by JaggedEdges » Thu Mar 09, 2017 11:54 am
ACs went stupid for a while until they figured out they had to run freon replacements at higher pressure for higher efficiency, or perhaps they knew, just couldn't be assed replacing all the old tooling. Used to have a 15,000 BTU freon unit that drew 12A and would chill a whole 1200 sqft house in an hour if placed upstairs. (I'm regretting getting rid of it when I moved into central air.)
Anyway, in recent years they've been "getting back to where they should be." with higher pressures and efficient motors.... even the cheapy cheapy 5200 you can grab in mallwart only runs 5 and a half amps I think, the "good" ones, drop at least another one.
Anyway, about wire sizes, it's partly about heat dissipation and heat generation in long runs. Wire of same gauge is rated higher for open rather than conduit use. Typically, conduit use is assumed. However, if you went all under floor, with weatherproof stuff, you'd not need to care about oversizing it. Bear in mind that it's also rated for much longer runs than are even possible in trailers so I see little point in oversizing. Only reason I'd consider it, is if you're running it the same side of the insulation to your skin, and solar heating of the skin is going to have it hot enough to cook eggs, then yah, go oversize.
Edit: It's also theoretically possible that larger size wiring will pull heat out of a circuit breaker and thus not cause it to break the circuit at the rated amps. For example, cool conditions, you went with bigass 10 gauge on a 15A and you might pull 17 or 18 amps before the breaker pops. Now you might regard this as just dandy, but it could be causing damage downstream, like your 15A plug melting at the hookup or something.
Jack of all trades, Doctor of rocket surgery and fellow of the noble college of shadetree meddlers. "in argentum tenax vinculum speramus"