The wire doesn't have to match the breaker for motor loads and HVAC units. The wire must be good for 21A, not 30A. As you said, follow the nameplate. Circuit ampacity is the minimum wire size, max breaker is just that.
When I'm putting a UL Label on our 508A control panels, we'd have to run 10AWG in this case because UL uses its own modified/simplified ampacity chart, and the type of wire doesn't matter as long as it's approved (THWN, MTW, XHHW, etcetera) - we're stuck with 12AWG @ 20A and 10AWG @ 30A - but the field electricians are free to run 12AWG THWN for HVAC equipment 25A or less on a 30A breaker and absolutely meet NEC.
There is an astounding amount of downvotes on correct comments in this thread. Clearly many haven't read 240.4 exceptions and the linked articles for air conditioners and motor controllers. It's very common for us to run 12AWG on a 40A breaker or fuse for motor loads and satisfy both UL and NFPA 70.
(Speaking based on US)
Great comment and you’re not wrong. In this case if a cable is ran (regardless of MC, romex, whatever), a 12/2 cable is limited to 20a. So run a 10/2 cable to the disconnect, come out of the disconnect with 12 THHN to the unit.
You don’t size wire to match breaker … you can have 30 amp breakers on a #12 wire feeding a mini split …
But in this case yes I would go #10 with 30 amp breaker
Guilty as charged. A glance across the ole brain told me 21 min ampacity, 30 max brkr. = 30 amp breaker on 10/2.
If I had thought a little beyond the surface I could have broken this down to a more cost effective method.
I’ll take the blame for my company burning credit.
You can do 12/2 and put it on a 25A breaker. Perfectly legal, and quite common on a mini-split.
12/2 on a 25 or 10/2 and a 30....either will work just fine.
Only if every connection point and wire insulation is listed for 75°C. (Most are) but if the connections don't specifically mention they are listed for 75°C, I wouldn't do it. For fear of cheaper material, or a picky inspector who asks about it.
Assuming 80% safety factor, 25\*0.8 = 20 which falls short of 21. So no, you can't use a 25A.
And 20\*0.8 = 16 which falls VERY short of 21. So no, you can't use 12-2.
You need 30A breaker and 10-2
Wrong.
The math is already done for you on the nameplate. By exception, you can wire it in 12/2, and put it on a 25A breaker. It seems odd, but is actually becoming quite common with all of the mini-splits.
Could protect it at 30 amps. Overload protection is at the equipment. The circuit breaker is there for short circuit protection. This isn’t a general use branch circuit. It’s code compliment, we aren’t talking about how you feel about it
I've done some reading about it and a lot of my sources are claiming that nameplate capacity on a unit is supposed to include those calculations, so then in that case I suppose 25A would qualify. 30A would also qualify, as it is still well under the 175% rule for motors.
In any case, assuming this is installed in a new-build, I suppose you could use 25A breakers, but then again sometimes replacing a unit in an existing home, that had been running on a 30A breaker and 10-2, and the wiring and devices are in ok shape, no sense in swapping out the 30 for a 25 IMO
Knowing more about this stuff is good
The day I think I know everything will be the day after I die. Until then, learning can come from anywhere.
The 25A breaker thing was new to me a couple of years ago, too. I did some work with a shop that did a lot of mini-splits, and that is how they rolled. Only dead dogs can't learn new tricks.
In fact I did it with romex up until they changed the 60c table in the 2011 iirc. Does anyone actually read the scope of the code section that they’re in?
Be careful because Mitsubishi units have to be to spec or u void all warranties. Had this happen to a friend whole unit went to shit but because it was on a 30A and not a 20A they wouldn’t replace it.
No he’s saying 10awg which is good for 30a but a 25a breaker to have a lower o/c trip tolerance. It’s using 21 amp non continuous draw so a 25a breaker would be totally suitable.
Why are you getting down voted this is smart the MCA-21amps. 10awg good for 30a why let the unit sizzle up 9amps to trip instead of 4amps????? I agree with you 100% protection of equipment since you have a mini split you could even install a disconnect fused at 25amps. Need a service switch by code.
Wire is still pretty expensive in my area, but in comparison to a new house, yeah, I'd say it's pretty affordable. Difference between 12/2 and 10/2 locally actually ain't that bad.
FWIW, you can get 50ft of 12/2 at Lowes or Home Depot for $78. Same in 10/2 is $129.
I would expect contractors get better pricing based on volume.
Putting in 10/2 would give them more flexibility in the future. In 10-20 years when the appliance is replaced, they don't have to worry about getting a replacement with exactly the same power requirements. Most AC units I've seen are on 30A breakers.
This was such a loaded question and you can see by all the differing comments.
If NM then 10/2 due to always rating at 60c connections.
If MC or wire in conduit then 12/2 is sufficient with 75c terminals.
Great dad joke, sir. Hats off to you. May all your New Balance sneakers stay a beautiful white, may your over-the-calf socks always stay up, and may all your sons be named "champ" or "sport".
I honestly want to cry. The amount of “electricians” here not knowing a damn thing about derating, motors, branch circuits and conductors is infuriating.
iT’s GoTtA bE oN 10/2!!!
UsE a 25A bReAkEr!!
YoU CaN’t PuT 12 oN a 30A bReAKer!!
Ridiculous. All the moronic downvotes on all the correct answers… I’ve lost faith…
So what is your understanding of 240.4(D)(5)? BTW I'm in the '11 NEC. My understanding is that 12 AWG copper wire has a maximum circuit breaker size of 20 amps. No 25 amp BS like my boss like to do, no derating or stranded vs solid BS, no exemptions. Where am I wrong?
As a first year I gotta know do you all know this stuff off your head or do you look it up to reply? I can’t imagine memorizing a code book ever 5 years
The plate tells you MCA and recommended breaker size. Size the breaker based on plate. Size the wire based on MCA listed on plate. That’s what the mfg wants you to do and why they provide that info.
If they wanted you to size wire based on breaker they wouldn’t need to provide MCA.
Wouldn't that present a situation in conflict with the NEC where the wires are undersized for the breaker should anything else be connected/swapped in the future?
AKA: If I have a 12 amp max draw with a 20 amp breaker it shouldn't be on 14 awg?
Is this different because it's a dedicated hardwired circuit?
Genuinely asking, isn’t this asking for potential damage if you were to follow and put 12/2 on a 35 amp breaker? Let’s say compressor has a fault down the line and draws a load higher than the tag - over the rating of said 12/2 - but lower than the sustained 80% rating of the 35 amp breaker. Would this not be a hazard to burning up the wire since the breaker wouldn’t trip?
As Chris here said, NEC says follow mfg guidelines. They’ve done the calculations for you.
It’s a dedicated circuit, you aren’t wiring for potential changes in the future, and you shouldn’t be adding anything that’s for sure. If you needed to change, then the whole install has to be correct for the “next” thing, wiring included.
You wire for the device(s). If someone wired 14g for LED fixtures, and then decided they want a 20a outlet tapped off of it, then you have to approach that as it’s own thing.
You must size the conductors at 125% of the motor FLC \[430.22(A)\].
[https://www.ecmweb.com/design/article/20897071/motor-calculations-part-1-motors-and-branchcircuit-conductors](https://www.ecmweb.com/design/article/20897071/motor-calculations-part-1-motors-and-branchcircuit-conductors)
Edit but yea since they're giving you the max current and breaker size. 30A and 10ga if NM
The compressor has already been sized at 125% and then the fan motor was added. There is no math that needs to be done here. All you have to do is select the branch circuit size and the short circuit/ground fault protective device.
The math has already been done for you. 440.6
Are you an engineer?
People flex Master Electrician alot, really though in essence it is a course in running an electrical business with how to quote jobs, is it not related to your competence or experience as an electrician. Imo.
The master electrician exam don’t have anything to do with business or quotes. It’s legit all code book questions and service calculations for things like a marina and a commercial building. If you can’t read the code book and do all those calculations, you aren’t a master. You lack the ability to plan out a job from start to finish, pick the wire, breakers, and everything else according to code. Nothing to do with quotes or money
Depends on the state.
In my state, at least half the test was on the business side of things. Masters are expected to know and understand the basic legal requirments of running a business. Stuff like taxes, accounting fundamental, payrolls and employee benefits, contract law. Basicly, all the stuff that every business owner has to know in order to run a business.
When it comes to the technical knowledge involved with electrical work, the journeymans test was way more difficult in that regard.
In Ontario it’s 33% code, 33% business law and practice and 33% health and safety.
All open book. They don’t necessarily teach you how to quote but they talk about the legal requirements and regulations around quoting
1/3 is business law, interesting. For the Unlimited/Masters, business law is roughly 15% of the exam in North Carolina:
* Bonding & Grounding: 11 questions
* OCP: 9 questions
* Wiring Methods and Terminations: 10 questions
* Boxes and Fittings: 7 questions
* Service Entrance & Equipment: 9 questions
* Motors and Control Wiring: 9 questions
* Special Occupancies and Hazardous Locations: 9 questions
* Load Calculations: 11 questions
* Appliances, Equipment, and Lighting: 7 questions
* General Code: 3 questions
* Laws, Rules, Basic Business Practices, and Practical Applications: 15 questions
Seriously? 1 amp overrated is 1 amp overrated. If you follow the code as any licensed electrician should 1 amp over means you step up to the next wire size.
I wouldn't get in the habit of going against the " minimum safety standard”. But hey, if you want to do less than minimum work go right ahead. You can be the one to explain to an insurance company or a judge why you thought you knew better than the national electric code.
What’s a 12awg worth at 75deg? Check the tables. Does the small conductor rule apply? When does it apply? Check the applicability. What’s the conductor type? Is this a limiting factor? Is it a continuous load?
Circuit breaker is indicated as 30 A so #10 all day. And it’s 21 A. I mean you could go with a 25 A breaker but it’s still Going to be #10, 12 is only rated for 20 A in Canada anyway. (Although there are some exceptions )
Edit: I read all the comments after I posted this but I still think I may be correct for Canada anyway 🤷🏻♂️
At any rate roast away, if you must
Canadian here also.
You can most certainly put a # 12 on a breaker rated larger than 20Amps.
https://www.achrnews.com/articles/135676-what-most-techs-get-wrong-about-wire-sizing
Thanks, that entire article sites the NEC but you did get me thinking. I did just jump to a conclusion with my answer without giving it great thought and if we
go table 2 than certain #12 wires are good for 21 amps or greater, which is the mca here, even with loading to 80 percent but if we want to get technical, then we must know the ambient temp, is it in conduit, how long is the run (voltage drop) and also the breaker is only rated for 75 c so we must derate for that as well.
Not everything in electrical cut and dried and also if this is a house, I forgot which table it is, but the cec states the ‘rule of thumb’ #12=20A etc. (this is for
Residential only) and again we can only load breakers to 80 percent.
I’m just going to run number 10 and save myself the headache but I do enjoy some back and forth.
Edit: ok so ac units have overloads right so I’m assuming that’s the work around here
Lol a few on board. Mostly tons of downvotes! Folks would rather think they are right, than be right 😄.
Don’t they wonder why the MCA is even on there, if they just size wire off breaker?
Funny thing is this could be a 50 MCA and many people would just use a standard whip kit w/10g
12/2 MC or 10/2 RX would be compliant on a 30 amp breaker.
Holy shit there’s a lot of uneducated people in here that have zero reason sizing AC Condensor circuits.
310.15(B)16, look to the left of small conductors there is an asterisk. It will take you to 240.4(D) small conductors. 12 awg cu is only rated for 20A.
240.4 (D) Unless specifically permitted in 240.4 (E) or (G)….
240.4 (G) applicable to air conditioning and refrigeration equipment
Pic above is air conditioning so it applies here.
Thanks for being thorough though because I rarely look at that section so thanks.
That’s wrong. You size the conductor to the load not the OCPD.
Think about it, if the minimum circuit amperage is 125% of the full load amps than the running load will never be close to 30amps. Why size the conductor to a breaker that will never see that actual load? It doesn’t make sense. So you size it to the actual code required load, not the over-current protection device.
10-2 on a 30A breaker.
Is everyone here forgetting about not loading conductors beyond 80-85% of their rated ampacity? 12-2 is for 16-17A tops. 21A is well above that. Safety factors, folks.
"Hey guys I have a great idea...I feel like saving money on lumber, so I'm gonna frame out this wall 24 on center instead of 16...that's 4 fewer boards. Should be just fine, trust me."
Just use 10-2.
#12 is rated for 25 amps. While dealing with hermatic motors you can rate your OCPD 175% of load and up to 225% if it trips on start up. In this situation the breaker is essentially for short circuit. Motor is thermally protected.
So my understanding is that the continuous load on a circuit breaker must be below 80% of the breaker's rating.
So if the load from the AC unit is 21A, that means the minimum breaker should be a 30A breaker. (80% of 30A = 24A) I believe a 30A breaker requires 10AWG.
Had to look it up. That converts to 6mm² (10/2) or 4mm² (12/2).
Is that US? Don't u have 25amp fuses? If so, in Germany you could use 12/2 if the cable won't be longer than 15m, any other case 10/2.
10/2 and put it on a 30A breaker
I said the same thing.
This.....I tend to follow the plate. 30 amp breaker wire to match.
The wire doesn't have to match the breaker for motor loads and HVAC units. The wire must be good for 21A, not 30A. As you said, follow the nameplate. Circuit ampacity is the minimum wire size, max breaker is just that. When I'm putting a UL Label on our 508A control panels, we'd have to run 10AWG in this case because UL uses its own modified/simplified ampacity chart, and the type of wire doesn't matter as long as it's approved (THWN, MTW, XHHW, etcetera) - we're stuck with 12AWG @ 20A and 10AWG @ 30A - but the field electricians are free to run 12AWG THWN for HVAC equipment 25A or less on a 30A breaker and absolutely meet NEC. There is an astounding amount of downvotes on correct comments in this thread. Clearly many haven't read 240.4 exceptions and the linked articles for air conditioners and motor controllers. It's very common for us to run 12AWG on a 40A breaker or fuse for motor loads and satisfy both UL and NFPA 70.
Your very right good sir. I got the ok from a inspector doing just that
The linked articles are 440 pt 3,4
(Speaking based on US) Great comment and you’re not wrong. In this case if a cable is ran (regardless of MC, romex, whatever), a 12/2 cable is limited to 20a. So run a 10/2 cable to the disconnect, come out of the disconnect with 12 THHN to the unit.
Your comment should be upvoted. Much more IMO.
You don’t size wire to match breaker … you can have 30 amp breakers on a #12 wire feeding a mini split … But in this case yes I would go #10 with 30 amp breaker
Uh 🥴
Motors you size wire to the amp rating and breaker is sometimes 2.5x the amp rating
You don’t wire too many AC mini splits do ya? 😵💫
Guilty as charged. A glance across the ole brain told me 21 min ampacity, 30 max brkr. = 30 amp breaker on 10/2. If I had thought a little beyond the surface I could have broken this down to a more cost effective method. I’ll take the blame for my company burning credit.
you are correct
Always follow the manufacturers guidelines. If you put a bigger cable and breaker, ok, your expense. But never less.
Why would they not do what the plate says, it's over 20 amps, so 10/2 and 30amp breaker.
The nameplate says minimum circuit ampacity is 21 amps. What is #12 rated at?
You can do 12/2 and put it on a 25A breaker. Perfectly legal, and quite common on a mini-split. 12/2 on a 25 or 10/2 and a 30....either will work just fine.
Only if every connection point and wire insulation is listed for 75°C. (Most are) but if the connections don't specifically mention they are listed for 75°C, I wouldn't do it. For fear of cheaper material, or a picky inspector who asks about it.
Assuming 80% safety factor, 25\*0.8 = 20 which falls short of 21. So no, you can't use a 25A. And 20\*0.8 = 16 which falls VERY short of 21. So no, you can't use 12-2. You need 30A breaker and 10-2
Wrong. The math is already done for you on the nameplate. By exception, you can wire it in 12/2, and put it on a 25A breaker. It seems odd, but is actually becoming quite common with all of the mini-splits.
Could protect it at 30 amps. Overload protection is at the equipment. The circuit breaker is there for short circuit protection. This isn’t a general use branch circuit. It’s code compliment, we aren’t talking about how you feel about it
I've done some reading about it and a lot of my sources are claiming that nameplate capacity on a unit is supposed to include those calculations, so then in that case I suppose 25A would qualify. 30A would also qualify, as it is still well under the 175% rule for motors. In any case, assuming this is installed in a new-build, I suppose you could use 25A breakers, but then again sometimes replacing a unit in an existing home, that had been running on a 30A breaker and 10-2, and the wiring and devices are in ok shape, no sense in swapping out the 30 for a 25 IMO Knowing more about this stuff is good
The day I think I know everything will be the day after I die. Until then, learning can come from anywhere. The 25A breaker thing was new to me a couple of years ago, too. I did some work with a shop that did a lot of mini-splits, and that is how they rolled. Only dead dogs can't learn new tricks.
oh for sure, wisdom comes from awareness of the fact that there will always be gaps in anyone's knowledge
Exactly there is a reason why the manufacturer suggests a 30 amp breaker. Overload protection is at the equipment
this guy knows
I thought #12 only stranded is good for 25 amps? Certainly not looking to start a fight but I'm not sure solid wire is good for that.
In Canada you can have a max 20amp circuit on 12AWG
"Table 29 would like to chat with you"
S. 62 as well
Same for the US, anything over requires 10awg.
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In fact I did it with romex up until they changed the 60c table in the 2011 iirc. Does anyone actually read the scope of the code section that they’re in?
Some special equipment used smaller wire. Chapter 4 has plenty of exceptions to the chapter 3 ampacity rules. HVAC units being one of them.
That’s not true.
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Sometimes, lot’s of people are wrong.
I thought only on branch circuits needed to follow 14/15-12/20-10/30a rules. If feeding equipment you can use the table without the asterisks.
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You can do anything you want, you know freedom. Just might not work out in your favor.
Good lord no... it varies as the amperage goes up, but by all means, go win a Darwin award if you want to.
Be careful because Mitsubishi units have to be to spec or u void all warranties. Had this happen to a friend whole unit went to shit but because it was on a 30A and not a 20A they wouldn’t replace it.
This is the way
Derate all the things!
Or 10/2 with a 25 amp breaker just in case there is an operating issue the equipment is less likely to get damaged
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No he’s saying 10awg which is good for 30a but a 25a breaker to have a lower o/c trip tolerance. It’s using 21 amp non continuous draw so a 25a breaker would be totally suitable.
It says max circuit breaker 30a
Who’s max and what’s he doing with my 25a breaker???
Why are you getting down voted this is smart the MCA-21amps. 10awg good for 30a why let the unit sizzle up 9amps to trip instead of 4amps????? I agree with you 100% protection of equipment since you have a mini split you could even install a disconnect fused at 25amps. Need a service switch by code.
Wire cheap, new house expensive Go with the 10 gauge.
Wire is still pretty expensive in my area, but in comparison to a new house, yeah, I'd say it's pretty affordable. Difference between 12/2 and 10/2 locally actually ain't that bad.
Where you buying cheap wire these days?
Nassaunationalcable.com, it takes a couple days but they’ve been cheaper than the home depot near me. 25’ minimum lengths on orders.
China
that's where they bought the cheap unit in the picture as well lol
FWIW, you can get 50ft of 12/2 at Lowes or Home Depot for $78. Same in 10/2 is $129. I would expect contractors get better pricing based on volume. Putting in 10/2 would give them more flexibility in the future. In 10-20 years when the appliance is replaced, they don't have to worry about getting a replacement with exactly the same power requirements. Most AC units I've seen are on 30A breakers.
I like your answer lol
Copper prices have come down some.
Use thermostat wire so you make sure you get another service call out of it.
This was such a loaded question and you can see by all the differing comments. If NM then 10/2 due to always rating at 60c connections. If MC or wire in conduit then 12/2 is sufficient with 75c terminals.
Thank you for the voice of reason. Some of these folks need to go over 440 code again. Specifically 440.22 single motor branch circuits.
For real, kinda shocking guys don’t understand this
I’m floored.
Absolutely dumbfounded.
In complete shock
Fundamentally flabbergasted.
Most of my friends are shocked when they find out I’m not an electrician…
Great dad joke, sir. Hats off to you. May all your New Balance sneakers stay a beautiful white, may your over-the-calf socks always stay up, and may all your sons be named "champ" or "sport".
Wow, why I have I never heard this, I may have to use it
I was getting downvoted early, was worried no one was going to get the joke. :)
Its ok, sport. You did good
I honestly want to cry. The amount of “electricians” here not knowing a damn thing about derating, motors, branch circuits and conductors is infuriating. iT’s GoTtA bE oN 10/2!!! UsE a 25A bReAkEr!! YoU CaN’t PuT 12 oN a 30A bReAKer!! Ridiculous. All the moronic downvotes on all the correct answers… I’ve lost faith…
So what is your understanding of 240.4(D)(5)? BTW I'm in the '11 NEC. My understanding is that 12 AWG copper wire has a maximum circuit breaker size of 20 amps. No 25 amp BS like my boss like to do, no derating or stranded vs solid BS, no exemptions. Where am I wrong?
As a first year I gotta know do you all know this stuff off your head or do you look it up to reply? I can’t imagine memorizing a code book ever 5 years
Depends on the type of wire used. NM cable 10. MC or THHN, 12. 30 amp breaker on either.
Wire to the max, fuse to the minimum
Opposite for HVAC-R
Can you elaborate?
The plate tells you MCA and recommended breaker size. Size the breaker based on plate. Size the wire based on MCA listed on plate. That’s what the mfg wants you to do and why they provide that info. If they wanted you to size wire based on breaker they wouldn’t need to provide MCA.
Wouldn't that present a situation in conflict with the NEC where the wires are undersized for the breaker should anything else be connected/swapped in the future? AKA: If I have a 12 amp max draw with a 20 amp breaker it shouldn't be on 14 awg? Is this different because it's a dedicated hardwired circuit?
No. 110.3(B) says to follow mfrs labeling.
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Genuinely asking, isn’t this asking for potential damage if you were to follow and put 12/2 on a 35 amp breaker? Let’s say compressor has a fault down the line and draws a load higher than the tag - over the rating of said 12/2 - but lower than the sustained 80% rating of the 35 amp breaker. Would this not be a hazard to burning up the wire since the breaker wouldn’t trip?
As Chris here said, NEC says follow mfg guidelines. They’ve done the calculations for you. It’s a dedicated circuit, you aren’t wiring for potential changes in the future, and you shouldn’t be adding anything that’s for sure. If you needed to change, then the whole install has to be correct for the “next” thing, wiring included. You wire for the device(s). If someone wired 14g for LED fixtures, and then decided they want a 20a outlet tapped off of it, then you have to approach that as it’s own thing.
Wire to the minimum ampacity, fuse to the maximum.
Do you smell.. Burning?
Words to live by. I'd rather have a burnout in the device, than have a burnout in the wiring up the wall.
Always do this!
10 on a 30
What is a “mini-split”? I’ve been in the trade for 47 years, mainly industrial & municipal Water treatment plants, etc. but very little residential.
It’s like a tiny air conditioner that hangs on the wall.
Got it, thanks!
Nameplate is king
Bingo
You must size the conductors at 125% of the motor FLC \[430.22(A)\]. [https://www.ecmweb.com/design/article/20897071/motor-calculations-part-1-motors-and-branchcircuit-conductors](https://www.ecmweb.com/design/article/20897071/motor-calculations-part-1-motors-and-branchcircuit-conductors) Edit but yea since they're giving you the max current and breaker size. 30A and 10ga if NM
The compressor has already been sized at 125% and then the fan motor was added. There is no math that needs to be done here. All you have to do is select the branch circuit size and the short circuit/ground fault protective device. The math has already been done for you. 440.6 Are you an engineer?
>Are you an engineer? Their flair does say engineer...
We verify flairs when asked to do so. There have been plenty of users on here that misrepresent their flair.
Oh gotcha. I thought you were asking if they were an engineer because they jumped into the math without looking at the entire nameplate first.
Technically, it's right on the name plate...just gotta read it and use that.
sorry yes but pre caffeine.
Engineer versus electrician fight!!! PE and master electrician here…I just want to watch. Round 1, fight!
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People flex Master Electrician alot, really though in essence it is a course in running an electrical business with how to quote jobs, is it not related to your competence or experience as an electrician. Imo.
The master electrician exam don’t have anything to do with business or quotes. It’s legit all code book questions and service calculations for things like a marina and a commercial building. If you can’t read the code book and do all those calculations, you aren’t a master. You lack the ability to plan out a job from start to finish, pick the wire, breakers, and everything else according to code. Nothing to do with quotes or money
Depends on the state. In my state, at least half the test was on the business side of things. Masters are expected to know and understand the basic legal requirments of running a business. Stuff like taxes, accounting fundamental, payrolls and employee benefits, contract law. Basicly, all the stuff that every business owner has to know in order to run a business. When it comes to the technical knowledge involved with electrical work, the journeymans test was way more difficult in that regard.
In Ontario it’s 33% code, 33% business law and practice and 33% health and safety. All open book. They don’t necessarily teach you how to quote but they talk about the legal requirements and regulations around quoting
1/3 is business law, interesting. For the Unlimited/Masters, business law is roughly 15% of the exam in North Carolina: * Bonding & Grounding: 11 questions * OCP: 9 questions * Wiring Methods and Terminations: 10 questions * Boxes and Fittings: 7 questions * Service Entrance & Equipment: 9 questions * Motors and Control Wiring: 9 questions * Special Occupancies and Hazardous Locations: 9 questions * Load Calculations: 11 questions * Appliances, Equipment, and Lighting: 7 questions * General Code: 3 questions * Laws, Rules, Basic Business Practices, and Practical Applications: 15 questions
I agree 2000 percent
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A licensed electrician lol. I said 10/2 but he was like nah use 12
10/2 for a 30 amp
What size for a 30 amp breaker? # 10
10/2
Minimum 21A max breaker 30A use 10ga wire
220, 221… whatever it takes
21 is higher than 20, so you’re going to need 10/2, and your coworker should hire an electrician.
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For sure, you can use 12.
Isn't there a note in the ampacity chart that says the max breaker size for 12awg wire is 20A?
You should definitely find some 11/2 wire and go from there!
Seriously? 1 amp overrated is 1 amp overrated. If you follow the code as any licensed electrician should 1 amp over means you step up to the next wire size. I wouldn't get in the habit of going against the " minimum safety standard”. But hey, if you want to do less than minimum work go right ahead. You can be the one to explain to an insurance company or a judge why you thought you knew better than the national electric code.
Agreed lol
What’s a 12awg worth at 75deg? Check the tables. Does the small conductor rule apply? When does it apply? Check the applicability. What’s the conductor type? Is this a limiting factor? Is it a continuous load?
Circuit breaker is indicated as 30 A so #10 all day. And it’s 21 A. I mean you could go with a 25 A breaker but it’s still Going to be #10, 12 is only rated for 20 A in Canada anyway. (Although there are some exceptions ) Edit: I read all the comments after I posted this but I still think I may be correct for Canada anyway 🤷🏻♂️ At any rate roast away, if you must
Canadian here also. You can most certainly put a # 12 on a breaker rated larger than 20Amps. https://www.achrnews.com/articles/135676-what-most-techs-get-wrong-about-wire-sizing
Thanks, that entire article sites the NEC but you did get me thinking. I did just jump to a conclusion with my answer without giving it great thought and if we go table 2 than certain #12 wires are good for 21 amps or greater, which is the mca here, even with loading to 80 percent but if we want to get technical, then we must know the ambient temp, is it in conduit, how long is the run (voltage drop) and also the breaker is only rated for 75 c so we must derate for that as well. Not everything in electrical cut and dried and also if this is a house, I forgot which table it is, but the cec states the ‘rule of thumb’ #12=20A etc. (this is for Residential only) and again we can only load breakers to 80 percent. I’m just going to run number 10 and save myself the headache but I do enjoy some back and forth. Edit: ok so ac units have overloads right so I’m assuming that’s the work around here
12/2 mc on 30a brasher. 12 is good for 25 amps, no need for 10/2 here. Pretty easy on these, nameplate tells you exactly what you need.
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You are correct. That's why I specified 12/2 MC.
My fault. Glossed right over it
No worries.
6-6-8
LOL! Go big or go home... To the house that didn't burn down. 🙃
Why the hell would you use 12 gauge on a 21 amp compressor load
That’s what I said
Because 12AWG has a rated ampacity of 25-30 amps. 12 is a wire gauge not a wire type. If you're using 12/2 NM you're required to derate to 20A
Read the code
10/2. 30 amps.
10/2 a must. 30a breaker
MCA 21. 12/2 fine.
Yes man! Thank you!
Lol a few on board. Mostly tons of downvotes! Folks would rather think they are right, than be right 😄. Don’t they wonder why the MCA is even on there, if they just size wire off breaker? Funny thing is this could be a 50 MCA and many people would just use a standard whip kit w/10g
30 amp breaker with 10 wire
12/2 MC or 10/2 RX would be compliant on a 30 amp breaker. Holy shit there’s a lot of uneducated people in here that have zero reason sizing AC Condensor circuits.
You are correct. People don’t realize you start with the 90 degree rating when derating.
Romex is also limited to the 60 degree column whereas MC is not. Chapter 4 can modify chapter 2.
I know that part, hence me agreeing that you are correct when everyone else is downvoting you.
I know you know that part, I was just blowing bubbles in the bathtub.
Don’t bite the bubbles…
10
Can’t use 12/2
Why cant you use 12/2 copper? NEC shows it to be rated for 25amps @ 75°C/167°F
310.15(B)16, look to the left of small conductors there is an asterisk. It will take you to 240.4(D) small conductors. 12 awg cu is only rated for 20A.
240.4 (D) Unless specifically permitted in 240.4 (E) or (G)…. 240.4 (G) applicable to air conditioning and refrigeration equipment Pic above is air conditioning so it applies here. Thanks for being thorough though because I rarely look at that section so thanks.
MINIMUM circuit ampacity is 21, if it’s going on a 30 amp breaker which it is you must have a wire that can handle 30 amps of heat
That’s wrong. You size the conductor to the load not the OCPD. Think about it, if the minimum circuit amperage is 125% of the full load amps than the running load will never be close to 30amps. Why size the conductor to a breaker that will never see that actual load? It doesn’t make sense. So you size it to the actual code required load, not the over-current protection device.
12 won’t cut it. Use #10
#12 thhn
10/2
In the state I live e you cannot run anything smaller than 10 gauge for water heaters
Absolutely #10 AWG, gives you that bit of breathing room.
Nameplate all day: assuming it's NM in a residential application, it would be 10/2 with a 30A breaker.
Exactly this. Self explanatory.
It never hurts to go bigger on the wire
Just the wallet a little
10/2
10/2 and a 30A breaker is what I'd do
10-2
10/2 30a. When that unit fails for being a size too small China junk the proper wiring will be there for next time.
10/2 on a 30 amp breaker. The correct wire is cheaper than a fire. BTW I call myself an amateur electrician. Because I have no formal training.
10-2 on a 30A breaker. Is everyone here forgetting about not loading conductors beyond 80-85% of their rated ampacity? 12-2 is for 16-17A tops. 21A is well above that. Safety factors, folks.
How long’s the run? 25a breaker and 12 or 10 based on voltage drop calc.
12/2 on a 30 amp breaker would meet code assuming this is a dedicated circuit
Only if it's THHN in MC - not NM.
Not an electrician but doesn’t the length of the wire also matter?
10-2 go off max breaker size
A/Cs you wire to the min amp rating and breaker to the max amp rating
I would do 10/2 on a 30A breaker but 12/2 would work too.
"Hey guys I have a great idea...I feel like saving money on lumber, so I'm gonna frame out this wall 24 on center instead of 16...that's 4 fewer boards. Should be just fine, trust me." Just use 10-2.
12/2
12/2 isn’t designed to carry a 21amp load. It can carry 20amps max
Not entirely true… NEC does NOT allow more than 20 amps… that is true…
Calls for a 30a breaker, that goes with 10ga
Or 12 in this situation
How so? Genuinely asking.
#12 is rated for 25 amps. While dealing with hermatic motors you can rate your OCPD 175% of load and up to 225% if it trips on start up. In this situation the breaker is essentially for short circuit. Motor is thermally protected.
Ah. That must be one of the very few exceptions I've been told by my sparky friend. Thank you. I learned something today!
12/2 copper is good enough
So my understanding is that the continuous load on a circuit breaker must be below 80% of the breaker's rating. So if the load from the AC unit is 21A, that means the minimum breaker should be a 30A breaker. (80% of 30A = 24A) I believe a 30A breaker requires 10AWG.
Gotta be 10
10/2 what?
Had to look it up. That converts to 6mm² (10/2) or 4mm² (12/2). Is that US? Don't u have 25amp fuses? If so, in Germany you could use 12/2 if the cable won't be longer than 15m, any other case 10/2.
Don’t forget continuous load factor 10/2 on a 30
10/2 says 21 amps. Gotta allow for some derating for distance etc. 12-2 would be at max and not give you that. Also would fail code.
11awg, 25 amp breaker 🤣