Yes, a phase converter can run a 3 phase welder on single phase power. American Rotary and Phoenix Phase Converters both say a rotary phase converter can run one. American Rotary's welder guide names MIG, TIG and stick welders. You size the converter from the input numbers on your welder's nameplate, using the rule from the maker whose converter you buy. The makers don't all use the same rule. At Built for Production, we take your welder's nameplate numbers, run them through each maker's published rule and show you the math. That way you can check the size yourself before you order.
To size yours, enter your welder's nameplate numbers in our phase converter sizing calculator and choose Welder from its Machine list. Or call with the numbers and we'll work them for you.
Can a phase converter run a 3 phase welder?
Yes. American Rotary and Phoenix Phase Converters both publish welder guides for their converters. American Rotary's is "How to Choose a Three Phase Converter for Welders and Metalworking." Phoenix's is "How to Choose a Phase Converter for a Welder," and Phoenix also has a welding page that lists the converters it offers for welders.
MIG. TIG. Stick.
American Rotary's welder guide says a three phase converter can run MIG, TIG and stick welders.
Per American Rotary, welder guide, read 2026-09-25. Installation by a licensed electrician.
Can I run a 3 phase welder on single phase without a converter?
Sometimes. Some welders list both a single phase and a 3 phase input rating on the nameplate or in the manual. Check your welder's manual, or ask the welder's maker, before you buy a converter. If your welder is rated for single phase input, you may not need a converter at all. If it's 3 phase only, our guide to running 3 phase machines on single phase power covers each way to do it.
What to read off your welder's nameplate
Every maker's rule starts from your welder's input numbers. Look on the nameplate, or in the manual if the plate is hard to read, for these:
- Input voltage and phase, such as 230V, 3 phase.
- Input amps at the voltage you'll run it on.
- Input kVA or kW, if the plate lists it. Our calculator's welder option takes amps, kVA or kW.
- The welder type. Phase-A-Matic's welder sizing form asks whether yours is a "Transformer/Rectifier" or a "Motor Generated" welder.
Write these down before you call or use the calculator. Every rule below works from them.
What size phase converter do I need for a welder?
The size depends on whose converter you buy, because each maker publishes its own welder rule.
| Maker | Document | The rule | What it starts from |
|---|---|---|---|
| American Rotary | Welder guide | "3-phase amps x 1.6 = required single-phase amps." Then: "Required single-phase amps x 1.2 = required single phase amps with 20% cushion." | Your welder's 3 phase input amps |
| American Rotary | Welder guide | "As a rule of thumb, you want to go 2:1, with your phase converter's capacity at 2 times the size of your equipment load." | The size of the load |
| Phoenix Phase Converters | Welder guide | "size the phase converter at twice the welder's power needs." | The welder's power |
| Phoenix Phase Converters | Welding phase converters page | Size a single welder to its full input kVA or hp equivalent. | The welder's full input kVA or hp |
| North America Phase Converters (NAPCco) | Sizing page | Lists "Welder" as a "Resistive" load. Its charts size resistive loads by Total Amps, Total VA (Total kVA on its Smart-Boost chart) and Total kW. | Amps, VA or kW. The page doesn't say which. |
| Phase-A-Matic | Welder page | No published formula. You send your welder's details through its sizing form. | Your answers on the form |
These rules don't agree, and Phoenix's two pages give two different figures for the same welder. We list every rule, with the math, so you can compare them for your welder. Each rule applies to that maker's own converters. If you haven't picked a maker yet, the worked example below shows how different the results are for one welder. If you pick Phoenix, ask Phoenix which of its two pages applies to your welder.
Worked example: a 230V, 30 A, 3 phase welder
Here's the math for a hypothetical welder, so you can see each rule applied to the same nameplate numbers. Say the nameplate reads 230V, 3 phase input, 30 A. Its input works out to 230 x 30 x 1.732 / 1,000 = 11.95 kVA, or about 12 kVA. (1.732 is the square root of 3. It's the standard multiplier for 3 phase power.)
| Maker's rule | The math | Result |
|---|---|---|
| NAPCco, Pro-Line chart | 30 A and 12 kVA against the Total Amps and Total VA columns. PL-20 lists 25 in Total Amps and 11 in Total VA, so it falls short on both. | PL-25, its 25 hp Pro-Line unit, which lists 30 in Total Amps and 15 in Total VA |
| NAPCco, Smart-Boost chart | The same check. SB-20 lists 25 in Total Amps and 11 in Total kVA, so it falls short on both. | SB-25, its 25 hp Smart-Boost unit, which lists 30 in Total Amps and 13 in Total kVA |
| American Rotary, amp method | 30 A x 1.6 = 48 A. Then 48 A x 1.2 = 57.6 A. | 57.6 required single phase amps, with the 20% cushion |
| American Rotary, 2:1 rule of thumb | 2 x the equipment load | The guide doesn't say which nameplate figure counts as a welder's load |
| Phoenix, welder guide | 11.95 kVA x 2 = 23.9 kVA | About 24 kVA of converter capacity |
| Phoenix, welding page | Full input | About 12 kVA of converter capacity |
| Phase-A-Matic | No published formula | Send your nameplate numbers through its welder form |
Of these rules, only NAPCco's chart ends at a converter you can order, because NAPCco names each unit by its hp. For this welder, that's its 25 hp units. NAPCco's page doesn't say which nameplate figure to match, though. Its chart also has a Total kW column. If you match your welder's kW against that column instead, the chart can point to a larger unit. Check with NAPCco which column applies before you order.
The other makers' welder pages give a capacity figure in amps or kVA, not an hp size. To turn that figure into a converter you can order, ask the maker or call us.
Your welder's numbers will be different. Run your own numbers in the sizing calculator by choosing Welder from its Machine list, or call with your nameplate and we'll work each maker's rule for you.
Do I size down because a welder doesn't run all the time?
No. American Rotary and Phoenix both say not to size down for duty cycle. American Rotary's welder guide says that when you size the converter, "you don't need to consider the duty cycle of your welding equipment." Phoenix's welding page says to size a single welder to its full input and not to derate it for duty cycle.
What if I run two welders, or a welder and other machines?
For several welders, Phoenix's welding page says a shop can apply a diversity factor, typically 60 to 70%, because not all the welders will be at full output at the same time.
60 to 70%
Phoenix's welding page: a shop running several welders can apply a diversity factor, typically 60 to 70%, because not all the welders run at full output at the same time.
Per Phoenix Phase Converters, welding phase converters page, read 2026-09-25. Installation by a licensed electrician.
For a welder plus motors, such as a compressor, we haven't found a maker page that shows how to add the two. American Rotary's welder guide says to size on "the total horsepower and overall amp draw." It doesn't show how to add a welder rated in amps or kVA to a motor rated in hp. NAPCco's page gives no rule for several loads at once. Our phase converter sizing guide sets out each maker's rule for the motors. To size the welder and the motors together, call with every nameplate.
Rotary or digital phase converter for a welder?
Phoenix offers both types for welding. Its welding page lists its NL Series (standard rotary) and its GPX Digital Series. American Rotary's welder guide is written around rotary phase converters.
A VFD (variable frequency drive) with single phase input is made to run one 3 phase motor. The makers' welder guides cited on this page are all written for phase converters, and none of them give a VFD rule for a welder. Our rotary vs digital vs VFD guide covers how the types differ.
What about a 480V welder?
For a welder that runs only on 480V, the converter maker's engineers need to size the setup. Phoenix's 480V article says, "On its own, a rotary phase converter produces a three-phase voltage that matches the input voltage." That means 240V single phase in gives you 240V 3 phase out. To get 480V 3 phase from 240V single phase, Phoenix pairs a rotary phase converter with a step-up transformer. The maker's engineers size that converter and transformer as a set, so we don't recommend a product for a 480V welder. Call the maker with your welder's nameplate, and ask a licensed electrician whether your service can carry the converter, the transformer and the welder.
Single phase in, 3 phase out, same voltage
Phoenix's 480V page says a rotary phase converter's output voltage matches its input. For a 480V welder, Phoenix pairs the converter with a step-up transformer.
Per Phoenix Phase Converters, 480V page, read 2026-09-25. Ask the maker's engineers or a licensed electrician.
Before you order: service size and install
A licensed electrician installs the converter, and your local inspector may need to sign off. Before you order:
- Ask a licensed electrician whether your shop's electrical service can carry the converter and the welder.
- Plan on a licensed electrician for the install. American Rotary's AD(X) owner's manual says, "Installation should be done by a licensed electrician who is familiar with phase converter installations."
- Talk to your local inspector first if the install will be inspected. American Rotary says to check with the inspector before you order a phase converter, to see what is required to pass inspection.
Per American Rotary, AD(X) owner's manual and page on UL listing, read 2026-09-25. Ask the maker's engineers or a licensed electrician.
We don't give breaker, wire or circuit sizes. Your electrician sizes those for your shop.
Size your welder by each maker's rule
Call or email with your welder's nameplate numbers. We'll run them through each maker's rule and send back each result, with the math. You can compare them and check them before you order. You can also choose Welder from the Machine list in the phase converter sizing calculator. Once you know the size, see our phase converters collection.
Call (855) 923-2610 or email contact@builtforproduction.com.