Mike Dolt Enterprises
Mike Dolt Enterprises
User: philly, Location: Chapel Hill, NC
Asked on: Friday, May 28, 2021 at 1:45 pm EDT
Answered on: Thursday, June 20, 2024 at 11:01 am EDT
Question: Are there specific cases where the cable ampacities in table 310.15(B)(17) can be used? My understanding has always been that based on 110.14 termination temperature ratings dictate that we are to use ampacities listed in 310.15(B)(16) regardless of application. 110.14(C) says that 310.15(B)(16) should be used and appropriately modified by 310.15(B)(17) (Not sure what that modification part intends to convey)I see the ampacities in 310.15(B)(17) applied a lot in cable tray applications with the basis of cables in "free air" I've always been confused in these cases where the termination temperature limitation comes into play in these cases? Can this table only be applied if the cable terminations are also in "free air" or is this table applicable when cables are in free air and termination is in an enclosure (panelboard, switchgear etc...)?Thanks
Specific Cases Where Table 310.15(B)(17) Ampacities Can Be Used
Table 310.15(B)(17) ampacities can be used in specific cases where: Cables are installed in free air (not in a raceway, enclosure, or cable tray). Ambient temperature is 30°C (86°F). Conductors are not grouped together (no more than six conductors in a group)110.14(C) and 310.15(B)(16) Modification110.14(C) states that 310.15(B)(16) should be used and appropriately modified by 310.15(B)(17). This modification refers to the fact that Table 310.15(B)(17) provides ampacities for cables in free air, which may be different from the ampacities listed in Table 310.15(B)(16) for cables in raceways, enclosures, or cable trays.
Termination Temperature Ratings
Table 310.15(B)(17) ampacities are based on the assumption that the cables are terminated at a temperature no higher than the termination temperature rating of the individual conductors. If the termination temperature is higher, the ampacities in Table 310.15(B)(16) should be used.
Cable Tray Applications
Table 310.15(B)(17) ampacities can be applied in cable tray applications where: Cables are installed in free air within the cable tray. Cables are not bundled together (no more than six conductors in a group). Cable tray is rated for the number of cables installed. Ambient temperature is 30°C (86°F). Termination temperature ratings are not exceeded.Enclosed Terminations
Table 310.15(B)(17) ampacities cannot be used if the cables are terminated in an enclosure, such as a panelboard or switchgear. In such cases, the ampacities in Table 310.15(B)(16) should be used and appropriately adjusted for the ambient temperature and conditions within the enclosure. Flag for review