Cable tray ampacity examples my thoughts, your corrections.

[dm9289]

I have been trying to understand cable tray and ampacity better. Could someone confirm or dispute my opinion. Lets use 3-single 500kcm conductors in cable tray with reduced ground, ventilated cable tray.

Normal table 310.16 @75 degrees 380amps
Cable tray flat single layer no separation 310.17 x 65%=403amps
Triangle shape with 2.15 space 310.20=496amps
Each cable flat 1 cable space in between 310.17=620amps

 

[Julius Right]

It is about of NEC Table 310.16 Ampacities of Insulated Conductors with Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried).
If it is an universal standard for all type of cables and all type of the running path, without mention of thermal resistance and environmental data-air, Earth thermal resistance and depth, sun influence and other, you have to consider the minimum.
In NEC Annex B is noted:
For additional information concerning the application of these ampacities, see IEEE STD 835, Standard Power Cable Ampacity Tables.
A conduit it is a perfect "raceway" and according to IEEE-835 3 single-core copper cables of 75oC, in a conduit, in air at 40oC -no sun, but the conduit is easily ventilated -the ampacity is 350 A. [page 30].
So, it is possible then, even less than 380 A.
The conductor resistance is the source of the heat. But the temperature is stated by the heat evacuation conditions.

 

[dm9289]

It is about of NEC Table 310.16 Ampacities of Insulated Conductors with Not More Than Three Current-Carrying Conductors in Raceway, Cable, or Earth (Directly Buried).
If it is an universal standard for all type of cables and all type of the running path, without mention of thermal resistance and environmental data-air, Earth thermal resistance and depth, sun influence and other, you have to consider the minimum.
In NEC Annex B is noted:
For additional information concerning the application of these ampacities, see IEEE STD 835, Standard Power Cable Ampacity Tables.
A conduit it is a perfect "raceway" and according to IEEE-835 3 single-core copper cables of 75oC, in a conduit, in air at 40oC -no sun, but the conduit is easily ventilated -the ampacity is 350 A. [page 30].
So, it is possible then, even less than 380 A.
The conductor resistance is the source of the heat. But the temperature is stated by the heat evacuation conditions.

My answers were based on 392.80(A)2

This seems to support my numbers. But this topic appear to not be clear to many. On this forum you generally get many good answers. But for this topic all are quiet.

392.80 appears to point you in other directions than 310.16 IMO to in some cases much higher ratings

 

[herding_cats]

I have wondered about this cable trays and free air schedules and how they might apply. POCOs get away with murder with free air wiring sizing.

 

[Julius Right]

I checked your calculations and I agree with your results.
However, the conductor supported on a messenger table number it is 310.20.I don't know when was 310.15 [I checked this up to 2005 and it was still 310.20]