US Mains Residential Code Compliance

[alank2]

Are all your household extension cords 14 ga or higher?  No. 

Which 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...

[drussell]

Which 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...

The 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... 

[hermit]

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.

[psteichen]

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.

That's something I hadn't thought of. I'm certainly capable of installing it myself, but I'd rather not. I'm really busy...

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[ratio]

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.

[Awesome14]

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.

[stevelup]

I have a new word in my vocabulary now anyway... Ampacity!

[Quarlo Klobrigney]

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.

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.

[sokoloff]

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.

There is no mismatch. The NEC is clear (IMO) that this is acceptable per NEC 440.22.

[hermit]

Assuming as you say, and you are in the US, the electrician and or HVAC installer should most likely pull a permit.

Permitting 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.

[james_s]

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 23 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 23 amp load.

B: Use a 40 amp breaker, and retain the 10 gage wire, as it is big enough to handle 23 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.

Option 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

Yikes! 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.

[psteichen]

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 23 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 23 amp load.

B: Use a 40 amp breaker, and retain the 10 gage wire, as it is big enough to handle 23 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.

Option 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

Yikes! 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.

I 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.

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[james_s]

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.

That'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

In 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.

[ratio]

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.

[james_s]

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.

[sokoloff]

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.

OP's code-compliant wire is already in place, behind finished drywall. It's not cheap for them to "do it right[er]" at this point.

[james_s]

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.