Conductors in Exhaust Plenum

[buddy91082]

Hi all.

We have a condition where existing 5kv conductors in RGS cannot be moved. To accommodate a new short run (25') of exhaust duct work that will only be exhausting air from a utility substation, the exhaust ductwork will wrap around the existing 5kV conductors in RGS. Don't worry about the plenum rating of conductors for now. Just looking for the procedure to determine the derating of the conductors in the exhaust duct. I think this is simple as looking at the NEC table for the specific exhaust temperature air and conductor derating factor.

Am I missing something else?

Thanks.
b

 

[7anoter4]

Usually we avoid penetrate a ventilation duct even with a cable in a conduit. Nevertheless NEC does not interdict this [300.21 Spread of Fire or Products of Combustion.] See [for information]:

http://www.ecmag.com/section/codes-standards/wiring-ducts-plenums-and-other-air-handling-spaces

 

[7anoter4]

Since utility company does not have to follow the NEC recommendations, I think you may calculate the cable temperature following Neher and McGrath method [or IEC 60287-2-1] for cable in conduit, at first in free air [if you know the temperature and the air velocity] and for the second time as a conduit in conduit-in this case you have to know all the losses-of your cable and the losses the duct air conveys ,the duct geometry and the position of the duct with respect of ceiling and walls.
For cable in conduit in air you may use IEEE 835/1994 IEEE Standard Power Cable Ampacity Tables- Horizontal Conduit in Air [type 1 5 kV unshielded or Type 3 for shielded.]