NEC recommended software 1

[7anoter4]

In order to state, according to NEC, the cable in Embedded Duct Bank Ampacity one could encounter a problem :
For number of ducts differing from 1,3,6,9 there is no tables so you have to follow :

NEC ch. 310.10
310.15 Ampacities for Conductors Rated 0–2000 Volts.
Ampacities for conductors shall be permitted to be determined by tables as provided in 310.15(B) or under engineering supervision, as
provided in 310.15(C).
There is no table for low voltage [0-2000 V] cable in embedded duct bank in this part.
(C) Engineering Supervision. Under engineering supervision,
conductor ampacities shall be permitted to be calculated
by means of the following general equation:
I=SQRT((Tc-Ta)/(Rac*(1+Yc)*Rca))
How are Yc and Rca calculated?

310.60 Conductors Rated 2001 to 35,000 Volts.
Here is something:
"Informational Note No. 1: For ampacities calculated in
accordance with 310.60(B), reference IEEE 835-1994 (IPCEA
Pub. No. P-46-426), Standard Power Cable Ampacity
Tables, and the references therein for availability of all factors
and constants."
(D) Engineering Supervision. Under engineering supervision,
conductor ampacities shall be permitted to be calculated
by using the following general equation:
I=SQRT((Tc-(Ta+Td))/(Rac*(1+Yc)*Rca))
How are Yc ,Td and Rca calculated?
There are some indications in Informative Annex B Application Information for Ampacity Calculation
"These ampacities were calculated as detailed in the basic ampacity
paper, AIEE Paper 57-660, The Calculation of the Temperature
Rise and Load Capability of Cable Systems, by J.
H. Neher and M. H. McGrath. For additional information
concerning the application of these ampacities, see
IEEE/ICEA Standard S-135/P-46-426, Power Cable Ampacities,
and IEEE Standard 835-1994, Standard Power Cable Ampacity Tables.
Here are tables for low voltage cables in Duct Banks for 1,3,6 ducts/bank for Three-Conductor Cable and 3,6,9 ducts for Single conductor cable.
Let's say we follow the IEEE 835-1994 calculation method. There are some parameters we shall search in the H. Neher and M. H. McGrath of 1957 publication. And it is not all: for three-cores cable we have to find the G factor from old IEC 287 C1,C2,and C3 ch.
Let's say the equations are still good but the Thermal Resistances are very different. I did for myself a VB6 program to calculate this in both NEC and IEC 60287 method and I know it is not so simple.
The question is:
Is there NEC recommended software for ampacity calculation?

 

[dpc]

Is there NEC recommended software for ampacity calculation?

No.

The NEC tables are based on the Neher-McGrath method. The parameters chosen should be based on the best available data and engineering judgement. Ampacity calculations done be a licensed PE (in the project's state) are generally accepted by the local AHJ.

The AmpCalc software has been around for a long time and should give results consistent with the Neher-McGrath method and satisfy NEC requirements. I've never used it because it has always seemed overpriced.

Most MV cable manufacturers will provide calculations to you at no cost if they think you might buy some cable.

But as I think you have found, the big issue with Neher-McGrath are all of the thermal constant data needed. This data is generally not available on a site-specific basis, so some assumptions are generally needed.

Also, as you probably are aware, none of this de-rating is necessary for low voltage circuits (per NEC anyway).

 

[7anoter4]

Thank you,dpc!