Arc Welding Is Powered By Electricity: What Really Drives the Welding Arc

A fabricator I once met was handed a brand-new TIG machine on a Friday afternoon, plugged it into the shop’s only available 120V outlet, and spent an hour wondering why the arc kept sputtering and dying before he realized the machine was starving for power, not malfunctioning. Arc welding looks like a trick of fire and steel, but every spark you see starts as electricity flowing from a wall socket, a generator, or an engine-driven welder — and understanding what powers the arc is the difference between a machine that welds and a machine that just hums.

Arc Welding Is Powered By Electricity: The Short Answer and Why It Matters

A fabricator I once met was handed a brand-new TIG machine on a Friday afternoon, plugged it into the shop’s only available 120V outlet, and spent an hour wondering why the arc kept sputtering and dying before realizing the machine was starving for power, not malfunctioning. Arc welding looks like a trick of fire and steel, but every spark you see starts as electricity flowing from a wall socket, a generator, or an engine-driven welder.

Understanding what powers the arc is the difference between a machine that welds and a machine that just hums.

What an Electric Arc Actually Is

An electric arc is a continuous electrical discharge that jumps a gap between two conductors. When the electrode comes close to the work, the voltage ionizes the gas in that tiny gap, turning it into a conductive plasma channel. Current then flows across the channel, and the resistance of that plasma column converts electrical energy into intense heat — hot enough to melt steel in a fraction of a second.

In plain language: the arc is electricity forced to travel through air, and air does not want to cooperate. The energy released in that struggle is what melts the metal.

Why Electricity, Not Gas or Pressure

It helps to separate arc welding from its neighbors. In oxyfuel welding, a chemical flame from burning acetylene or propane provides the heat. In resistance welding, heavy mechanical pressure plus large currents passed through overlapping sheets heat the joint from the inside. Arc welding is different: the heat source itself is the electrical discharge, and the operator controls it by controlling current and voltage.

That distinction matters practically. Because the energy arrives as electricity, the machine can regulate it instantly and precisely — which is why a welder can dial in penetration for thin sheet and then crank up for a heavy fillet on the same power source.

The formal definitions line up with what you see on the shop floor. TWI states that a welding power source’s prime objective is to deliver controllable welding current at the voltage demanded by the welding process. American Welding Society course material puts it from the other side: all arc-welding processes require a continuous supply of electrical current in sufficient amount (amperage) and of proper voltage to maintain an arc.

And no, the machine is not making power. ESAB explains that most welding power supplies do not generate power; they are transformers or inverters that convert utility or generator power into welding-appropriate current. Your wall supplies the energy. The machine reshapes it.

The Vocabulary You Will Use Every Day

If you are searching this topic, you are probably also bumping into eight terms. Here is the short version of each:

• Power source — the machine itself (transformer, rectifier, or inverter) that converts incoming power into welding output.
• Welding circuit — the complete loop current travels through: machine, electrode cable, arc, base metal, work lead, and back.
• Electrode — the consumable or non-consumable element that carries current to the arc: a stick, a wire, or a tungsten.
• Work lead — the cable and clamp returning current from the workpiece to the machine; often called the ground lead, though it is a return path, not a safety ground.
• Amperage (amps) — the volume of current; this is what determines heat input and penetration.
• Voltage — the electrical pressure that maintains the arc across the gap; it rises and falls with arc length.
• Duty cycle — the percentage of a ten-minute window the machine can run at rated output before it must rest.
• AC vs DC — alternating current reverses direction; direct current flows one way, giving stable arcs and controllable polarity (DCEN and DCEP).

How This Article Is Built

We will follow the electricity itself. First comes the complete welding circuit, from the outlet to the arc and back. Then the physics inside the arc: how electrons, ionized gas, and plasma become melting heat, and how polarity shifts that heat between electrode and work. From there we open the machine — transformers, rectifiers, and modern IGBT inverters — before moving to what your facility actually has to deliver in voltage, breakers, and duty cycle.

The middle sections handle the technical decisions that confuse people most: constant current versus constant voltage, and which processes need which. Then we cover power when the wall socket is not an option, the electrical safety rules that keep welders alive, real energy consumption numbers, and a closing checklist of common powering mistakes.

Keep that fact in view and the rest of welding equipment starts to make sense. The puddle is only as consistent as the power feeding it.

The Complete Welding Circuit: How Electricity Flows From Outlet to Arc

Before we look inside the arc itself, it helps to trace the one thing every arc welding process shares: a complete, unbroken loop of electricity. Think of it like water moving through a hose that forms a closed circle. If you cut the circle anywhere, the flow stops instantly. Electricity works the same way, and the welding circuit is the path it travels from the wall, through the machine, across the arc, and back again.

Step by Step: The Path of the Current

Follow a single stick welding pass around the loop and you can see exactly where every electron goes:

1. Incoming supply power. Line voltage enters the machine from a wall receptacle, a generator, or an engine-driven welder’s own alternator.
2. Transformer or inverter. Inside the machine, that input is transformed down to a safer, workable level and, in most modern units, converted to DC and switched at high frequency.
3. Secondary welding terminals. The transformed power leaves the machine at the electrode (positive or negative, depending on polarity) and work terminals.
4. Electrode cable. Current travels through the electrode lead to the stinger or torch.
5. Electrode, stick, or wire. The filler metal carries the current to the very edge of the joint.
6. The arc gap. Current crosses the air gap between electrode tip and base metal as an arc.
7. Base metal. The current spreads through the workpiece toward the clamp.
8. Work clamp and ground cable. The return lead carries it back to the machine, closing the loop.

As Lincoln Electric’s Arc Welding Fundamentals puts it, an arc is simply an electric current flowing between two electrodes through an ionized column of gas. That ionized column is the bridge that lets current jump a gap that would otherwise be an open switch.

Why the Circuit Must Be Closed

An open circuit means no current, and no current means no arc. This is why the work clamp is not an accessory, it is half the machine. When the machine is energized but the electrode has not yet touched the work, you typically see an open-circuit (no-load) voltage waiting at the electrode, generally in the range of about 20V to as high as 100V depending on process and machine design. The moment the circuit closes through the workpiece, that voltage collapses to a much lower, stable arc voltage and current begins to flow in earnest.

Surface contamination is the most common culprit. A clamp biting into fresh paint or heavy rust forces current through a poor, high-resistance contact, so the arc wanders, sputters, or simply refuses to start. Scrub the clamp contact area to bright metal and reposition it close to the weld. The same logic applies to the cables themselves: damaged insulation or exposed bare conductors must be replaced outright, and any cable splices have to use connecting means specifically intended for that purpose under OSHA’s welding standard, not tape twisted over copper.

The ionized gas column inside the arc deserves special mention because it behaves very differently from solid copper. A normal air gap is an insulator. The heat of the initial strike rips electrons from gas atoms, creating a plasma of charged particles that conducts readily. This plasma column carries current across a gap no wire can span, and its resistance converts electrical energy directly into the intense heat that melts the metal.

Cable Sizing, Resistance and Voltage Drop

Every foot of cable adds resistance, and resistance steals voltage before it ever reaches the arc. The practical effect is called voltage drop: undersized or excessively long cables leave the arc starving for power even when the machine’s settings are perfect. Welding cables are intentionally fat and flexible to keep that drop low. A few guidelines keep the loop healthy:

• Use the shortest practical cable run for both electrode and work leads.
• Match cable gauge to rated output current and total lead length.
• Uncoil tightly wound cables before welding, since bundled cable raises resistance and heat.
• Inspect connections regularly for corrosion, loose lugs, and heat discoloration.
• Never use coiled extension cords as a substitute for properly sized welding cable.

One rule deserves its own warning: pipelines and conduits are never legal ground returns. OSHA explicitly prohibits using pipelines containing gases or flammable liquids, or conduits carrying electrical circuits, as a welding ground return under 29 CFR 1926.351. Stray welding current through a fuel line can ignite its contents, and current running through building conduit can damage or trip unrelated circuits. Always run a dedicated work cable back to the machine.

With the full loop mapped, the next question is what actually happens in that fraction of an inch where current crosses open air and turns electrical energy into molten metal.

Inside the Arc: Turning Electrical Energy Into Melting Heat

Everything covered so far happens before the arc even exists: power leaves the wall, gets shaped by the machine, and travels down a cable. The interesting part starts in the half-inch of open air between the electrode tip and the steel. That gap is where raw electrical energy stops being electricity and becomes heat, light, and a pool of molten metal. Understanding what happens in that gap is what lets you predict how a weld will behave instead of just hoping it holds.

Cathode, Anode and the Stream of Electrons

Every arc welding circuit has two poles: a negative cathode and a positive anode. Electrons stream off the cathode and slam into the anode across the arc gap. To get the arc started, the electrode is usually touched briefly to the work and then withdrawn a few millimeters. That momentary contact completes the circuit and heats the contact point enough to release electrons, and once the gap opens, the voltage supplied by the power source keeps pulling them across. This is why an arc is so easy to strike and so frustrating to restart when your machine is underpowered: you need enough open-circuit voltage to jump that gap in the first place.

As federal welding safety and equipment guidance under 29 CFR 1910.254 sets out, the negatively charged cathode and positively charged anode are what create the intense heat of the welding arc, with ions accelerated through the column between them. The electrons carry enormous kinetic energy, and when they hit the opposite surface, that energy converts almost instantly into thermal energy. Roughly two-thirds of the arc’s heat develops at the anode and one-third at the cathode, which becomes a big deal when we talk about polarity below.

From Gas to Plasma: Why the Column Is So Hot

Open air between two conductors is an insulator; current should not cross it. What changes that is ionization. The electron stream knocks electrons loose from the atoms of the shielding gas and the vaporizing flux coating, turning the gas into a mix of free electrons and positively charged ions. Physicists call that mixture plasma, the fourth state of matter. Plasma conducts electricity extremely well, which is why the arc sustains itself once established, and why the column glows so brilliantly.

The temperature inside this column is staggering. A typical welding arc reaches about 6,500°F at the tip, which is roughly three times the melting point of mild steel. Both the base metal and the electrode melt together into a single pool, and as that pool solidifies, the metals are fused at the metallurgical level rather than merely stuck together. That fusion bond is the entire point of the process.

The shielding gas or flux coating does double duty here. It protects the molten metal from oxygen, and it also becomes part of the conductive column. A stick electrode’s flux coating burns into a gas and slag that stabilize the arc, while a TIG machine relies on argon or helium to carry the current from a tungsten tip that itself does not melt.

Where the Heat Lands: The Crater and the Weld Pool

The arc is not a uniform ball of fire. It is cone-shaped, and its most intense point sits at a small, concentrated spot on the workpiece, sometimes called the anode spot or arc crater. That spot is what liquefies the plate, and the molten puddle behind it solidifies into the weld bead. Heat builds here faster than the surrounding metal can carry it away, so the pool stays fluid while you move along.

This is also where technique matters. Strike an arc and hold it still for two seconds too long, and that concentrated spot burns a deep hole. Move too fast and the pool never reaches fusion temperature, giving you a cold lap with no penetration. The heat balance in the arc tells you what to do with travel speed, arc length, and amperage.

Polarity: The Dial That Moves Heat Between Electrode and Work

Polarity decides which side of the circuit receives most of the heat. TWI’s technical guidance and welding power supply references describe the standard arrangements like this:

DC electrode positive drives more heat into the base metal, which is exactly why DCEP is the default choice when penetration is the priority. DC electrode negative flips that balance, heating the electrode harder, which melts filler wire quickly but gives shallower penetration into thick plate. AC is the compromise: half the time on each polarity, plus a cleaning action that blasts the stubborn oxide layer off aluminum so the puddle wets out properly.

Getting polarity wrong does not always produce a visible failure. It produces a weld that looks acceptable and underperforms exactly where it matters most. Match the polarity to the electrode classification, keep the arc length tight so the heat stays focused, and the pool will tell you it is happy by staying fluid, shiny, and evenly rippled from start to stop.

The Power Source Family: Transformers, Rectifiers and Inverters

Every arc welding process, whether it’s stick, TIG, MIG or flux-cored, depends on one piece of hardware doing a very specific job: taking whatever power comes in from the wall, a generator or an engine, and reshaping it into a controlled, high-current, low-voltage output that can strike an arc and hold it steady. That hardware is the welding power source, and it comes in three main generations. Understanding the differences between them explains why an old transformer machine weighs as much as a person, why a modern inverter fits on a shelf, and which one makes sense for your work.

Transformer Machines: The Heavyweight Workhorses

The classic arc welder is a transformer-type machine. It uses a large iron-core transformer to step down utility voltage (230V or 460V) to a safer, usable welding voltage while stepping up current to the hundreds of amps needed to melt steel. Because the transformer operates at line frequency (50 or 60 Hz), it needs a lot of iron and copper, which is why these machines are heavy, bulky and usually rated for AC output only.

The upside is simplicity. There are few electronic parts to fail, the design is rugged, and repairs are generally cheap and straightforward — any competent shop with a replacement contactor or transformer can get one running again. For students, farm shops and heavy structural work where the machine rarely moves, a transformer welder remains a sensible, affordable choice. The trade-offs are weight, coarser control and, in older units, poor efficiency and low power factor, which can irritate utility meters on industrial sites.

Rectifier Machines: Adding DC to the Mix

A rectifier machine takes the transformer concept one step further: the step-down transformer feeds a bridge of diodes (or, in later designs, silicon-controlled rectifiers) that converts the outgoing AC into DC. That gives the operator the polarity control that processes like DC stick welding and DC TIG demand, allowing heat to be pushed toward the electrode or the workpiece as needed.

Rectifier machines are a middle generation — more capable than basic AC transformers, still heavy, and still built around line-frequency magnetics. They dominated professional shops through the 1980s and plenty of them are still welding happily today.

Inverter Machines: High-Frequency Switching in a Small Box

Modern inverter welders throw out the massive iron-core transformer entirely. The process works in stages: incoming utility AC is first rectified to DC, then that DC is switched on and off through a high-frequency inverter running at a switching frequency typically of 10 kHz or higher, feeding a small, light step-down transformer. Because transformer size drops as frequency rises, the magnetic components shrink dramatically. The high-frequency AC is then rectified again to produce clean DC output to the arc.

The device that made this practical is a high-power semiconductor, most commonly the insulated-gate bipolar transistor, or IGBT (MOSFETs appear in smaller units). These switches chop current thousands of times per second with very little loss, which is why inverter-based sources are lighter, more efficient and offer better parameter control than their predecessors.

The control advantages go deeper than convenience. Because output is regulated electronically thousands of times per second, an inverter can respond to arc conditions almost instantly, holding a stable arc even on a marginal extension cord where an old transformer would sag. On AC TIG specifically, inverters allow precise balance control between cleaning and penetration, plus much smoother square-wave output — something line-frequency machines simply cannot do.

Engine-Driven Machines: Your Own Power Plant

When there’s no grid at all, the power source brings its own. Engine-driven welders combine an internal combustion engine — diesel, gasoline or propane — with an onboard generator and welding output in one package. As arc welding fundamentals demand clean, stable power, these units are built to deliver it far from the nearest outlet, which is why they dominate pipeline construction, structural erection, shipyards and remote field repairs. OSHA’s welding rules under 1910.254 and construction’s 1926.351 apply to these machines just as they do to shop equipment.

They also serve double duty: auxiliary power outlets run grinders, lights, compressors and tools off the same machine, which is why a diesel welder-generator is often the most valuable single item on a jobsite.

Which One Should You Choose?

• Transformer: lowest purchase price, dead-simple repair, AC-only or basic output, heavy.
• Rectifier: DC output for professional stick and TIG, still heavy, moderate cost.
• Inverter: light, efficient, generator-friendly, excellent arc control, higher purchase price, board-level repair.
• Engine-driven: total grid independence, higher fuel and maintenance cost, doubles as a generator.

Note: Inverter welders now dominate portability, TIG AC balance control and generator-friendly input draw — modern inverter units tolerate the voltage fluctuation of small generators far better than transformer machines, which is why most field crews have switched. Whatever you pick, match the machine to the process first and the power supply second; the arc will tell you quickly if you got it wrong.

What the Grid Delivers: Input Voltage, Phases, Breakers and Duty Cycle

Arc welding is powered by electricity that travels a long road before it reaches the puddle: utility transformer, service panel, branch circuit, plug, cord, and finally the primary side of the machine. Every link in that chain shapes how the welder behaves. Supply voltage sag and the machine derates or shuts down. A breaker sized too tight and you reset it mid-weld. Duty cycle ignored and a welder that looked perfect on paper spends half the job in thermal cutout.

Match the Machine to the Service You Actually Have

Dual-voltage inverter machines sense the incoming supply and adjust, which is genuinely convenient, but 120V is not a free lunch. The wall circuit can only deliver so much current, so output drops accordingly. Manufacturers generally specify roughly ±10% voltage tolerance; a machine rated for 240V fed with 215V will not make rated amps, and one fed with 250V runs hotter. If you plan your shop around a specific machine, check the nameplate before you buy the wire — our guide to reading welder nameplates walks through the numbers that matter.

Single-Phase vs. Three-Phase: Why Shops Grow Into Three Wires per Leg

Single-phase power pulses twice per cycle, dropping to zero twice along the way. Three-phase delivers three overlapping pulses per cycle, so total supply power never dips. For a transformer-rectifier machine that means less ripple on the DC side, a steadier arc, and more usable output for the same kVA drawn. Three-phase also spreads the load across legs, which keeps a busy panel happier when the lights and the compressor come on.

The trade-off is commitment. A 480V three-phase machine needs real three-phase service, and running it through a phase converter typically costs you output compared with native three-phase. Three-phase is worth it when a machine lives on a production cell; for a general home shop, a good single-phase 240V machine is the sensible choice, as covered in our piece on setting up a home welding shop.

Breakers and Wiring: The Part Nobody Reads Until It Trips

Branch-circuit sizing for welders is governed by NFPA 70, the National Electrical Code, which recognizes welding equipment as an intermittent load and permits demand factors instead of treating it like a continuous 100% duty machine. That flexibility is real, but code-minimum protection still has to carry the machine’s actual full-load current indefinitely. Practical rules that keep breakers quiet:

• Give it a dedicated circuit. Shared circuits invite nuisance trips from the fridge or the air compressor at the worst moment. OSHA’s welding and cutting guidance expects welding work to be wired and maintained safely, cords included.
• Size wire for the run, not just the amps. Long cords at 120V sag noticeably. An inverter welder behaves like a constant-power load: when line voltage falls, it pulls more current to hold output, pushing the breaker toward tripping exactly when you’re working hardest.
• Use the right receptacle and no cheap adapters. Most 240V welders use a NEMA 6-50 circuit; 120V machines want a solid 15- or 20A outlet. Loose or undersized adapters add resistance and heat.
• Check ground and conductor integrity. A poor ground path shows up as erratic arcs and nuisance GFCI or breaker trips.

Duty Cycle: The Ten-Minute Rule

Duty cycle describes how long a machine can run at a stated output within a fixed ten-minute window, tested at roughly 40°C (104°F) ambient. A 60% duty cycle at 200 amps means six minutes of welding and four minutes of rest per ten minutes. It is a thermal limit on the transformer, rectifier and inverter modules, and the thermal overload will cut output before damage occurs.

Two cautions. First, amperage without duty cycle is meaningless: a 250A machine at 30% duty and a 250A machine at 60% duty are different purchases. Second, real duty depends on you — trigger discipline, ambient temperature, altitude and a cabinet packed with dust all shorten it. Buy the duty cycle your longest continuous seams demand, then leave headroom for hot afternoons.

Constant Current vs Constant Voltage: Matching the Power Source to the Process

Here is the question that separates people who own a welding machine from people who actually understand one: when you turn the amperage dial on a stick welder, why does the machine guard that number so jealously, while a MIG welder happily takes volts and then quietly changes the current behind your back? The answer lives in the two great families of welding power source output — constant current and constant voltage — and once you see how their volt-ampere curves behave, a huge chunk of arc behavior stops being mysterious.

The Two Output Classifications Every Welder Uses

Every welding power source in service today is built to hold one of two variables steady, according to the classic framework documented by TWI’s technical knowledgebase on power source characteristics:

• Constant current (CC), also called a drooping characteristic source. You set the amperage, the machine holds it, and arc voltage floats depending on how long the operator holds the arc.
• Constant voltage (CV). You set the voltage, the machine holds it, and amperage rises or falls automatically to keep the arc in balance.

Neither is “better.” They solve different physical problems. Manual welding processes need current control because heat input into the puddle is fundamentally a current question. Semi-automatic wire processes need voltage control because the wire is being fed at a fixed mechanical rate and something has to compensate instantly when that wire touches the puddle.

Drooping Characteristics: Why Stick and TIG “Feel” the Amperage Dial

Shielded metal arc welding and gas tungsten arc welding are hand-guided processes. The welder is the feedback loop, and the distance between electrode and workpiece changes constantly — every heartbeat, every reposition, every bevel that gets tighter as you go.

On a drooping volt-ampere curve, the output current stays nearly flat across a wide range of arc voltages. Stretch the arc longer and the voltage climbs, but the current drops only slightly. Squeeze the arc short and the current barely rises. That stability is what makes a long-arc stick weld forgiving and what lets a TIG welder pedal the arc without the current runaway you’d get on a stiffer curve.

It also explains a tactile thing every stick welder knows: the amperage dial feels like the real control, because it is. Poor technique — wild arc length swings — shows up as inconsistent penetration because you’re nudging that current and the puddle responds. As Lincoln Electric’s arc welding fundamentals describe, arc length is a live variable the operator manages, and the drooping source exists to keep that variable from wrecking the weld.

Constant Voltage: Why MIG Settings Are Volts

Gas metal arc welding and flux-cored arc welding feed consumable wire at a set speed from a motor. That wire is a column of solid metal that will keep advancing whether the arc is stable or not. The moment it touches the puddle, arc length collapses and current spikes — and the arc must recover faster than a human could ever react.

A CV source does exactly that. Voltage is the held variable, so the instant arc length shortens and arc voltage dips, the machine slams current upward, the extra heat melts the wire off faster, and the arc length self-corrects. Stretch the arc and the reverse happens. This is why MIG machines are set in volts plus wire feed speed in inches per minute, and why the process is so operator-tolerant once dialed in. ESAB University’s guide to power supply types makes the same point: constant voltage is what makes semi-automatic wire processes self-regulating.

The Volt-Ampere Curve in Plain Language

Picture a graph. Horizontal axis: arc voltage. Vertical axis: output current. A CC machine’s curve drops steeply — a “drooping” line where big voltage changes produce small current changes. A CV machine’s curve is nearly flat, where the current swings while voltage hardly moves. Same axes, opposite personalities.

That difference ripples into process selection. Pulsed MIG programs, AC TIG balance, synergic wire settings — all of them are electronic refinements layered onto these two basic curves, as covered in the technical overview of welding power supplies. Multi-process machines earn their versatility by switching internally between CC and CV output modes, which is why the manual always tells you which mode your process requires before you strike an arc.

What This Means at the Machine

Next time you’re choosing a power source, read the spec sheet through this lens. For stick or TIG work, you want an honest drooping CC curve with enough voltage headroom to restart a hot rod. For wire processes, look for a true CV output with fast electronic response. And if you’re running multiple processes on one machine, confirm it genuinely switches characteristics rather than compromising on a hybrid curve that does everything adequately and nothing well.

Understand the curve, and the dial on the front of your machine stops being a guessing game and starts being what it always was: a precise instruction to the electricity.

When the Wall Socket Isn’t There: Generators, Engine-Driven Welders and Battery Power

Plenty of arc welding never happens in a shop. Pipeline crews, structural ironworkers, farm repair rigs and disaster-response teams all face the same problem: the arc still needs electricity, but the nearest outlet might be fifty miles away. In those places, “powered by electricity” means a machine that makes its own electricity, or stores it. Understanding how those sources differ from grid power is what keeps a field welder from buying the wrong rig and going home early.

Engine-Driven Welders: The Workhorse of the Field

An engine-driven welder is exactly what it sounds like: a diesel or gasoline engine bolted to a generator and a welding power source in one skid. Lincoln and Miller build them as towable units; Esab and others make them for pipeline spreads where they get dragged behind trucks all day. Their biggest advantage is independence from the electrical grid, and their second biggest is the ability to power auxiliary equipment at the same time. One machine can run the welder, a 120V receptacle for a grinder, a work light and a battery charger off the same engine.

That dual role is why sizing matters so much. A unit rated at, say, 7 kW of auxiliary output has to cover both the steady welding draw and the surge current of tools started on the same unit. An angle grinder or chop saw pulls several times its running current for a fraction of a second at startup, and that surge is what trips a small generator offline mid-arc. Always size for the highest starting load you intend to run alongside welding, not just the average draw.

Portable Inverter Generators and the kVA Question

When a full welder-generator is overkill, welders often pair a separate portable inverter generator with a small DC stick or TIG machine. Here the sizing unit is kVA, which combines volts and amps into apparent power. Most compact generators publish both a starting kVA (surge) and a running kVA, and the gap between them is where people get burned.

There is a second, less obvious issue: modern inverter welders are non-linear loads. Their rectifiers and high-frequency switching draw current in sharp pulses rather than a smooth sine wave, which can distort the waveform and make a small generator work harder than its nameplate suggests. A generator rated “5,000 watts” may deliver noticeably less to a welder than to a resistive heater. The fix is margin: buy more generator than the arithmetic says you need, or choose a machine with power-factor correction and generator-friendly input draw.

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