Basic Wiring 101 ???

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  #1  
Old 10-08-14, 02:08 PM
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Basic Wiring 101 ???

When wiring an outdoor split system air conditioner, I first checked the Data Sheet for the model ac specs - as follows: 1) Unit Supply Voltage - 208-230v, 2)Minimum Circuit Ampacity - 12.4, and 3) Max. Overcurrent Device Amps - 20.

This tells me that a #12ga 2 wire (I drove a ground rod at ac pedestal with #6 copper wire) hooked to a double 20amp breaker should be sufficient.

The ac installer comes along and says it is industry standard to use 10 or 8ga wire otherwise you'll burn your 12ga or damage the unit.

I'm throwing the BS flag on that one. How does using 10ga wire connected to a 20amp breaker increase the ampacity UNLESS it is one long a** wire run. The whip conduit from the ac pedestal to the ac unit is 6 feet.

What's wrong with my thinking?
 
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  #2  
Old 10-08-14, 02:12 PM
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Welcome to the forums.

If the A/C is further from the panel then 50' then I'd consider #10. #10 will fit into the breaker and the disconnect terminals.

You would not burn the #12 you would just have a voltage sag on startup.
 
  #3  
Old 10-08-14, 04:07 PM
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Thanks PJmax...the distance is 25 feet, and I agree, with a long run I'd do #10 too.
 
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Old 10-08-14, 04:23 PM
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There is no need or requirement for a ground rod for the unit.

The manufacturer tells you the wiring and breaker sizes for the unit. The #12 was all you needed.
 
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Old 10-08-14, 04:24 PM
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I'm not sure a ground rod should replace a ground back to he panel. I'm sure an electrician will be around soon.

Edit - Two wire plus ground is what you need back to the panel.
 
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Old 10-08-14, 05:04 PM
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A ground rod will do nothing in this installation.

The OP could have installed #14 and been in compliance.

The load on the circuit is based on the load, not the wire sizes feeding the unit.
 
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Old 10-09-14, 02:55 AM
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Yes sir, the devil is in the details. This install was to a mobile home. Call it what you will, but a 200amp service panel disconnect and meter socket were installed less than 25 feet from the pedestal servicing the a/c unit mentioned before - btw, the manufacture lists wire size as 10/8, which was way further down the list on the data sheet - I "saw" 20amp max and figured "double 20 with #12 solid copper"...which I buried from the panel to the pedestal and inserted a ground rod in the trench with a number 6 copper to the a/c disconnect (why #6? Cause I had plenty). Why a ground rod? Cause the grounding of the panel and neutral buss bars are connected not separate at the 200amp panel. I actually buried 12/3 and spared out the white and copper ground, using the red and black to the hot sides of the a/c disconnect and the #6 to the ground lug. The white and copper lead are sparred out at both locations - thanks for the help!!! I e-mailed the manufacturer's service rep and he said 10 or 8 is "industry standard" and in 30yrs on install, he's never seen #12 - I asked what is wrong with 12 via basic wiring 101 and he said probably will work - can't nail him down, and in ND, I don't want to redo the burial - not that we'll need a/c anytime soon.
 
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Old 10-09-14, 05:52 AM
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The egc in the circuit needs to be used so the breaker will trip. It cannot be spared out. The ground rod has nothing to do with tripping a breaker.
 
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Old 10-09-14, 06:13 AM
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btw, the manufacture lists wire size as 10/8, which was way further down the list on the data sheet
That part of the data sheet is obviously not unit specific, but generic for all size units they make under that model. The data you should use is what you first listed about your specific unit.

1) Unit Supply Voltage - 208-230v, 2)Minimum Circuit Ampacity - 12.4, and 3) Max. Overcurrent Device Amps - 20.
You say you ran 12-3. Was it UF-B cable direct buried?
 
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Old 10-09-14, 06:41 AM
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The information you posted from the data plate states that you only needed #14. Sounds like someone looked up the wrong unit.
 
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Old 10-09-14, 12:03 PM
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Loud & Clear pcboss...I'll spare out the neutral/white lead, connect the copper ground to the ground buss at the breaker panel and might as well dig out that 8 foot ground rod by the a/c pedestal.
Thanx
 
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Old 10-09-14, 12:07 PM
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Yep CasualJoe...the Data Sheet covered a number of models, and all reccomended 10/8. Also I did use 12-3 UF - miserable flat grey cable with each conductor individually coated with the exception of the copper ground.
 
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Old 10-09-14, 12:17 PM
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I got the right unit pcboss as stated earlier although the Data Sheet contained a number of models, ALL come with a 10/8 reccomendation, and that is the original point of this thread - WHY? This particular a/c installer who didn't do the wiring to the ped, claimed after hooking up the thermostat leads and freon lines that I had used too small of line wires to the ped and too small wires in the whip to the unit. Claimed I'd either burn the leads up or burn out the unit. He's been doing it 30+ years (Not the electrical - just low voltage) Then another guy I emailed regarding the purchase of said unit claimed it was "industry standard" to use 10 even to a 20 amp breaker. Is the a/c industry re-writing wiring 101? Why the overkill if the distance is short?
Thanx all...
 
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Old 10-09-14, 12:32 PM
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It sounds like a lot of installers work off past practices and never read the code rules.
 
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Old 10-09-14, 06:57 PM
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Your installer obviously has a lot of experience, but isn't the sharpest knife in the drawer.

Then another guy I emailed regarding the purchase of said unit claimed it was "industry standard" to use 10 even to a 20 amp breaker.
There is no such industry standard and never has been. I suppose to those who don't know, bigger is better.
 
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