And another 2008 question

[ryan_618]

Does a metal raceway that penetrates a rooftop vertically and enters directly into the bottom of a disconnect (cutout box) have to comply with the ampacity adjustment rules of (new) section 310.15(B)(2)(c)? If yes, is there any way around derating the conductors?

[Pierre C Belarge]

Does a metal raceway that penetrates a rooftop vertically and enters directly into the bottom of a disconnect (cutout box) have to comply with the ampacity adjustment rules of (new) section 310.15(B)(2)(c)? If yes, is there any way around derating the conductors?

After a quick peak at the change, here is my take.

Yes, the raceway penetrating the roof and installed in a vertical position will require derating - "installed in conduits exposed to direct sunlight ON or ABOVE rooftops."


Notice this says CONDUITS and EXPOSED TO DIRECT SUNLIGHT

I would think they were very specific in this wording.
If so, then raceways may not be the proper term, but conduits which include...RMC, IMC and RNC. I wonder, by the wording they chose, if they meant to not include EMT-electrical metallic TUBING ?
What about a trough (wireway) installed in rooftop locations?

[celtic]

I wonder, by the wording they chose, if they meant to not include EMT-electrical metallic TUBING ?
What about a trough (wireway) installed in rooftop locations?

You might want to re-read 100~ Raceway

[Pierre C Belarge]

Conduits are raceways, but not all raceways are conduits...

[celtic]

Maybe I oughta read your question again

I see what you mean...CONDUITS is the question, not RACEWAYS

[Dennis Alwon]

if they meant to not include EMT-electrical metallic TUBING ?
What about a trough (wireway) installed in rooftop locations?

I cannot imagine why EMT would be excluded from this derating. I would assume that the derating has to do with the heat that is produced from the rooftops thus incresing the ambient temp.

I would guess that masts for services would also be affected.

[ryan_618]

What about the part that says "bottom of conduit". Does that mean it only applies to horizontal raceways?

[Pierre C Belarge]

Ryan
I read the wording out of the analysis book. I do not see where it says the "bottom" of the conduit. It the wording different in the actual code book?

[ryan_618]

I don't have my code book here, but I am pretty sure that the table is measured to the "bottom" of the conduit.