I only know what the meter says. There may be some kind of unloader in there but I really think it is just that it can't take in any more air. This is the C/H diaphram oilless compressor with a 6.25 sticker and a 1HP motor. In the middle of the range it actually draws more than the labelled FLA, then tapers off. That was the day I bought it. If you have the January archives of this NG, I posted the actual curve
2 ga. copper is the -smallest- you should consider using.
I tend to go on the basis of "figure out what the requirements are, and go one size larger", so I'd likely run #1 in that situation.
As you know, materials cost for a project like this is trivial, relative to the labor effort involved -- some 'over engineering' is 'cheap insurance' for handling expanded future needs.
If it is a 'dim' scenario, you didn't budget enough for lighting!
Note, I was expressly talking about 'worst case' situations -- any rational engineering *does* _design_ to the worst-case scenario specifications. Yes, you can 'get away' with 'less' in many situations, but, eventually, it *WILL* 'bite' you, probably "at the worst possible time, in the worst possible way". There is a reason, borne of painful experience, that O'Brien's Law ("Murphy was an optimist!") exists.
The _last_ thing you want is the *feeder* to a building with sharp, rapidly spinning metal thingies to shut down. You lose all the lights -- and thus can't see _where_ those sharp thingies are -- *and* they're still spinning, at least until they coast to a stop. This is a significant argument in favor of a _separately_ protected, separate feeder for the lighting circuits. And for splitting the lighting across (at least) two circuits, as well. ("Yes, I _do_ have far more experience in dealing with Messrs Murphy and O'Brien than I really care to; why do you ask?" :)
As for the rest, lighting is a 'static' load; an air-conditioner draws quite close to 'rated' amps while the compressor is running; the air-compressor -- kicking in to 'top off' the tank -- is going to draw around 80% of rated load; a dust collector runs 'normally' at close to rated load, as well.
Re: your comment about a 2hp motor, and a 5hp one drawing similar current under similar loading; that claim _is_ true, but only as far as it goes -- static load, under static conditions. The 5hp motor will draw *considerably* more at start-up; also at other times when the motor undergoes a significant increase in load, over the short term.
One final comment: For power feeder/distribution, the 'cost' associated with "over-engineering" the implementation to 'worst case' specifications is minor. Materials cost is usually swamped by labor expense. Also, the 'down side risk' of finding out _after_the_fact_ that the newly done work is 'inadequate' and requires replacement, puts the minor additional cost of the 'do it right the first time' approach in the realm of "*really* cheap insurance".
Thanks for the comments. I've still got a lot of "figure out what the requirements are" calculating to do before I commit. My 100amp figure is straight off the wall and may wind up either being serious overkill or woefully inadequate. All I really know is that the current service won't do.
Tom Veatch Wichita, KS USA
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