What size breaker do you need for a welder?
The answer is on your machine's rating plate, not in a rule of thumb — and the number most people quote is the wrong one entirely.
The direct answer
Size the breaker from your welder's rated input amperage, which is printed on its rating plate and in its manual — not from its advertised output amperage. Typical 120-volt wire-feed welders specify a 20-amp circuit; 240-volt machines commonly specify 30 to 50 amps. A licensed electrician sizes the breaker and conductors to the National Electrical Code and local rules.
| Machine type | Supply | Typically specified circuit |
|---|---|---|
| 120V flux-core wire feed | 120 V | 20 A |
| 120V gas MIG | 120 V | 20 A dedicated |
| Dual-voltage MIG on the low setting | 120 V | 20 A |
| Dual-voltage MIG on the high setting | 240 V | 30–50 A, machine-specific |
| 200 A class AC/DC TIG | 240 V | 30–50 A, machine-specific |
| 50 A plasma cutter | 240 V | 30 A or above, machine-specific |
Input amps and output amps are not the same number
This is the single most common confusion in the whole subject, and it sends people to electricians asking for circuits that do not exist.
A welder advertised as a 140-amp machine produces up to 140 amps at the arc. That is the output. What it draws from your wall is much less, because the machine is a transformer or an inverter: it trades voltage for current. Your house supplies a relatively high voltage at a modest current; the welder converts that into a very low voltage at a very high current, which is what melts steel.
The figure your circuit must satisfy is the rated input amperage at a stated output, and it is on the rating plate. It is why a 140-amp welder happily lives on a 20-amp circuit.
How to read the rating plate
The plate is usually on the back or underside of the machine. You are looking for three things.
Input voltage and phase — for example 115/230 V, 1-phase, 60 Hz. If two voltages are listed, the machine is dual-voltage and there are two answers to this page.
Rated input amperage, sometimes written as I1max or as input amps at rated output. This is the number an electrician needs. It is usually quoted alongside the output it corresponds to, such as "20 A at 90 A output".
Rated output and duty cycle — for example 90 A at 19 V, 20% duty cycle. Useful for understanding the machine, not for sizing the circuit.
If the plate is unreadable, the manual has the same table, and manufacturers publish manuals online for essentially every current machine.
Why welders get dedicated circuits
Manufacturers routinely specify a dedicated circuit, and it is not caution for its own sake. A welder's draw is heavy and intermittent — it spikes every time you pull the trigger. That is precisely the pattern that nuisance-trips a breaker shared with a motor load, because a freezer or compressor starting at the same moment as your arc pushes the total over the limit.
Sharing a circuit is also how people convince themselves a new machine is faulty. If your welder trips the breaker only sometimes, the first thing to check is what else is on that circuit.
What to tell your electrician
Give them four things and the quote will be accurate first time:
The machine's make and model. Its rated input amperage and input voltage from the plate. The plug type it ships with — a NEMA 6-50P is common for 240-volt welders, and naming it means they fit the matching receptacle. And the distance from your panel to where the machine will live, because conductor sizing depends on run length.
It is also worth asking whether your panel has spare capacity, because that is where a straightforward job turns into a subpanel conversation.
The part that is not optional
Everything above is how to arrive at your electrician's door with the right information. It is not a substitute for their judgment. Breaker and conductor sizing depends on the National Electrical Code, on your local jurisdiction's amendments, on conductor type and insulation rating, on run length and on ambient conditions — and in many places a new circuit requires a permit and inspection.
Your machine's own manual governs its electrical requirements. Where this page and your manual disagree, your manual is right. Have the work done by a licensed electrician.
What we would buy
1. For finding out what your machine really draws
Klein Tools CL800 digital clamp meter
Measures actual input current and voltage drop instead of guessing at either.
A clamp meter answers the question this page is about empirically. Clamp it round one conductor of the machine's supply lead, weld at the settings you actually use, and read the input current. That tells you whether a circuit is comfortably sized or marginal.
It also reads voltage at the outlet under load, which is the real diagnosis when a machine welds poorly on a long run — see welder extension cords.
It tells you what is happening. It does not make anything safe, and it is not a substitute for an electrician sizing the circuit.
What works
- Lets you measure real input current at real settings, which is the only way to know whether a breaker is marginal or fine
- Reads voltage drop at the outlet under load — the actual diagnosis when a machine underperforms on a long run
What does not
- It tells you what is happening; it does not make anything safe. Circuit work still belongs to a licensed electrician
- More tool than you need if you only ever plug into one known-good outlet
Who this is wrong for: Anyone hoping a meter reading will justify running a machine on an undersized circuit. Measurement informs the electrician; it does not overrule the code.
2. A worked example
Hobart Handler 210 MVP
Ships with both a 115V and a 230V plug, so the circuit question has two answers.
This machine is a useful illustration of why the plug matters as much as the breaker. Hobart supplies it with a 5-15P plug for 115-volt use and a 6-50P plug for 230-volt use, which tells an electrician exactly which receptacle to fit without any interpretation.
Knowing the plug type before the electrician visits is what stops the second visit.
What works
- The multi-voltage plug means you can buy it before you have run a 240 V circuit and get the full 210 A later
- 3/8 in single-pass capacity covers essentially every home fabrication job
- 30% duty cycle at 150 A is a real working duty cycle, not a demonstration figure
What does not
- Heavy enough that you will want a cart, which is another purchase
- On 115 V you get 140 A — no more than the Handler 140, at a much higher price. The value only appears once you have the 240 V outlet
- No spool gun included, so aluminum is a further purchase
Questions people actually ask
What size breaker for a 240V welder?
Most 240-volt home welding machines specify somewhere between 30 and 50 amps, and the exact figure is on the machine's rating plate as its rated input amperage.
A 200-amp output class machine does not need a 200-amp circuit — the input and output figures are entirely different numbers.
What size wire for a welder outlet?
Conductor sizing follows the breaker size, the conductor's insulation rating, the length of the run and the National Electrical Code, plus any local amendments.
This is exactly the calculation a licensed electrician does as part of the job, and it is not something to size from a chart on a website because too many of the inputs are specific to your installation.
Can I put a welder on a 15-amp circuit?
Most 120-volt welders specify 20 amps, so a 15-amp circuit is below the manufacturer's requirement. In practice the machine will often run at low settings and trip at higher ones.
Running a machine on an undersized circuit repeatedly trips the breaker, which is the protection working as designed — not a problem to work around.
Does a longer run need a bigger breaker?
No — a longer run needs larger conductors, not a larger breaker. The breaker protects the wire, so increasing it without increasing conductor size removes the protection.
Voltage drop over distance is handled by going up in conductor size, which is part of why electricians ask how far the run is.
My welder trips the breaker at high settings only. Is it faulty?
Usually not. That pattern is almost always an undersized or shared circuit, or a long extension cord adding voltage drop and raising current draw.
Try the machine on a known-good dedicated circuit of the specified rating, with no extension cord, before concluding the machine is at fault.
Sources
Read next
- How many amps does a welder use?
Input amps by machine type and voltage, and why it is a completely different number from the output on the box.
- 120V vs 240V welders: which one do you actually need?
The decision that sets your ceiling: what each supply voltage welds, and what the circuit really costs.
- The best 240V welders for a home shop
The machines worth running a 240V circuit for, and how to size that circuit before you buy.
- Welder extension cords: how to size one properly
Voltage drop, gauge and length — why a thin cord makes a good machine weld badly.
- Gas and power: the two things that decide what you can actually run
A machine you cannot plug in is a machine you do not own yet. This is the hub for the two questions that quietly decide every purchase on this site.
Back to Gas & Power, or start over at Find Your Level.
Ryder M.
Ryder M. is the hands-on owner behind Magoo Media Group. He writes Arc & Bead's buying guides and picks every machine on the site. What every recommendation is based on — and what it is not based on — is set out on How We Pick.