PSC 114.242 HistoryHistory: CR 07-021: cr. Register January 2008 No. 625, eff. 2-1-08; CR 13-039: r. and recr. Register June 2014 No. 702, eff. 7-1-14; renum. PSC 114.242 from PSC 114.242F under s. 13.92 (4) (b) 1., Stats., Register March 2015 No. 711; CR 18-007: am. (intro.) Register February 2020 No. 770, eff. 3-1-20.

PSC 114.250(1)(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 kZ and GRF 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 · (Vm/s)2 · kZ · GRF · I · Cd · A(m2)

Load in pounds = 0.00256 · (Vmi/h)2 · kZ · GRF · I · Cd · A(ft2)

Table PSC 114.250-2 (Metric)
Velocity Pressure Exposure Coefficient, kZ
Gust Response Factor, GRF

Table PSC 114.250-2 (English)
Velocity Pressure Exposure Coefficient, kZ
Gust Response Factor, GRF

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.

PSC 114.250 NoteNote 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 kZÌGRF 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.

E. Longitudinal capability

Each supply line designed to operate at 300 kV phase to phase or above shall be constructed to limit the effects of a cascading-type failure to a line segment not exceeding 9.6 km (6 mi) to 16 km (10 mi) in length. Such construction requirement may be met by providing, at appropriate intervals, structures and associated facilities having full dead-end capability under the loading provisions of Rules 250 A, B, C and D. Consideration shall be given to factors such as structure type and material, length of line, distance between dead-end or heavy angle structures, and other basic design criteria in determining the length of such individual line segments. For lines supported by “flexible” structures designed with plastic, energy-absorbing capability in failure, this requirement may be met if such design and construction will provide equivalent limitation to longitudinal cascading.

PSC 114.250 HistoryHistory: CR 07-021: cr. Register January 2008 No. 625, eff. 2-1-08; CR 13-039: r. and recr. Register June 2014 No. 702, eff. 7-1-14; cr. PSC 114.250 (title) under s. 13.92 (4) (b) 2., Stats., renum. (1) and (2) from PSC 114.250C and 114.250E under s. 13.92 (4) (b) 1., Stats., Register March 2015 No. 711; CR 18-007: am. (1), Table PSC 114-250-2 (Metric), Table PSC 114.250-2 (English), (2) (intro.) Register February 2020 No. 770, eff. 3-1-20; correction in (1) (formula) made under s. 35.17, Stats., Register February 2020.

PSC 114.253PSC 114.253 Load factors for structures, cross arms, support hardware, guys, foundations, and anchors. Table PSC 114.253-1 [NESC Table 253-1, p. 225] Load factors for structures1, crossarms, support hardware, guys, foundations, and anchors to be used with the strength factors of Table 261-1 (Changes)