- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Do you think that the space inside a panelboard needs to be considered when calculating the ampacity of conductors leaving that panelboard?
It very clearly applies in the panel.I see it as applying to raceways and cables, but I fail to see how it could apply to the interior of a panelboard. IMO, the exception kwired mentioned begins taking effect at the raceway connector.
I just saw a graphic that indicated otherwise, confused me.
(2) Adjustment Factors.
(a) More Than Three Current-Carrying Conductors in a Raceway or Cable. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.
Bingo. I think the text that Don highlighted refers to cables.IMO, Don's comment makes some sense however, the heading states more than 3 current carrying conductors in a raceway or cable.
The title is "raceway or cable." The first scenario covers single conductors contained in a wiring method, and the second scenario covers cables that are not installed within a raceway for physical protection. (Edit: ) An example of a chapter 3 wiring method employing single conductors rather than cable would be USE within a trench.(3) Adjustment Factors.
(a) More Than Three Current-Carrying Conductors in a
Raceway or Cable. Where the number of current-carrying
conductors in a raceway or cable exceeds three, or where
single conductors or multiconductor cables are installed
without maintaining spacing for a continuous length longer
than 600 mm (24 in.) and are not installed in raceways, the
allowable ampacity of each conductor shall be reduced as
shown in Table 310.15(B)(3)(a). Each current-carrying conductor
of a paralleled set of conductors shall be counted as
a current-carrying conductor.
(Edit: ) An example of a chapter 3 wiring method employing single conductors rather than cable would be USE within a trench.
Thoughts?
I agree that the heading for the section does not match the wording of the section, however the section I highlighted refers to both single conductors and cables.Bingo. I think the text that Don highlighted refers to cables.
You said the panel is not a raceway and so it is my opinion that the section applies to single conductors no matter where they are installed. Maybe a proposal for the 2014 code to change the heading would clear this issue up.(2) Adjustment Factors.
(a) More Than Three Current-Carrying Conductors in a Raceway or Cable. Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.) and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.
Single conductors are not always in a raceway...
So the question is if they're not in raceways does the 24" rule apply? If it does not why do we need any wording in this section mentioning not in raceways?
Are there not single conductors that are not in a raceway and not in a panel?
Sure, they're in junction boxes and as George mentioned trenches, etc. But if the section in question only applies to raceways and cables why mention single conductors not in raceways? The argument seems to be that this only applies to raceways and cables as per the wording in (3)(a).
Lets say we have a large distribution panel with 6 mains that feed 6 - 3 phase panels next to the distribution panel. All the conductor runs are 20' or less. Now if there is 3' of wire in the main distribution panel and 4 conductors per run we have at least 18 CCC in the panel.
10% of 20' is 2' and we have 3' in the panel. This is less than 10' so we must derate all those feeders at 50%. Do you think this is the intent?
I have no idea why it is mentioned in here other than in reference to similar installs when not in a raceway. IMO, a panel was not the intent but that is only my opinion. My presumption is that they wanted to make sure de-rating also applied to non raceways.
Lets say we have a large distribution panel with 6 mains that feed 6 - 3 phase panels next to the distribution panel. All the conductor runs are 20' or less. Now if there is 3' of wire in the main distribution panel and 4 conductors per run we have at least 18 CCC in the panel.
10% of 20' is 2' and we have 3' in the panel. This is less than 10' so we must derate all those feeders at 50%. Do you think this is the intent?
If they are all bundled together I think it needs consideration.
Most of the time each feeder will be bundled separately and have some space between bundles.
Well the question was asked about a panelboard. All the conductors are together but there always seems to be a space here and there so the question becomes what is bundling? and how much space is needed.
So after thinking about this I would say that if they are bundled in a panel then it would apply. I was not thinking that George was asking about bundling but rather whether the panel was considered for derating even if they were not bundled.