Is their a minimum height for an electrical run in a garage. The outlets are mounted at 45 inches. But the main feed coming from the main panel is run out the bottom of the panel and is fed through the wall studs across the back wall at 21 inches above the garage floor.
If you're referring to the service entrance cable, then I would not be comfortable with that installation unless the cable is protected by a fused disconnect outside (in which case it's a feeder, not the service entrance). Service entrance cables must be protected from physical damage. What you describe is not adequately protected. If the service entrance cable gets damaged and shorts, the results are pretty spectacular - and very bad for your house.
Or when you say "main feed", are you just talking about the circuit for the receptacles? In that case it's still not generally accepted to run NM cable exposed in a garage below about 8' without protection, but it's much less of a big deal.