Greg I think you are confusing personal choice and code requirements.
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ten conductors in ANY raceway is bad design.
If you prefer to run separate raceways and your customer does not mind paying for higher labor costs you can do that and avoid derating for the number of conductors in the raceway.
The code is not a design manual, it is a minimum set of standards.
If someone wishes to place 50 conductors in a raceway the code has rules that make that installation safe.
I spend much of my time wiring office buildings, a typical electric rooms may have six 42 circuit panels all fully filled.
If I use your method of limiting each raceway to 3 current carrying conductors I would need to run 84 raceways out of that electric room.
There is no way I am going to do that, I will run two 2" EMTs out of each panel for a total of 12 raceways each with 21 current carrying conductors.
As these are typically all 20 amp circuits we will run 10 AWG. in the 2" raceways. (Note Massachusetts has a different derating table, in other states this installation would require 8 AWG.
Greg we can go back and forth on good design and bad design, the fact is much depends on the particulars of the job.
We would quickly start losing work if we bid
all work as separate raceways.
That said I agree with you that many times it is a better installation to run separate raceways. If you have a fault in a raceway with many circuits in it you interrupt service to a large area as opposed to just one circuit.
IMO the design is more often influenced by installation costs rather than long term service.
Bob
[This message has been edited by iwire (edited 03-18-2005).]
