correction factors

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p051981

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Houston, Texas
I have a question on correction factors for a 200 amp service. From my meter can I am running approximently 100 feet of schedule 40 pvc underground and about 30 feet riser up the utility pole to the transformer. Well my question is do you have to apply the tempeature correction factor to the wires in the conduit? There is 3 wires in the conduit. The other question is can I use 3/0 THHN?
 
IMO, it is always good to consider the ambient temperature. At 104 deg F, 88% correction factor of 200 (the rating of 3/0) is 176 amps. T310.16 correction factors.

You can still protect the wire at 200 amps. 240.4(B), 240.6.

If this is residential, you can still call it a 200 amp service rather than 176 without regard to the temperature. 310.15(B)(6).

The 3/0 can can carry a full 200 amps without an unreasonable voltage drop. http://www.mikeholt.com/documents/freestuff/other/VoltageDropCalculator.xls

Although it is the same wire, it is a good habit to call it THWN or THWN-2 when you say underground or outside (though it bugs the counter guys!:roll:).
 
If using 3/0 copper THWN-2 insulation that has a 90? temperature rating with an ampacity of 225 amps, you would use .91 Correction Factor for 104? ambient temp, this would give you an ampacity rating of 204.75 or 205 amps (225 X .91 = 204.75). Back to using the 75? column for the terminations that has a rating of 200 amps. You?re good to go.
 
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