Abstract: Welding systems and methods include a welding unit for joining a first and a second source of wire, in which the welding unit includes a wire feed tunnel defining a travel path through the welding unit for the first and second sources of wire. The welding unit further includes a pair of wire feed ports disposed on opposite ends of the wire feed tunnel, and a wire joining zone disposed along a portion of the feed tunnel and configured to weld together an end of the first wire source to an end of the second wire source by applying weld heat to at least part of the respective ends of the first and second wire sources. The welding unit also includes a switch configured to adjust the inner diameter of the wire feed tunnel until the inner diameter is substantially the same as the exterior diameter of the first and/or second sources of wire.