Air-Conditioning, Circuit Sizing, NEC 2020 - [440.4(B)], (5min:33sec)
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- 440.4(B) Air-Conditioning, Circuit Sizing - www.MikeHolt.c.... The first time you’re called upon to size a conductor and overcurrent device for central air-conditioning and you look at the nameplate requirements that clearly state that a 10 AWG copper conductor and a 50A OCPD are required, it may contradict everything you’ve learned about small conductors. In fact, you may adamantly insist that 6 AWG is required by the Code and you’d be wrong! Learn why in this video on section 440.4(B) of the NEC.
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Inspectors should learn these rules. They will call you out on it. I've shown them the NEC before and they still huffed and puffed
Hello Mike. Im happy and proud to say that with the help of your content, I have passed my license test on my first try yesterday!
That's what I"m talking about! Now call my office 352.360.2620 and start studying to get you to the next level.
Sooooo helpful! We literally just had this happen today. 45 Max Fuse on the condenser. 26.1 minimum ckt ampacity. 10 wire from the main panel to the fused disconnect. Inspector wanted 45 amp protection at the main panel. We watched this video and now realize the inspector was right. _(Don't tell anybody I said that, lol)_ Thanks Mike for the lesson. Mind Blown! Shared with my whole team and now we know!
Inspector was not right. 26.1 Ckt is the conductor, which would be a 10. 45a protection would be the breaker
@@jarrydee2799 isn't that what OP stated?
Motors have their own overcurrent protection system.That's why you can put a 10 guage wire on a 50A breaker, because the motor will not allow more 30A to pass through it
False. It's for inrush current. The stationary motor will draw around 50 amps to start moving the motor then level out to around 30 so to reduce nuisance breaker tripping a larger breaker is permitted
Overload
I’m going back and forth with an inspector now on some of these rules. If you’re wiring a condenser or heat pump and the name plate rating says 25 MOP and min circuit 23.1 amps. You’re using NM (romex). According to the manufactures you can install it in 90 degree Celsius locations but you must rate it using the 60 degree column. The breaker/lugs are rated at 75 degrees.
So manufacture and 60 degree column tells me 12 is good for 20
But 75 degree tells me 12 is good for 25.
Now we have the * on the 310.16 chart and you go to 240.4G then you end up in article 440 3/4/5 I’m so turned around and confused I don’t even know what’s correct anymore.
I was of the understand that if the name plate says min circuit you go to 75 degree 20 good for 25 amps MOP is 25 throw it on a 2 pole 25 good.
When using NM cable (Romex), you size the conductor to 60C of Table 310.16 [334.80]. If the MCA is 23.1A, then 10 AWG rated 30A is required.
Awesome Mike ;) so much real good information, by watching your videos , I got my Master Electrical license last year 🙏🙏🙏🙏🙏. GOD BLESS YOU
I’m installing a 5 ton AC soon and this info comes as a blessing, tnx Mike
Every time I have an evaluation I get asked, "how well do you know the code ?" I always respond by asking if they'd put a 10 gauge wire on a 50 amp breaker. They say you can't, I say you can, I show them this video, then they stop asking questions. I think next year I may change it up and ask about festoon lighting.
That is a great system? So effective!
Just be careful when wiring from the main panel to the outdoor disconnect. Many will use NM cable (romex for this). The wire inside the romex is rated 90C but the romex (entire cable) is only rated 60 degree C. So NM cable always has to be protected at the 60 degree rating.
In the Case in the video above you would have to use #6 NM Cable
Since 99% of residential installations use nm-b (Romex) wouldn’t the conductors be required to be sized to 60°c. 30.2 amps would be 8 gauge on a dpst 50?
Asking myself the same question. 334.80 limits use of NM cable to 60 degree column. I quess Mike was talking about THHN or something rated to 75 degree
Type NM is not rated for a wet location. This would be for the wires going in the whip. Provided your flex is rated for 75c
Run #8 to outside j box or disc, then switch to #10 thhn
Its too sad to see AHJ here wants to see #6 under a 50A breaker. I am gonna study and take this AHJ's job
We got 310.16 back! 🙋♀️
thank you for the free content mike
I see hvac techs install new compressors all the time and not change the existing breaker according to the equipment’s label. Mostly, the existing breakers are too large and exceed the maximum amps allowed per equipment’s label.
Why do hot tubs (that also have multi Motors) have their nameplate ratings inside their hot tub? Not to mention having to unscrew 6-8 screws and removing the front cabinet panel just to be able to read their very vague sticker nameplate rating.
God bless you and your family
The air handler call for 45 amps. The panel and disconnect it has 40 amps breaker. The disconnect box it has breaker and the wires size is correct 6 awg?
For years I have increased 1 wire size when I pull long A/C runs (over 50') in conduits to eliminate wire buzzing in the conduits upon compressor start-up. Example #8s for a 30 amp load. We are 100% metallic pullable systems in Chicagoland area and I have found this buzzing/rattling of the wires on many residential service jobs where the minimum required size is used. It's a very annoying sound and is more prevalent with larger 4-5 ton units. Increasing one wire size always solves the problem even though the smaller conductor is perfectly within its required amperage capacity for the length of run. Am I violating a code rule by doing so?
Wire the equipment per the nameplate and twist the wires when you pull them in the raceway to eleminate the buzz on start up.
@@MikeHoltNEC excellent suggestion!
@@steveloux4709 did twisting the wires fix the buzzing?
@@skliros9235 you’d have to ask @Dave Nag.
@@steveloux4709 oops
there has always been some confusion for me on this in regards to wiring an air conditioning disconnect with NM or NMS cable ( Romex ) in a residential application. and it seems to be a constant hot topic with inspectors. In 334.80 it says the ampacity of NM, NMC, and NMS cable shall not exceed that of a 60 degree C rated conductor. so in regards to the above Air conditioner, if im going to wire the disconnect with romex. then i would have to use # 8 correct?
Correct
Follow up question. If you are running NM to the disconnect then running THHN from the disconnect to the A/C unit can you run #8 NM then down size the THHN to #10 in the seal tight going to the A/C unit? Thank for the great video, we recently picked up a contract with an HVAC company and I want to be as informed as possible.
As long as the terminals are rated for 75degrees Celsius
Is UF classified to be treated as 60°C cable too?
With #14 UF Cable could I still use it, and at the 90 °C column at 25 amps, by using #12 THHN to splice at the panel and the disconnect, terminating the #12 THHN into the circuit breaker & Disconnect terminals.
Now, have I created max 25 amps for #14 UF ?
@@markkoenig4113 I know it's done regularly but I would think the Outdoor Disconnect would be considered a damp location and not permitted to run NM into it.
Why assume the 75 degree column.
I’m a 40+ year HVAC&R tech (currently studying for my electrical license) if the breaker is sized just over the minimum circuit a ampacity will protect the compressor under brown out, condenser fan, and other failures.
The authorities having jurisdiction would require that the wire size match the breaker size not the ampacity of the equipment.
Then you have unqualified inspectors.
Right, I’ve been doing this for 30years in the pacific nw. I know 20 or more inspectors and none of them allow this.
So the 10ga wire is sufficient to carry a 30A load, but the breaker is sized at 50A. I'm guessing the thinking on that is: If the compressor locks up or goes dead short, it'll trip the breaker before the wire melts?
The breaker is sided for 'short-circuit and ground-fault' conditions, not for 'overload' conditions. Overload protection is provided internally with the a/c equipment. Answer: Yes to your statement.
Awesome video on this topic!!
More please!
The 50A is the MAX; I think I can still use 30A breaker with #10 ... correct?!
You could place a 15A breaker, but why take the chance when you know 50 will work and not trip.
@@MikeHoltNEC Noted and thanks for your reply!
Thanks Mike
You are most welcome.
Is there a specific code that all nameplate ratings have to be located outside of the unit?
I think that it's around 430 or 440.
why wouldnt it be 60C since its under 100A
In reality, all 'terminals' under 100A are are rated 75C. That's why!
I have been wondering this same question?i understand the whole concept but it says in 110.14 (c)(1)(a)that anything under 100 amps should use the 60°column.unless the it is marked otherwise.so im guessing the breaker,disconnect,and ac unit all say good for 75°??
@@davidschuld4771 that’s what I thought too so I’m confused when he says under 100A use 75°c
I get for the purpose of this lecture you are using the 75C table , but code wise should you not be using the 60C table ? regardless of insulation rating , you are under 100 amp and unless the terminals on all sides are labeled to be rated above 60C you should be using 60 C table
VD aside , to me this is 8 ga wire on a 50 .
All terminals in reality are rated 75C, so you size to 75C, except if you use NM cable, then you size to 60C [334.80].
Hello Mike, awesome information here. I'm an electrician in Canada, it seems that the NEC and CEC are very similar. This is how many in the HVAC industry size their wire and breakers but some inspectors don't seem to be aware of this and will tell us we need a wire the can handle 50A. I'm curious if you can confirm that the CEC would size the same way you are showing us in your video here?
I have no clue what the CEC requires, sorry.
@@MikeHoltNEC Let's try a different angle here...points and two questions... The CEC and NEC are inline (CEC was based of the same code as NEC and UK and there is a movement now for globalization). Mike, would you agree that the heat pump in your example could be put on a smaller over-current device and that the cable size therefore could be reduced, as long as it met the minimum circuit ampacity? To the question of increasing the cable size, where the nameplate states maximum overcurrent device at 50Amps, if you install a 50A CB it must protect the cable, therefore the cable size shall meet the 50 CB (typically 80% of it's continuous rating so 40Amp cable)? I don't agree with this necessarily but I believe it is what D is asking.
Mike, what about the wire size feeding the 50amp ocp? Can that be 10awg also?
... well... there are not NEC rules that address this condition. Clearly it makes no sense to run larger conductors to the disconnect than from the disconnect to the equipment. But, the NEC doesn't give us guidance. So only use a non-fused disconnect to solve this problem.
@@MikeHoltNEC thanks for the clarification Mike! 👍🏼
Thanks for the video =)
And now lets go get that 50A GFCI breaker to boot.... Ugh. 210.8(F)
Would this also apply to the Air Handler since it is considered a single motor load?
The air-handler is sized per Article 424, not 440. But the conductor size and protection is also marked on the air-handler, so you size it per the nameplate.
Am I limited to the 60° column after the disconnect if my LFMC is rated 60° wet location?
350.10(4) conductors, or cables rated at temperature higher than the listed temperature rating of LFMC conduit shall be permitted to be installed in LFMC, provided the conductors or cables are not operated at a temperature higher than the listed temperature rating of the LFMC per 110.14 C.
You are almost correct... 350.10(4) "limits the current" on LFNC to the 60C values listed in Table 310.16. In this example, the a/c compressor is 23.9A and the fan is 1.2A which totals 25.1A. If we used 10 AWG, it's rated 35A at 75C and the maximum current is limited to the 60C column value of 30A. Okay
The flexible liquid tight conduit coming out of the HVAC unit. How much slack does it suppose to have before you strap it to the wall.....
See Article 350, let us know what it requires.
@@MikeHoltNEC from what I understand conduit is to be fastened within 12in of termination points and at intervals not greater than 4 1/2 ' feet.
Hi mike, how about the 125% required for conductor sizing? can we apply it to the minimum circuit current?
The 125% is already incorporated in the nameplate MCA.
@@MikeHoltNEC thanks a lot
Hello sir.
When can I use this codes 440.22 (A) (B) and 440.33(1)(2)(3)
Wire sizing: compresor 23.90x1.25 =29.87 plus fan motor 1.20 = 31 amps
Breaker sizing: compressor 23.90x 1.75=41.82 plus fan motor 1.20=43 amps
Never, that is for the manufacturer. Just follow the nameplate as explained in the video.
Would your AC disconnect have to be rated for 60 amps?...since their normally rated 30A, 60A, 100A...
440.12 a 1 - at least 115% of rated load current or bcsc, whichever is greater.
How would you size the Grounding conductor for AC units? Is it based on the max or minimum ampacity on the name plate?
250.122(A)
Excuse me ...in this case “ can I use the wire # 10 /3 from panel to the disconnects ( 30 amp) and the breakers twins ( 40 amp ) ????? Distance 50 ft ???
Post your question on MikeHolt.com/Forum
Is the 10 awg only for the wires from the breaker or fuse box to the unit? What about the cables feeding from the panel to the fuse/breaker box. Does those wires should be size at 8 awg or 6 awg according to table 310.16?
The wires and protection start at the panel (circuit).
@@MikeHoltNEC Thanks Mike...
What if the unit is fed with type NM-B (Romex) which is pulled from the 60°C column on Table 310.16?
Correct! We size the wire to 60C, per 334.80.
@@MikeHoltNEC Thank you for the quick response!
Can you fuse/breaker at the minimum circuit amps? Example: 29 max circuit Amps, 50A max fuse and say you run a 10g wire, can I do 30a or 40a breaker or do I have to do a 50a?
The nameplate indicates the 'maximum' size protection. So anything less is permitted. There is a reason they gave 50A and I would use 50A, but you are welcome to use anything not greater than 50A in this example.
Hello Mike holt I had a question on the sizing, I have recently ran into it with an inspector where I have sized the wire off of the minimum circuit ampacity on the nameplate, and he is stating that it’s not sized for the “continuous duty” meaning the 125% I thought the nameplate had a lot of that accounted for, is that not the case? Do you still need to multiply the 1.25 by the minimum circuit ampacity? Any thing helps. Thank you.
Please watch the video again on how to size the a/c conductors (the a/c nameplate value for MCA uses the compressor amperes x 125% plus the fan load) see the nameplate in the video.
If i the minimum circuit amps is 30 amps, that means the smallest wire you can use is 10 gauge, right?
Does that also mean you can go bigger on wire? Could i use 8 gauge?
Nope, doesn't work that way for a/c equipment. Please watch the video again. The breaker is sized to the nameplate and the wire is sized to the nameplate.
@@MikeHoltNEC
Oh ok. I think you answered my question. I was just wondering if when it comes to wiring, and I know we are supposed to go by what it's rated for, but i was curious if you could go bigger on wire. I already knew you can't go smaller. But i thought you could go bigger. That's why it says minimum circuit amps. I don't see a maximum circuit amps.
@Bible Bloopers Of course you can run a larger wire than what is required by the load. But why run 8 AWG to a water heater, when all you need is 10 AWG. Why install a 400A service on a home that only needs 200A... If someone ran a larger wire than is required, who is paying for this 'wasted' larger wire? If you are then I'm good with that, do it. If you plan on passing the cost to the customer, then I feel you are not serving the customer. If you are the electrical contractor and you are not passing the cost to the customer, then it's stupid, but some contractors are not that 'business savvy'. I personally follow the NEC, and would charge accordantly.
@@MikeHoltNEC
I agree. It was just a question out of curiosity. I do HVAC. So I was just wondering if I was ever in the event in an emergency situation if I could go up in bigger size wire in the event I didn't have the correct size wire.
Thank you for your quick response time
@@biblebloopers946 bigger wire is always good. But cct breaker is specific to that rule on the HVAC.
If for example: its a long run and at the instant the compressor motor starts the motor must draw very high start current. Its min. locked rotor current is 6 times the motor load amperage or maybe more for hermetic motor. The cct breaker at 50 AMP specfied in code is high enough to let the spike current to pass through without premature tripping. Voltage at that start must not be more than a 5 percent line drop total (supply to the load.) The conductor installed if number 10 or you increased it bigger for which I explained above if you had to would reduce line loss. But the breaker remains at 50 amps. Limiting the fault current just as code requires.
Hi Mike! Is this 10 awg NM or loose conductor in race way.
Wires in raceway if we are sizing at 75C or 60C for NM cable.
I tried to buy you master test online course but something doesn’t allow me to buy it
Filo, Give our office a call at 888.632.2633 and we will take care of you. I am not sure where you were trying to purchase from but we checked the products on our website and the links seem to be working now, click here www.mikeholt.com/product-category-list.php?id=8.
Thanks, and have a great day!
For that disconnect feeding the AC unit, does 440.14 have to comply with 110.26?
Read 110.26 and let me know what you think.
@@MikeHoltNEC I belive it does need working space, yet I find disconnects mounted above suspened ceilings and also in crawl spaces that had to have been inspected. 440.14 states that it is allowed to be mounted "within" the unit, which in my opinion could never give proper clearance.
@@bradrolleri2909 Of course 110.26 applies to disconnects. Your 'experience' is distoring your reading of the NEC.
MikeHoltNEC you are definitely right! Thank you for your videos
Nameplate says max overcurrent protection 35A. What do we do in that case?
You use a 35 A breaker lol
Follow the name plate since 35 amps is a standard ampere rating size I would match this with a 35 amp breaker .
What about small conductor rules?
240.4(G) takes you to other articles that override those rules. As it explains in the video.
Do you apply continuous load factor on top of the MCA of an AC? Or motors?
You size the wire per the manufacture nameplate instructions. Please watch the video again.
@@MikeHoltNEC thank you. This applies for the branch conductors but what about the feeder conductors serving for example 10 ac units? Does all the load add up and a 1.25 multiplier applied to that number (since the ac loads are continuous) ?
What is the minimum size breaker allowed? I had a situation where the name plate stated max. breaker of 30, min. circuit ampacity of 23 and a rla of 15.5. They put in a 20 amp breaker and one inspector said that was ok and another said it needed a min. of 25. Any help on this would be appeciated.
Using your example of Max 30A breaker and Min 23A wire, then you should not install a breaker that is rated less than the min required wire ampacity. However nowhere is this covered in the NEC. What happens if you put a 20A breaker on a 10 AWG wire for your example? Well maybe the a/c unit won't trip the breaker, if it does, then you put a 25A or 30A breaker. There is no hazard to install a smaller breaker.
Thanks for the quick response. That is the problem the NEC does not address this. One inspector was using the continuous duty of 125% x rla 15.5 and that is why he was saying a 20 amp breaker was ok. What do you think? Thanks@@MikeHoltNEC
@@tonyhddodge4282 I don’t have anything further to add to my response. Sorry.
@@mikeholt9781 I understand. Thank you for your first responce and the work you have put into doing what you do.
I understood none of this haha, I ended up here watching a DIY Mini split install, and somebody used certain wiring for 36K BTU and lower breaker for 12k BTU.
is it still ok to size the cable as per the 50A circuit breaker? because im doing it for a lot of projects i made
Jpatristan Torralba you could end up violating 250.122B (B) Increased in Size. Where ungrounded conductors are increased in size from the minimum size that has sufficient ampacity for the intended installation, wire-type equipment grounding conductors, where installed, shall be increased in size proportionately, according to the circular mil area of the ungrounded conductors.
The equipment grounding conuctor is 'not' required to be increased in size, see 250.122(A) and 250.122(D).
MikeHoltNEC that’s not how I’m reading it “(A) General. Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122, but in no case shall they be required to be larger than the circuit conductors supplying the equipment. Where a cable tray, a raceway, or a cable armor or sheath is used as the equipment grounding conductor, as provided in 250.118 and 250.134(A), it shall comply with 250.4(A)(5) or (B)(4).”
@@armandocepeda7533 Okay, you are welcome to read it as you like.
@@MikeHoltNEC This is an arrogant answer I did not expect from you!
🤙🤙🤙🤙🤙
Why does everyone that agrees with you ignore 440.6
440.6 simply tells you what 'current' to use for conductors and protection. Conductors are sized at 125% of 440.6 current [440.32] and protection is sized to 175-225% of 440.6 current [440.22(A)]. These are the values that the manufacture uses for the nameplate. Do you agree that the article by the IAEI written by my friend Keith Loftland is 100% correct as explained in the video? If not, then assume you are just one of the 'unteachables.'
I’m installing a 5 ton AC soon and this info comes as a blessing, tnx Mike