Larger conduits as "branch" feeders

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gcaill

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Warrenton, VA
Hello,
My question / concern is this: I understand derating, but still have seen an application several times recently that has me puzzled.
The scenario is that large conduits, typically 3" are being used as like a "branch-feeder" for Data Racks in some areas. Other areas to serve Office workstations.
The run will typically be under 100' and hit 3 larger jboxes w/sealtight whips with one receptacle.
So there would be a potential of gradually adding conductors over time to this "branch-feeder" and you could end up with over 41 CCC's on a 42 circuit panel-knocking the amp value down to 35% of what started out at 50%, a #10 was good for 20A, now only 14A and still on a 20A breaker.
I need to explain to those who are "uneducated" in codeology or theory why we don't run a 3" with 50+ CCC's in it.
Any suggestions on how to walk someone who is basically clueless through less, and yes they are in management.
Help.
 
I would think most folks would understand the concept that any conductor carrying current develops some heat.. the more the conductors the higher the heat, the more confined the higher the heat. The higher the heat the more the likelihood for insulation failure.
 
Are these pipes filled to the point of 35% deration now? Or are you anticipating it happening down the road so you're going to make a fuss now?


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gcaill said:
Hello,
My question / concern is this: I understand derating, but still have seen an application several times recently that has me puzzled.
The scenario is that large conduits, typically 3" are being used as like a "branch-feeder" for Data Racks in some areas. Other areas to serve Office workstations.
The run will typically be under 100' and hit 3 larger jboxes w/sealtight whips with one receptacle.
So there would be a potential of gradually adding conductors over time to this "branch-feeder" and you could end up with over 41 CCC's on a 42 circuit panel-knocking the amp value down to 35% of what started out at 50%, a #10 was good for 20A, now only 14A and still on a 20A breaker.
I need to explain to those who are "uneducated" in codeology or theory why we don't run a 3" with 50+ CCC's in it.
Any suggestions on how to walk someone who is basically clueless through less, and yes they are in management.
Help.
Click to expand...

If you are in Massachusetts, there is a get out of jail free card. See page 9 of this document. It overrides 310.15(B)(3)(a).
http://www.mass.gov/eopss/docs/dfs/osfm/cmr/cmr-secured/527012.pdf
 
"large conduits, typically 3" are being used as like a "branch-feeder" for Data Racks..."


On the off chance I am reading this wrong, data/phone/coax cable is not subject to derating. If it's power wires (class 1), why so many wires to a data rack?
 
JFletcher said:
"large conduits, typically 3" are being used as like a "branch-feeder" for Data Racks..."


On the off chance I am reading this wrong, data/phone/coax cable is not subject to derating. If it's power wires (class 1), why so many wires to a data rack?
Click to expand...
Was kind of my original thinking at first, but then after reading OP again - I think he meant that this raceway is feeding power to data rack equipment and not communications cables.

If that is correct, and there is that many circuits involved with this kind of equipment there probably is high harmonics as well which can also contribute to heating.

I will also say that even though code wants us to consider receptacle circuits to be considered to be capable of carrying full 20 amps on a 20 amp circuit - right or wrong people may have gotten by with no issues in situations like OP described because the circuits are not actually loaded to near full capacity.
 
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