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This paper investigated experimentally the interaction behaviors of flames spreading over two parallel adjacent electrical wires at various separation distances. Experiments were carried out with thin electrical wires of copper inner core and polyethylene (PE) insulation. The separation distances between the two parallel electrical wires (their core center distance) were ranged from 1 mm (flames merge) up to 20 mm (flames completely separate with behavior identical to that of one single electrical wire) to reveal the transition of the flame behaviors with increasing separation distance. The flame base width along the wire (W f), flame height (H f), average mass loss rate (AMLR, m ˙) and flame spread rate (FSR, V f) were measured to quantify this transition. Results showed that the flame height, the AMLR and the FSR all increased first and then decreased with increasing of separation distance. The FSR and AMLR were maximized at the same separation distance during the transition of flames separating from its base to complete separation with increasing separation distance. Five regimes were identified for the variation transition of flame spread rate with increasing separation distance, which can be interpreted physically by the change of convection and radiation feedback with separation distance. The maximum FSR of the wire-pair, which occurred at the separation of about 8∼10 times of the wire outer diameter, was around 12% ∼22% greater than that over one single wire. Such FSR increment was more remarkable if the wire size was larger. This experimental study provides fundamental knowledge, quantitative data and physical understanding of the phenomenon of flame spreading interactions over two parallel adjacent electrical wires. [ABSTRACT FROM AUTHOR]