Underground Ductbanks
- Thread starter rey-man
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- Location
- Mission Viejo, CA
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- Professional Electrical Engineer
Re: Underground Ductbanks
See Table 300.5, Note 1
See Table 300.5, Note 1
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: Underground Ductbanks
Bob: I started to type a response that was essentially the same (I would have cited the same note). Then I stopped myself. I was not, and still am not, sure that it applies to the question at hand. That table seems to me to apply to conduits that do not have a concrete encasement.
Then I started looking at the ampacity tables, and at the related notes. It confused me even more. For example, 310.60(C)(2) (and at least one other place in the code) talks about installations that have a burial depth ?modified from the values shown in a figure or a table.? But I could not, in the time I allowed myself to look, find any figure or table that specifies a depth.
For example, Table 310.16 clearly states that it applies to an ambient of 30C, and gives correction factors for different temperatures. By counter-example, Table 310.77 (I have used this one several times in the past) does not state its assumed burial depth. It does refer the reader to Figure 310.60 for installation details. But that figure also does not state its assumed burial depth.
So I am stuck. I have no answer to the original question. Do you know what I am missing?
Bob: I started to type a response that was essentially the same (I would have cited the same note). Then I stopped myself. I was not, and still am not, sure that it applies to the question at hand. That table seems to me to apply to conduits that do not have a concrete encasement.
Then I started looking at the ampacity tables, and at the related notes. It confused me even more. For example, 310.60(C)(2) (and at least one other place in the code) talks about installations that have a burial depth ?modified from the values shown in a figure or a table.? But I could not, in the time I allowed myself to look, find any figure or table that specifies a depth.
For example, Table 310.16 clearly states that it applies to an ambient of 30C, and gives correction factors for different temperatures. By counter-example, Table 310.77 (I have used this one several times in the past) does not state its assumed burial depth. It does refer the reader to Figure 310.60 for installation details. But that figure also does not state its assumed burial depth.
So I am stuck. I have no answer to the original question. Do you know what I am missing?
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
Re: Underground Ductbanks
I guess I'm so used to using the Table 300.5 Note for such questions I just don't think about it that much.
Section 310.60 refers to Figure 310.60 and the Note refers you back to 300.50 which in turn refers you to Table 300.50 and it's Note 1 which is the same as Table 300.5 Note 1.
Back before it was "Annex B," an analogous series of references started in what is now Figure B.310.2 and its Note 1.
In both Figures the "electrical duct" referenced is the "hole" in the duct bank.
I guess I'm so used to using the Table 300.5 Note for such questions I just don't think about it that much.
Section 310.60 refers to Figure 310.60 and the Note refers you back to 300.50 which in turn refers you to Table 300.50 and it's Note 1 which is the same as Table 300.5 Note 1.
Back before it was "Annex B," an analogous series of references started in what is now Figure B.310.2 and its Note 1.
In both Figures the "electrical duct" referenced is the "hole" in the duct bank.
john m. caloggero
Senior Member
Re: Underground Ductbanks
Hello Rey-man: I need more information, what is the application, are u trying to determine burial depth, what is the voltage? OR are u trying to calculate the ampacity of the conductors using the Neher-McGrath calculations?
John Caloggero
Hello Rey-man: I need more information, what is the application, are u trying to determine burial depth, what is the voltage? OR are u trying to calculate the ampacity of the conductors using the Neher-McGrath calculations?
John Caloggero
Re: Underground Ductbanks
There is some software available to do these calcs that I found on the web, check out this link:
http://www.usi-power.com/USAmpInfo.html
There is some software available to do these calcs that I found on the web, check out this link:
http://www.usi-power.com/USAmpInfo.html
sandsnow
Senior Member
- Location
- Southern California
Re: Underground Ductbanks
If you are NOT using Neher McGrath, then I've always considered duct banks to be regular UG conduits that happen to be in conduit. Is there something else here to be concerned about? Such as seperation between duct banks or limiting the number of conduits in the duct bank. Code minimum AND good engineering practice views would be great
If you are NOT using Neher McGrath, then I've always considered duct banks to be regular UG conduits that happen to be in conduit. Is there something else here to be concerned about? Such as seperation between duct banks or limiting the number of conduits in the duct bank. Code minimum AND good engineering practice views would be great
john m. caloggero
Senior Member
Re: Underground Ductbanks
Where the ducts (conduits) are installed in a concrete duct bank, the measurement for calculation purposes is from grade level to the top of the concrete duct bank.
Where the ducts (conduits) are installed in a concrete duct bank, the measurement for calculation purposes is from grade level to the top of the concrete duct bank.
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