This is so annoying.

If I would have wanted to place down an underground belt I would have done so myself. When Im placing a BELT Im expecting a BELT to be placed instead of the game deciding it knows better than me and placing something else.

Big thanks to the OP for making this guide, very useful, i just made my first network(an alarm system to warn when coal runs low in the boilers). A few hours ago i thought i would never understand what those combinators do