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tray current is defned as current that flows through unwanted paths.1 Current leakage from highvoltage power lines through a concrete pole can damage the concrete and cause other serious problems in power networks. High-voltage power lines are isolated from the ground by some electrical resistances. The resistances are not constant and vary with ambient effects. If concrete pile quality and technology are low, a deposit layer from air pollution forms on the insulators, and if grounding systems do not work well, high-voltage alternating current (AC) can creep from the surface of the insulator into the concrete pole. Stray Alternating S Current Problems in Concrete Power Poles Problems Encountered Release of Cable from Clamp A. AghAjAni, M.A. golozAr, A. SAAtchi, And K. rAeiSSi, Dept. of Materials Engineering, Isfahan University of Technology, Isfahan, Iran M. Urgen, Istanbul Technical University, Istanbul, Turkey S. ShAbAni, Subsea R&D; Center, Istanbul University of Technology, Isfahan, Iran High-voltage alternating current (AC) can leak through the surface of insulators and enter concrete poles. Tis can create problems that may afect the power network, such as the release of power cables from clamps, melting and cracking of insulator surfaces, melting of the insulator, and degradation of the concrete poles. Tis article explains how stray AC damages power poles, and outlines methods to prevent it. Creep of high-voltage AC from the surface of the insulator can release a power cable from a clamp. Figure 1 shows a typical clamp before and after the effects of creeping AC from the surface of the insulator. The stray AC was high enough to burn and melt the contact surfaces of the cable and clamp. In this condition, the compressive force of the clamp on the power cable is reduced and the cable releases from the clamp. This occurs in regions with polluted air. Pollution and moisture from the air cause oxidation of the clamp and cable contact surfaces. Electrical resistance of the clamp contact surface increases and high electric heat is generated in the clamp when high stray AC occurs. Resistance between the clamp and cable increases as the oxide layer on the surface of the clamp and cable is formed. To mitigate this problem, air and water clamp seals have been installed. Grounding System Grounding high-voltage power transmission systems is different from ground- 36 MATERIALS PERFORMANCE May 2013 NACE International, Vol. 52, No. 5