Why "Line / Load " ( ? )

When I first started performing solar electrical installations, as a journeyman's apprentice, one of the first things I really noticed was how confused the old-school electricians were about the interconnection.

They'd say, "Hey, is that thing on the line or the load side?"  And by that they meant, was it drawing power or generating it?  To an electrician, an inverter is just like any other 240v electrical device in a home such as a clothes dryer or rangetop stove.  At least, it's wired the same.

With that said, there's a practice of keeping the load side of the current tied in to the bottom of a disconnect.  They couldn't figure out whether it should be wired to the bottom or the top.

"Isn't that thing generating power?" they'd ask.  And we'd say, "Yeah."  To that, they'd respond "Well then shouldn't it be wired to the top of the disconnect?"

It was an endless argumentative point of confusion with the old-school electricians.  They'd use it as an excuse to get donuts.  They'd say, "hey, we're gonna need a cup of coffee and some donuts before we can really figure this out."  And then, they'd leave for an hour and come back, tie in the disconnect any which way they wanted, then vanish, not to be seen again until their next subcontracting gig.