cross sectional area

[xara]

is it true about # of conductors and their ampacity?
the sum of the cross sectional areas of all conductors at any cross section of a wireway shall not exceed 20% of the interior cross sectional area of the wireway?

 

[ron]

Yes, 376.22

 

[Jraef]

Yes, 376.22

And violated all the time unfortunately...

Back in 2004 I got peripherally involved in an investigation of a fire at the Bellagio Hotel in Vegas (http://m.lasvegassun.com/news/2004/apr/12/bellagio-blackout-creates-surreal-scene/).

It turned out to be that the concrete duct used for the service conductors was over filled, the bottom conductors over heated and caught fire. The ducts exceeded a 20% fill, but the drawings showed otherwise. What happened is that the main service conductors AND the conductors coming from the backup generators were put in the same duct. The drawings for each set showed them as separate, no fill violation, but the draftsman accidentally put the same duct number on both ducts, so the EC stuffed both runs in there. Then the inspector failed to notice it (or was paid off to look the other way when he found it, it is Vegas after all...). So when the main service conductors caught fire and the breaker tripped, the emergency power conductors, being in the same duct, ALSO caught fire and they had no power for about a week.

 

[domnic]

cross sectional area

Can you give me a example . using 1" EMT. I THINK IM LOST.

 

[don_resqcapt19]

Can you give me a example . using 1" EMT. I THINK IM LOST.

EMT is a raceway in the code. A wireway is a duct. The wireway has the 20% fill. A conduit has a 40% fill for more than 2 conductors, a 31% fill for two conductors and 53% fill for one conductor. See Chapter 9 Table 1 for those numbers, and Chapter 9, Table 4 for the raceway area.

 

[JFletcher]

And violated all the time unfortunately...

Back in 2004 I got peripherally involved in an investigation of a fire at the Bellagio Hotel in Vegas (http://m.lasvegassun.com/news/2004/apr/12/bellagio-blackout-creates-surreal-scene/).

It turned out to be that the concrete duct used for the service conductors was over filled, the bottom conductors over heated and caught fire. The ducts exceeded a 20% fill, but the drawings showed otherwise. What happened is that the main service conductors AND the conductors coming from the backup generators were put in the same duct. The drawings for each set showed them as separate, no fill violation, but the draftsman accidentally put the same duct number on both ducts, so the EC stuffed both runs in there. Then the inspector failed to notice it (or was paid off to look the other way when he found it, it is Vegas after all...). So when the main service conductors caught fire and the breaker tripped, the emergency power conductors, being in the same duct, ALSO caught fire and they had no power for about a week.

Oops.

From your link:

"The hotel's emergency power allowed people to get into their rooms using the electric locks.."

Are there hardwired door locks in hotels, or is this just lay speak for battery powered door locks, which work regardless of building power?

 

[MiElectrician]

Other names for a wireway are trough and gutter. You'll see them run above a bunch of panels in the electric room a lot of times.

 

[Carultch]

is it true about # of conductors and their ampacity?
the sum of the cross sectional areas of all conductors at any cross section of a wireway shall not exceed 20% of the interior cross sectional area of the wireway?

It is true, but that rule in particular has nothing to do with ampacity. This is a geometry requirement, about how many conductors you can physically fit inside the wireway, without overloading the available space.

The ampacity rule for multiple current-carrying conductors in a wire trough/wireway or equivalent structure, is such that you can fill up to 30 CCC's without thinking about correcting ampacity. This is contrary to raceways in general, where you have bundling adjustment factors for 4 CCC's and above. The instant you add a 31st CCC, the ampacity adjustment for 31 wires applies.