OK, back to the subject at hand. I'm assuming that you all agree with sticking to the #6 copper for this long of a run? Yes? No, I think the consensus was that #8 copper would suffice. The reason that's somewhat tentative has to do with the power demands of HVAC motors (i.e., a heat pump--and trust me, we do understand how a heat pump works). Had this been a simple requirement for a 50-amp general purpose circuit, then I think #6 wire would have been the straight-up choice. However, HVAC equipment behaves a bit differently than a general purpose circuit in that it has both a minimum and maximum circuit ampacity rating and special code sections apply. Cutting to the chase (and at the risk of oversimplifying), the minimum circuit ampacity is what the equipment needs to run after it has overcome the starting surge of its major component--the compressor motor. The maximum circuit is to allow for the starting surge, which can be several times the running load, lasts only briefly and does not pose a significant threat of overheating the conductors. Thus, a heat pump is a specific situation where it is appropriate to use a larger OCPD (circuit breaker) than might ordinarily be used with a specific wire guage. But this isn't done by "guess and by golly"; it's based on the known faceplate ratings of the dedicated equipment. In the thread discussion above, you'll note that there was some variance of opinion. Because I couldn't locate info on the minimum circuit rating, I initially took the conservative tack of recommending #6. (Forgive me if I'm wrong, but I think jmvd20 took a similarly "safe" route too.) At the very least, the OP would have a safe result that would be uncontroversial in the view of any inspector. Ron, on the other hand, being more familiar with the particular type of equipment, was certain enough that the MCA was low enough to be fed by #8CU under these environmental circumstances. After some discussion about that, I'm inclined to agree with him although, as someone who doesn't deal with this equipment frequently, I'd tend verify the manufacturer's specs (which were not available online) before opting in that direction. But I'd add that Ron's interpretation also satisfied my "common sense" test based on a rough guestimate of the approximate wattage consumed by a 5hp motor. Thus, it isn't at all certain that #6CU is required. I believe the consensus is that #8AWG/CU is adequate. "To allow for both voltage drop and terminal size problems that the larger diameter #2 aluminum would cause, per my bad experience!? With the entier distance in conduit as you all are "by the bookers", Right? In making our recommendations, both Ron and I (and perhaps others) considered voltage drop at the 200' distance. Using 35 amps as the estimated running load, here are my calculations: A 200' run of #8CU in conduit, delivering 35A at 240V yields a voltage drop of 4.9%, which is under the usual target of 5% (i.e., it's borderline, as I said, but acceptable). At 50A, the drop is about 6.5%--a drop that most motors can tolerate quite readily. Under the same assumptions, if we use aluminum wire instead of copper, it will need to be upsized to #6 in order to meet ampacity requirements. Again at 200', the voltage drop calculations for #6 aluminum are very close to those for #8 copper (4.7% @ 35A and 6.8% @ 50A). Any way you look at it, #2AL is way, way overkill for the OP's application. And that's why I called you on the statement that you used a chart that equated #2AL with #6CU due to the distance. That doesn't make sense to me and I'd love to see that chart. Now, if it was the only underground-rated AL wire that happened to be available from your supplier, then fine, just say so. Now here's what strikes me as particularly ironic: While you take issue with "going by the book" because, you contend, the book is mostly overkill, it was going by the book--strictly--that led the cost-saving recommendation to use a smaller and less expensive wire guage! OK, sorry, enough of that. 1. As I have stated in both previous thread entries. "I would NOT have attempted the project if I thought it was dangerous to anyone's safety"! So you all are saying that you "always" complete your "own" projects per the "letter" of the law and not the "spirit" of it. Meaning, on your own land when you know that if you where to deviate from the law/code, the chances of the "risk" taken is a billion to one shot of going wrong that you would still ALWAYS go by the letter of the law? In my opinion, The code is an "overkill" guide so that people that have very little common sense will not get themselves or others injured or killed. Agreed? No, not agreed. In fact, the less you know, the less capable you are of assessing the risks and, therefore, there's all the more reason to adhere to code strictly. Personally, I'll admit to doing some pretty half-a$$ed things in the past but, honestly, the older I get (I'm 62 now), and the more I learn, the more I do, in fact, "complete [my] 'own' projects per the 'letter' of the law." As for the code being "an 'overkill' guide so that people that have very little common sense will not get themselves or others injured or killed", I agree only to the extent that there are certain safety margins built in, much like there is a over-design requirement when engineering a bridge. And I'd also agree that a few of the requirements seem like unnecessary nuisance and expense--child proofing all the receptacles in an adult-only home comes to mind. But even there, standard requirements contemplate not only your personal requirements and tolerance for risk, but those who may occupy the premises at a later time. As the code evolves, with new editions coming out every three years, a great many of the new requirements are based on actual documented experience. That is, there is statistical evidence of a problem that caused actual fires, actual injuries and actual deaths. Since there are only about 300 million people in the U.S., these problems are not in the order of one in a billion or they would not have statistical support. 3. The thick plastic around the wire & plastic conduit for that matter becomes very brittle and is degraded very quickly from the sun / UV rays, due to the 100 plus degree temps in summer and 320 days of sun a year. SO the best place for the wire IS underground. And metal conduit would just melt any plastic sheathing on wire from the suns heat. No one here disputes that the OP's proposal to run the conduit underground is a good idea and I certainly didn't hear anyone suggest metal conduit. Interestingly, if you familiarize yourself with the code, you'll discover that all these factors are well-accounted for. Ambient temperature, for example, is a definite factor in selecting cables and wires. So, too, is sun exposure. Where conditions fall outside normal expected ranges, there are wire types and methods specifically designed for such conditions. BTW, if you post for advice here, make sure to mention that your project is in the desert where the temperatures and light exposure are very high and you'll get competent advice for those conditions. In sum, there is no real reason to "choose the 'illegal' way." Jes my 2c and a "good day" to you too, sir.

Why start a new thread??? You should continue this topic in it's original thread to avoid confusion. Anyone not familiar with your original question is scratching their heads going "What the heck is option 2?". Here is a link that might be useful: Original thread on this topic

Technicians don't have licensing (at least not in Texas). Many companies claim this, but anyone with $20 and a clean back ground can submit their application to TDLR and get a "Technician License" if that's what you want to call it. It means nothing. HVAC contractor's license: what I have gives you this: TACLB28416E (requires much more than just money to get it.) That is a 'REAL' license. The other is more or less a registration with the state, that provides a way for the state to keep tabs on those with criminal records, because by and large the HVAC companies never follow thru.

I'm hoping to get up there this afternoon to get the model, and look at the control unit. This is a 1967 house. Oddly, it was built in Las Vegas without AC--we replaced the original furnace in 2009, and found a add-on AC unit bolted on, and a rafter cut to fit it. The ducts were not upgraded from 18" to 24". (and the incompetent of the installation of the replacement work is its own storyi, featuring the combination of a separate duct to each bedroom from the plenum, compounded by leaving the duct to the front half of the house turned sideways and blocked by the installation [put a bunch of those yellow guys screaming in horror here]). Anyway, what has led to me wondering about this is the apparent failure of the control module (?) on the attic unit. We had been blaming the thermostat, but after replacing, further investigation found that shorting R to G will sometimes turn the fan on, and sometimes not. The new thermostat turns on the burner, but usually not the fan (it did once). The fan has also refused to shut off entirely three times. Pulling the thermostat didn't do it; I had to kill the breaker. This is what led to my interest in B: do I really have four used wires, or five. If blue was only attached to B to not be loose, I can use it for C on a replacement thermostat. (for that matter, why do they use C rather than just drawing from R, at least on units that don't have a separate Rc? mm, another note: the reason that this was such a sudden discovery is that it had been a while since we used the AC--we have a large, central swamp cooler with a 1 HP motor. Since using a panel to change the flow so that it didn't all go into the family room, it's meen enough for most of a desert summer. We actually got as high as 117F while only 82 in the house on a 2% humidity day. (We switch to AC once it hits 83) thanks hawk