76 of the spring 30 presses against the interior side of the second housing part 22 when the housing is assembled somewhat compressing the convex portion of the spring the convex portion 76 is sufficiently compressed that when the housing expands in response to the heating of the heating element 26 the convex portion rebounds to cause the spring 30 to remain in contact with the second housing part 22 and to continue to apply pressure against the second electrical contact 28 the convex portions 80 and 82 of alternative embodiment spring 30 b and 86 of alternative embodiment spring 30 b function in that same way thus regardless of the spring embodiment 30 30 a 30 b used the spring helps maintain a positive pressure contact between the second electrical contact 28 and the ptc heating element 26 and thus indirectly between the first electrical contact 24 and the ptc heating element even during thermal expansion of the housing in fact because the spring 30 receives heat directly from the heating element 26 by conduction through the second electrical contact 28 the spring tends to expand to an extent proportionally greater than the expansion of the housing which tends to urge the convex portion of the spring even more securely against the housing the combination of convex and concave portions of alternative spring embodiments 30 a and 30 b allows those curved parts to.