The estimation of the polymer fuses features

Abstract-The protection of electrical circuits against the overload or short circuits is usually achieved by the single use of blow-out fuses. The paper contains the examining results of the multiple use of polymer fuses. The static and dynamic characteristics of selected fuses are acquired on the test station. Some interesting features of the polymer fuses, not included in datasheets, are carried out. The courses of characteristics in comparison to their technical data with elements of accuracy analysis are discussed. I. The polymer fuses attributes Fuses are the basic protection devices used in circuits. Except fuses there are also used bimetallic devices. The first ones break the circuit in the event of short circuit. The second ones provides overload protection. Both devices prevent damage to the connected equipment and cables. The disadvantageous feature of the traditional fuses is their blow-out. In consequence of that there is a break in a circuit and necessity of replacement. The typical bimetallic devices does not need to be replaced. They can back to their idle state. However they can reset even if the fault is not removed. It causes a cycling on and off between the fault event and a protected state which may damage the equipment. Nowadays above mentioned elements may be replaced by one freed from described problems. It is polymer fuse (PPTC- Polymeric Positive Temperature Coefficient), called resettable fuse [1-14]. It realizes functions like devices above, however it does not need to be replaced and it does not expose the equipment on damage. The PPTC fuses are constructed with a non-conductive polymer plastic, which can change in two phases. In normal state (without a temperature increase) the polymer has a crystalline or semi-crystalline structure, where the molecules form a regular structure (Fig.1.a). a) b