What is a common cause of arc blow?

• A. Moisture on the workpiece
• B. Low ambient temperature
• C. High filler metal viscosity
• D. Magnetic fields from nearby equipment

Answer: (D)

Arc blow occurs when magnetic fields interact with the welding current and push or deflect the arc off its intended path. Magnetic fields from nearby electrical equipment, such as motors, transformers, or other power apparatus, create a local field that, through the Lorentz force, causes the arc to wander. This magnetic interference is a common cause of arc blow, leading to an unstable arc and irregular weld beads. The other options don’t cause this deflection: moisture on the workpiece tends to create porosity and hydrogen-related issues, not arc wandering; low ambient temperature and high filler metal viscosity affect other aspects of welding but not the magnetic interaction that drives arc blow.