in a switching circuit , at least two bus bars are fixed with an insulator interposed therebetween and secured to a substrate of the switching circuit . being combined with the bus bars , the insulator serves not only to insulate those bus bars but also to enhance the bending rigidity and bending strength of the switching circuit . as current flows in one of the bus bars in a direction opposite to a direction in which current flows in the other bus bar , the inductance of the bus bars is reduced , resulting in the decreased fly - back voltage generated upon switching operation .