Derating Multiconductor Tray cable

[Journeyman106]

I need some clarification on the derating of multiconductor tray cables. The installation that we have here on-site is a cable tray system utlizing tray cable. The tray runs to above the panels and then a conduit runs from the panel to the cable tray. In most instances the conduit is 10 to 20 ft. in length. Multiple cables are then installed within the conduit and brought down to the panel. A typical installation may be a 3" conduit with say 6 multiconductor cables in it. I know that in single conductor installations anything over 4 or more current carrying conductors must be derated. Is this the case with the multiconductor tray cable as well?

 

[weressl]

I need some clarification on the derating of multiconductor tray cables. The installation that we have here on-site is a cable tray system utlizing tray cable. The tray runs to above the panels and then a conduit runs from the panel to the cable tray. In most instances the conduit is 10 to 20 ft. in length. Multiple cables are then installed within the conduit and brought down to the panel. A typical installation may be a 3" conduit with say 6 multiconductor cables in it. I know that in single conductor installations anything over 4 or more current carrying conductors must be derated. Is this the case with the multiconductor tray cable as well?

The ampacity rules are detailed in ARTICLE 392.80 Amapcity of Conductors.

Installing tray cables in conduit - although a common practice - is defeating the pruporse of installing tray/cables in the first place and usually results in an installation that has flaws.

 

[Smart $]

I need some clarification on the derating of multiconductor tray cables. The installation that we have here on-site is a cable tray system utlizing tray cable. The tray runs to above the panels and then a conduit runs from the panel to the cable tray. In most instances the conduit is 10 to 20 ft. in length. Multiple cables are then installed within the conduit and brought down to the panel. A typical installation may be a 3" conduit with say 6 multiconductor cables in it. I know that in single conductor installations anything over 4 or more current carrying conductors must be derated. Is this the case with the multiconductor tray cable as well?

If the part in the conduit is greater than 10% of the length in tray* or 10 ft., whichever is less, yes. [310.15(A)(2) Exception]

* Derating would also apply for more than 30 ccc's in any cross-section of the tray regardless of length in conduit.