Expanding on what Den said, for something to get shocked with an electric netting, they have to be touching the ground and a hot wire at the same time. Otherwise the electric circuit is not complete.
Their feathers or a baby chick’s down will insulate them. But if they touch a hot wire with their comb or wattles while they are touching the ground the circuit is complete and they jump back. They kind of learn not to do that after a while but sometimes it takes some of them a while. My baby chicks can walk through the electric netting until they are about 7 or 8 weeks old, then they are too large to fit through the holes.
From what I’ve seen the electricity has nothing to do with them not flying over. The normal way chickens escape is by flying up to something solid to perch on and then they fly down on the other side. The top is not substantial enough for them to perch on so they don’t fly up there to start with. They certainly can fly over the fence if they are motivated enough, but usually they don’t. Mine fly up five feet to get to the roost at night so they could easily clear that 48” netting.
About the only time I ever have anything other than young chicks going through the fence escape mine is when a chicken gets trapped against the fence when they are being attacked. They go vertical to get away and accidentally come down on the wrong side of the fence. On very rare occasions this is a hen trying to get away from an amorous rooster. Most of the time it’s when I have cockerels in the flock and they are getting into their fighting.
A couple of tricks I’ve learned to help them not get caught against a fence is to flatten the corners. 90 degree corners aren’t too bad, but don’t make them any sharper. Flatter is even better. The other trick is to not make long narrow corridors. Spread it out more into a square than a narrow rectangle. Since I learned this, I seldom have even a cockerel escape, even with a lot of skirmishes.