E fences don't work like an electrical outlet. The fence charger amplifies the electric charge from either 6 or 12 volts from a DC powered charger like mine.....or 120 volts from an AC charger......all the way up to a short burst of juice that measures from 6,000 to 12,000 plus volts like mine. But it is a short burst.......like that of a static electric shock or more like a spark plug in a gas engine. But ramped up like that, it is very painful. Like the feeling your arm was just yanked off.
Chickens get zapped like everything else and that is the beauty of it too. They learn it is a boundary they do not want to cross. I use a light wire system, and when training the birds to it, only one wire held only a few inches off the ground. Mine always walk up to it and step on it to get over it, so they get zapped on the bottom of their foot and may well launch 5 to 10 feet in the air when they do. They will then strut around in protest, trying to figure out a way back inside where their friends are. They do that by lifting up and hopping back over. But once back inside, they are not willing to risk whatever it was that bit em, so tend to stay away from it. Up to it....but not past it.
That is with the wire fence........with poultry netting, it more or less resembles a real fence, so they may well fly over it. If they have stuck their neck through and got zapped....maybe not, but for an E fence to work, they must get zapped.
Again, it does no permanent harm to anything, but nothing and nobody wants to get that twice.