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Why do surge arrest typically looks like this ?

I found one of the reason is to prevent ingress of water by using slippery rubber material but it does not explain the reason for the shape of the surge arrest.


It is to increase the length of the surface path from one side to another. The surface is more conductive and has lower spark voltage than the middle of a material (because it can be coated with dust etc). The discs are there to make the surface path longer without increasing the length of the surge arrestor.

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    \$\begingroup\$ Creepage distance is another term for this. Video description. \$\endgroup\$ – Nick Alexeev Jul 13 '15 at 0:36
  • \$\begingroup\$ Hi, @Pentium100, I understand ! The design is such that to prevent the high voltage current from running across the surface of the surge arrest instead. Thanks for the explanation and the video ! \$\endgroup\$ – SDog Jul 13 '15 at 15:23

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