Air-Conditioning, Circuit Sizing, NEC 2017 - [440.4(B)], (8min:54sec)
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- Опубліковано 11 вер 2024
- 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.
This video is extracted from Mike Holt's 2020 Understanding the National Electrical Code Complete Library, for more information visit www.MikeHolt.c... or call 888.632.2633.
For over 40 years, Mike Holt Enterprises has been providing quality electrical code training to help electrical professionals learn the code, prepare for exams, and improve their electrical knowledge. Visit www.MikeHolt.com for exam preparation tips and training, instructor and curriculum support, continuing education options, free videos and graphics, and so much more.
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I’ve gotten into many discussion with electricians that tell me inspectors (the dinosaurs) are making them use the larger wire. So glad to know the code well enough to show them what I’ve known and you showed in this video. Thanks for this video. I’ll pass it along to the electricians that I come across in my inspection day. God bless and thanks for all you do for our trade. 🙏🏻
Thank you for helping me get the truth out.
@@MikeHoltNEC know the truth and the truth shall set you free. 🙏🏻
@@RobertSmith-lw2bx Oh my goodness... this is exactly what I'm trying to say. I'll be using this for now on.. thank you.
@@MikeHoltNEC your welcome. John 8:32.
@@RobertSmith-lw2bx Exactly!
Just finished reviewing article 440 on your study guide this evening. What a great follow up getting on here and seeing this. Thank you Mr. Mike!
You are most welcome.
Best explanation of this that I’ve ever watched. Thanks for making things simple
This information is so helpful, it's easier to send and inspector this video to break it down perfectly. Also you saved me a ton of extra work, replacing the wire. Thanks mike!
Thank you Mike for all the accessible information for people who continue to learn.
Also,
Big shout out to all the old timers learning new
tricks and guiding the youth- Sparky
Mike you explain everything so simple.
Thanks.
Thank you! Every one from apprentice on up should know about these exceptions for circuit sizing, and tapping rules.
They really teach about how wire, terminal and breaker sizing work together to keep things cool & reliable.
These are actually not 'exceptions' these are the 'rules' for a/c circuits; which are different than motors, taps or other circuits. Glad you enjoyed the video.
One thing I see a lot is A/C guys replacing a condenser unit and not putting in a smaller breaker for the new equipment that draws less for the same tonnage. This usually happens when I am installing a car charger and doing a calc for the panel. We go around to all the equipment like A/C units, stoves, pool motors, heaters etc. and add up the label info.
Does this same breaker and wire sizing apply to mini splits? The one in question is not just an "air-conditioner" but also a "heater".
At 2:55 "where ambient temperatures do not exceed *85F
i miss the regular videos. i understand it though. whatever you guys can do, appreciated!
What is a 'regular' video?
@@MikeHoltNEC sorry, should have said 'more frequent videos'
@@DavidFRhodes There are over 100 videos at MikeHolt.TV that you probably have not watched!
Thanks
Thank you for your ceaseless dedication to the trade
I love you guys...
I agree that it meets code. However, your rationalization for the short circuit condition is a little out there. Go look up the response time of a breaker at rated amperage. It certainly won't be three hundredths of a second. And the short circuit protection inside the device if the short occurs outside of the device.
God blessed you and your family
Thank you...
Here is my concern with all of this. For the moment let us forget about all of the codes and ampacity of the circuit. looking at the nameplate we are seeing the running load, not the start-up current. The voltage drop across the smaller-sized wire at start-up will make it harder on the compressor to start and possibly shorten its life.
Voltage drop is a separate calculation. For all practical purpose, if the circuit is less than 200 feet, then this is a moot point. Visit MikeHolt.com/App and get my app that does a/c calculations and lets you know the maximum circuit length to accommodate VD.
Glad I'm not a dinosaur and sizing my hvac circuits correctly.
Had a minimum 18.1 max 25a fail with 12 ga romex. 🤦🏻♂️ these inspectors don’t know.
Mike, great content, does this also apply to "Mini-split" AC units where the indoor headunits are powered off the outdoor condenser?
Good question
I would say 100% yes
Total novice here but found your video while researching this topic. I just had a new high efficiency air conditioner installed. The HVAC installer said I need to replace the 20 amp breaker in my panel with a 30 amp breaker to pass inspection. Being a novice I am a bit leery of putting in larger breaker since the wires from panel to AC are 12 gauge (Romex?) which I thought were limited to 20 amps. I don't want to burn my house down. The face plate on condenser states min ckt ampacity Amperage Min 18, Max fuse ckt breaker 30. Based on this video it seems like that is acceptable. Am I correct? Thank you in advance for sharing your expertise. Super helpful!
Yep
@@MikeHoltNEC so in his case, he can use either a 20 amp breaker or a 30 amp breaker?
I really like that format Mike.
Help me understand, what format?
@@MikeHoltNEC rather than having four or five people contributing on multiple topics. You addressed one issue and follow it all the way through to the end. Sizing air conditioning circuits in this case.
Where would you have a situation like this? Other than maybe you can’t source a smaller breaker or you run new conductors while using an existing breaker? The problem I typically run into is the existing breaker is larger than the new equipments maximum allowed because the newer equipment has a lower kw/ton.
I'm don't I understand "where would you have a situation like this?" You would have this 'everytime' you install an a/c circuit.
@@MikeHoltNEC To refine my question; why upsize the breaker? If 12 gauge wire and a 20 amp breaker is sufficient for the application, why use a 40 amp breaker?
@@briancoulomb We are not 'upsizing' the breaker, we are sizing the breaker per the NEC, UL, and manufacture requirements. This protection device is for 'short-circuit ground-fault' protection, and if you are an electrician, then you know that if the wires shorted out (12 AWG), the short-circuit current will instantly rise and to the instantaneous range of the circuit breaker which will open in 0.30 seconds. Why size it 225%? Because this is an inductive load and the starting current (LRA) is 96A. Please watch this video again before you respond. Does this help?
@@MikeHoltNEC I did watch the video. I understand the inrush current and the fact the fault current would still trip the breaker if sized to the maximum allowable. The minimum breaker size would also be sufficient. I have never encountered a situation where the breaker was tripping due to inrush current and required upsizing. It’s good to know the breaker can be sized up in this particular case or with other inductive loads (following the name plate) and NEC. I enjoyed the video, I’ve just never encountered this scenario before.
@@briancoulomb the point isn't to find a situation where you need to upsize a breaker. The next time you are running a feed to a new A/C unit, and you see the "Max Fuse" at 40 amps, and the "Minimum Circuit Amps" at 24 amps. Instead of wasting time and money buying 8 Guage wire to feed this unit, you now have the knowledge to install 12 wire MC, and save yourself some money. The scenario your looking for would be ANY time your sizing for your A/C.
I agree with everything. For some reason mocp is at 25 but when I do the math with compressor at 17.5 amps at 225% plus the fan motor at (.78) I get a number much higher then the units 25 amps..
Manufacturers are permitted to set the MOP to 225%, see 440.22(A) Ex. 2.
Can or is pool heaters considered the same? Can I size from nameplate? Code reference please
🦕 🦖
Thanks again for the videos!
🍺🍺🍺🥃🥃🎯🏌🏻♀️
You bet!
I encountered this today with a unit of 19.8 amps and a max overcurrent protection at 30. My question, was that it was ran in NMB cable to the disconnect and thhn to the unit, so therefore, would I not be able to go from the disconnect with a #12 gauge thhn wire to the unit, keeping the disconnect at 20 amp, and the main breaker at 30?
12 AWG is rated 20A per Table 310.16 at the 60C column per 334.80. So 12 AWG is fine.
Thank you Mike.
Thank you for the great explanation of code! Sadly sometimes it’s cheaper to upsize the wire than get on a dinosaur inspectors bad side. 😓 But with the price of copper today it will be good to have this knowledge in my pocket!
Are A/C circuits exempt from 80% rule for continuous use circuits?
Please watch the video again so you answer your question about the 'so called' 80% rule.
@@MikeHoltNECI guess I was looking for a specific exception to that but realize that’s not how the code is written. A/C circuits are covered separately from the general purpose circuits as you indicated. It’s hard to shed all that dinosaur training a lot of us get from day one! Thanks again for this video!
@@mikereliford55 Great response!
How to install a new circuit breaker
Not one of you took into account that AC's can run constantly on hot days and on first start up of a hot home and as such the conductors should have been treated as a constant load circuit and derated per electrical codes (80% I believe). It is better to install the larger wire than to have it overheat under constant load conditions. I have been on too many AC calls where the supply wiring was causing voltage/current issues.
I noticed someone mentioned Romex-I don't know any mechanical inspector that would let that pass inspection on a permanent install in the state of Oklahoma.
The NEC doesn't list the A/C as a continuous load. However, the 125% calculation of the highest motor load is already figured into the minimum circuit ampacity, thus eliminating the likelihood of overheating the conductors. I've come across failures at the terminals due to improper conductor torque and failed "pull-out" style disconnects where the clamps become loose around the blades of the pullout. In fact, I recently tore my pull-out disconnect apart to squeeze the clamps back down because I noticed a little heat coming from the "pull-out" portion of my disconnect and that it pulled out rather easily. Heat is gone now.
NM cable (Romex) is not permitted to be installed in a wet location (regardless if it is consealed within LFNC or equivalent)(see 300.9 and 334.12(B)(4) of the NEC.) However, I see no issue with it supplying a disconnect, where it would switch over to THWN or equivalent conductor/cable that is rated for use in a wet location.
@@chadherriott116 If they go the way I think they are going and start putting 2 compressers in these residential units, then that highest motor load rule will have to be thrown out or revised to cover all motor loads combined. With matching compressors, you could have 200% of the highest motor load before adding in the fan motors. From what I have seen, they are not including the fan motors in these calculations or they are rounding down when they should be rounding up on this safety calculation. Simple wording-highest motor load-so fan motor is not highest so it is left out of calculation, and I see them doing the same with saying one compressor is the highest and one is not so it gets left out of calculation. Hopefully you can see why I think we some issues with this that could become an even bigger problem in the future.
I would love to see if you or anyone else could get Mike Holt to read our conversatin here and see what he thinks.
All you need to do is follow the manufacture instructions [110.3(B)] and size the wire and protection in accordance with the label. It's no more complicated than that.
@@MikeHoltNEC As resistant as people are with this topic, you'd think that you'd see a house burning down every night on the evening news because of someone putting 10 gauge wire on a 50 ampere breaker for an A/C. It's amazing how many people fail to understand how simple it is. The easiest way I've found to explain it to people is to "wire to the minimum, breaker to the maximum." Can't go wrong there.
@@chadherriott116 you would think that is simple enought..
And I passed my master's test yesterday!!
How cool is that! You worked your butt off and I'm sure your family is very proud of your efforts. Not its time to learn 'business.' After you come down from Cloud 9, call 352.360.2620 and get going on your next step to the top.
how would you size the breaker supplying power to the feeder disconnect ? is that a different calculation ? this video describes how to calculate conductor size and disconnect / branch circuit size for the ac unit but NOT the feeder circuit size
The 2023 NEC clarified that the feeder to the a/c disconnect is sized the same as the branch circuit, see 440.33.
Do you size circuit breakers for three phase AC equipment the same way? I have been familiar with sizing breakers and wires for single phase motors and Ac but never got into three phase equipment.
Yes
Watch the video, read the nameplate and size the wire to what the nameplate states. Amperes is amperes.
just came to say 10's on a fitty!....
I have an a/c condenser with a MCA of 20.1 amps. 20A would be good for 12 ga NM. Would this .1 A push it into 10 ga NM or can it be rounded down to 20A?
220.5(B) Fractions of an Ampere. Calculations shall be permitted to be rounded to the nearest whole ampere, with decimal fractions smaller than 0.5 dropped." But I'm not 100% convinence that this rule applies, so I would say no...
@@MikeHoltNEC thank you. I had one more question on the subject. Clearance from A/C disconnect box (non-fused) to a residential condensing unit. Does this fall under 110.26 and require maintaining the 30"/36" clearance side and front and no higher than 6'7" or does article 440.14 take precedence which requires only for it to be accessible and within sight? I've generally thought that it just had to be accessible and not located behind the unit.
110.26, is a 'general requirement' so it always applies. Note: the 2023 NEC actually added a reference to 110.26 in 440.14
Just to be clear, If the nameplate has 34.5 FLA and I use UF (60 degree) column then I can use #8 UF because I don't need to take the 34.5 and multiply it by 1.25? Also, I could use a 40 Amp breaker?
God Bless you Mike, you have helped me out so many times over the years!
A/C loads do not have FLC, they nave "minimum circuit ampacity' and 'maximum overcurrent protection." So just size the wire and breaker per the nameplate. Please watch the video again, since your comment suggests you are still unclear.
@@MikeHoltNEC Thanks for the response, I can't believe the "Tom Brady" on electricians responded to my question!
@@PPyle Your question was important...
I'm a dinosaur and I put my poo on all aluminum connections!😄
Please watch MikeHolt.com/Dino
@@MikeHoltNEC That's where I got that from, great story!! I'm not really a dino....but I like to play one on Facebook. I am a continuing education supporter and a Holtee.
@@electvolt67 Lol... that was a good one. I never considered that some people are just screwing with me. I'm really not that smart...
@@MikeHoltNEC I'm from NY...I can't help it. I only wish I was as dumb as you!
Great video thanks.
Suppose there is only one space left in the panel for a two pole breaker and two AC units need to be wired. Is there an explicit or implicit provision in NEC'20 that permits taking exception to the nameplate data to accomplish this feat.
The nameplate specifies minimum circuit ampacity, so this is required. The OCP is required to not be greater than maximum' OCP', so you can size the breaker smaller; maybe it would hold...
@@MikeHoltNEC I think you misunderstood my question. Two AC units need to be installed in one circuit.
In such case the ampacity of the conductors needs to be increased and that is not a problem. The MOCP is also likely to increase and this is a problem because the AC label specifies the maximum size alowed. It is implicit that circuit wiring requirements on the label apply only for that unit in a dedicated circuit. So, does the NEC allow multiple AC units on a circuit??
@@shieldcracker Sure, as long as you comply with MCA and MOCP on the equipment label. But I think if you do the math, you probably can't accomplish this.
Partial screen makes the graphics of a good presentation hard to follow,
I know... I screwed up. I need to make a UA-cam video for this and repost. Sorry.
My 5 ton max overcurrent is 60 and the min circuit ampacity is 41.7. The installer said he needed to use a 40 amp breaker. But I hired an electrician who said the breaker has to be over the 40 so he installed a 50amp breaker. Who is correct?
Machine needed 41 amp minimum why not use the 50 . 50 it’s correct with 6 # wire
The correct answer is 8 gauge wire rated at 75c thhn in conduit or mc cable for example, on a 60 amp breaker. You could also do 6 gauge romex on a 60 amp breaker. The 40 amp breaker is wrong. The guy with the 50a is a little better, it should be 60a though.
How do you size conductors and overcurrent for welding machines?
Please review Article 630, specifically 630.11 and 630.12. This is asked on exams, and it is covered in my Exam Prep Program. MikeHolt.com/Exam
Very informative video sir may i use 30MiliAmp GFCI or RCCB for 1.5TON Air conditioner...
1. We don't use RCCB in the USA. Why are you asking this question?
@@MikeHoltNEC
Thanks for immediate reply.
In india there are many fire cases due to short circuit [sparking) in AIr Conditioner split type. Can earth fault protection breaker prevent fire . Or C Type MCB fulfill all the requirements.
@@pramodgavit7666 I'm sorry but I don't have all of the details, but RCD would most likey reduce some of the fires.
I think the camera needs to rotate 90degrees
I know, this was intended for Social Media and then I decided to put on UA-cam. I plan on redoing landscape and then replacing this video... sorry.
It's amazing how many dinosaurs still exist
Tell me about it...
@@MikeHoltNEC God bless you man.
I'm sending this message as im Iistening
to your grounding and bonding video lol
I've learned so much from your videos over the years. Appreciate it!!
@@josepheskenazi2392 Thank you, and God Bless you and your family
Please make your video horizontal. We are not TikTok!
I know... I screwed up. I'll fix.
@@MikeHoltNEC it's ok Mike, you got the info out, that's what counts! Thanks! 👍
Romex is for trailer parks
Say you know nothing about the electrical industry without actually saying you know nothing about the electrical industry.
I was thinking the exact same thing. But felt it would be inappropriate for 'Mike Holt' to make this statement. Thank you! By the way, I love Romex for the poper applications (as permitted by 334.10)... just saying.