I can't speak for squirrels. However, owning a rabbit, you quickly learn that rabbits like to "clean up" the cables (roots) in their den—so you have to carefully guard the cables so the bunny doesn't get fried.
Also, our rabbit tends to ignore cables that are flat along the ground. Only diagonal ones that cross her path ever seem to draw her attention.
You won't find any, because electrocution is deadly by definition ;-)
Joke aside, I think when they reach the wire the contact surface is not very large, so they probably get a sensation similar to touching an electric fence rather than an electric shock.
Source: we had a rabbit when I was very young. I learned quickly not to touch some of the electric cords laying on the ground.