Skip to main content Accessibility help

Conductive polymer switching mechanism for high power current-limiting applications

  • J. J. Shea (a1)


Various thermoplastic and thermo-set based polymers, blended with acetylene carbon blacks and graphite fillers to form electrically conductive polymers, were investigated to determine the switching mechanism under high power short-circuit fault conditions. Presently, a positive temperature coefficient (PTC) effect is the accepted switching mechanism for low power overcurrent devices. However, for high power, distribution level devices, this mechanism has been assumed to be the same under high fault conditions. This work proposes another possible switching mechanism responsible for a steep change in resistance under high power faults. The proposed mechanism of resistance change comes, not from the PTC change in the material, but rather from the vaporization of the conducting polymer contact areas at the polymer/electrode interface. A comparison between low power polypropylene based devices with a positive temperature coefficient (PTC) effect (thermal expansion of the polymer bulk) and high power devices was done to support this theory. A model was developed along with numerous short-circuit tests to support this theory. Modifications with e-beam irradiation were made to alter the PTC characteristics of thermoplastics but had little effect on high fault short-circuit switching. Also, numerous short-circuit testing on thermo-set based materials without any PTC transition still switched under high fault currents. These all supported the proposed theory that switching, under high fault currents, was from vaporization of the contact areas at the polymer surface rather than thermal expansion in the bulk of the conductive polymer as previously accepted.


Corresponding author


Hide All
[1] Narkis, M., Ram, A., Flashner, F., Polym. Eng. Sci. 18, 649 (1978)
[2] Narkis, M., Ram, A., Stein, Z., J. Appl. Polym. Sci. 25, 1515 (1980)
[3] Meyer, J., Polym. Eng. Sci. 13, 462 (1973)
[4] P.H. van Konynenburg, Electrical Devices Comprising Conductive Polymer Compositions, US Patent 4304987 (1981)
[6] L.M. Middleman, J.H. Evans, A.E. Blake, V.A. Scheff, Circuit Protection Devices, US patent 4352083 (1982)
[7] Doljack, F.A., Trans, IEEE. Comp., Hybrids, Manuf., Technol. CHMT 4, 372 (1981)
[9] J.E. Wilson, Radiation Chemistry of Monomers, Polymers, and Plastics (Marcel Dekker, Inc., NY, 1974), pp. 369–384


Conductive polymer switching mechanism for high power current-limiting applications

  • J. J. Shea (a1)


Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed