Big Blue® 400X Pro


Maximum flexibility - Miller Electric combines advanced inverter technology with Auto-Line™ technology, offering the most flexible AC/DC TIG/Stick power supply in the welding industry.

Maximum flexibility - Miller Electric combines advanced inverter technology with Auto-Line™ technology, offering the most flexible AC/DC TIG/Stick power supply in the welding industry.

The professional welder’s choice

designed with the professional in mind, the Big Blue 400X Pro is the best for ease of use, reliability and fuel economy.


Heavy duty low-speed industrial diesel engine KUBOTA

Dynamic DIG™ technology

Ultra-adaptive arc control. Unlike conventional DIG that provides a preset amount of short-clearing current, Miller-exclusive Dynamic DIG technology works on a time-based algorithm that automatically adjusts the amount of current required to clear a short. Delivers a smoother more consistent arc that can be tailored to match application, material, fit-up and welder technique.

ArcReach® technology (option)

Parameter control at the wire feeder or pendant without needing a control cord. An ArcReach system allows you to change weld settings from your ArcReach feeder or Stick/TIG remote, saving a trip to the power supply. ArcReach technology uses the existing weld cable to communicate welding control information between the feeder or Stick/TIG remote and the power source. This technology eliminates the need for control cords, and their associated problems and costs. ArcReach-equipped power sources work with non-ArcReach accessories; however the ArcReach benefit is only realized with the complete ArcReach system. This includes an ArcReach-equipped machine and one or more of the following accessories:
• ArcReach SuitCase feeder
• ArcReach Smart Feeder
• ArcReach Stick/TIG Remote

Digital meters

with SunVision™ technology enable welding parameters to be viewed with greater clarity than analog meters — at virtually any angle. Meters can be seen clearly even in direct sunlight.

Meters display

• Process settings for quick and easy setup
• Preset and actual amperage

Simple-to-set controls

require no elaborate procedure — just select process and weld.

10.000 watts of pure generator power.

Plug in an extra Miller® inverter-based power source for a second welding arc.

Industrial USB port.

Quickly upload the latest software and download machine log files.

Thermal overload protection

prevents machine damage if the duty cycle is exceeded or airflow is blocked.

Arc control

is beneficial when welding with stick and solid wires for easier fine-tuning of tough-to-weld materials and out-of-position applications.

Standard 14-pin receptacle with Auto-Remote Sense™

for simple connection of remote controls and wire feeders.

Low OCV stick (VRD),

when enabled, reduces the open-circuit voltage to 30 volts when the welding power source is not in use, increasing operator safety without compromising arc starts.

HD powder coat

with zinc-rich primer protects sheet metal from rust and corrosion.

Standard features include

adjustable Hot Start,™ output contactor control, automatic idle, 120-volt block heater and Dynamic DIG™.

Easily update technology

With the industrial USB port, you can easily upload the latest software and download machine log files to retrieve in-depth information from your machine such as diagnostics and statistics. Visit to download the latest software updates.

Less noise

Quieter jobsites are safer and more productive because work crews can communicate easier. The Big Blue 400X Pro is only 71.6 decibels (96 Lwa) under a full load, allowing for easier jobsite communication. Optional wireless interface control makes it easier to shut off your machine when it’s not in use, so you can lower jobsite noise levels and hear what’s going on around you.

Jobsite safety

Reduce the need to walk back to or climb into the truck bed to make process and parameter changes, or turn your machine on/ off. ArcReach® technology provides parameter control at the wire feeder or Stick/TIG remote and optional wireless interface control provides full front panel control in the palm of your hand, so you can lower the risk of encountering potential jobsite hazards.

What’s included

Stick (SMAW)
Flux-cored (FCAW)*
Pulsed MIG (GMAW-P)**
Air carbon arc (CAC-A)
Rated: 4.8 mm (3/16 in.) carbons
Capable: 6.4 mm (1/4 in.) carbons


General specification
Title Big Blue® 400X Pro
Industries Interests Mechanical contractors
Structural steelwork
Pipe welding
Material Thickness
Weldable Metals Thin to thick,
All materials,
0,8-1.6 mm solid,
Cored wires
Input Voltage
Input Phase
Input Hz 50 Hz
Amperage Range
Current Type
Rated Output DC stick 20–400 A
MIG/flux-cored 14–40 V
DC TIG 20–400 A
Max Open Circuit Voltage 85 VDC
30 VDC Sense voltage for Lift-Arc™ TIG and stick with VRD on.
Weld Output CC/DC (TIG)
CC/DC (Stick)
Net Width 667 mm (26.25 in.)
Net Height 813 mm (32 in.)
Net Length 1.422 mm (56 in.)
Net Weight 431 kg (950 lb.)
Warranty 3 Years
Miller’s True Blue Warranty