the arc tube to be swung back as shown in fig2 for passage of the mount assembly through the neck of the jacket electrical connection to the lower electrode inlead 16 is made through a two segment connector 31 32 having a bendable join 33 uniting the two parts the segments 31 and 32 may consist of nickel plated iron ribbons and the bendable joint may be a small piece of nickel ribbon welded to the segments to form a hinge the shorter segment 31 is welded to the laterally turned end of lead in wire 7 after partly encircling it for greater flexibility while the longer segment 32 is welded to inlead 16 the stiffness of the members is such that bending occurs primarily in the joint 33 and to a lesser extent next to the lead in wire 7 the arrangement allows the arc tube to be swung back as shown in fig2 with the segmented connector 31 32 folded upwards like a knee joint as illustrated in fig1 lead in wire 7 to which conductor 31 32 is attached is turned to the far side relative to the plane of the paper while lead in wire 8 to which capacitive probe 12 is attached is turned in the opposite direction to the near side folded conductor 31 32 is thus displaced to the far side while probe 12 is displaced to the near side when the arc tube is swung back as shown.