It is truly the pits. I don't know why it is the way it is. Some folks work around by entering equipment as material, but of course that has a different set of issues (no accounting for allocation). I would try setting the max units to very tiny. As I said earlier, you can check effort-driven. I would try to assign all other resources first, then uncheck effort-driven, then assign equipment. If you later need to make a change, check-effort-driven first.

There is no answer to your very good question, best I can tell. And many people have had the same question and it remains that MS Project simply does not do a good job dealing with equipment.

You probably already have done this, but if not, do some searches and see all the Project MVPs (MS Most Valuable Professional), who have no answer for this either, just workarounds like set max units very low, uncheck effort-driven if you can, maybe make it material instead. http://www.eggheadcafe.com/software/...equipment.aspx

Bottom line is that Project does not see the difference between human work resources and equipment resources and treats them the same though obviously they are not.