2014 change to 90C conductor ampacity- table 310.16

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greenspark1

Senior Member
Location
New England
I just noticed that apart from changing the table name to 310.15(B)(16), at 90C the ampacity of #3 & #1 AWG CU increased by 5 amps. I didn't think to look for changes in this table because I thought these ampacities were established decades ago and practically set in stone. Any idea why the change?
I often work from photocopies of other standard tables from my 2005 NEC (equipment ground, grounding electrode, min cover, etc). Have I missed any other appreciable recent changes to other 'standard' tables?
 
The 2014 got rid of the residential table for services and used 83% instead

310.15)B)(7) 120/240-Volt, Single-Phase Dwelling Services and
Feeders. For one-family dwellings and the individual
dwelling units of two-family and multifamily dwellings,
service and feeder conductors supplied by a single-phase,
120/240-volt system shall be permitted be sized in accordance
with 310.15(B)(7)(1) through (4).
(1) For a service rated 100 through 400 A, the service
conductors supplying the entire load associated with a
one-family dwelling, or the service conductors supplying
the entire load associated with an individual dwelling
unit in a two-family or multifamily dwelling, shall
be permitted to have an ampacity not less than 83 percent
of the service rating.
(2) For a feeder rated 100 through 400 A, the feeder conductors
supplying the entire load associated with a onefamily
dwelling, or the feeder conductors supplying the
entire load associated with an individual dwelling, unit
in a two-family or multifamily dwelling, shall be permitted
to have an ampacity not less than 83 percent of
the feeder rating.
Click to expand...
 
Carultch said:
Is there any particular reason that 310.15(B)(7) started as a separate table, when that table was directly based off 310.15(B)(16)?
Click to expand...

Perhaps the CMP met some of the folks I deal with daily who have no idea which column to use from 310.15(B)(16) and don't know how to "cipher" 83% :).
The Table they understood.. to some degree
 
Carultch said:
Is there any particular reason that 310.15(B)(7) started as a separate table, when that table was directly based off 310.15(B)(16)?
Click to expand...
The old table was still 83% of "normal". What the table didn't allow for that is now more clearly required is ampacity adjustments for ambient temperature or number of current carrying conductors in a raceway.

If no adjustments are needed you still end up with same size conductor the old table gave you.
 
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