No, Table 310.17 is not typically used for sizing conductors/cables installed in cable tray.Here's why: Table 310.17 is for free air installations. It's titled "Allowable Ampacities of Insulated Conductors Rated Up to and Including 2000 Volts, 60°C Through 90°C, Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried), Based on Ambient Temperature of 30°C (86°F)". Notice the keywords raceway, cable, or earth (directly buried) are followed by a "Not More Than Three Current-Carrying Conductors". Cable trays usually contain more than three current-carrying conductors. When you have more than three current-carrying conductors in a raceway or cable, you need to apply derating factors as per NEC 310.15(C)(1). Table 310.17 does not account for these derating factors. Cable trays fall under specific sections in the NEC that address ampacity and derating. The primary sections for cable trays are Article 392 and specifically 392.80(A) for conductor ampacity. Correct Ampacity Determination

You'll typically use the following process:1.

Start with the ampacity from Tables 310.15(B)(16) or 310.15(B)(17)

These tables provide the ampacity for conductors based on their temperature rating and insulation type before any derating is applied.2.

Apply derating factors as required by NEC 310.15(C)(1)

This is crucial due to the number of current-carrying conductors in the cable tray. You also need to consider ambient temperature correction as per 310.15(B)(1).
3.

Consider any other applicable adjustments

Cable trays may have fill requirements or other limitations affecting ampacity. See NEC Article 392.

In summary: Using Table 310.17 for cable tray installations would likely result in undersized conductors, potentially leading to overheating, insulation damage, and fire hazards. Always consult the NEC and apply the appropriate derating factors for the number of current-carrying conductors in the cable tray. Use 310.15(B)(16) or 310.15(B)(17) as a starting point and then derate. Flag for review