Plasma cutters explained: rated cut, sever cut and the air behind them
What a plasma cutter is, why the thickness on the listing is not the thickness you can cut cleanly, and the compressed air and power it needs.
A plasma cutter turns compressed air and electricity into a jet hot enough to cut steel like a hot knife through wax. For a home shop it replaces hours with an angle grinder. The listings, though, lead with a number you should not plan around.
Three figures decide whether a plasma cutter suits you: its clean cut thickness (not the sever thickness in the headline), the air it needs in CFM at a stated pressure, and its input current. Makers do not always publish all three.
How a plasma cutter cuts
Inside the torch, an arc (an electrical discharge) passes through a stream of compressed air and heats it until it ionizes into plasma. A small nozzle squeezes that into a fast, narrow jet. The jet melts a thin line through the metal and blows the molten metal out the bottom. The work clamp completes the circuit, so the metal must conduct electricity.
Terms you will meet:
- Pilot arc. The torch can start its arc without touching the work, which helps on painted, rusty or expanded metal.
- Drag cutting. The torch tip rests on the work as you cut, which steadies your hand. Check that the consumables fitted allow it.
- Consumables. The electrode and nozzle in the torch wear out and are replaced regularly. Wet or oily air wears them faster.
Clean cut versus sever cut
This is the plasma version of the amps on a welder’s badge. A figure such as “cuts up to 3/4 inch” is usually the sever thickness: the most the machine can get through, slowly, with a ragged edge. The clean cut figure is lower, sometimes much lower.
Published figures for one machine show the gap, and show why the source matters. For the YesWelder MCT-520’s 50 amp cutter, YesWelder’s own documents disagree with each other, so we print the lower of each pair:
| YesWelder MCT-520 | On 110 V | On 220 V |
|---|---|---|
| Cut current range | 20 to 35 A | 20 to 50 A |
| Clean cut | 8 mm (about 5/16 in) | 12 mm (setting chart; the product page says 13 mm) |
| Sever cut | 12 mm (setting chart; the product page says 13 mm) | 16 mm (product page; the setting chart says 18 mm) |
| Duty cycle, cut mode | 60 percent at 35 A | 60 percent at 50 A |
| Max input current, cut mode | 40 A | 39 A |
| Air flow | 2.8 to 3.5 CFM (product page only) | Same |
| Air pressure | 45 to 70 PSI (product page); 50 to 60 PSI (setting chart) | Same |
Sources, checked 2026-09-19: YesWelder MCT-520 product page, operator’s manual and setting chart.
By contrast, the ARCCAPTAIN MIG205MP manual gives a cutting speed chart and an air pressure, and no rated cut thickness and no air flow figure at all. For that machine, both are “Not published”.
The air behind the cut
A plasma cutter needs a steady supply of clean, dry compressed air. Two numbers matter, and you need both:
- Pressure, in PSI, at the cutter’s inlet while air is flowing.
- Flow, in CFM (cubic feet per minute), at that pressure.
A compressor’s tank size only decides how long you can cut before the pump has to keep up on its own. If the pump’s delivery at the needed pressure is below the cutter’s requirement, long cuts will starve. Compressor makers rate delivery at a stated pressure, often 90 PSI, so compare like with like. Moisture in the line ruins consumables and cut quality, so a filter or dryer at the cutter is standard practice.
Published figures for eight cutters, and how to read a compressor label against them, are in plasma cutter air requirements.
Power
Cutting draws real current. In cut mode the MCT-520 lists 40 amps maximum input on 110 volts and 39 on 220. The same limits apply as for welders: a household outlet supplies about 2,400 watts. See welder amp draw and what size breaker a welder needs. Duty cycle applies to cutting as well.
Standalone or combo
A combined welder and cutter saves space and money, and means one machine down takes out both jobs. Two of the picks in our multiprocess roundup include a cutter. A standalone cutter usually publishes fuller cutting specs. We rank seven in best plasma cutters.
Safety
Plasma cutting throws molten metal out of the underside of the cut, often several feet. Clear the area below and behind the work. The arc is bright enough to need a proper filter: see the plasma rows of the helmet shade chart. Cutting makes fume, more so on painted, plated or galvanized metal, so keep air moving away from you. Never cut a container that has held fuel or anything flammable. The general gear list is in welding for beginners.
Frequently asked questions
What is a plasma cutter?
A machine that cuts electrically conductive metal with a narrow jet of ionized gas. An arc inside the torch heats compressed air until it becomes plasma, and the jet melts the metal and blows it out of the cut. It cuts steel, stainless, aluminum and copper, and does not cut wood, plastic or glass.
What is the difference between rated cut and sever cut?
Rated or clean cut is the thickness the machine cuts at a reasonable speed with a tidy edge. Sever cut is the most it can get through at a crawl, leaving a rough edge that needs grinding. Listings tend to headline the sever figure. Plan your purchase around the clean cut number.
Do I need an air compressor for a plasma cutter?
Yes, unless the cutter has one built in. The cutter's manual states a pressure and an air flow. Your compressor has to deliver that flow continuously at that pressure, and the air has to be dry. Some makers publish pressure and leave out the flow figure, which makes the compressor impossible to size from their documents.
What lens shade do I need for plasma cutting?
The OSHA minimum is shade 8 for plasma cutting under 300 amps where the arc is clearly seen. The American Welding Society suggests lighter shades at the low currents home cutters use when the arc is hidden by the workpiece. Both are set out in our helmet shade chart. Sunglasses and grinding shields are not enough.
Can a plasma cutter run on a household outlet?
Small ones are sold for 120 volts, with reduced output. As with welders, check the input current in the manual. The YesWelder MCT-520 lists a 40 amp maximum input in cut mode on 110 volts, which is well beyond a household circuit at full output.