60Amp A/C Wire Size

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  #1  
Old 07-09-05, 06:03 PM
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60Amp A/C Wire Size

One of my roof AC units quit working and it turns out I have a junction box in my attic where I had a splice burn up. Have a home warranty but they won't touch it because there's not supposed to be a junction box on the way yo the A/C unit and the Electrician wants a lot of money to re-wire. I can climb up there and re-splice the wires, but I'm thinking about just running a new dedicated line all the way to the unit.


My question is what size/type of cable to use. It's on a 60 amp breaker and right now it's wired with 6-6-6 AL type SE cable (but not enough to reach) is it appropriate to use this type of cable for my AC or should I use something else. The run is all interior mostly attic space.

Thanks
 
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  #2  
Old 07-09-05, 06:45 PM
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Call the sleezy home warranty company back. There is no rule against a junction box on the way to the A/C. Even if there was, it seems the warranty should cover it. Do they only cover perfect things? If so, they probably don't pay many claims.
 
  #3  
Old 07-09-05, 06:51 PM
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I agree, call the home warranty company back. If necessary make a quick call to a lawyer. Better yet, tell the home warranty company you will be calling your lawyer, and only do so if they refuse to budge.

Home warranties are a racket. They are usually worthless, and not a wise purchase. They only make sense to purchase if the buyer of your house wants one and you agree to buy one to make the sale. Then it's their problem when something goes wrong and the company gives them a hard time.

You could have ten junction boxes and it wouldn't be a violation, as long as they were all accessible. I wouldn't recommend it, but you could.
 
  #4  
Old 07-09-05, 07:03 PM
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OK well then, I've already been up there just to inspect the thing so I can just as well fix it. If I don't need a straight run, I'll just replace the j-box (it's kinda melted) and re-splice...so the service entrance cable is OK though ?

I'm with you in the home warranty thing.. they're terrible, but I figured if I could get them to fix it what the heck... the thing is there still may be a problem with the AC... the whole story is that the AC went out, I called the Home Warranty co and then they FAX a work order to the contractor (AC contractor in this case). That takes like 2 days then I finally get them to come out and he says there's no power to the unit so it's not his problem ... need an electrician.. SO here we go again warranty co FAXES a work order to the electrician and a couple days later he comes out and won't fix it... personally I think he just didn't want to climb up in the attic since this is Phoenix and the outside temps have been over 110. So now once I fix the splice I still may need the AC guy.

Thanks
 
  #5  
Old 07-09-05, 07:09 PM
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If the heat was caused by a poor splice, then a new box and a new splice should fix you right up. But if the heat was caused by something else, such as undersized wires, then the problem is going to happen again. You might want to have a knowledgeable person inspect it for problems.

One other problem with the home warranty is that they probably charge you $25 for any work. You can fix it yourself for less.
 
  #6  
Old 07-09-05, 09:26 PM
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"My question is what size/type of cable to use. It's on a 60 amp breaker and right now it's wired with 6-6-6 AL type SE cable (but not enough to reach) is it appropriate to use this type of cable for my AC or should I use something else. The run is all interior mostly attic space."

azbass,

A new (copper) 6-2 with ground (AL) from breaker to disconnect will do the job. Also, doing so will get ride of the splice which is uncalled for anyway, "Shabby Work" to say the least! This will be your cheapest, best and most reliable way to get power to this unit afterwhich, you can use your home warrenty!

God Bless,
Dave
 
  #7  
Old 07-09-05, 10:43 PM
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Aside from Johns concerns it would really be great if you could give us everything that appears on the nameplate for this A/c unit. The 60 amp breaker isnt really enough information IMO to size the conductors, we also
dont know if it is the correct breaker. It could be a factor in why the splice melted.
 
  #8  
Old 07-11-05, 09:33 AM
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AC Unit Info

It's a Carrier 50hx-048 ... the MCA is 43.1 and the Max Breaker size is 60 ...

After further review, I found even more nastiness in the attic. Apparantly it was previouly wired with 8 gauge AL cable with an open splice in the ceiling. It looks like that splice burned up at some point so the previous owner disconnected that and ran new 6 gauge cable up to a j-box below the unit (inside the attic) and then left the 8 gauge from there to the unit (that's the splice that burned up this time).

This weekend I went ahead and pulled both the old cables out and ran new 6 gauge copper that's rated for 65Amps all the way to the unit on the roof. It'll be hooked up today and I should have AC again !!

Thanks for your help
 
  #9  
Old 07-11-05, 11:23 AM
ally68
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Looks like the 8 guage AL wire was not big enuf the first time or the second time. not sure what amp 8 guage AL is rated to? but the 6# should due the trick.

Also that is one big A.c. Min amp is 43. is that like a 5 ton?
 
  #10  
Old 07-11-05, 11:45 AM
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For this application, #8 Al is not sufficient. #6 Al or #8 Cu would be acceptable. #6 Cu is more than required by code, but not in any way a problem.

IMHO copper is to be preferred because the splices are much more reliable. I bet the #8 would have worked just fine if the splice was correct. Going oversized on the cable will result is lower voltage drop to the unit and thus slightly better efficiency. Seems like a good solution to me.

-Jon
 
  #11  
Old 07-11-05, 12:24 PM
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-048, I would say 4 ton. MCA is minimum circuit ampacity of the conductors. I'd use winnie's advice & go with #8 cu if terminals are rated for 75C condutors.
 
  #12  
Old 07-12-05, 07:55 AM
Duckman_wi
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?Did I read this right? He's mixing Aluminum and Copper wire together. Aluminum and Copper will have a chemical reaction over time if they are connected together. They need to be seperated by a brass terminal. For 60amp circuit he should be using #6 if its cable, #8 if run in conduit and it all depends on the insulation type. I'd stick with #6 copper all the way around and it sounded like that's exactly what he did.
 
  #13  
Old 07-13-05, 09:42 AM
solipsist9
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Originally Posted by Duckman_wi
?Did I read this right? He's mixing Aluminum and Copper wire together. Aluminum and Copper will have a chemical reaction over time if they are connected together. They need to be seperated by a brass terminal. For 60amp circuit he should be using #6 if its cable, #8 if run in conduit and it all depends on the insulation type. I'd stick with #6 copper all the way around and it sounded like that's exactly what he did.
al and cu don't need to be separated; anti-oxidation paste is necessary though.
you said this is phoenix, and the connection is in the attic. i'm guessing the installer did NOT correct for ambient temperature (most electricians ignore this part of the code). that, and the fact that it's al wire (which should be banned, imo), may likely have contributed to this situation.

assuming you need 60 amps conductors (also assuming se cable, which allows you to use the 75C column of 310.16. if you're using nm cable, must use 60C column) and the fact that you're in phoenix, it would be safe to assume your attic will reach 120F. if you're using se cable, #6cu is normally rated for 65 amps; al for 50 amps. applying ambient temp correction factor of 75%, your ampacity is reduced to 49 amps for cu and 38 amps for al. i would go with #4 cu in this installation, which gives you a corrected ampacity of 64 amps. seems like overkill, i know, but heat is possibly one of the culprits here, though it sounds like a bad connection probably started this.
if your f.l.a. on the ac unit is less than 49 amps, go with #6 and a 50 amp breaker. i would definitely go to the larger conductor; heat and voltage drop can result in a snowball effect and possibly damage a compressor - seen it many times.
john.
 
  #14  
Old 07-13-05, 09:57 AM
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It's all done and working now... I think the problem was the connection in the junction box. Put in #6 cu cable. The funny thing is whoever installed it put a 60amp breaker in the service panel, but the disconnect at the unit has 50 amp fuses in it. I tested the amperage with the unit running and it's only pulling like 24 amps with both the fan and the compressor running
 
  #15  
Old 07-13-05, 10:33 AM
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Who installed the junction box there in the first place? If you bought this home warranty plan when you bought the house, and if the junction box was already there at that time, then it has to be covered unless the plan specifically excluded it in writing. If they merely exclude wiring not in compliance with NEC, then it is covered as long as there is no evidence that the original work violated the NEC. Demand that they point out a specific clause that allows them to exclude it from coverage.
 
  #16  
Old 07-13-05, 11:47 AM
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I've been taught you must use the 60C column regardless of insulation rating for conductors less than 1 awg when sizing for air conditioning and refrigeration equipment. Can anyone agree or disagree?
 
  #17  
Old 07-13-05, 05:23 PM
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This seems to have installed some new editing software that is going crazy. It is picking A S S out of the middle of words. The "b r a s s" is being edited to br***.
 
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