The main features that could affect the degradation rate are the heat dissipation capa-bility of the complete housing [66, 68, 93] and the voltage distribution along thearrester column. As will be discussed later, the voltage distribution along an arrester column is distorted by stray capacitances, and may enhance the non-uniform temperature distribution, which in turn will accelerate the degradation of the arrester. Besides, extensive laboratory measurements [69, 70] showed that degradation could affect the collar material (rim) severely, which may overshadow the ageing of the ZnO body. New organic materials are, however, more efficient as far as corona [94] and long term stress [70] are concerned.