I'm wanting to build a wall perpendicular to a wall having a load center on it. How close can that wall come to the edge of that load center?

What type of wall are you talking about?

Working clearance requires a min. of 3'. So I wouldn't come any closer than that with the wall,

You must have 30" of clear width from side to side in front of a panel and a clear space of 36" in front of the panel. Maintain this and put your wall where you want...

The 30" side to side clearance is correct. Thing is, the panel can be anywhere in that 30" space. It does not have to be centered.
So for instance, if there is 30" to one side, the panel can be right up against a perpendicular partition wall.

Thanks!

Thanks!