# Maximum allowable ampacity?



## matt1124 (Aug 23, 2011)

338.10(b)(4)


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## matt1124 (Aug 23, 2011)

http://www.electricallicenserenewal...ation-Courses/NEC-Content.php?sectionID=292.0


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## JasonCo (Mar 23, 2015)

I do see in article 338 where it states that that it shell be in accordance with 60C column, but how would I know to go to Article 338? The article is on Type SE and USE cables o_0

My question states "6 AWG XHHW aluminum SER cable", but I just don't see from that information why I'd go to that article? 

Obviously this must be a green AF question to ask, but **** it....


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## matt1124 (Aug 23, 2011)

SER cable is SE cable, it just has an extra conductor, making it *R*ound


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## matt1124 (Aug 23, 2011)

Just like SEU is SE cable, its just *U* shaped, and also has a concentric ground.

Here, the ampacity of SE cable ran in an interior wall or attic is zero, unless made of copper. City doesn't allow Al past the incoming meter jaws. :biggrin:


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## JasonCo (Mar 23, 2015)

Oh... Well thanks! lol. :wallbash: Appreciate you clearing this up for me, big help! Hope you have yourself a good night, thanks again


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## tjb (Feb 12, 2014)

Similar question would pertain to NM-B, even though it is comprised of THHN insulated conductors. The conductor insulation is mentioned to trick you.


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## Dennis Alwon (May 9, 2009)

What code cycle are you testing on. The column used for se cable has changed over the years. The 2017 is pretty much at the 75C column again.


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## brian john (Mar 11, 2007)

matt1124 said:


> Just like SEU is SE cable, its just *U* shaped, and also has a concentric ground.
> 
> Here, the ampacity of SE cable ran in an interior wall or attic is zero, unless made of copper. *City doesn't allow Al past the incoming meter jaws.* :biggrin:


Because your city officials do not know their butt from a hole in the ground. Remind them it is 2018 not 1972.


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## Fishbulb (Jun 9, 2016)

JasonCo said:


> "Determine the MAXIMUM allowable ampacity of a 3-conductor size 6 AWG XHHW *aluminum* SER cable installed in the attic of a one-family dwelling where the ambient temperature is 44 degrees C."


Start by paying close attention to what the question is really asking.



> Real answer is 47.85 amps.


XHHW is a 90C conductor when in dry locations. Aluminum #6 in the 90C column has an ampacity of 55A in recent code versions. The temperature adjustment multiplier for a 90C conductor at 44C ambient is 0.87.

55A x 0.87 = 47.85A.


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## emtnut (Mar 1, 2015)

Fishbulb said:


> Start by paying close attention to what the question is really asking.
> 
> 
> 
> ...


Not bad Fishstick :wink:

:biggrin:


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## McSparkitus (6 mo ago)

Determine the MAXIMUM allowable ampacity of a 3-conductor size 6 AWG XHHW aluminum SER cable installed in the attic of a one-family dwelling where the ambient temperature is 44 degrees C.
A. 41.2 amperes
B. 52.2 amperes
C. 47.9 amperes
D. 56.2 amperes
Answer: c

explanation: To determine the allowable ampacity of the 3-conductor size 6 AWG XHHW aluminum SER cable, refer to Table 310.104(A) and note the cable is rated for 90Âº C when used in a dry location. Next, find the ampacity of the conductors before derating, which is 55 amperes, from Table 310.15(B) (16). Finally, due to the elevated temperature, apply the temperature correction factor found on Table 310.15(B) (2)(a). Do the math as shown: Size 6 AWG AL XHHW ampacity before derating = 55 amperes 55 amperes x .87 (temperature correction) = 47.85 amperes


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## emtnut (Mar 1, 2015)

McSparkitus said:


> Determine the MAXIMUM allowable ampacity of a 3-conductor size 6 AWG XHHW aluminum SER cable installed in the attic of a one-family dwelling where the ambient temperature is 44 degrees C.
> A. 41.2 amperes
> B. 52.2 amperes
> C. 47.9 amperes
> ...


Nice answer McSpark, but after 4 years, hopefully Jason has already finished the test 

Oh, and welcome to ET


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## Almost Retired (Sep 14, 2021)

Welcome !


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