A　study　of　sustaining　or　igniting　the　arc　between　tips　of　two　wires　in　twin-wire　indirect　arc　welding　(TWIAW)　with　AC　is　challenging.　In　comparison　with　conventional　gas　metal　arc　welding　(GMAW)　where　one　of　the　arc　terminals　is　the　base　metal　which　is　stationary　and　large,　both　arc　terminals　in　TWIAW　are　wire　tips　which　are　small　and　subject　to　variations.　The　alternating　of　the　polarity　among　the　two　wires　in　AC　TWIAW　further　increases　the　challenge　in　sustaining　the　arc　between　the　two　wires.　To　meet　the　challenges,　i.e.,　sustaining　the　arc　between　the　small　and　varying　wire　tips　despite　the　alternating　polarity,　the　effects　on　the　arc　behaviors　from　different　working　parameters　are　observed,　measured　and　analyzed　in　this　study.　The　inter-wire　distance　which　characterizes　the　instability　of　the　inter-wire　arc　between　the　two　wires　in　TWIAW　is　found　to　increase　as　the　AC　current　frequency,　the　inter-wire　angle　and　the　wire　diameter　decrease　as　well　as　the　amperage　of　the　current　increases.　This　definite　tendency　provides　the　foundation　to　control　the　inter-wire　melting　and　droplet　detachment/metal　transfer　to　successfully　sustain　the　inter-wire　between　the　two　small　wires　dynamically　such　that　the　AC　TWIAW　may　operate　as　desired　to　deliver　its　desirable　properties　low　heat　input　and　high　deposition　rate.　(C)　2015　The　Society　of　Manufacturing　Engineers.　Published　by　Elsevier　Ltd.　All　rights　reserved.