Keeping electrical supply line/wire cool?

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Old 08-07-18, 04:17 PM
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Keeping electrical supply line/wire cool?

I was considering running a 10 guage romex circuit in conduit to the other end of my house (approx 70 feet) to supply an air 10k btu conditioner. The best way is through the attic which gets unholy hot (approx 120 degrees F) in the summer. Is there a standard way to cool the wire through the conduit, such as forced air, or would it be unnecessary. I could get away with 12 guage but due to heat thought 10 g would be better... Just a thought, is such a consideration/method fairly non-standard?
PS I do use dedicated smoke detecors at the ends of conduit runs (especially heavy guage wire) and in or near load centers because I'm a safety sally and have a ****ton of new high quality detectors that I inherited....
 
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Old 08-07-18, 04:26 PM
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#12 wiring for the A/C is fine.....even thru the attic. The additional heat will not be a problem.
 
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Old 08-07-18, 05:24 PM
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I was concerned about the resistance. It turns out that its a 220v monster and 12/2 would probably still work fo a shorter run but without looking it up would 10/2 be a better bet?
 
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Old 08-07-18, 06:05 PM
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No one asked why are you running romex in conduit, which is a big no no, plus cost more and would be a pain to do.
 
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Old 08-07-18, 06:49 PM
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I was concerned about the resistance
Resistance does not change with temperature with copper. As far as the NEC is concerned temperature of the attic will give you an adjustment factor of .89 @ 120 degrees F. The wires inside Romex are THHN wires which has a temperature rating of 90 degees C and have a ampacity of 30 amps. 30 x .89 =26.7 Amps That is still higher then the allowed ampacity for small conductors (#10 and smaller) so #12 should be fine for your 10K BTU A/C unit unless it draws more then 16 amps.
 
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Old 08-09-18, 11:31 AM
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Modern building wire has an operating rating of 90C = 194F. The attic is too hot for humans, but fine for wire.
 
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Old 08-09-18, 11:42 AM
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hi Joe, I appreciate your post. I may be throwing terms around incorrectly here, I generally have been using NM-B 12/2, 10/2 wire through grey PVC conduit in places where it is "exposed" or could be damaged by objects in the environment. I believe using the term romex was incorrect and refers to wire that is inside a metal shield/jacket? Sorry about that. But do you find it acceptable to run NM-B inside PVC if correctly sized? My only regret s that I've learned that metal conduit is superior in its ability to "resist" emp and electrical noise radiation. I appreciate any advice that you might have. PS I do have 30 years of experience doing my own work and am past the point of knowing enough just to kill myself (but I have a deep respect for electricity and am a safety sally when it comes to my work (personal only)) and am constantly alert for carelessness on my part. I never ignore the pro's advice and am always open to learning. You're adviced is very much appreciated.
 
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Old 08-09-18, 11:49 AM
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Hi IronHand! I erred using the term romex and stand corrected thanks to joe. I'm using NM-B 12/2 and 10/2. Is there any concerns you would pass on or is it the same type of conditions? Thanks a ton for the advice. I'm thankful for pro's like you folks and I do take notes. Rgads...
 
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Old 08-10-18, 10:42 AM
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Romex is a company who manufactures NM-B (as well as other cabling types I believe). It's sort of like Kleenex or Velcro; NM-B is the generic term, but everyone knows what you're talking about when you say "Romex'.

Residential wiring codes have been developed with a safety factor in mind for all typical residential issues. The attic is hot, and technically does affect the current carrying capacity of the wire, but it's negligible and already figured in to the sizing and max ampacity. I'm sure there are scientific papers out there that explain why 14ga is suitable for 15A in residential use taking all that into account - but the work has been done for us in the code books.

As far as PVC vs EMT conduit, again, it's all about the same for residential use. There's never (very very rarely) any EMF issues in residential wiring these days. Even communications wiring (CATV, network, etc) is so well shielded and noise-cancellation designed, you don't really have to worry about interference these days. So conduit is really only used for protection.

PVC provides enough protection and according to code is equivalent to EMT. (Rigid conduit can be used in certain cases for service entry and shallow burial). I personally like the way EMT looks as it doesn't droop, so I'll use it along walls over PVC when it's visible. But other than that, it's all about the same.
 
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Old 09-03-18, 06:50 PM
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With respect to your experience and no disrespect towards you is intended, I understand that in many cases using romex inside conduit is "fobidden" by code but it makes no sense. How is someone expected to protect romex in an exposed area, ie transistion space, etc? Saying that the concern is overheating by being in an enclosed space is illogical since installing it within a wall is as enclosed as one can get. Steel conduit will radiate heat away better than say wood and drywall and would starve any poential fire of oxygen. Someone isn't thinking this through in my opinion. Its half baked rules like this that cause people to loose confidance in "codes". This is the first code that I've encountered that makes absolutely no sense and should be addressed, unless there is something that I'm not taking into consideration. Can you explain or shed some light on the logic involved in this particular code? Much appreciated.
 
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Old 09-03-18, 06:58 PM
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Can you cite the code reference that forbids NM-B (Romex) in conduit?

As far as I'm aware, there's no code-reason that cable can't be used in conduit. It's usually discouraged, since it's
1) a pain to pull
2) can be more easily nicked/damaged when being pulled (because of the extra pulling force required)
3) it's easier to pull individual conductors.

But as you stated, it's common for conduit to be used for protection for a couple feet of cable. But if you're planning on pulling any significant length, I'd at least consider individual wires.
 
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Old 09-03-18, 07:07 PM
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I understand that in many cases using romex inside conduit is "fobidden" by code
It is not forbidden.
It is forbidden when the conduit is run outside because romex cable is not approved for wet location.
 
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Old 09-03-18, 07:10 PM
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The NEC allows NM in a conduit or a sleeve.for protection against physical damage.
 
 

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