- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I just read this from another site and could not believe the response the person got from the electricians who run the site.
This is the response from a question that asked what size wire for a 5 ton unit 135' away with a mca of 33.9 amps. Residential thru a hot attic of say 122? max. I guess a 2/0 would work also... I think a #8 would work am I nuts??? Don't answer that. :lol:
This is the response from a question that asked what size wire for a 5 ton unit 135' away with a mca of 33.9 amps. Residential thru a hot attic of say 122? max. I guess a 2/0 would work also... I think a #8 would work am I nuts??? Don't answer that. :lol:
Typically, 6/3 would be used in this installation scenario. Technically, at 135' you would have a 33.9 ampacity rating and still be within the recommended 3% voltage drop guideline utilizing a #8 conductor, but at 136' you would need a #6 so we'll just say #6 for all intents and purposes.
What I'm about to say next is topic of debate, but it's a topic I insist on taking into consideration on all of my jobs. The ambient temperature of the attic is often overlooked when calculating the circuit ampacity. Table 310.16 says that #8 NM is rated at 55amps but when you make the adjustment for an ambient temperature of 114-122 degrees (which is a very reasonable assumption for a typical attic):
55 x .58 = 31.9
You can see that this circuit should only be rated at 31.9 amps. For this reason I must recommend and would install 4/3 here.
70 X .58 = 40.6
As you can see, #4 would adequately meet the ampacity requirements for your circuit, with the ambient temperature of the attic taken into consideration.
Read more: Im haveing a 5 ton a/c system installed and will have to run - JustAnswer http://www.justanswer.com/electrica...-system-installed-will-run.html#ixzz1wA33I7ae
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