# Whats the best way to size a disconnect for a AC Condenser



## wildleg (Apr 12, 2009)

Sparky1744 said:


> I am installing an AC Condenser and I need to install a disconnect. The Condenser is a single phase 208 volt, 60 Hz, 12.1 Full load amps, 14.8 Wire sizing amps and 25.0 Over Current Protection Device.


its a disconnect. any disconnect at a rating of more than 208/30 will do. if it is fused, you will need to comply with 440. I'm answering the question you asked, but not sure if you didn't ask the question you thought you asked ?

You didn't post horses or locked rotor, but here's the beginning of the article you should read in 440:



> 440.12 Rating and Interrupting Capacity.
> (A) Hermetic Refrigerant Motor-Compressor. A disconnecting means serving a hermetic refrigerant motorcompressor shan be selected on the basis of the nameplate rated-load current or branch-circuit selection current, whichever is greater, and locked-rotor current, respectively, of the motor-compressor as follows.
> (1) Ampere Rating. The ampere rating shall be at least 115 percent of the nameplate rated-load current or branchcircuit selection current, whichever is greater.
> Exception: A listed unjilsed motor circuit switch, without jitseholders, having a horsepower rating not less than the equivalent horsepower determined in accordance with 440.12(A)(2) shall be permitted to have an ampere rating less than 115 percent of the spec~fied current.
> ...


(I'm stuck on NEC2014, but I don't think much has changed here)


----------



## tmessner (Apr 1, 2013)

Cheapest one that meets the hp. Usually a 60 amp non fused for less than 20 bucks.


----------



## telsa (May 22, 2015)

Sparky1744 said:


> I am installing an AC Condenser and I need to install a disconnect. The Condenser is a single phase 208 volt, 60 Hz, 12.1 Full load amps, 14.8 Wire sizing amps and* 25.0 Over Current Protection Device*.


It's a puppy, but still you'll be using a 30A frame size safety switch.

Is this an apartment or micro commercial? I say that because 208 VAC single phase is not seen in ordinary commercial.

Most condensers that small are dual voltage rated anyway. They expect 240 VAC but will put up with 208 VAC.

Even cheop residential discos -- with fuse pull blocks -- are still fused -- and the label is telling you to got with 25A fuses -- time delay or slo blow. 

The Hertz is irrelevant to you.

You might go with #12 conductors. as 12.1 FLA is 0.1 Amps over the 80% of 15Amp #14 limit. But this is fundamentally a motor load. So even #14 wire will suffice. 

Read 440.

In my Commercial world, #14 is out of the question. #12 is automatically the lowest we can go. (Local amendment)


----------



## Going_Commando (Oct 1, 2011)

telsa said:


> It's a puppy, but still you'll be using a 30A frame size safety switch.
> 
> Is this an apartment or micro commercial? I say that because 208 VAC single phase is not seen in ordinary commercial.
> 
> ...


I don't bother with a fused disconnect if the max ocpd rating is a standard sized breaker. I pop in the right sized breaker, then use an $8 60A pull out style non-fused disco.

ETA: This is obviously for single phase small A/C systems. Thought I'd throw in that caveat.


----------



## JoeSparky (Mar 25, 2010)

25 amp breaker (if you can get one), 14 awg or larger feed - i'd run at least 12. And a cheap $7 60 amp pull out non-fused disconnect from home creepo. If you can't find the 25 then, use a 30 and a $12 fused disconnect from the creepo with 25a time delay fuses.


----------



## JoeSparky (Mar 25, 2010)

Whats the best way to size a disconnect for a AC Condenser?
You size it by profit 1st and amperage 2nd :thumbup:


----------



## John R (Aug 20, 2019)

*John R retired electrician from Fed Gov*



Sparky1744 said:


> I am installing an AC Condenser and I need to install a disconnect. The Condenser is a single phase 208 volt, 60 Hz, 12.1 Full load amps, 14.8 Wire sizing amps and 25.0 Over Current Protection Device.


 Most AC has the MFG information on them. Is this coming from a 208 3 phase. We do not have 208 single phase in this part of the world


----------



## CoolWill (Jan 5, 2019)

John R said:


> We do not have 208 single phase in this part of the world



Sure we do. Any two legs of three phase 208 is single phase 208.


----------



## John R (Aug 20, 2019)

*John R retired electrician from Fed Gov*



CoolWill said:


> Sure we do. Any two legs of three phase 208 is single phase 208.


 My question was it coming from a 208 3 phase.


----------



## CoolWill (Jan 5, 2019)

John R said:


> My question was it coming from a 208 3 phase.



It would have to be in order to be 208. Lots of apartments and offices are fed with a 208/120 three phase service and distributed to the units as single phase.


----------



## readydave8 (Sep 20, 2009)

telsa said:


> In my Commercial world, #14 is out of the question. #12 is automatically the lowest we can go. (Local amendment)


Looseleaf?:biggrin:


----------



## JoeSparky (Mar 25, 2010)

telsa said:


> In my Commercial world, #14 is out of the question. #12 is automatically the lowest we can go. (Local amendment)



Can you post a copy of this local amendment? Surely, you own a phone capable of taking pictures of this document. Or maybe a link to the PDF this amendment is contained in.
I personally would locate the AHJ in question and grovel for the return of your balls which he is currently carrying in a brown bag and taunting you with:surprise:


----------



## joebanana (Dec 21, 2010)

John R said:


> Most AC has the MFG information on them. Is this coming from a 208 3 phase. We do not have 208 single phase in this part of the world


 If you're going to use the phrase "this part of the world", you really should fill out your profile, so we know where "this part of the world" is. We have members from all over the world, (even Canada), and little details, like location, are helpful in providing meaningful replies. 

In this part of the world, we can only get single phase 208v, from 3-phase 208v, otherwise it's 120v. Also, all A/C equipment must have a nameplate, or it won't pass inspection.


----------



## joebanana (Dec 21, 2010)

telsa said:


> It's a puppy, but still you'll be using a 30A frame size safety switch.
> 
> Is this an apartment or micro commercial? I say that because 208 VAC single phase is not seen in ordinary commercial.
> 
> ...



Isn't that pretty much standard anywhere? I've never seen #14 on a commercial project, except maybe BMS.


----------



## macmikeman (Jan 23, 2007)

joebanana said:


> Isn't that pretty much standard anywhere? I've never seen #14 on a commercial project, except maybe BMS.


Lay off Telsa. After all his old girlfriend was a penthouse pet of the year. I think she couldn't take all his constant studding her. He's a beast.


----------



## Southeast Power (Jan 18, 2009)

Sparky1744 said:


> I am installing an AC Condenser and I need to install a disconnect. The Condenser is a single phase 208 volt, 60 Hz, 12.1 Full load amps, 14.8 Wire sizing amps and 25.0 Over Current Protection Device.


I would use one of those $6 30amp non fused pull-outs unless someone wants to pay for something fancy. 
Im not a big fan of installing a fused disconnect at a consumer site. If its a commercial job, and they wanted to pay for it, I would install a small fused disconnect to make it easy for the maintenance guy.


----------



## Southeast Power (Jan 18, 2009)

Sparky1744 said:


> I am installing an AC Condenser and I need to install a disconnect. The Condenser is a single phase 208 volt, 60 Hz, 12.1 Full load amps, 14.8 Wire sizing amps and 25.0 Over Current Protection Device.


I would use caution sizing the conductors. They call out 14.8 to force you into #12s but, you need to pull out the installation manual. That little book will call out the conductor size based on the length of the run. You should follow those recommendations.


----------



## telsa (May 22, 2015)

readydave8 said:


> Looseleaf?:biggrin:


Actually, yes. :smile:


----------



## HackWork (Oct 2, 2009)

joebanana said:


> Isn't that pretty much standard anywhere? I've never seen #14 on a commercial project, except maybe BMS.


It's an unwritten schoolyard "standard". In some cases job spec. Very similar to using 3/4" pipe for everything. I never saw 1/2" pipe once in commercial work. Even for a pair of conductors going down to a single switch, we used 3/4 pipe.

But it's not code.


----------



## JoeSparky (Mar 25, 2010)

telsa said:


> Actually, yes. :smile:


Surely they taught you how to use the camera on your phone in Mensa class 
Take a picture of this definitely real :no: and not totally made up :yes: local amendment and post it.


----------



## Kevin (Feb 14, 2017)

HackWork said:


> It's an unwritten schoolyard "standard". In some cases job spec. Very similar to using 3/4" pipe for everything. I never saw 1/2" pipe once in commercial work. Even for a pair of conductors going down to a single switch, we used 3/4 pipe.
> 
> 
> 
> But it's not code.


Same thibg for wire here.
I've asked several times why we use #12 for commercial here in ottawa. I've been told it's a standard everyone follows because it's usually a spec for the job. No code reference and no loose leaf amendments

Sent from my Samsung using Tapatalk


----------



## JoeSparky (Mar 25, 2010)

Typically #12 is minimum size I run for THHN, MC and UF. No codes involved, just $$$. I don't stock 14awg in all of the above because I rarely need to run a 15a ckt using those wiring methods. It's just not worth the money or shelf space to stock both. Hell, 14/2 and 12/2 MC are almost exactly the same price. If I am going to use the whole roll in 1 shot, I'll get 14awg if that is what will get the job done and put more profit in my pocket.
No local amendments, no job specs, no loose leaf binders


----------



## MTW (Aug 28, 2013)

JoeSparky said:


> Typically #12 is minimum size I run for THHN, MC and UF. No codes involved, just $$$. I don't stock 14awg in all of the above because I rarely need to run a 15a ckt using those wiring methods. It's just not worth the money or shelf space to stock both. Hell, 14/2 and 12/2 MC are almost exactly the same price. If I am going to use the whole roll in 1 shot, I'll get 14awg if that is what will get the job done and put more profit in my pocket.
> No local amendments, no job specs, no loose leaf binders


----------



## Service Call (Jul 9, 2011)

I just now realized this post is 4 months old. Hope he found a disconnect


----------



## telsa (May 22, 2015)

#12 really is in our County loose leafs.

Sorry kids.

It's demanded for ALL Commercial work.

It's not required for control circuits -- or for residential.

I LOVE it when out of area electricians question me about our crazy local Code.

Not a chance in the world that I'm wrong... not a chance in the world that I'm interested in correcting you.

ALL of my nearby competition knows the rules of the road the same as I. That's all that counts.

The idea of taking on City Hall -- you guys must be crazed.

How in heaven do I come out ahead doing that?

At some point, when I have the time, I'll post the amazing story of Maverinc.

Yes, it's a laugher.


----------



## telsa (May 22, 2015)

Don't get me started on Title 24.

It's crazier still.


----------



## joebanana (Dec 21, 2010)

macmikeman said:


> Lay off Telsa. After all his old girlfriend was a penthouse pet of the year. I think she couldn't take all his constant studding her. He's a beast.


Wait.....what? Admittedly, I don't read every post on here, and I seem to have missed some interesting ones. What is an "old" Penthouse pet of the year? Or do you mean _old as in, can no longer afford?_ Actually, I was havin' his back. All the commercial prints I've seen specify #12 minimum. It's in the specs.


----------



## telsa (May 22, 2015)

For us it's in the local Code.

Period.

Yeah, I de-flowered a Penthouse cover girl. Now both of us are senior citizens. 

Yeah, it's not the same as nailing a teen, yesterday.

As for my college lover: Mensa IQ -- introverted in the extreme -- and a knock out.

She wore NO make-up for her shoot -- just that dang wrist watch. It scratches.

It's hers -- not the photographers.

As for shock, you can't imagine mine when I saw her while buying gas at Seven-Eleven.

Much of her life story was blended into "Looking for Mr. Goodbar" -- the movie -- not the book.

I just about fainted when I saw it.

I was directed to this gal flick by a mutual friend, Annie. She INSISTED that I had to see it.

I could not get over how many links fed back to my old lover -- which Annie noted straight off.

Yeah, it was that obvious.

I bought "Looking For Mr. Goodbar" years later. I found it tough going. It barely follows the movie plot.

How did my lovely get into film? Her roommate was the daughter of Hollywood behind-the-cameras folks -- their entire lives.

Their son became the basis for Dr. Doogie Howser M.D. Yeah, there REALLY is a guy that was that young and an M.D. He had to leave the USA to get his degree. He, the real dude, was educated in Liege, Belgium. And yes, he was an adolescent when he GRADUATED!!!

His sister, my lover's roommate, was sixteen. She only had an IQ of about 155 and perfect grades.

Their parental connection was how both Howser and my lover made it to the media.

BTW, when I first saw Doogie Howser -- I flashed back to my college days.

BTW, what of the doctor? He is world famous. He, uniquely, takes on the most extreme surgeries to save a child's life. You can find astounding film on his techniques if you are willing to watch a ton of blood. He lifts the ENTIRE front of the patients skull -- yes, cutting it away with bone saws -- to expand the brain cavity. In France and Belgium he is a medical god.

Curiously, his sister compared me to being his equal. And she has a genius IQ.

As for my own contributions to planet Earth -- I'll not indulge you. 

This is no place for an autobiographical.

It would go on way too many pages.

As for my test scores growing up -- they blew the roof off of ALL prior norms. They freaked out every national testing laboritory. --- Much to my sorrow. I perform all my work beyond belief... and no-one can tolerate that. Absolutely no-one wants to discover that they are fantastically outclassed.

Yeah, it really is that bad.

It is FALSE that employers want staggeringly bright employees. They only want dudes smarter than the wire -- and, with hope, barely above that minimum.

Having any employee chronically teach an EC (C-10 holder) how to do things -- yeah, it wears out VERY quickly. Then it turns to anger. Suddenly, profits no longer matter. Self ego does.


----------



## Southeast Power (Jan 18, 2009)

I posted this a couple of years ago and, I just saw your reply:

Had a Penthouse magazine girlfriend, sailfished off Cuba with Hemingway, ran the Iditarod, summited Everest, sailed the Kon Tiki route, taught French Foreign Legion modern hand to hand combat, lived in Tibet for 10 years, was a Texas Ranger and a classically trained pianist.

That's him.


----------



## HackWork (Oct 2, 2009)

joebanana said:


> Actually, I was havin' his back. All the commercial prints I've seen specify #12 minimum. It's in the specs.


Job specs are completely different than code or local amendments.


----------



## macmikeman (Jan 23, 2007)

Marlarky


----------



## telsa (May 22, 2015)

Southeast Power said:


> I posted this a couple of years ago and, I just saw your reply:
> 
> Had a Penthouse magazine girlfriend, sailfished off Cuba with Hemingway, ran the Iditarod, summited Everest, sailed the Kon Tiki route, taught French Foreign Legion modern hand to hand combat, lived in Tibet for 10 years, was a Texas Ranger and a classically trained pianist.
> 
> That's him.


Annis, I didn't know that you even liked girls, just yourself... all three of you.


----------



## Incognito (Apr 14, 2019)

Kevin_Essiambre said:


> Same thibg for wire here.
> I've asked several times why we use #12 for commercial here in ottawa. I've been told it's a standard everyone follows because it's usually a spec for the job. No code reference and no loose leaf amendments
> 
> Sent from my Samsung using Tapatalk


I've ran 14 awg in commercial buildings (in Ottawa) many times. Mainly for pot lights that did not have a lot of room for wires in the little JB's attached, but for other things too.

There is no code or local amendment against it in Ontario. Most specs do have it though and thats why many assume it's code. There are only a few engineering firms in smaller cities and they cut and paste the same spec for almost every job.


----------



## JoeSparky (Mar 25, 2010)

WTF did I just read?:001_huh: 
Next time, log out and log back in as your other account - Chicken Steve : rolleyes:




telsa said:


> For us it's in the local Code.
> 
> Period.
> 
> ...


----------



## CoolWill (Jan 5, 2019)

JoeSparky said:


> WTF did I just read?:001_huh:
> Next time, log out and log back in as your other account - Chicken Steve : rolleyes:



Pfffttt.. Chicken Steve never wrote anything as clear and readable as Telsa. All of Telsa's words are spelled and used correctly.


----------



## MTW (Aug 28, 2013)

Telsa = FBI controlled opposition. Thoughts?


----------



## MTW (Aug 28, 2013)

telsa said:


> #12 really is in our County loose leafs.


:no::no:


----------



## JoeSparky (Mar 25, 2010)

telsa said:


> #12 really is in our County loose leafs.
> 
> Yeah, I de-flowered a Penthouse cover girl


Pics or it didn't happen!


----------



## readydave8 (Sep 20, 2009)

Dear Telsa,

Is the TI business that good that your not doing something popularly believed to be difficult? Brain science, rocket surgery, etc.:vs_whistle::vs_sad::vs_clap::vs_cake:


----------



## readydave8 (Sep 20, 2009)

used the cake because it takes it


----------



## Dan the electricman (Jan 2, 2011)

telsa said:


> As for my own contributions to planet Earth -- I'll not indulge you.
> 
> This is no place for an autobiographical.
> 
> It would go on way too many pages.


----------



## UnaSutherlands (Jun 24, 2021)

To be honest, I don't understand anything about air conditioners at all. Of course, I tried to figure it out myself, but each time I only made it worse. Although everything is simple in the drawings. I don't understand why this is so.


----------



## MadSparky (Mar 2, 2018)

Also bear in mind that the wording of the nameplate must be heeded regarding max ocpd or max fuse, breaker. If it says max ocpd, then you can use a breaker only but not says max fuse, you must use time delay fuses. I've never seen one that says max circuit breaker, though. Breakers must be HACR rated but I think all modern ones pretty much are now.

Sent from my SM-A326U using Tapatalk


----------



## micromind (Aug 11, 2007)

If you're talking about electrical requirements, it's usually simpler than it seems........

Most equipment will have a nameplate that states 'minimum circuit ampacity'. This is the smallest wire that you can use. If it's NM cable, use the 60C table, just about everything else, use 75C. Also, the #14-15amp, #12-20 amp and #10-30 amp rules do nor apply, you can use the table values as they are.

It'll also have a maximum fuse size and/or a maximum HACR breaker size. (HACR = Heating, Air Conditioning Refrigeration).

Often, the net result is a smaller wire than we usually use for a given breaker size but it's completely compliant because it's air conditioning equipment.


----------



## kb1jb1 (Nov 11, 2017)

For once it was not me that fell into an older thread loop. Although this thread is only several years old. I usually go for the 10 year old ones.


----------



## micromind (Aug 11, 2007)

A lot of these older threads are still relevant, sometimes it's easier to add on to one than start a new one.


----------



## Dennis Alwon (May 9, 2009)

UnaSutherlands said:


> To be honest, I don't understand anything about air conditioners at all. Of course, I tried to figure it out myself, but each time I only made it worse. Although everything is simple in the drawings. I don't understand why this is so.



I think the biggest issue is that people don't understand the nameplate. The max overcurrent protective device tells you what size fuse or circuit breaker allowed. 

There is the minimum circuit ampacity- since this is the minimum then 125% is already figured in this number.
So why can I have a #12 wire with a 35 amp breaker as the nameplate suggests? That is because the a/c unit has built in overload protection. This will stop the unit before there is an issue with overload. The circuit breaker or fuse is only there for short circuit or ground fault issues. The overload will protect the conductor from seeing more than it can handle.


----------



## MadSparky (Mar 2, 2018)

Dennis Alwon said:


> I think the biggest issue is that people don't understand the nameplate. The max overcurrent protective device tells you what size fuse or circuit breaker allowed.
> 
> There is the minimum circuit ampacity- since this is the minimum then 125% is already figured in this number.
> So why can I have a #12 wire with a 35 amp breaker as the nameplate suggests? That is because the a/c unit has built in overload protection. This will stop the unit before there is an issue with overload. The circuit breaker or fuse is only there for short circuit or ground fault issues. The overload will protect the conductor from seeing more than it can handle.


With built-in overload protection, would one be able to use, say #12 copper on a 30 Amp breaker?

EDIT: wow I'm blind. Sorry for the useless post haha. That's cool that that exception is.allowed in residential. I don't think I'd want to test any cookie cutter inspectors though. Haha. 

Sent from my SM-A326U using Tapatalk


----------



## Dennis Alwon (May 9, 2009)

electrokinetix said:


> With built-in overload protection, would one be able to use, say #12 copper on a 30 Amp breaker?
> 
> EDIT: wow I'm blind. Sorry for the useless post haha. That's cool that that exception is.allowed in residential. I don't think I'd want to test any cookie cutter inspectors though. Haha.
> 
> Sent from my SM-A326U using Tapatalk



In some cases yes but it depends on what the max overcurrent protective device on the unit states and what is the min. circuit required. But yes I have used #12 with a 30 amp overcurrent protective device many times.


----------



## MadSparky (Mar 2, 2018)

Dennis Alwon said:


> In some cases yes but it depends on what the max overcurrent protective device on the unit states and what is the min. circuit required. But yes I have used #12 with a 30 amp overcurrent protective device many times.


Right right. But let's say the nameplate says:

Max fuse 25 amps

Could I run #12 on a 30 Amp breaker to a fusible disconnect with 25 Amp fuses installed? 

Sent from my SM-A326U using Tapatalk


----------



## Dennis Alwon (May 9, 2009)

It used to be if the FLC was 16 amps then the mca was (125%) which would be 20 amps. The code allowed 175% of the flc which is 28 so a 30 amp overcurrent protective device was allowed. Today the units are so much better that the max overcurrent protective device is usually not much more then the mca. In this case it may be 20 amp or even 25 amp.

Another thing to remember is that 240.4(G) allows us to use wire sizes 10-14 at the amps stated in T. 310.15(B)(15)


----------



## Dennis Alwon (May 9, 2009)

electrokinetix said:


> Right right. But let's say the nameplate says:
> 
> Max fuse 25 amps
> 
> ...


Yes as long as the minimum circuit wasn't greater than the #12 allows. But as I mentioned above while you were posting a #12 is legal at 25 amps if you use a 75C wiring method... That is only for motors and ac units.


----------



## Dennis Alwon (May 9, 2009)

Let say you ran a #12 nm cable. Since #12 nm is rated 20 amp at 60C then as long as the mca is not more than 20 amps we are good but the overcurrent protective device can be 175% of the flc or nameplate whichever is lower.


----------



## MadSparky (Mar 2, 2018)

Dennis Alwon said:


> Yes as long as the minimum circuit wasn't greater than the #12 allows. But as I mentioned above while you were posting a #12 is legal at 25 amps if you use a 75C wiring method... That is only for motors and ac units.


Well next time install an AC disconnect I'm going to save some money! 

Sent from my SM-A326U using Tapatalk


----------

