Models with NEMA 6-50P plug may be used with a 50 amp protected 6-50R receptacle, or with a maximum 70 amp protected 6-50R receptacle if dedicated for the welder." It adds that its wiring and protection figures are "based on the 2005 U.S. National Electric Code," and that its input ratings include a 20 A load on the machine's 115 V outlet.
Walk the TIG through the same code steps. With an I1eff of 39 A in the spec table, the wire must carry 39 A. #10 at 35 A in the 75 C column falls short, and #8 at 40 A in the 60 C column clears it. The welder limit is 85 A x 2.00 = 170 A. The wire limit on #8 is 40 A x 2.00 = 80 A. Lincoln's 50 A, and its 70 A for a dedicated circuit, both sit under 80 A.
Two lessons carry over to the AC225. Lincoln picks the bottom of the code's band, not the top. And it asks for a delay-type device because, in its own words, smaller ones trip on inrush.
Long runs: when #10 becomes #8
Lincoln's manual switches to "#8 or larger wire in conduit" for runs over 100 ft (31 m), "to prevent excessive voltage drops." That is not an ampacity rule, since #10 still carries 22.5 A at any length. It is about volts lost along the wire, which grow with length. The same arithmetic sets the gauge of a tool's cord in our extension cord gauge guide. For the welder, Lincoln has done the sum: #8 past 100 ft.
What this answer does not cover
This page reads Lincoln's figures against the NEC text as published. It does not tell you what your inspector will accept.
- Local code and the inspector decide. The NEC text quoted here is the 2008 edition, through a reproduction, and the 1964 Wisconsin code. Later editions may number or word things differently. Your area may have adopted a different edition or amended it. The authority having jurisdiction, usually the local inspector, has the final word.
- The AC/DC 225/125. It shares the same manual and the same circuit instructions. Its input current was not on the spec sheet checked here, so the arithmetic above is for the AC225 only.
- 50 Hz machines. The K1290 export model is 220 V, 50 Hz, 15 percent duty and 63 A input. The figures above do not apply to it.
- GFCI protection. Whether a welding receptacle in a garage needs ground-fault protection is a separate code question. This page does not settle it.
- Receptacle rating against breaker size. Lincoln's 70 A figure for its TIG on a dedicated 6-50R is Lincoln's statement, made on the 2005 NEC. Whether your inspector accepts a breaker above 50 A on that receptacle is their call.
- Hot spaces and bundled wire. Cerrowire's figures carry no temperature correction. Wire in a hot attic or bundled with other circuits can need a larger size.
- Published figures only. Everything here comes from Lincoln's manuals and spec sheet and from the code text. No welder was put on any circuit for this page.
Have a qualified electrician do the work, as Lincoln's manual says.
Where the welder sits in the shop
A 240 V saw lands somewhere else. Motors fall under Article 430, which sizes wire at 125 percent of a table current, as worked in our 3 HP table saw circuit guide. Plan both outlets before the wall storage goes up. The AC225's rods need care once the can is open, as set out in how to store opened 7018 rods. Cutting gas brings its own spacing rules, in the oxygen and acetylene storage guide.
The thirty-second check
- Read the rating plate: input current at rated output and duty cycle. For the 60 Hz AC225 that is 50 A at 230 V and 20 percent.
- Size the wire on the duty cycle:
50 x 0.45 = 22.5 A. Lincoln asks for #10 copper or larger in conduit, #8 past 100 ft. - Fit a 50 A super lag fuse or 50 A double-pole breaker with a delay in its trip. That is under the code's 60 A ceiling on #10.
- Mount a NEMA 6-50R for the welder's 6-50P plug. Skip the 30 A dryer outlet.
- Take the plan to your inspector, who has the last word.