Originally posted by k
Same thing happened to me, but i think it is because the turbine run out of power. I took a new invincible turbine and electric trap and done!
That's not the reasoning behind it though. It has to do with the hit damage from the electrical trap and the health amount of the zombies. As you may notice, that when the rounds proceed to increase, there are more zombies and they are harder and harder to kill. This is because each round that you progress through, the more zombies that will spawn in the map. The same effect happens with their health. You will notice on the first round it only take 1 knife lunge to kill. Then on the second round it is 2 knife lunges and so on and so on. After round 55 the electrical traps stop dealing a sufficient amount of damage to the zombie in order to kill them. And you may have also noticed that they can only attack one trap at a time, thus there cannot be two traps dealing damage to the zombie, making it not death-able. Hope you read through everything and understand why this happens ^_^