Table 310-16 (I'm still Confused!)

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LocoKen

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Alright. I've been reading all sorts of threads here on the use of 310-16 and how it all depends on the terminations really than the temperature rating of the wire. What I'm trying to find out is the correct wire size for an electric furnace and I apologize that I do not know the terminal ratings, but I do know the following information.


========Minimum Circuit Ampacity=======Maximum Breaker or Fuse====
------------------------------------------------------------------------
Circuit #1_________44 amps______________________45 amps__________
Circuit #2_________60 amps______________________60 amps__________

Can I use #8 cu for circuit #1 and #6 cu for circuit #2? Or do I still need to know the terminal ratings before I can select the wire size. To my knowledge, we have never used #4 cu before in a house but I may be wrong. And I'm taking it that if I do have to use the 60 degree column, #4 cu will be what I need for circuit #2 and #6 cu for circuit #1. Thanks for the help!
 
If your wiring method is NM cable you must use 60 degree as per 334.80 and your exam would be incorrect. But if you are use an SE cable, thhw or thhn wiring method you wold be correct in your wire size
 
#8 and #6 respectively represent using ampacities from the 75 degree C portion of table 310.16. As Bea mentioned, if you're using NM cable you must use the 60 degree column or 75 degree C column for his other wiring methods. However, you cannot use the 75 degree C ampacity unless the terminations are also rated for 75 degrees C. As it stands today almost all terminations are rated for 75 degree C.
 
Every wire calculation has two parts, the ends (termination) and the middle (de-rating). Then compare the two, the final ampacity is based on the lowest result.

Remember that a chain is only as strong as the weakest link...
 
Sorry for the late reply, but thanks so much everyone! I truly appreciate everyone's input here and your vast knowledge. Thanks again!

Ken
 
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