What's inside
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Match the cutter to the generator
A plasma cutter’s advertised cutting thickness is only part of the buying decision for mobile work. The machine also has to start and run on the generator you can transport, and its air supply has to keep up. Check the cutter’s manual for input voltage, maximum input current, recommended generator capacity and air requirements before buying. Do not size the generator from the cutter’s output amps alone.
As a rough starting point, a 240-volt cutter drawing about 20 amps needs around 4,800 volt-amps while operating; one drawing 30 amps needs around 7,200. Generator capacity is commonly advertised in watts, and the relationship between watts and volt-amps depends on the load and generator. Allow headroom rather than choosing a unit whose rated output exactly matches the arithmetic. The cutter maker’s generator recommendation takes priority.
Look at the generator’s running or continuous rating, not just its larger starting or surge figure. A machine that can briefly supply enough power may still sag or trip when the cutter runs continuously. Voltage drop, long extension cords, other tools sharing the circuit, and a generator operating at altitude or in high heat can reduce the margin further.
Choose a useful output range
For occasional cuts in thin sheet and light repairs, a small 120-volt cutter can be convenient. It is easier to power from a modest generator, but cutting speed and capacity are limited. Many compact units advertise cuts around 1/4 inch, with a slower or less clean cut near their upper limit. If you regularly cut thicker plate, expect to move to a 240-volt machine and a substantially larger generator.
A 30–40 amp, 240-volt class cutter is a practical middle ground for field fabrication. It can handle common brackets, panels and moderate plate, while remaining less demanding than a high-output industrial unit. For frequent cuts near 1/2 inch or more, compare the manufacturer’s rated cut with its recommended severance capacity. Severance means the machine may get through the material, but the edge can be rough and the cut slow. Buying to the severance number leaves little reserve for real work.
Compare mobile options
| Setup | Good fit | Main trade-off |
|---|---|---|
| 120 V compact cutter with small generator | Thin sheet, light repair and occasional cuts | Limited speed and thickness; may not support long cuts at full output |
| 240 V, 30–40 A cutter with appropriately sized generator | General mobile fabrication and moderate plate | Heavier, costlier setup; verify continuous generator capacity carefully |
| Higher-output 240 V cutter and large generator | Frequent thick-material cutting or production work | More fuel, transport weight and cost; may be excessive for repair jobs |
If your work is mostly thin material, a 120-volt plasma cutter can be the sensible choice. For a more versatile field setup, compare 240-volt 30–40 amp plasma cutters, but confirm the exact input draw rather than assuming all machines in that class need the same generator.
Check air and consumables
Most air plasma cutters need a clean, dry supply at a specified pressure and flow rate, often stated in PSI and cubic feet per minute (CFM). A small compressor may reach the required pressure but fail to maintain the required airflow during a long cut. The result can be a sputtering arc, poor cut quality, excess dross or shortened consumable life. Check the cutter’s air specification and the compressor’s delivered CFM at the stated pressure; its tank size alone does not tell you whether it can keep up.
Water and oil in the air line are common causes of erratic cutting. Drain the compressor, use suitable filtration, and keep hoses and fittings sized to avoid starving the cutter. If you plan to run the compressor from the same generator, add its running load and motor-starting surge to the power plan. A cutter that works by itself may trip the generator when the compressor cycles on.
For remote jobs, consider whether your preferred portable compressor for plasma cutting can meet the cutter’s airflow needs continuously. If not, a larger compressor or a separate power source may be more reliable than trying to compensate with higher air pressure.
Generator and setup details
Choose a generator with the correct outlet and voltage for the cutter, and check its breaker rating as well as its advertised wattage. A 240-volt receptacle does not guarantee that the circuit can deliver the cutter’s full input current. If the generator also runs lights, grinders or a welder, include those loads in the plan or use equipment one at a time. A generator-powered 240-volt inverter generator may be easier to transport and can provide stable output, but it is not automatically the right choice: compare its continuous rating, outlet capacity, weight and service support with a conventional generator.
Use a short, correctly sized extension cord when one is needed; an undersized or very long cord can cause voltage drop and nuisance shutdowns. Set the generator on stable ground outdoors, away from doors and windows, and never run it in a vehicle, trailer or enclosed shop. Plasma cutting also produces sparks, fumes and intense ultraviolet light. Clear combustibles, protect nearby people with welding screens, and wear suitable eye, hand and body protection.
Buying checklist
Before choosing a cutter, write down the thickest material you cut often, the generator’s continuous output at 240 volts, the cutter’s maximum input current, and the compressor’s delivered CFM at operating pressure. Then check duty cycle: a 40% duty cycle at a stated output means roughly four minutes of cutting in a ten-minute period before cooling time is needed. Higher output may shorten that usable window. If the machine will spend most of its time cutting thin stock, a smaller, cheaper unit can be entirely adequate. Pay extra for capacity only when your regular work, not an occasional worst-case cut, justifies it.