Abstract: An electric heating element is proposed, which has a contact unit formed from at least one PTC component and contact plates resting on either side thereof and a casing, whereby for ensuring a good contact pressure in the end product in the unpressed state of the heating element the contact plates (12, 13) are curved and rest with their convex side on the PTC components (14), the casing (2) is made from dimensionally stable light metal and in the unpressed state has an inner wall (17, 18) with a finite radius of curvature (r1) facing in convex manner the contact arrangement (12, 13, 14) and which is larger than the radius of curvature (r2) of contact plates (12, 13).

Abstract: A sensor (1) for detecting frost deposits, particularly on evaporators of refrigeration plants or the like is proposed, in which between the spaced heat source (3) and heat sensor (4) is provided a thermal connection (2) made from a material, whose thermal conductivity coefficient is of the same order of magnitude as that of frost.

Abstract: Thermal protective switches (1) that are used for limiting the temperature of electrical appliances by automatic opening of the circuit should only reset themselves again after a large change in temperature. In this respect, when the load (9) is overheated, the contact (5') fixed to the bimetallic strip (5) is moved clear of the counter-contact (4) into its open position so that the current through the contact assembly is interrupted. If the fault is not put right there is continuous switching or hunting and there is a danger of the contacts of the thermal protective switch becoming welded to each other. For this reason, for stopping the contacts closing again, the design is such that in the open position the contact assembly, is shunted by the PTC resistor (6). The parts are kept in the open position until the load (9) is turned off by hand.