Thread: 35 Amp Breaker and 10 GA wire for AC Condenser

My question regards a 35AMP double pole over current device (breaker) connected to 10 gauge wire running to an AC condenser unit. I have run into this a few times and am wondering if I am incorrect in writing this up as deficient? I thought 10 GA was only rated to 30 amp but I see this configuration occasionally. Thanks!

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I believe you can use the smaller wire size depending on the minimum ampacity of the A/C unit.

Thanks Gary,

Yeah, I was wondering if that was the case. Seems strange though as the over current device is there to protect the wiring also right?

Leo

For A/C units:
The breaker can be sized according to the "Maximum overcurrent device".
The conductors can be sized according to the "Minimum circuit ampacity".

The NEC has special rules for things like motors and welders. In this case, there is supposed to be an overload built into the AC unit that will trip if the unit malfunctions.

You are allowed to install a breaker large enough for the compresser to start as long as the breaker isn't larger than 225% of the circuit rating or compresser rating, whichever is larger, unless there are manufacturer's directions to the contrary.

However, the issue becomes the wire size specified by the manufacturer and what if any maximum size breaker they allow.

Originally Posted by Speedy Petey

For A/C units:
The breaker can be sized according to the "Maximum overcurrent device".
The conductors can be sized according to the "Minimum circuit ampacity".

Those are found on the nameplate of the unit.

Whatever is specified on the nameplate is permissible for that unit.

Yes, I always check the nameplate min/max ratings against what is protecting the circuit but I didn't realize how this is applied to the gauge of the wire. I really appreciate the input from everyone.

Leo

You are allowed to install a breaker large enough for the compresser to start as long as the breaker isn't larger than 225%

Crap, I thought it was 125%. Time to go look it up.

I ran into the same scenario yesterday only it was a 12 gauge wire to a 30 Amp breaker. It was wired to A/C condenser unit with no neutral wire.

Why would you ever need a neutral wire for a 240v a/c?

Originally Posted by Tom Rees

I ran into the same scenario yesterday only it was a 12 gauge wire to a 30 Amp breaker.

As long as the nameplate says that is allowed, then it is allowed.

I assume your refering to table 310-16 ampacity. No mention of type of wire insulation used; i.e. thhn, uf sleved in a raceway, (type nm cannot be used outdoors because it is only approved for normally dry locations, see art 334.10(4)(a) of the NEC).
Important to remember that the first 3 chapters of the NEC are the general rules, the following chapters may amend the general rules for specific applications.

I'm glad you posed this question as i will use it as a case in point.
If you'll notice in the table 310.16 of the NEC:
Different ampacities for different insulations of same gauge wire.
These are maximum ratings in their respective temp range.
#10 guage copper of thhn in the 90 degree Cel column = 40 amps.
Notice the * after the '14, 12, 10,' guage wire column which tells U
at the bottom of the page to see 'article 240.4(d).
Art 240.4(d) limits these three conductor sizes to '15, 20, and 30'
respectively. It also states 'unless specifically permitted in......and gives
some rules and a table of articles that do not limit the ampacity as mentioned.
See table 240.4(g). One that is listed in the table is art 440 parts III and VI. In short, if the AC condenser is the 'hermetic refrigerant' type, that is where the motor is actually in the refrigerant and has internal overloads,
the nameplate on the unit will give 'maximum breaker size and minimum ampacity of the conductors'.
It therefore follows that one could see: Maximum breaker size= 40, and minimum wire capacity=10 amps, ETC.
Note that the nameplate will indicate whether a fuse or breaker or both may be used as the protective device.

Other notes; Article 430 motors are among the articles after chapter 3 of the NEC. amongst others.
Ambient temperature, and # of conductors in a raceway further reduce the ampacity of a conductor in a given application, however, the tables for these reductions are to be applied to the 'maximum' ampacity of the piticular conductor/insulation as indicated in table 310.16.
Another limiting factor is the temperature rating of the terminals at which the conductors terminate.
Panelboards and the like will indicate the temperature rating of the terminations on their door sticker.
Type NM, NMC, and NMS, are to use the 60 degree C collumn in accordance with art 310.15, but use the 90 degree collumn for derating purposes as mentioned above, but cannot exceed the 60 degree collumn.

I hope this clears up allot of misconceptions regarding ampacities of conductors.
Bob Smit, a Michigan County Electrical Inspector.

Originally Posted by bob smit

One that is listed in the table is art 440 parts III and VI. In short, if the AC condenser is the 'hermetic refrigerant' type, that is where the motor is actually in the refrigerant and has internal overloads, the nameplate on the unit will give 'maximum breaker size and minimum ampacity of the conductors'.

Correct, which means that if the nameplate says it is okay, it is okay.

Welcome aboard, Bob.

Leo, from two different units data plates, breaker size listed and minimum circuit ampacity.

Originally Posted by Rick Vernon

Leo, from two different units data plates, breaker size listed and minimum circuit ampacity.

The first one could be wired w/ 14 AWG & a 20A OCD, 2nd one 12 AWG & 25A OCD......

Originally Posted by Rollie Meyers

The first one could be wired w/ 14 AWG & a 20A OCD, 2nd one 12 AWG & 25A OCD......

Exactly.

If you have a 35 amp breaker you would need a #8 wire that would handle
the load. When compressors start they pull a lot of start up amperage. When they lock up "LRA" they will pull for a few seconds maybe 5 times normal running amps. The manufactor recommends the size of the fuse or breaker if it has one at the condenseing unit but remember the wire comes from the main panel from the house. Do you think it would be ok for a manufactor to recommend a #12 wire for a dryer that only pulls 18 amps? I don't think so . I also believe it is 125%.

Originally Posted by Cobra Cook

If you have a 35 amp breaker you would need a #8 wire that would handle
the load. When compressors start they pull a lot of start up amperage. When they lock up "LRA" they will pull for a few seconds maybe 5 times normal running amps. The manufactor recommends the size of the fuse or breaker if it has one at the condenseing unit but remember the wire comes from the main panel from the house. Do you think it would be ok for a manufactor to recommend a #12 wire for a dryer that only pulls 18 amps? I don't think so . I also believe it is 125%.

I hope that this is not how you write up all your reports with AC compressor wiring. The rules for sizing the wires and breakers are not the same as branch circuit wiring for lighting and receptacles.

As has been stated several times above you need to check the nameplate. Otherwise you are just costing someone money to have someone else check the wiring and report that it is proper and was incorrectly noted as a defect.

Cobra, you believe? How about you should know.

Please go back and re-read all the posts in this thread.

Because of the misconceptions regarding ampacities of conductors and their insulation in various applications, is why i took the time to write the extensive thread previously, please read it.
It is appearant that most of U are aware of all the rules in this regard, however, some may still need further study.

In addition, the protecting device for hermetic refrigerant motors are kept cool as a result, and as in the application of most motor circuits, they have 'OVERLOAD PROTECTION' which is set to protect the conductors from overloads. The breaker and/or fuse required by the nameplate is for short circuit protection in these applications.
A #10 thhn for example, will handle an enormous amount of amperage for a short peroid of time...plenty enough to trip the overloads, and in the case of a ground fault or short circuit, the breaker and/or fuse will trip/blow in plenty of time regardless of the time/current envelope designed into the device.
Bob Smit, County Electrical Inspector

Bob, Speedy, Jim, I write up my reports as I see them. I do not second guess the experts on wiring sizes and max fuse or breaker needed to protect the wiring and the consumer. With Regards to lighting or other systems the breaker to use follows the size of the wiring used. A stereo or TV on a twenty amp circuit may have only a 2 amp fuse inside to protect them but the NEC requires a # 12 wire to be used. I think what is being said with all of the mumbo jumbo uttering of rules, have to do with the wiring inside of the ac unit. Those wires just like in your car use different insulation ratings due to the excessive heat some are in. As far as overload protectors go, all are inside of the compressor oil not the refrigerant it self. Most units have overload protectors mounted to the side of the compressor itself, so it can just be replaced and not the compressor. There are other components in different systems to protect the compressor, solid state sensors, high pressure, high temp, high amperage to mention a few. I recently was starting five new heat pumps and happened to be there when the electrical contractor was getting his final inspection, the inspector told him he had to change the fuses in the disconnect because the contractor had installed the fuses according to the manufacture but was not the right size for the wiring installed. Virginia is still in the 2006 NEC book and will not go to the 2008 until next year, but I could not find in the book about any changes about allowing smaller wiring can go to larger fuses or breakers. The inspection reports I use requires that the main panel for the house be opened to inspect the kind of wiring by size not temp. rating but according to the breaker or fuse that is installed. Lastly most utility boxes that electricians install at the condensing units at houses just have a pull out that has two ways to install it right side up says on and upside down says off, there are no fuses or breakers involved at the unit.










i

The rules for A/C's are different & the NEC allows the use of wires sizes that are not "normal" for the uninformed if the A/C unit data plate supports it.....

Originally Posted by Cobra Cook

Lastly most utility boxes that electricians install at the condensing units at houses just have a pull out that has two ways to install it right side up says on and upside down says off, there are no fuses or breakers involved at the unit.

A/C pullout discos come in a fusible and non-fusible types,one size does not fit all...










i

Originally Posted by Cobra Cook

Bob, Speedy, Jim, I write up my reports as I see them. I do not second guess the experts on wiring sizes and max fuse or breaker needed to protect the wiring and the consumer.

But you said that the 35 amp compressor needs #8 wire. Sounds like a second guess to me, especially when you don't know the proper way to size the wire and OCPD.

Originally Posted by Cobra Cook

Lastly most utility boxes that electricians install at the condensing units at houses just have a pull out that has two ways to install it right side up says on and upside down says off, there are no fuses or breakers involved at the unit.

What do you percieve as the problem with this? This is a service disconnect, nothing more. Fuses would only be required if the nameplate said "Maximum Fuse Size".

AFAIK, the sizing rules in Article 440 have not changed in recent history.

Originally Posted by Cobra Cook

I recently was starting five new heat pumps and happened to be there when the electrical contractor was getting his final inspection, the inspector told him he had to change the fuses in the disconnect because the contractor had installed the fuses according to the manufacture but was not the right size for the wiring installed.

Then the guy obviously had no clue.

What do you propose 9 1/2 wire? Number 8 wire is rated at 40 amps period., as referenced to a home inspection. It seems that this discussion has went into lala land. Leo simply asked a question as a home inspector is #10 wire ok for a thirty five amp circuit, for a home inspector it is no, it is required to be a # 8 copper or 6 if aluminum. It is better to be safe as an inspector than to second guess the engineers who tested and confirmed the proper wire sizes for the amps the circuit will pull. In looking at the name plates presented and the thousands i have looked at or the years, I never saw one that said what size wire to run, only the min and max amp draw of the unit. If it states 15.1 amps then you would have to go up to a 20 amp breaker with # 12 wire, if it said 14.9 then with all of the multitude of advice about 125%to 225% i am sure 15 amp breaker and # 14 wire would work but the code would require # 12 wire to this type of branch circuit but with a 15 amp fuse would be ok. What does the Bob electrical inspector think about that advice? Speedy I'm not sure if Leo was talking about the service disconnect or the main breaker panel.

Cobra,

Why is it that you cannot understand that the rules for air conditioners are not the same as a general use branch circuit? Have you looked at the ampacities in Table 310.1x?

Yes, the installer can certainly install conductors larger than the nameplate calls for. However, if you continue to use the wrong criteria in your inspection process you are doing the customer a disservice and costing someone extra money when there is no need. I get upset enough when I see stuff unnecessarily called out as a defect when I am making money because of some alleged defect. Imagine how the homeowner would feel if they agreed to an unnecessarly fix of something that isn't broken. Do you feel that that adds credibility to either your report or to the HI industry? Maybe it would be the homeowners fault for agreeing to fix something that didn't need to be fixed?

Opinions are like fingers ... most of us have handfulls of them. Data id what sets an opinion apart.

Now, as for wire sizes ... think for a moment ... where does anyone get this silly idea that you need (for example) #10 wire on a 30 amp breaker?

Chances are, you'll say 'it's code,' and point to table 310.16 in the NEC. Let's go there.

Aha ... there's a little asterisk by #10. This is for the note at the bottom of the page, which directs us to 240.4(D). Let's follow this trail ....

240.4(D) tells me that, in effect, your #10 wire is limited to 30 amps; but take note: this paragraph begins "Unless specifically permitted in 240.4(E) or 240.4(G)." Looks like our "requirement" is 'on hold' until we look at those two 'exceptions.'

240.4(E) discusses tap conductors, which are not relevant here.

240.4(G) refers us to table 240.4(G), whick lists ten circumstances where different rules apply in sizing the wires. We need not go into the 'how' and the 'why' here, just to know that therer are ten circumstances where the 'usual rules' go out the window.

First on this list are Air Conditioning and refrigeration equipment. We are referred by the table to Article 440, parts III and IV.

Now, it's perfectly OK to be baffled by all the ifs, ands, or buts in Article 440. It's only to be expected, since to make a proper set of calculations in the field you pretty much have to dissect the equipment. Even then, the water is muddied by 440.22(C), which tells us not to exceed the nameplate instructions as to ampacity and overload protection. Here's where it helps to have the handbook

As a note after 440.33, the NEC Handbook shakes this all down to: "Branch circuits for listed air conditioning and refrigeration equipment that have a nameplate marked with the branch circuit conductor size and branch circuit short-circuit protective device size are not required to have the branch circuit conductors sized in accordance with 440.33. The testing laboratory includes (all the calculations; therefore the actual nameplate full-load amperes for the complete assembly can be used to size the branch circuit conductors." Mind you, that may just be a note, but the note adds nothing to what is not already in the text of Article 440 - the article just has the information scattered all over the place.

To put it in even simpler terms ... every factor has been taken into consideration, tested, and verified by a third party, so you can use the wire and breaker the nameplate says you can use.

So, to use another imaginary example, if the nameplate says a minimum ampacity of 22 amps, we look at table 310.16, and see that #12 is listed as 25 amps. Forget the asterisk; we can use #12 for this air conditioner - even if the same nameplate says I have a maximum breaker of 40 amps.

If you think this is bad, wait until you deal with welding equipment. I've seen circumstances where you could put #12 on a 100 amp breaker!

I hope this makes the matter clear for everyone. I have tried to use small words and short sentences. I haven't really added anything to this thread, it's just that a few were unwilling to see it. Perhaps this walk through the NEC, holding their hands, will help them to find their way through the forest.

MFG Nameplates overrule the NEC. Same for Hot water heaters, etc. there is always a clause saying the MFG recommendation over-rule, since they are the ones that test what is safe and not safe for that specific device.

The breaker on the AC is strictly for short-circuit protection and in case the compressor seized, either of which would put a huge load on the line for less than a second, plenty of time for a breaker to trip, and well before the wire had a chance to heat up.

The wire is sized for the RUNNING current of the AC, i.e. what is normal 24/7 running.
The trouble is when an AC turns on it has a larger startup load which lasts about one second. If the wire has the normal breaker (14awg=15amp, 12awg=20amp, etc.) that breaker would trip every time it turns. The NEC and MFG's agreed that the easiest solution and most cost effective is to just upsize the break as required to get it to start, while still providing the protection needed to avoid the wire from melting in an over current condition.

Some one also mentioned about the ON/OFF pullout, that is just a cut-out that is required to be on all units so that a tech can safely cut-out the power and know that it's not energized. A locking breaker can serve the same purpose. Some disconnects have a built in fuse, they should be rated for the max current of the AC. (I prefer units without fuses as the breaker is resetable already.)

So just because a breaker is over-sized, doesn't mean the unit draws that much power, it just keeps from blowing it everytime it turns on... in the old days, Slow-Blow fuses would have been used.

Originally Posted by Cobra Cook

What do you propose 9 1/2 wire? Number 8 wire is rated at 40 amps period., as referenced to a home inspection.

Where do you get that at?

The rating of a conductor is no different "as referenced to a home inspection" than it is "as referenced to a code inspection".

Originally Posted by Ken Lyons

MFG Nameplates overrule the NEC. Same for Hot water heaters, etc. there is always a clause saying the MFG recommendation over-rule, since they are the ones that test what is safe and not safe for that specific device.

Manufacturer name plates and recommendation do not "overrule" any code, they are tested, listed, and labeled, and are therefore code by reference - i.e., the codes allow, specifically require, installation to the nameplates and installation instructions.

The NEC has a little blurb in the front

90.1(C) Intention. This Code is not intended as a design specification
or an instruction manual for untrained persons.

At the very least, if you're going to use the NEC as a basis for determining circuit wire size versus breaker size then the least you owe your customers is to read the list of exception to these same rules, even if you don't understand how they're applied.

There is a big difference between general use circuits and certain dedicated use circuits. General use circuits are usually able to have different loads applied by changing/adding lamps or cord and plug connected appliances and they have VERY different rules than circuits that feed certain dedicated loads. These rules are just as valid as the rule that limits the breaker size on a #14 wire to 15 Amps on a general use circuit.

Being able to make these distinctions is what makes the difference between being a professional and a hack, either as an electrician or a HI, or any other trade for that matter. You do yourself no favors as a business person when the outcome of an inspection is the buyer, the (very irate) seller, the bank, the realtors, and an electrician sitting around a table picking apart the electrical inspection part of a report that has needlessly delayed a sale. I can tell you from experience that even though you view yourself held harmless because you are merely voicing concerns that word does get around.

And now, it would appear, that in spite of having the availability of professionals willing to help with the education so you don't look a fool, you choose to ignore it.

This is my third post on this topic.
I cannot endure much more. Most of U have have made good/accurate observations and have even reiterated some of what I have originally posted. I'm comforted that most of U Home Inspectors get it.

Here's one that i rarely write in my rejections, but is note worthy here.
Please read NEC 110.3(b)
It's referred as the Manufacture Spec write by Electrical Inspectors:
It basically states that equipment SHALL be installed according to the instructions provided by the Manufacturer. This is due to the fact that the listing and labeling (also required by the code), was obtained using the parameters labeled by the engineers who designed the product and tested using said instructions/methods.

Some of my fellow Inspectors even go as far as requiring an installation be performed exactly as written, rejecting the work if the electrician installs 'over and above' the requirements'. This of course is misguided according to the other 99% of us, as we understand the code as 'minimum requirements'.
Bob Smit,
Registered State Electrical Inspector, Licensed Master Electrician.

Originally Posted by bob smit

Some of my fellow Inspectors even go as far as requiring an installation be performed exactly as written, rejecting the work if the electrician installs 'over and above' the requirements'. This of course is misguided according to the other 99% of us, as we understand the code as 'minimum requirements'.

Bob,

They are intend misguided, as, if they read the installation instructions they are going by, they would see that the instructions state the minimum requirements, and, occasionally, the maximum allowances (an example would be clothes dryers which state a maximum duct length base on type, number of elbows, and the discharge outlet style).

Right on Jerry. However, I wasn't refering to our AC example in piticular, was meant to be in general. I only actually know 2 E-inspectors who love to write 110-3(b). I've convinced one of two that this code reference shouldn't be used as a hammer. I call the other inspector 'Man Spec', and another inspector friend of mine I call '90 dash 4', which gives the AHJ authority to interpret the code. When 90-4 can't find a code article to support what he wants, he writes it under 90-4.
99% of us Electrical Inspectors do not abuse our position and I hope that applies to 99% of HI as well.
Authority is not a privilege, it is a responsibility best served with humility.
Bob Smit

Originally Posted by bob smit

Authority is not a privilege, it is a responsibility best served with humility.

Bob,

Agreed.

I frequently tell people that when an inspector says "Because I said so." that means the inspector has no idea what he or she is writing up (no known code) and is only doing it because either they were taught that way or that is what they think is best. Sounds like your friend 90-4 uses that to say "Because I said so.".

I do not think that although the name plate say total min current MCA 25.5, and the Max OCPD being 40amp for example my unit means run a 10awg wire with a 40 amp breaker
I believe that is the Max circuit can use not what has to be used (what a manuf tech rep told me once) but if use a 40 amp I firmly believe should then use 8awg wire according to the ampacity rating on the wire, since the breaker is to protect the wire from overheating if shorted not the device itself
But I like to take safe approach not a minimalist as long as not against code ?
just my opinion
as in my example, the manuf tech rep I talked to said that could run based on distance of the run 10awg wire on a 30 amp breaker since HACR breaker required would not trip on start up surge that the MAX size was that not what had to use just had to meet the minimum
?
For that example used 40amp breaker with 8awg wire just in case for future use and feel is safer for wiring protection ?

Originally Posted by Mike Clarke

I do not think that although the name plate say total min current MCA 25.5, and the Max OCPD being 40amp ...

The nameplate ratings mean exactly what they say - in your example above, that means it is allowed to use 10 AWG to that unit, and to protect that 30 amp rated circuit with 40 amp overcurrent protection.

That 40 amp overcurrent protection size allows for startup current not to trip the breaker/blow the fuse.

You do not need #8 for a 25 amp load.

Originally Posted by Mike Clarke

I do not think that although the name plate say total min current MCA 25.5, and the Max OCPD being 40amp for example my unit means run a 10awg wire with a 40 amp breaker
I believe that is the Max circuit can use not what has to be used (what a manuf tech rep told me once) but if use a 40 amp I firmly believe should then use 8awg wire according to the ampacity rating on the wire, since the breaker is to protect the wire from overheating if shorted not the device itself
But I like to take safe approach not a minimalist as long as not against code ?
just my opinion
as in my example, the manuf tech rep I talked to said that could run based on distance of the run 10awg wire on a 30 amp breaker since HACR breaker required would not trip on start up surge that the MAX size was that not what had to use just had to meet the minimum
?
For that example used 40amp breaker with 8awg wire just in case for future use and feel is safer for wiring protection ?

The compressor has overload protection so the fuse/circuit breaker is just for short circuit protection, that is why we can use the nameplate info to use different wire/fuse or circuit breaker combos then what is required for normal branch circuits, BTW if wiring A/C equipment, & using THWN conductors (THHN is for dry locations) 10 AWG is 35 ampere rated, while if NM cable, or a branch circuit, it is 30A rated.

You can use larger conductors if you want but unless someone else is paying for it, it's comes out of your pocket & does not make it more safe, as to not using the largest breaker permitted on the data plate, compressors can draw more current at start up as they age leading to nuisance tripping because of a misguided installer.

Originally Posted by Leo Leidlein

My question regards a 35AMP double pole over current device (breaker) connected to 10 gauge wire running to an AC condenser unit. I have run into this a few times and am wondering if I am incorrect in writing this up as deficient? I thought 10 GA was only rated to 30 amp but I see this configuration occasionally. Thanks!

Mike Holt covers this in detail on this Youtube video https://www.youtube.com/watch?v=9lPDYEAgWD4

has mentioned the breaker is for protection of the wiring, so regardless of overload protection in the device itself, if the "Wiring" shorts, how is having a larger breaker more than the ampacity rating of the wire itself is safe ? Oh well.

Originally Posted by Mike Clarke

has mentioned the breaker is for protection of the wiring, so regardless of overload protection in the device itself, if the "Wiring" shorts, how is having a larger breaker more than the ampacity rating of the wire itself is safe ? Oh well.

Because the overcurrent protection is an inverse time/trip function.

Conductors are not rated at their "failure point", they are rated for long term loads without overheating - long term overheating can cause fires.

A 30 amp rated wire can take the startup current without any problem. However, if that startup current was to go on for a long time, it is likely that the heating from that current would not cause the overheating which could cause a fire.

A short, on the other hand, cause a very high current very quickly, and if left alone, would end with 'not good results' (how "bad" the results would be would depend on many various things).

The almost instantaneous rise of current will trips breaker very quickly.

And I was just going to say that the breaker will trip on a short in a couple of cycles and never heat up long enough to cause an issue.