A few of my collegues have done electrical design installations where they install panelboards behind doors, for example in Janitor's closets, garbage closets, etc. There's nothing in the Code that says you can't do this. When the closet door is shut you have your clearance as required by Code. The only downside to this I see is that if someone is working on this panel with the cover off and someone opens the door. Is this an acceptable practice? Does the Authority Having Jurisdiction (AHJ) have final say in this?