Q about Table 310.12

Status
Not open for further replies.
O

olly

Senior Member
Location
Berthoud, Colorado
Occupation
Master Electrician
Table 310.12 Single phase dwelling services and feeders.

Does this table apply to a garage sub panel?

This house has a 200 Amp main disconnect one the pole that feeds a "distribution panel" this is where the garage, house and out building panels are feed from. I am not sure if table 310.12 applies to these feeders that feed each panel.
 
Hopefully someone else with the proper code language whill chirp in because I do not remember it exactly.

But I believe for a garage sub panel your feeders would have to be full sized,(if I understand your question correctly )I believe to use the table and or 83percent rule(2017code) which results in the same I believe, the conductors have to feed the entire dwelling.
 
Dsg319 said:
Hopefully someone else with the proper code language whill chirp in because I do not remember it exactly.

But I believe for a garage sub panel your feeders would have to be full sized,(if I understand your question correctly )I believe to use the table and or 83percent rule(2017code) which results in the same I believe, the conductors have to feed the entire dwelling.
Click to expand...
Yes I am wondering if I can use #2 CU to feed the 125A panel or do I need #1 CU conductors
 
olly said:
Table 310.12 Single phase dwelling services and feeders.

Does this table apply to a garage sub panel?

This house has a 200 Amp main disconnect one the pole that feeds a "distribution panel" this is where the garage, house and out building panels are feed from. I am not sure if table 310.12 applies to these feeders that feed each panel.
Click to expand...
You can not use 310.12 for theses feeders.
 
olly said:
Table 310.12 Single phase dwelling services and feeders.

Does this table apply to a garage sub panel?

This house has a 200 Amp main disconnect one the pole that feeds a "distribution panel" this is where the garage, house and out building panels are feed from. I am not sure if table 310.12 applies to these feeders that feed each panel.
Click to expand...
What code cycle you looking at? I find no reference in NEC 2017 of 310.12. The wording most closely matching your reference is in 310.15(B)(7).
 
Table 310.12 Single-Phase Dwelling Services and Feeders
Conductor
(AWG or kcmil)
Service or Feeder Rating
(Amperes)		CopperAluminum or Copper-Clad Aluminum
10042
11031
12521/0
15012/0
1751/03/0
2002/04/0
2253/0250
2504/0300
300250350
350350500
400400600
 
Fred B said:
Does the 2020 table build in correction factors for ambient temperature or the 83% rule?
Click to expand...
No. The table can only be used where no ampacity adjustments are required. That was the reason the 83% rule was put in. If you do the math you will see that the table is 83% without any adjustments. They put the table back in just because typically there are no adjustments to made and it just makes it more convenient and to stop all the whining after the table was removed.
 

My understanding is that you cannot use the above table 310.12 (83%) for feeders unless the feeder feeds the same total connected load that the Service conductors feed
 
I know at one time SE cable with XHHW conductors did not have to be de rated for ambient temp. I looked for that wording in the 2020 and can't seem to find it??
 
texie said:
No. The table can only be used where no ampacity adjustments are required. That was the reason the 83% rule was put in. If you do the math you will see that the table is 83% without any adjustments. They put the table back in just because typically there are no adjustments to made and it just makes it more convenient and to stop all the whining after the table was removed.
Click to expand...
I need a refresher on how to properly size conductors. Does anyone have a resource off hand?
 
Eddie702 said:
I know at one time SE cable with XHHW conductors did not have to be de rated for ambient temp. I looked for that wording in the 2020 and can't seem to find it??
Click to expand...
That was never a general rule that I know of...the only rule that said you don't have to do an ampacity correction for high ambient was one that said you did not have to do it for the roof top ambient adder if the conductors were XHHW. 310.15(B)(2) in the 2020 code 310.15(B)(3)(c) in the 2017.
 
acin said:
That table is in 2011 . not in 2014 or 2017. Guess its back in 2020
Click to expand...
Table 310.15(B)(3)(c), is in the 2014 code. Starting with the 2017 code there is a single adder of 60°F for raceways or cables that are installed less than 7/8" above the roof surface. The exception to the temperature adder that applies to XHHW-2 that was added in the 2014 code, is also in the 2017 and 2020, however the table is not in those two editions.
 
Status
Not open for further replies.
Top