O-Calc Pro Updates for NESC 2023 Compliance
Overview
The O-Calc Pro Master Catalog has been updated to reflect the 2023 version of the NESC Code. The following document will describe the changes made to the O-Calc Pro Master Catalog to implement these updates in O-Calc Pro.
All the necessary updates for the NESC 2023 code are contained in the O-Calc Pro Master Catalog.
The O-Calc Pro Master Catalog containing the NESC 2023 updates is revision 9-04-2024. These changes can be seen under the Load Cases sub folder labeled NESC 2023 and are divided into categories based on the 250 rule being applied.
Under each 250 rule, load cases are further divided into grade of construction and loading district. Users can select the applicable load case to add to the structure for the pole scenario.
NESC 2023 Updates
Rule 250C and Gust Response Factor
The NESC has updated the Gust Response Factor (Grf) calculation for 2023. The Gust Response Factor is now calculated differently as given in the screen shots below:
There is no change in the calculations in the first 60 feet above the structure’s groundline. This includes the structure itself nor any attachments to the structure. The only difference in the equations is the removal of the Importance Factor.
The Basic Wind Speed, V changed from NESC 2017 Figures 250-2 (a-e) and are now based on the 50 and 100 year Mean Recurrence Interval (MRI). The Exposure Category C now references ASCE 7-16 in the NESC 2023 code, whereas in NESC 2017 it referenced ASCE 7-10.
The second paragraph above, “In the application of Rule 250C...” Is completely new for NESC 2023. The third paragraph here, “In special terrain conditions…” and onward is the same as in NESC 2017, just the table reference has been updated. The Gust Response Factor (Grf) applied to structures is now based on Table 250 – 3(a) (see below). The Gust Response Factor applied on wires is now calculated using the height, h of the wire at the structure and the span length, L.
Note: There are no changes to the Exposure Coefficient Kz
Here are some significant changes compared to the NESC 2017 code. In NESC 2017, there was one table that included both the Structure and Wire Gust Response Factors. The Structure Grf was a function of height and the Wire Grf was a function of both height and span length. Now the Structure and Wire Gust Response Factors are two separate tables. There is now a lesser dependence on structure height, just one threshold at 200ft and 250ft height above the groundline or water level. Also note the formulas within the tables have also changed. The tables do not explicitly give the Gust Response Factor value themselves. The values must be calculated from the imbedded formulas.
Note: Some of the screenshots within this WIKI article are taken directly from the “2023 National Electrical Safety Code (NESC) C2-2023” published by IEEE Standards Association. This safety code book can be purchased at https://standards.ieee.org/products-programs/nesc/products/
NESC Rule 251 Updates
The O-Calc Pro Master Catalog has been updated to include the NESC Rule 251 for Conductor Loading. This rule adds a small linear weight to conductors depending on the loading district. In O-Calc Pro this value can be seen as an additional attribute in Loadcases called the Wire Load Constant.
Transverse Pole Load Factor Update
For Loadcases under NESC Rule 250C and wind speeds greater than 100 miles per hour the Transverse Pole Load Factor attribute was updated to the value of 0.75 per NESC guidelines.
Ice Density
In the 2023 NESC code the value for the ice density was updated to 56 pounds per cubic foot. The Ice Density attribute has been updated on all NESC 2023 Loadcases accordingly.