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Old 07-16-2012, 08:54 PM   #16
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Installing Conditioning disconnect


rrodgers,

The nameplate should tell you the mininum amperage and maximum amperage. Which means that you can either go minimum or maximum or if you have the serial # and model #, I can tell you the requirment. I typically go in between. so for example, min=28, max=40. I usually put in a 35 disconnect and 35 breaker. As for wire size, this guys (electrician should help you). That distant seem pretty long. You sure you want to do this by yourself? I am an hvac licensed contractor and I wouldn't even touch that kind of work (out of my scope, typically we sub it out to an electrician). Do you know if your breaker panel are sufficient to handle the 4 ton unit? This 4 ton unit would probabally running at around 12-20 amps (Depend on the unit, and startup can be x7. You have already spend alot of money on the new A/C, why not just call an electrician and do it right. Just my two cents.


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Old 07-16-2012, 08:57 PM   #17
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Installing Conditioning disconnect


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Taking this at face value, #10 is quite sufficient for the load ...
Lol, I even scrolled back looking for such a post, not sure how I missed it, and I agree... #10 is acceptable...

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Old 07-16-2012, 09:03 PM   #18
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Installing Conditioning disconnect


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rrodgers,

The nameplate should tell you the mininum amperage and maximum amperage. Which means that you can either go minimum or maximum.
That is NOT what it is telling you.... The minimum amperage is the SMALLEST possible size wire required, the MAXIUMUM is the largest circuit breaker possible, but has NOTHING to do with the wire size.

These numbers are pre calculated at the factory using NEC Article 440....

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Old 07-16-2012, 09:09 PM   #19
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Installing Conditioning disconnect


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Originally Posted by Mr.HVAC View Post
rrodgers,

I typically go in between. so for example, min=28, max=40. I usually put in a 35 disconnect and 35 breaker. As for wire size, this guys (electrician should help you).
What do you mean by a 35 disconnect? And for specs, I generally install the smallest wire size and the largest over current device listed... You use table 310.16 for wire size selection by the way...
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Old 07-16-2012, 09:18 PM   #20
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Installing Conditioning disconnect


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That is NOT what it is telling you.... The minimum amperage is the SMALLEST possible size wire required, the MAXIUMUM is the largest circuit breaker possible, but has NOTHING to do with the wire size.

These numbers are pre calculated at the factory using NEC Article 440....
I am not talking about electrical wire size, I am talking about the amperage for breaker and disconnect to use for the new A/C. Wire size and how to install it, that's an electrician job, not mine. I just tell the electrician that I need a 35amp breaker and running wire to the disconnect box (35amp). He is the one that determine which wire size and how to wire it properply and if the breaker panel is sufficient to handle the 35amp for the new A/C. He doesn't have to worry about how much amperage the new A/C can handle, cause I told him already.

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Old 07-16-2012, 09:49 PM   #21
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Installing Conditioning disconnect


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Originally Posted by stickboy1375 View Post
That is NOT what it is telling you.... The minimum amperage is the SMALLEST possible size wire required, the MAXIUMUM is the largest circuit breaker possible, but has NOTHING to do with the wire size.

These numbers are pre calculated at the factory using NEC Article 440....
LOL, not trying to be in an arguement with you, but you are talking to someone who is a licensed hvac contractor that read those nameplates like dinner. I am not an electrician, but let say you put in a 30 amp electrical wire from the breaker to the disconnect box and a 50 amp breaker and a 50 amp disconect box. If for someone reason that A/C pulls 40 amps (which sometimes happen) and the breaker doesn't trip and fuse don't trip because it is rated for 50amp, what could happen to 30amp electrical wire? Anyway, sorry buddy for jumping in. I was actually asking questions over here on how to wire my gfci, and I am still having problems with it :-).
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Old 07-16-2012, 10:00 PM   #22
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Installing Conditioning disconnect


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LOL, not trying to be in an arguement with you, but you are talking to someone who is a licensed hvac contractor that read those nameplates like dinner. I am not an electrician,
And I'm not an HVAC guy, nor pretend to be one. But you are reading the nameplates wrong.

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but let say you put in a 30 amp electrical wire from the breaker to the disconnect box and a 50 amp breaker and a 50 amp disconect box. If for someone reason that A/C pulls 40 amps (which sometimes happen) and the breaker doesn't trip and fuse don't trip because it is rated for 50amp, what could happen to 30amp electrical wire? .
Nothing, because the thermal overload in the motor will shut down the unit.


The breaker being installed doesn't provide over current protection, just ground fault and short circuit protection, the overload protection is built into the hermetically sealed motor, where do you think the numbers on the nameplate come from?





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Old 07-16-2012, 10:07 PM   #23
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I just tell the electrician that I need a 35amp breaker and running wire to the disconnect box (35amp). He is the one that determine which wire size and how to wire it properply and if the breaker panel is sufficient to handle the 35amp for the new A/C. He doesn't even have to worry about reading the nameplate or how much amperage the new A/C can handle, cause I told him already, 35 amp!
You are so incorrect in your ways, and if an electrician actually just went off that, he isn't an electrician but just a monkey pulling wire. You need to reeducate yourself in the NEC and article 440.

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Old 07-16-2012, 10:54 PM   #24
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You are so incorrect in your ways, and if an electrician actually just went off that, he isn't an electrician but just a monkey pulling wire. You need to reeducate yourself in the NEC and article 440.

LOL, I guest there is a misunderstand between us two. I shouldn't even start on the wire selection size. Like I told you I am not an electrician so please ignore my comment about 50amp breaker/fuse and 30amp wire. Now since you say that. My last A/C add on, the electrician did ask me for the minimum circuit amp. I thought you were talking about min/max breaker/fuse. There is a different between minimum circuit amp. Minimum breaker/fuse and maximum breaker/fuse to use. LOL, sorry, I am talking about electrical that I shouldn't. I was directing to the op for what breaker/fuse to use.

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Old 07-16-2012, 10:57 PM   #25
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Installing Conditioning disconnect


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LOL, I guest there is a misunderstand between us two. I shouldn't even start on the wire selection size. Like I told you I am not an electrician. Now since you say that. My last A/C add on, the electrician did ask me for the minimum circuit amp. There is a different between minimum circuit amp. Minimum breaker/fuse and maximum breaker/fuse to use. LOL, sorry, I am talking about electrical that I shouldn't.
Its fine, I just don't want you misunderstanding what exactly the numbers are there for....
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Old 07-16-2012, 10:59 PM   #26
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Installing Conditioning disconnect


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LOL, not trying to be in an arguement with you, but you are talking to someone who is a licensed hvac contractor that read those nameplates like dinner. I am not an electrician, but let say you put in a 30 amp electrical wire from the breaker to the disconnect box and a 50 amp breaker and a 50 amp disconect box. If for someone reason that A/C pulls 40 amps (which sometimes happen) and the breaker doesn't trip and fuse don't trip because it is rated for 50amp, what could happen to 30amp electrical wire? Anyway, sorry buddy for jumping in. I was actually asking questions over here on how to wire my gfci, and I am still having problems with it :-).
Stickboy already said it, but just to back it up: You're doing it wrong. The bold/underlined part above is the problem - that can't and won't happen, because the compressor has built-in thermal overload protection. NEC Article 440 covers this in detail and sets forth all the rules applicable to sizing wire and overcurrent protection for these installations. It's entirely clear. You can size the wire to the running load, and the overcurrent protection can be larger. The breaker protects ONLY against short-circuits and locked-rotor conditions, not overloads. Knowing this is an electrician's job...
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Old 07-16-2012, 11:10 PM   #27
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Stickboy already said it, but just to back it up: You're doing it wrong. The bold/underlined part above is the problem - that can't and won't happen, because the compressor has built-in thermal overload protection. NEC Article 440 covers this in detail and sets forth all the rules applicable to sizing wire and overcurrent protection for these installations. It's entirely clear. You can size the wire to the running load, and the overcurrent protection can be larger. The breaker protects ONLY against short-circuits and locked-rotor conditions, not overloads. Knowing this is an electrician's job...

Like I told you, please ignore my comments. :-). I have no clue what I am talking about when dealing with electrical wire/size/breaker/ or how it works. You are right that the compressor has a thermol overload protection and would shut off the compressor when it hits that and that typical depends on the RLA or run load amp which also means minimum circuit amp (Typically manufacture will rated higher than the running load amp. LRA is pretty much for starting up and that is for breaker size.

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Old 07-17-2012, 05:44 AM   #28
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Like I told you, please ignore my comments. :-). I have no clue what I am talking about when dealing with electrical wire/size/breaker/ or how it works. You are right that the compressor has a thermol overload protection and would shut off the compressor when it hits that and that typical depends on the RLA or run load amp which also means minimum circuit amp (Typically manufacture will rated higher than the running load amp. LRA is pretty much for starting up and that is for breaker size.
Nothing wrong with learning...or wanting to learn.
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Old 07-17-2012, 02:12 PM   #29
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please ignore my comments
It is usually the job of other forum members to discredit posters
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Old 07-17-2012, 02:27 PM   #30
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Nothing wrong with learning...or wanting to learn.
It's great to learn new things, but sometime you just gotta limit to your trade. I've been doing HVAC for a while, and still don't know everything. So I am just gonna stick to what I am good at. I typically don't do A/C add-on alot, cause 98% of home already have A/C. I rather sub it out to the electrician and let him handle everything and do it right. :-). I have to know some minor electricals, but that's the least of my worry :-). Since we are talking about wire size, what would happen if you put in a higher amp rated wired for A/C. I would assume it would be ok, just not cost wise?

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