Conductor Ampacity Adjustment

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Dale Hayes

Senior Member
More than 3 wires in a conduit requires ampacity adjustment. Is conductor ampacity adjustment ever required for wires inside an Industrial Control Panel?
 

Npstewart

Senior Member
This would probably fall under 366.22 (A) or 366.23 (A) where you adjust as required if the # of conductors exceeds 30.
 

Smart $

Esteemed Member
Location
Ohio
More than 3 wires in a conduit requires ampacity adjustment. Is conductor ampacity adjustment ever required for wires inside an Industrial Control Panel?
Perhaps... based on 310.15(B)(2)(a) where it states...
...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).
However, this requirement should never apply because of another requirement...
312.7 Space in Enclosures. Cabinets and cutout boxes shall have sufficient space to accommodate all conductors installed in them without crowding.
The intent here is to not have conductors all bunched together. However, note the requirement is for sufficient space, not the distribution of conductors within that space.

There may be something in NFPA 79 also.
 

Smart $

Esteemed Member
Location
Ohio
Why would this not fall under article 409?
I don't know, because it does. Article 366 does not.

Assuming control panel is 600V or less, only thing I see is 409.104.
Again, nothing directly relating to ampacity adjustment... and also another requirement which places conditions on space for wires but nothing about distribution of wires within that space.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
I don't see Article 366 as applying to this installation. Maybe 376 or 378, but I don't think so. It is my opinion that if the panel is covered by the NEC that 310.15(B)(3) and 310.15(A)(2), Exception applies to power conductors. Derating is not required for control conductors. 310.15(B)(3).
It is likely that the control panel in covered by NFPA 79 and not the NEC. I don't know what that code says about this issue.
 

renosteinke

Senior Member
Location
NE Arkansas
No adjustment is necessary. A panel is not a raceway, though wires may pass through it. Nor do you derate for wires in the 'Panduit' troughs.

There's plenty of space for the wires to be seaprated. There are vents. Heck, some even have air conditioners.

Plus, let's be clear here .... how would you treat control wires, which are not 'current carrying' in any meaningful sense? It would be pretty silly to base things on the OCPD in that instance.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Since you posted this in the UL section, we can assume you mean in a UL 508 listed control enclosure. There is no requirement for "adjusting" (de-rating) based on the number of conductors in the enclosure. But, UL508A requires that all conductors used for internal wiring be rated for 90?C (29.6), but sized from a chart for 60? or 75?C (table 28.1, as called for in 29.6). So you end up with a form of de-rating anyway.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
.... Nor do you derate for wires in the 'Panduit' troughs. ...
Why not? In my opinion 310.15(B)(3) applies to panduit if the installation is covered by the NEC, however the Exception to 310.15(A)(2) will in many cases eliminate the need to derate in the panduit.
(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.
Where conductors of different systems, as provided in 300.3, are installed in a common raceway or cable, the adjustment factors shown in Table 310.15(B)(3)(a) shall apply only to the number of power and lighting conductors (Articles 210, 215, 220, and 230).
In my opinion the words in bold would apply to power or lighting conductors installed in a panduit wireway. In many cases the conductors in the panduit would be not be power or lighting conductors and derating would not be required.

Note that the section title only says "conductors in a raceway or cable". At this point the CMP is insisting that the words in bold do not apply anywhere and derating is only required for conductors in raceways or cables. We will see what happens at the ROC stage. If they don't apply anywhere, why are they in the code section?
 
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