Derating in underground ducts
- Thread starter bigfish92
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- Lockport, IL
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- Semi-Retired Electrical Engineer
Re: Derating in underground ducts
None of the figures or examples in Annex B includes a 24-duct configuration. It would require a ?Neher-McGrath calculation,? as is briefly described in 310.15(C) and in Annex B, to determine ampacity (or derating factors) for this type of installation. There are several commercially available software packages that can perform such a calculation, but their use would require ?engineering supervision.?
Can you run four ductbanks, each comprising 6 ducts and each containing one circuit, with at least four feet of horizontal separation? If so, you should be able to use the Annex B tables, and disregard the impact on any one ductbank on the other three ductbanks.
None of the figures or examples in Annex B includes a 24-duct configuration. It would require a ?Neher-McGrath calculation,? as is briefly described in 310.15(C) and in Annex B, to determine ampacity (or derating factors) for this type of installation. There are several commercially available software packages that can perform such a calculation, but their use would require ?engineering supervision.?
Can you run four ductbanks, each comprising 6 ducts and each containing one circuit, with at least four feet of horizontal separation? If so, you should be able to use the Annex B tables, and disregard the impact on any one ductbank on the other three ductbanks.
flightline
Senior Member
Re: Derating in underground ducts
If you have difficulty applyig the Neher-McGrath calculations, ther is a software program that can help you. Amp Calc UG is a software package that can assist you in making this type of calculation. I hope this helps.
Gregg
If you have difficulty applyig the Neher-McGrath calculations, ther is a software program that can help you. Amp Calc UG is a software package that can assist you in making this type of calculation. I hope this helps.
Gregg
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