Reading a Welding Machine Nameplate: What the Numbers Mean

Every welding machine has a metal plate or sticker full of numbers. It looks like engineering homework, but it tells you exactly what the machine can and can't do — and what power it needs. Here's how to read it in plain language.

Input voltage and current

This is what the machine draws from the wall, not what it puts into the weld.

• Input voltage: usually 120V, 240V, or dual voltage. Match it to your outlet — never force a 240V machine onto a 120V circuit
• Input current (amps): how much the machine pulls at full load. Your breaker and wiring must handle it
• Phase: most small shop machines are single-phase, which is what homes and small shops have

Output: amperage range and duty cycle

• Output amperage range: the lowest and highest welding current the machine delivers, for example 30–200 amps. A wider range means more jobs, from thin sheet to thicker plate
• Duty cycle: the percentage of 10 minutes the machine can weld at a given amperage before it needs to cool down. A 60% duty cycle at 200 amps means 6 minutes welding, 4 minutes rest
• Open circuit voltage (OCV): the voltage at the terminals when you're not welding. Higher OCV usually means easier arc starts, especially for stick

What to check before you buy

• Make sure your shop's circuit matches the machine's input requirements — check the manual, not just the nameplate
• Compare duty cycle at the amperage you'll actually use, not at the lowest setting
• Look for the certification marks and the manufacturer's model and serial numbers for warranty and parts

A quick example

A nameplate reading "Input 240V, 24A — Output 30–200A, 60% duty cycle at 200A" tells you: it needs a 240V circuit with room for 24 amps, it welds from thin material up to serious plate, and at full power you weld 6 minutes out of every 10.

The nameplate is the machine's honest resume. Read it before you buy, and keep the manual — it has the full story the plate only summarizes.

Explore our welding machines, MIG welders, TIG welders, and stick welders to compare models side by side. At RGV Welding Supply, you can see the machines in person at our Weslaco and Pharr stores. All sales are in-store pickup.