Arc initiation in welding — the electric arc between electrode and workpiece is initially established primarily by which electrical factor under typical manual or mechanized arc-welding conditions?

Introduction / Context:
The welding arc is a sustained electrical discharge through an ionized gas (plasma) between the electrode and the work. Understanding what initiates the arc helps with parameter selection (open-circuit voltage, arc length) and troubleshooting difficult starts.

Given Data / Assumptions:

• Power source provides an open-circuit voltage (OCV) adequate for breakdown of the air gap.
• Once the arc is established, current flow sustains and heats the arc column.
• Contact resistance during striking contributes to local heating when touching/scratching to start the arc.

Concept / Approach:

Arc initiation requires dielectric breakdown of the gap, achieved when the instantaneous voltage across the gap exceeds the breakdown threshold (dependent on arc length, gas composition, pressure). Thus, sufficient OCV is critical to ionize the path. After initiation, the power source transitions to a lower arc voltage at the commanded welding current, and current becomes the dominant factor for heat input and droplet transfer. Contact resistance may assist by preheating during the scratch/tap start but is not the primary governing factor in gap breakdown.

Step-by-Step Solution:

Verification / Alternative check:

Manufacturer specifications list minimum OCV requirements (e.g., ~50–80 V for SMAW) to ensure reliable arc striking, confirming the primacy of voltage in initiation.

Why Other Options Are Wrong:

“Flow of current” sustains heat after initiation but cannot occur across an insulating gap without prior breakdown. “Contact resistance” helps during touch start but is auxiliary. “All of these” overstates roles; initiation is primarily a voltage (breakdown) phenomenon.

Common Pitfalls:

Confusing arc starting (breakdown) with arc heating (current); assuming high current alone can jump a gap without adequate OCV.

Final Answer:

voltage