Wisconsin Administrative Code › Public Service Commission › Chapter PSC 114 - Wisconsin State Electrical Code, Volume 1 › Subchapter III - Omissions, Changes or Additions to NESC-2017 › Part 2 - Safety Rules for the Installation and Maintenance of Overhead Electric Supply and Communication Lines › 25 - Loading for Grades B and C › Section PSC 114.250 - General loading requirements and maps

Current through June 24, 2024
(1) EXTREME WIND
					 LOADING. [Alternative to NESC 250C, p. 203] As an alternate to NESC Tables
					 250-2 and Table 250-3, the following Table PSC 114.250 -2 and the related
					 definitions and formulas for k Z and G RF may be used. (NESC Figure 250-2(b)
					 "Basic Wind Speeds" is a part of this rule by reference.)
C. Extreme wind loading
If no portion of a structure or its supported facilities
						exceeds 18 m (60 ft) above ground or water level, the provision of the rule are
						not required, except as specified in Rule 261A1c, 261A2e, or 261A3d. Where a
						structure or its supported facilities exceeds 18 m (60 ft) above ground or
						water level, the structure and its supported facilities shall be designed to
						withstand the extreme wind load associated with the Base Wind Speed as
						specified by NESC Figure 250-2(b). The wind pressures calculated shall be
						applied to the entire structure and supported facilities without ice.
The following formula shall be used to calculate wind
						load.
Load in Newton = 0.613 " (V m/s) 2 " k Z " G RF " I " C d
						" A(m 2)
Load in pounds = 0.00256 " (V mi/h) 2 " k Z " G RF " I "
						C d " A(ft 2)
Where: -
0.613
Ambient Air Density Value, reflects
								the mass
0.00256
density of air for the standard
								atmosphere, i.e., temperature of 15ºC (59ºF) and average sea level
								pressure of 760 mm (29.92 in) ofmercury. (No adjustment in the velocity
								topressure coefficient has been made relative tochanges in air density with
								altitude.) The dimensions associated with this coefficient are, for metric,
								0.613 NÌs2/m4;
								and, for English, 0.00256
								lbÌhr2/mi2Ìft2.
kZ
Velocity-Pressure
								Exposure Coefficient, asdefined in Table PSC 114-250-2
V
Basic wind speed, from NESC 250C,
								Figure250-2 given in m/s at 10 m (mi/h at 33 ft)above ground
GRF
Gust Response
								Factor, as defined in TablePSC 114-250-2
I
Importance factor equal to 1.0 for
								utilitystructures and their supported facilities
Cd
Shape Factor as defined as defined in
								NESCRule 252B
A
Projected wind area,
								m2 (ft2)
Table PSC 114.250 -2 (Metric) Velocity Pressure
						Exposure Coefficient, kZ Gust Response Factor,
						GRF
kZ
.
GRF
For Structures:
For Wires:
For structures with a total height of 30 m or
									 less above ground or water level
1.0
0.85
For structures with a total height exceeding 30
									 m above ground or water level
0.93+0.00245(h)
0.78+0.00245(h)
Table PSC 114.250 -2 (English) Velocity Pressure
						Exposure Coefficient, kZ Gust Response Factor,
						GRF
kZ
.
GRF
For Structures:
For Wires:
For structures with a total height of 100 ft or
									 less above ground or water level
1.0
0.85
For structures with a total height exceeding
									 100 ft above ground or water level
0.93+0.00075(h)
0.78+0.00075(h)
Where:
h = height of the structure above ground or water level.
						For wind loads on wires attached to the structure, the height of the highest
						wire attachment above ground or water level may be used if less than the height
						of the structure. In unique terrain where the height of the wire above ground
						at mid-span may be substantially higher than at the attachment point,
						engineering judgment may be used to determine an appropriate value the height
						of the wire.
Note 2: The height of all wire attachments should be
						based on the height of the highest attachment or total structure height. The
						formulas to determine k ZG RF were based on this premise, not the height of
						each attachment.
The wind pressure parameters (kZ,
						V, and GRF) are based on open terrain with scattered
						obstructions (Exposure Category C as defined in ASCE 7-98). Exposure Category C
						is the basis of the NESC extreme wind criteria. Topographic features such as
						ridges, hills, and escarpments may increase the wind loads on site-specific
						structures.A topographic Factor, kzt, from ASCE7-98 may
						be used to account for these special cases.