Is VIN directly connected to USB power?
I plan on powering my Uno via USB. I wanted to know if anything would blow on the uno if it drew too much current. I learned my lesson using the VIN for VIN and 5V to power a 5V rail and LCD. Thanks.
No.
Vin goes through the regulator, the output of the regulator is connected to the 5v rail. To get 5v out, you need ~7v on Vin. It is better to supply external power via the barrel jack, as there's a schottky diode between that and the Vin rail, so if you connect it backwards, it won't damage anything (whereas doing that to Vin will trash every active component on the board).
When powering via USB, there is a self resetting (ptc) fuse to protect against overcurrent conditions (and the USB standard requires USB hosts to have overcurrent protection, though not all devices do this rigorously, and many Chinese USB chargers don't do it at all).
Thanks, I'll contemplate using the barrel jack if I can find some that fit...
I just wanted a 5+V on-board to make quick connect and disconnects of the board from it's home.