Table 310.15(B)(2)(a) vs. 310.15(B)(2)(b)
- Thread starter MWayne
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Good question... for which I do not know the answer. I found the initiating ROP, which I quote in part below...
Substantiation: Acceptance of this new section will harmonize the ampacity
correction factors for various ambient temperatures between the NEC and the
CEC, consolidate the ampacity correction and adjustment factors into a single
section [310.15(B)], and consolidate seven ambient temperature correction
tables into two tables.
The equation proposed to be added is the same equation that is permitted in
310.60(C)(4) to calculate the ampacity correction factors for various ambient
temperatures based on the conductor temperature ratings in the tables. The term
?TD was omitted from the equation since it is not necessary to include it for
cables rated below 46kV as the temperature rise due to dielectric heating is
insignificant compared to the conductor losses. This equation also appears in
3.4.1 of IEEE STD 835, IEEE Standard Power Cable Ampacity Tables.
Since the NEC is used internationally, the lower and higher ambient
temperatures were added to provide the appropriate ampacity correction factors
for colder and warmer climates.
Some of the ambient temperature ranges were revised to 5?C increments to
harmonize with the proposal submitted for the CEC, to correlate with existing
NEC Tables 310.20 and B310.3, and to provide consistency with the 30?C
table.
The ampacity correction factors for 85?C (185?F) that are included in Table
B.310.3 were not included in the revised table since, due to environmental
restrictions, paper and lead cable is no longer commonly used in applications
covered by the NEC. The ampacities remain in Table B.310.3 for reference
in existing installations and the ambient temperature correction factors can be
calculated using the equation in 310.15(B)(2).
This Proposal was generated by the NFPA/CSA NEC/CEC Ampacity
Harmonization Task Group...
- Location
- Connecticut
- Occupation
- Engineer
You would use 310.15(B)(2)(a) when correcting ampacities from Tables 310.15(B)(16) and 310.15(B)(17), both of which are based on an ambient temp of 86degF.
You would use 310.15(B)(2)(b) when correcting ampacities from Tables 310.15(B)(18), 310.15(B)(19) and 310.15(B)(20), all of which are based on an ambient temp of 104degF.
You would use 310.15(B)(2)(b) when correcting ampacities from Tables 310.15(B)(18), 310.15(B)(19) and 310.15(B)(20), all of which are based on an ambient temp of 104degF.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
One may ask why the tables are based on different temperatures. I think because the tables that have a higher temp. are in free air where they will like be dealing with higher temperatures.
- Occupation
- Licensed Electrician
I used to have a good opinion of our neighbors to the north. After dealing with the new tables, not so much.:roll:
- Location
- New Jersey
- Occupation
- Journeyman Electrician
IMO we shouldn't be harmonizing anything with the CEC. If they want harmony then they should change their code to match the NEC. :slaphead:
And while we're at it lets put all of the metric conversions after the American standards in the codebook. :rant:
mivey
Senior Member
That's heavy dude.
mivey
Senior Member
Same problem with the NESC. Silly foreigners!
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Sorta. Most, but not all, questions will be based on Table 310.15(B)(16) in my experience - but ya gotta pay attention, no guarantees.
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