Good question....after all, we have a "general purpose 110 plug," don't we?
Sure we do....for the smallest of our circuits those that are 110 volts and less then 15 amps.
Increase the volts, increase the amps, and there's more energy being used. This means more damage when things go wrong.
So, to reduce the risk, and prevent actually creating a hazard by acidently supplying an appliance with the wrong "flavor" of electricity, we've developes a whole collection of plug types.
Every appliance -compresor, welder, whatever- has a nameplate that contains the information needed to size the circuit correctly. Besides "volts" and "amps," the plate may have phrases on it such as "duty cycle", "minimum circuit ampacity", "maximum fuse", and the like. This information, together with a copy of the code, tell you what size wire to use, the overload protection needed, etc.
A 30 amp breaker will let thirty amps through......maybe not a good thing if the appliance is only supposed to use 10! Use the larger breaker, and you've given away a large part of the protection the breaker is supposed to provide.
A 30 amp plug sugests that there is 30 amp wire behind it. Not really a good thing if there is really 15 amp wire, and a 50 amp breaker in the circuit instead.
Different appliances have differing electrical properties. Even a circuit perfectly designed for a 30 amp welder may be completely inadequate for a 30 amp air conditioner- even though the two use the same plug.
This is because, besides the general circuit sizing rules, there are ten "exceptions" that are specific to different types of equipment.
I am sure that there are times where using two different apppliances on the same receptacle haas "worked fine for years." That is very possible, just as it is quite possible that the solution was absolutely correct.
Without knowing the details of all the equipment used, I just can't say. A plug is only one part of the system- and probably the least important part at that!
So I say, 'think it over.' Look at those nameplates, and the code book. Look at your supply wire, and the breaker that regulates it. Then decide.
Don't fall for the trap of "bigger is better." You wouldn't buy a pair of shoes two sizes too large!
