Auxiliary Gutter Fill
The rules for the maximum number of conductors which can be installed in an auxiliary gutter are found in Section 366.6. The above is an example of auxiliary gutter fill.
This installation meets the NEC requirements because the cross-sectional
area of all conductors is less than 20% of the cross-sectional area of the
auxiliary gutter and there are no more than 30 are current carrying conductors.
In the above example, the signal circuit wires are not Class 2 or 3 circuits,
but are Class 1 circuits that are functionally associated with the current
For wireways the same rules apply and are located in Section 376.22 for metallic wireways and Section 378.22 for nonmetallic wireways. Wireways are classified as a raceway. However, auxiliary gutters are not found in Article 100 under the definition of a "raceway." Additionally, the maximum length of an auxiliary gutter is 30 feet.
In general, Class 2 circuit and Class 3 circuit conductors cannot be installed in an auxiliary gutter or wireway with Class 1 circuit or power and lighting conductors. There are ways around this rule by allowing the Class 2 or Class 3 circuit conductors to be installed in metal raceways within the enclosure. Installing Class 1 or power conductors in a raceway that is installed inside a wireway that contains Class 2 circuit conductors is also used to maintain separation..