US Mains Residential Code Compliance - Page 1
Forum section: electronics / beginners

author: psteichen
author_rank: Contributor
timestamp: October 23, 2017, 10:02:32 pm
content: I realize that this may be a bit off topic for an electronics forum, but I couldn't think of a better place to ask. Often electronics pros have some knowledge in this area as well, so mods feel free to delete if inappropriate.I'm looking for a used heat pump, as my existing one failed. I will have an electrician and HVAC contractor install it, but I want to make sure that I buy an appropriate unit. The existing house wiring from the panel to the unit uses a 30 amp 240V breaker and 10 gage solid copper wire.The unit I'm interested in buying has the attached data plate. As you can see it recommends a minimum 40 amp breaker, and yet the minimum circuit requirements are only 24 amps. Can I comply with the code in one of the following ways (local codes do not modify the national standards)?A: Disregard the plates recommendation for a 40 amp breaker, use the existing 30 amp and 10 gage wire as it is plenty big for the 24 amp load.B: Use a 40 amp breaker, and retain the 10 gage wire, as it is big enough to handle 24 amps.C: Electrician must run all new 8 gage wires through the house, and install 40 amp breaker.Option C would be cost prohibitive (wire is 60 feet through finished drywall), and will force me to keep looking for a different unit.I'm sure some will recommend simply calling an electrician to ask, but I'd rather know the answer upfront to avoid the usual result of asking a professional. You get a quote for the most work possible, rather than the minimum to comply. Most electricians also refuse to answer questions over the phone, and want a $100 service charge to stop out.Thanks for any advice!

author: sokoloff
author_rank: Super Contributor
timestamp: October 23, 2017, 10:53:08 pm
content: Quote from: psteichen on October 23, 2017, 10:02:32 pmOption B is legal (and safe).Option A is out. Equipment specifies a 40A HACR breaker. (All breakers that meet UL 489 meet the HACR spec, so you need to see either marking.)Option C is overkill.See this well-written post, including an identical example to your case on page 3:http://www.dantespeakheatingcooling.com/upload/Mike_Holt_NEC.pdf

author: jmelson
author_rank: Super Contributor
timestamp: October 23, 2017, 10:56:37 pm
content: Hmmm, bunch of comments. Do you REALLY want to install an R-22 unit in 2017? Have you priced R-22 in quantity sufficient to recharge the whole system after the outside unit is replaced? (Answer: Better be sitting DOWN before asking!)So, the real question is:Will the existing 30 A breaker trip more than once a year when this unit is attached to it? Note at the bottom of the data plate photo, locked rotor amps on the compressor motor is 104 Amps. That's what it draws EVERY time the compressor starts, for just an instant. Depending on the curve of the breaker, it may be prone to trip every few starts, or not.Is the LRA rating of this new unit greater than the OLD unit? If NOT, then you should be in the clear. There is no NEC requirement to put in a larger breaker, but there IS a requirement that the breaker be the right rating to protect the wire. So, upping the breaker without upping the wire size seems like a no-go. You CANNOT put a 40 A breaker on #10 wire (I think, I'm a little rusty on these) based on the steady-state draw of the appliance. That is totally irrelevant. You MUST select the breaker capacity based on the wire gauge.One possible solution is to try it, and if the breaker trips, obtain a breaker with a greater magnetic time delay for motors that take more starting current, but same 30 A continuous rating.Another option would be to put a hard start kit on the compressor (assuming it is a standard 240 V capacitor-run compressor, and not a variable speed motor. The hard start kit is a larger starting capacitor and a relay to cut it out after the motor starts. This will reduce the time for the compressor to start, making the breaker less likely to trip.Jon

author: Gregg
author_rank: Super Contributor
timestamp: October 23, 2017, 10:59:53 pm
content: If you PM me, I’ll send you some scanned pages from the 2005 National Electric Code; the files are too large to post here and I don’t want to run into copyright issues.A. I wouldn’t personally do this; it is strictly against the NEC guidelines. It would probably work if your voltage is always above 230 volts; the heat pump is also rated for 208 volts in which case the motors would draw a lot more amperage for a lot longer time in the start mode and need the 40 amp circuit. If you dig deeper into the unit, you may find motor labels that list the current for both voltages and add them all up for 230 volts vs 208 volts and make your own comparison.a. You are on your own here and your insurance may not cover a fire caused by the heat pump system.B. NO, NO, NO! The breaker must be sized according to the wire feed size; you can use larger wire, but not a larger breaker. The NEC does list 10ga as capable of 40 amps but only if it is labeled 90 degrees C or higher which is highly doubtful for a residence. No certified electrician would do this.C. Expensive but may be a good long term solution. You can run your own wire and save, but 8 ga can be expensive. Some locations allow plastic conduit on interior and exterior surfaces and it is fairly easy to use.

author: psteichen
author_rank: Contributor
timestamp: October 23, 2017, 11:00:27 pm
content: Quote from: sokoloff on October 23, 2017, 10:53:08 pmAwesome, thanks. That's exactly what I needed!Sent from my SM-G900P using Tapatalk

author: hermit
author_rank: Frequent Contributor
timestamp: October 23, 2017, 11:00:43 pm
content: Ignore the rating at your own peril. At worst it will trip the breaker every time it tries to start up. It might just trip intermittently or not at all. I doubt anyone on this forum would tell you to ignore the plate ratings though.I used to do refrigeration. Mainly domestic refrigerators and freezers. I don't know about heat pumps specifically but I'd never buy a used compressor. Opening sealed systems can lead to oil contamination. Have you checked first to see if you can find a technician that is willing to install a used unit? You'd be hard pressed to find a repair technician on the domestic side who would be willing to take the risk without payment up front and written assurances they wouldn't be held responsible for ANY failure of the thing.

author: psteichen
author_rank: Contributor
timestamp: October 23, 2017, 11:27:25 pm
content: Hey everyone, thanks for the quick feedback.I am surprised that the Mike Holt document link does indeed indicate that option B is the best answer. Option C seems like it would also be legal, but unnecessary.I've always thought, as several of you mentioned, that the circuit breaker always must be sized to prevent current in excess of the conductor rating. And yet it seems that there is a special loophole for air conditioning equipment that allows as much as a 50 amp breaker on a 10 gage wire! Seems wrong, but this certainly helps in my situation.Thanks everyone.Sent from my SM-G900P using Tapatalk

author: drussell
author_rank: Super Contributor
timestamp: October 23, 2017, 11:28:11 pm
content: Quote from: Gregg on October 23, 2017, 10:59:53 pmYou're wrong on this one... Of course you can oversize fuses / breakers for motor starting loads with the smaller wire. You need to re-read your rules...

author: drussell
author_rank: Super Contributor
timestamp: October 23, 2017, 11:39:57 pm
content: Also, I'm not sure where you are but in most countries, there are many hydrocarbon substitutes for the ghastly "real" R-22. Here in Canada I can walk into pretty much any parts store and buy R-22a, basically a propane/butane mix which is far more efficient than "real" R-22 for a pittance.I think they still don't allow these good refrigerants in the US, though, due to hysterical but effective marketing and lobbying by the producers of the CFCs, HFCs, etc... they are all highly addicted to fluorine, I guess, and need to keep polluting everything, everywhere for their precious captive-market share.Their main argument is that "well it is flammable!" Have you ever heard of something blowing up / burning down from < a pound (or in this case it would be about 3 lbs) of hydrocarbons blowing up when it spontaneously all leaked out of their air conditioner? No, of course not...But since it "might blow up", it is not allowed anywhere in the US...So sad... Hopefully you're not actually in one of those insane parts of the US!https://www.princessauto.com/en/detail/a-c-22a-refrigerant-recharge-kit/A-p8327173e

author: Gregg
author_rank: Super Contributor
timestamp: October 24, 2017, 12:02:26 am
content: Quote from: drussell on October 23, 2017, 11:28:11 pmMaybe you can get away with it in Canada, but the OP stated he was inquiring about the US. If you can show me the NEC article that allows this, I'll believe you, but NEC table 310.16 clearly states 10ga copper wire no more than 2 conductors in a raceway (like Romex, for instance) is rated for 30 amps unless it has a higher temperature rating as I stated.Furthermore Article 440.6 (A) states."Exception No. 1: Where so marked, the branch-circuit selection current shall be used instead of the rated load current to determine the rating or ampacity of the disconnecting means, the branch circuit conductors, the controller and the branch-circuit short-circuit and the ground fault protection.

author: sokoloff
author_rank: Super Contributor
timestamp: October 24, 2017, 12:03:51 am
content: Quote from: drussell on October 23, 2017, 11:28:11 pmThis is true, but I don't understand how it makes any sense with respect to physical safety.Take a 240VAC load, two lengths of 10AWG wire, and a 6 ohm (at temperature) resistor. That'll draw 40A and presumably be a fire hazard, so we restrict 10AWG wire to a 30A breaker for general use.Make the circuit have an HVAC unit on it and suddenly a 40A (or even 50A in some circumstances) breaker is now code-compliant, despite the fact that a 6 ohm near-short still represents the same fire risk as before.

author: sokoloff
author_rank: Super Contributor
timestamp: October 24, 2017, 12:05:26 am
content: Quote from: Gregg on October 24, 2017, 12:02:26 amDid you read 440.22 as posted in the Mike Holt article above?

author: Gregg
author_rank: Super Contributor
timestamp: October 24, 2017, 12:25:56 am
content: Quote from: sokoloff on October 24, 2017, 12:05:26 am440.22 basically is setting the maximum branch circuit protection (not the minimum which is better addressed in 440.6.) Usually the earlier (lower numbered) articles have some precedence over the later articles in the NEC.440.22 (B)(1) addresses the compressor load being the largest and states that the combined loads not exceed what is listed in 440.22(A)440.22(A) states that the branch circuit wiring and protection not exceed 175% of the total load ratings.

author: psteichen
author_rank: Contributor
timestamp: October 24, 2017, 12:27:03 am
content: Quote from: drussell on October 23, 2017, 11:39:57 pmI think all of the US is that crazy drussellBut I use propane anyway. The propane/butane mix sold for gas grills isn't great, because it contains some moisture, but the inline dryer is capable of absorbing a fill or two. I've been using it in leaky cars and my home A/C unit for 30 years. Never had a problem.I don't have time to install it myself this time though, so I'll probably let the HVAC guy use R22.What's the brand name or product name for the propane refrigerant sold in Canada? I'd love to grab a 20 pounder next time I'm in Winnipeg!....edit: nevermind. Just saw your link! Thanks.Sent from my SM-G900P using Tapatalk

author: psteichen
author_rank: Contributor
timestamp: October 24, 2017, 12:43:59 am
content: This stuff looks good too.https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F152647899854Sent from my SM-G900P using Tapatalk

author: bson
author_rank: Unknown
timestamp: October 24, 2017, 12:53:24 am
content: Quote from: psteichen on October 23, 2017, 11:27:25 pmGenerally awg currents are determined for continuous loads - and with plenty of safety margin, but you don't want to compromise your safety margin of course. For random assorted loads that can't be easily characterized we assume the worst case and that they're continuous loads. In the case of HVACs though we know for a fact they're not. As a class they have a characteristic load that permits up-rating the wiring. Obviously, this means it needs to have its own circuit (= breaker + wiring). This is why it's considered safe. I don't know if HVAC equipment is required to meet certain load specifications, but it wouldn't surprise me at all if it does.

author: Awesome14
author_rank: Regular Contributor
timestamp: October 24, 2017, 01:03:52 am
content: The wiring inside the wall is usually just fastened at the ends. I've successfully fished new cable by simply attaching the new wire to the old and using it as a fish wire. You have to pull hard enough to break the two staples. But I've done it probably 50 times at least.Then you could cheaply install 8ga. and a 40A breaker. I've even used this method using old BX cable as the fish wire. And, of course, if you have conduit, it's a no-brainer.

author: Old Don
author_rank: Regular Contributor
timestamp: October 24, 2017, 01:09:10 am
content: I assume you looked for new "'dry-ship" R-22 units and couldn't find one in stock around you? If not, you might get lucky and find a more efficient new unit that draws 30 amps or less.

author: drussell
author_rank: Super Contributor
timestamp: October 24, 2017, 02:27:14 am
content: Quote from: Gregg on October 24, 2017, 12:02:26 amI don't have a copy of the US code, however, I know all that is covered in 430 and 440. 430 is motors in general, 440 is hermetic refrigerant types. In Canada, motors are all in our section 28 and I know the rules are similar, though quite likely not identical. There are many nuances depending on the type of motor (hermetic type refrigerant motors are covered separately, specifically, for example), the duty rating, demand factor for intermittent use, etc. etc.In essence, it generally all comes down to the fact that the conductor must be sized for 125% of the FLA (full load amperes) like most loads are computed, so in this case the 10ga is just enough at 24A x 1.25 = 30A (probably why they rated it right at 24A) but you can use a larger circuit breaker or "standard code fuse" to prevent tripping on startup from the instantaneous current spike. Though you would generally use the lowest amperage that would prevent nuisance tripping, in most situations you are actually allowed to use all the way up to up to 175% if necessary, though there are tables that you must consult to ensure you're not too far over the ampacity of the given conductors. For time delay fuses it is more like 150% of the FLA.It is basically the same kind of reason that you're allowed to plug an 18ga corded appliance into a standard 15 A circuit. It can still carry enough fault current intermittently to open the overcurrent device on a short (or, in this case of a motor, a locked rotor.) "Tinsel cord" (christmas lights) is even allowed to be all the way down to 27ga and plugged into a 15 A breaker, but at that point I would think the wire would act as a fuse before the breaker tripped.I don't have my code books handy or I would look up the specific tables but that is irrelevant anyway since we're talking US NEC, though I know the rules on motors and the allowed oversizing of breakers is similar. Always sizing the conductors for the starting load or for the LRA (locked-rotor amperes) would be silly and wasteful. The code has allowances for that, just for starting motor loads...The OP would probably be fine with a 30 A type T, I don't expect it would probably blow all the time but a 40A breaker or standard code fuse would obviously be the ideal choice. A standard 30A breaker probably wouldn't work reliably... Nuisance trips...If anyone can point me to a copy of section 430 and 440 of your code, I would be interested to read it out of curiosity...

author: drussell
author_rank: Super Contributor
timestamp: October 24, 2017, 02:43:21 am
content: Quote from: sokoloff on October 24, 2017, 12:03:51 amI suppose it is considered safe because it is supposed to never end up in that condition. It should either be humming along at below 24A or try to draw 100+ amperes if it is stuck.In between those extremes it is supposed to have some kind of overload protection, be it thermal or some other kind of sensor system / motor protection to stop it from drawing, say, 45 amperes continuously and eventually heating the wires to destruction.There are plenty of conflicting silly conundrums like that in code but millions of installed units generally operating properly without constant incidences of things bursting into flames apparently makes it safe enough to be allowed by code.Don't get me started about free air vs raceway ratings of large conductors in auxiliary splitter gutters... LOL... I guess because they tend to be very short people always seem to size them for free-air instead of raceway but they're certainly not exactly free air. They never seem to get even warm, though, even at high load (total resistance is low enough that the heat it is dissipated easily enough, I guess?) and they pass inspection anyway...

author: alank2
author_rank: Super Contributor
timestamp: October 24, 2017, 02:51:15 am
content: Isn't the breaker sized for the WIRE attached to it? If the wire can handle 40A, then you could go UP to a 40A breaker? Why can't you go smaller with the breaker - wouldn't it just trip for a lesser load?

author: drussell
author_rank: Super Contributor
timestamp: October 24, 2017, 02:54:51 am
content: Quote from: psteichen on October 24, 2017, 12:27:03 amYeah, Duracool and Emzone are the two biggest players in the retail market here. I think they're both based here in Calgary. They're just well controlled, filtered hydrocarbon mixes. WorkGREAT!Colder outlet temp with less load on the compressor? What's not to love?!The R22a is readily available here, both in the little single cans that look like aerosol cans or in larger cylinders more like a propane tank or disposable helium-balloon tank (like the "real" flourocarbon refrigerants come in) for use by the professional instead of the home-gamer. It seems to me the last time I saw a 20/25 lb, (whatever it was, about that size) of R22a it was about $200 Canadian. I expect that is a whole lot cheaper than "real" R22...Pretty much all you need is a halfway decent vacuum pump to evacuate the system first and you're good to go.

author: drussell
author_rank: Super Contributor
timestamp: October 24, 2017, 03:02:14 am
content: Quote from: alank2 on October 24, 2017, 02:51:15 amIn general, yes, you can use UP TO a certain breaker on a cable of a given ampacity (on long runs, for example, you might want to use a size larger to prevent voltage drop). Nothing prevents you from using a larger cable for lower current.... Lower voltage drop, long runs, future upgrading to larger load, etc. are all valid. Normally the wire and breaker must be sized at 125% of whatever load is being powered by it. There are exceptions for things like fixed resistive heaters where power factor is unity and you're allowed to put, say 4800 W of baseboard heater on a 20A, 240V circuit. Code loves exceptions.Normally you obviously are not allowed to use wire of a lesser ampacity than the overcurrent device ahead protecting it but, again, there are exceptions in code, just for the starting of motor loads. The overcurrent device may be oversized in many cases to allow reliable starting while the conductor ampacity is only required to be 125% of the operating current at full load.Are all your household extension cords 14 ga or higher? No.If you plug a 1500 watt space heater into an 18ga extension cord, will it get very hot? YES!Don't do that.

author: psteichen
author_rank: Contributor
timestamp: October 24, 2017, 03:19:19 am
content: Quote from: drussell on October 24, 2017, 02:54:51 amYup, got oneAs I said, so far I've used propane sold for grills and relied on the line dryer to absorb the moisture that is present in cheap propane. And it works great. I've even thought of using an in-line desiccant dryer for compressed air to filter and remove the water while charging, but haven't tried it yet. Basic propane is around 10 cents per pound, so it's great for a leaky car (slow exterior leak). Even works in the newer 134a systems.Sent from my SM-G900P using Tapatalk

author: drussell
author_rank: Super Contributor
timestamp: October 24, 2017, 03:27:52 am
content: Quote from: psteichen on October 24, 2017, 03:19:19 amProbably not a bad idea to actually replace the inline drier eventually, anyway...

author: alank2
author_rank: Super Contributor
timestamp: October 24, 2017, 03:29:41 am
content: Quote from: drussell on October 24, 2017, 03:02:14 amWhich brings the question - shouldn't the heat pump itself have some sort of internal circuit breaker to protect itself from over current irregardless of the premise wiring? Is the name plate showing the breaker their way of not having to do that...

author: drussell
author_rank: Super Contributor
timestamp: October 24, 2017, 03:37:35 am
content: Quote from: alank2 on October 24, 2017, 03:29:41 amThe motor will have some kind of protection in it, yes.... Just for this purpose. That protection is essentially why all this is allowed by code....Often they are just those little doodads made by companies like Klixon.... Such a great name... Klixon.. Clicks off... Clicks on... The Klixon...

author: hermit
author_rank: Frequent Contributor
timestamp: October 24, 2017, 04:22:58 am
content: I was required by the major manufacturer I worked for to walk away from any units with a 'tap valve' since those units were considered potentially contaminated and the cost of destroying the recovered refrigerant was pretty high. Again, check to see if anyone will even work with a used unit before you buy one. You might get the 'local yokal' only interested in turning a buck to work on it but you might have a hard time getting a legit contractor to do the job.

author: psteichen
author_rank: Contributor
timestamp: October 24, 2017, 04:26:29 am
content: Quote from: hermit on October 24, 2017, 04:22:58 amThat's something I hadn't thought of. I'm certainly capable of installing it myself, but I'd rather not. I'm really busy...Sent from my SM-G900P using Tapatalk

author: ratio
author_rank: Regular Contributor
timestamp: October 24, 2017, 11:47:31 pm
content: This is all very interesting. I'll have to look into 22a, that sounds like it could be useful to know about. In any case, the NEC requires that the unit be protected at no higher than the nameplate MOCP (maximum over current protection), and must be fed with conductors no smaller than the nameplate MCA (minimum circuit ampacity). Unless your local jurisdiction has adopted a stricter code, with that particular unit you can fuse that #10 wire at 40A all day and all night. It is also possible that the 30A breaker will be adequate, as the unit should only be drawing max current when the outdoor temp is 90+ degrees.

author: Awesome14
author_rank: Regular Contributor
timestamp: October 25, 2017, 05:27:31 am
content: There seems to be some confusion about portable and permanent wiring. Permanent installations are covered by the electrical code differently than portable installations. Portable installations must have an easily accessible, user-operable disconnect. Extension cords are portable wiring, as are appliance cords, and everything else that plugs into an outlet.If you want to use a 100 foot 18 AWG extension cord for your arc welder, you can do that, because the cord is portable. But if the wiring is permanent, that is, there is no easy disconnect, it must be sized according to the breaker.There are different types of breakers for different load types. Typical household breakers handle considerably higher current than their nominal rating, for several minutes at least, before tripping. But the rule is 100% noncontinuous current + 125% continuous current dictates the size of the breaker, and the size of the breaker dictates the size of the wire.

author: stevelup
author_rank: Regular Contributor
timestamp: October 25, 2017, 10:03:07 am
content: I have a new word in my vocabulary now anyway... Ampacity!

author: Quarlo Klobrigney
author_rank: Super Contributor
timestamp: October 25, 2017, 10:48:25 am
content: Assuming as you say, and you are in the US, the electrician and or HVAC installer should most likely pull a permit. An inspector will have to do his or her job and approve of the install mismatch. In my experience they will not. Unless you know them or have the appropriate grease necessary to fulfill the task. (Overload) The NEC is your friend.Quote from: psteichen on October 23, 2017, 10:02:32 pm

author: sokoloff
author_rank: Super Contributor
timestamp: October 25, 2017, 01:44:56 pm
content: Quote from: Quarlo Klobrigney on October 25, 2017, 10:48:25 amThere is no mismatch. The NEC is clear (IMO) that this is acceptable per NEC 440.22.

author: hermit
author_rank: Frequent Contributor
timestamp: October 25, 2017, 02:52:46 pm
content: Quote from: Quarlo Klobrigney on October 25, 2017, 10:48:25 amPermitting is local/regional but in no way national. I did appliance repair for years. One community around Cleveland, Ohio actually required pulling a permit to change a garbage disposal. No one I know of did it. Most didn't even know. Mostly a replacement is probably considered a repair so less likely to be subject to a permit. Good point that the OP should check local regs on this though.

author: james_s
author_rank: Super Contributor
timestamp: October 25, 2017, 06:40:03 pm
content: Quote from: sokoloff on October 23, 2017, 10:53:08 pmYikes! No! That's wrong!10AWG wire is rated for 30A, you must never use a breaker larger than 30A on 10AWG wire, the breaker exists to protect the wire and should be sized accordingly. You can get delay trip breakers for motor and ballast loads that will allow a *momentary* overload without tripping but they will still trip if the load exceeds the rating for a prolonged period.Putting a heat pump that draws 24A on a 30A circuit is safe, though you may experience nuisance trips on very hot or very cold days when the unit is working particularly hard but really that shouldn't occur.Regarding R22, it's a shame they phased it out. The alternatives are inferior and require larger equipment and operate at nearly double the pressure so you need brazed lines, with R22 you can get away with silver soldering. R22 has only 5% the ozone depletion factor of R12 and as long as you properly recover it and don't just vent it into the atmosphere it's not a problem. The ozone hole occurred because R12 is horrible stuff in that regard, it's a very stable molecule that sticks around for ages and it was used *everywhere*. Leaky systems, especially in cars, service people would routinely just vent it out of systems they worked on, and it was used as a propellant in aerosols.Propane does make a very good replacement for R22, it behaves almost identically and is actually a bit more efficient. The flammability is a potential issue though and using it as a refrigerant in the US is a federal crime so tread carefully. The US has some weird laws regarding refrigeration though, for example R134a is perfectly legal to use as an aerosol propellant, air duster, air horns, etc and you can vent it all you want. Put it into a refrigeration system and magically it's a federal offense to vent it to the atmosphere because now it's classified as a refrigerant. It's also illegal to put refrigerant back into a system once you have extracted it for servicing, you're supposed to pay someone to accept it and they then process it and sell it back to people at an inflated price. I'm sure they had reasons but it doesn't make much sense. The road to hell is paved with good intentions so the saying goes.

author: psteichen
author_rank: Contributor
timestamp: October 25, 2017, 07:09:22 pm
content: Quote from: james_s on October 25, 2017, 06:40:03 pmI agree with everything you said, except that it turns out that using 10AWG with a 40A breaker (or even 50A breaker!) is technically okay per the NEC for air conditioning and heat pump compressors. Don't fully understand why though. My intuition agrees with you.Sent from my SM-G900P using Tapatalk

author: james_s
author_rank: Super Contributor
timestamp: October 27, 2017, 09:01:52 pm
content: Quote from: psteichen on October 24, 2017, 04:26:29 amIn my (limited) experience, most HVAC guys are only interested in selling you a brand new unit because they make a big profit on the sale. Lots of perfectly serviceable older heat pump and AC units are replaced due to problems that would be trivial to repair simply because it's much more profitable to replace than to spend 30 minutes installing a $20 part. It's part of the reason I got certified myself, I bought a new scratch & dent system and installed it, total spent was around $1,000. At the time I was quoted nearly $10k to have a comparable system installed and guys told me the "junk" I bought wouldn't work. Well it's been working perfectly for around 12 years now so I would take anything they say with a grain of salt.

author: ratio
author_rank: Regular Contributor
timestamp: October 27, 2017, 11:40:11 pm
content: It's not hard. You size the breaker to provide over current protection for the conductors used.With a few exceptions.One of them is hermetic motor-compressors. Like your air conditioner. With those, the conductors are sized, by the manufacturing engineers, for the proper ampacity; and the breakers are sized, again by the engineers, to avoid nuisance tripping at it's design conditions. In theory, you could work out the math (per NEC section whatever) and get the same answer.You are allowed, of course, to go larger on your wire size. The Code is, after all, a minimum that should guarantee a safe install. But you don't HAVE to, unless you want to spend the extra money on oversized wires. Which is fine, but sometime Sparky gets a little worked up about it.

author: james_s
author_rank: Super Contributor
timestamp: November 15, 2017, 09:03:48 pm
content: Personally I would never cut corners by going with a smaller wire size even if it's legally allowable with a particular load. In the grand scheme of things it's relatively cheap to go up a size when dealing with typical homes. The larger wire will run cooler and reduce losses, and you will have room to increase the load some day down the road if it becomes necessary without running a new wire.

author: sokoloff
author_rank: Super Contributor
timestamp: November 16, 2017, 02:06:29 am
content: Quote from: james_s on November 15, 2017, 09:03:48 pmOP's code-compliant wire is already in place, behind finished drywall. It's not cheap for them to "do it right" at this point.

author: james_s
author_rank: Super Contributor
timestamp: November 17, 2017, 07:50:06 pm
content: True in this case of course. I would still stick with the 30A breaker though, then if nuisance trips become an issue look into a delayed trip breaker made for motor and lighting loads.