zylezuin
New member
- Location
- San Diego, CA, USA
Can anyone explain why the two tables (NEC and CEC) referenced in the title are so drastically different? 1-6 conductors are the same, but after that NEC is significantly more conservative. The tables for a #12 90c THHN (T90 equivalent) in both codes give a 30A starting value. For 20A circuits you need to move to a #10 after the 9th conductor in NEC, but not until the 25th in CEC? What am I looking past? Thanks!
Table 310.15(B)(3)(a) NEC 2014
Number of conductors vs derating value
4-6 = 80%
7-9 = 70%
10-20 = 50%
21-30 = 45%
Table 5C
Number of conductors vs derating value
4-6 = 80%
7-24 = 70%
25-42 = 60%
Table 310.15(B)(3)(a) NEC 2014
Number of conductors vs derating value
4-6 = 80%
7-9 = 70%
10-20 = 50%
21-30 = 45%
Table 5C
Number of conductors vs derating value
4-6 = 80%
7-24 = 70%
25-42 = 60%