In some other countries where they use a lot of concrete for construction of residential houses I have seen them run electrical wires throughout a house via a black corrugated flex conduit. this also allows them to pull new wire in the future by vacuuming a during from one end and pulling the new wire through. I thought this was great because if you ever need to make a new circuit from the panel there is very little destruction to do. Is something similar possible under NEC rules? Say you had a tiled floor and wall in the room where the panel is and to avoid destroying this in future, you build in a safeguard access conduit for new pulls?

I have a square d homeline panel and recently had to replace a breaker. I noticed that when you put the covers on, you can see a slight space between the breakers... like they don't sit flush upon the one stacked below it. There is also a little wiggle in each of the single pole breakers. Is that normal? How do you know when the breakers are securely grasping the power buss? The side of the breaker with the little pivot feet..... if the feet are not inside the brackets correctly, would the other side still be able to grasp the buss?