ELECTRICAL TRANSMISSION AND SUBSTATION STRUCTURES 2012 © ASCE 2013 427

Applying the 2010 ASCE 7 Wind and Ice Requirements to Transmission Line
Design

Adam J. Beyer, EIT, A.M.ASCE1

1
Engineer, American Transmission Company, LLC, 2 Fen Oak Ct., Madison, WI
53718; email: abeyer@atcllc.com

ABSTRACT

ASCE/SEI 7-10 - Minimum Design Loads for Buildings and Other Structures
introduced wind maps and a new way to evaluate wind loading compared to its
predecessors (e.g. ASCE/SEI 7-05, ASCE/SEI 7-02, etc.). The changes will present
challenges to current codes and manuals which utilize the previous maps and
methodologies, specifically the National Electric Safety Code (NESC) and ASCE
Manual No. 74.

The purpose of this paper will be to show a comparison of the extreme wind loading
and combined ice and wind for ASCE 7-10 to the ASCE 7-05 values as they apply to
Transmission Lines. To begin that discussion, the author will look back on work
previously done by others. The intention of this paper is to begin a public discussion
of possible directions the NESC and ASCE Manual No. 74 should consider.

1 INTRODUCTION

The ASCE-7 committee made the decision that it was better to assume a higher wind
speed (longer return period) in their loads and reduce the load factor from 1.6 to 1.0
in the latest revision of Minimum Design Loads for Buildings and Other Structures
(ASCE 7-10). NESC adopted the ASCE 7-05 maps except set all load factors at 1.0.
As a result, the NESC loading requirements were below those in ASCE 7-05. If
ASCE Manual No. 74 and the NESC decide to adopt the wind maps with the higher
return period in their next revisions the wind pressures will increase by a ratio
governed by the velocities squared for both structures and wires. This will certainly
have an impact on the Extreme Wind load case. Not only did the Extreme Wind
maps change, but the Extreme Ice with Concurrent Wind maps changed as well. This
change will also have an impact on the Extreme Ice with Concurrent Wind case.

The NESC and ASCE Manual No. 74 have a few courses of action:
• Use a factor to reduce the wind speed on ASCE 7-10 maps
o How does an engineer justify the validity of using a factor to reduce or
modify the wind pressures to their previous values?
• Adopt the new maps with increased wind speed and ice thicknesses.
o Does experience (failures) justify an increase in design loads?
• Reference the 50-year occurrence wind map in the appendix.
o Can NESC justify using the 50-year occurrence ASCE maps?
ELECTRICAL TRANSMISSION AND SUBSTATION STRUCTURES 2012 © ASCE 2013 428

The following examples will use structures and span configurations that will be
included in the appendix. All hand calculations were performed using Microsoft
Excel and all structural analysis calculations were performed using Powerline
Systems’ PLS-CADD/POLE software.

2 EXTREME WIND LOADING REQUIREMENTS

2.1 Converting ASCE 7-05 to ASCE 7-10 Extreme Wind Speeds

The values in the table below were tabulated using the Applied Technology Council’s
“Wind Speed by Location” tool. This tool is used by entering the location of the
building site (latitude-longitude) or manually clicking the location of the building site
on the map. The results that are provided include the ASCE 7-05 and ASCE 7-10
wind speeds.

Table 1 ASCE 7-05 (50 Year MRI) and ASCE 7-10 (700 Year MRI) Extreme Wind Speed Values
ASCE 7-05 ASCE 7-10
Area of Interest Latitude Longitude Ratio
(m/s) (m/s)
Eureka, CA 40.81 -124.17 38.0 49.2 1.675
Portland, OR 45.94 -122.71 38.0 49.2 1.675
Anchorage, AK 61.23 -149.82 46.0 59.0 1.642
American Samoa - - 55.9 71.5 1.638
Las Vegas, NV 36.10 -115.22 40.2 51.4 1.633
Madison, WI 43.06 -89.42 40.2 51.4 1.633
San Antonio, TX 29.51 -98.49 40.2 51.4 1.633
US Virgin Islands - - 58.1 73.8 1.611
Houston, TX 29.76 -95.40 48.3 60.4 1.563
Hawaii - - 46.9 58.1 1.533
Alaska 54.68 -164.15 58.1 71.5 1.515
Boston, MS 42.40 -71.40 46.9 57.2 1.486
Key West, FL 24.56 -81.79 67.1 80.5 1.440
Alaska 68.56 -166.26 55.9 66.6 1.421
Alaska 71.30 -156.68 53.6 63.0 1.381
Puerto Rico - - 64.8 76.0 1.375
Miami, FL 25.80 -80.23 64.4 75.1 1.361
Corpus Christi, TX 27.78 -97.40 55.9 64.4 1.327
Guam - - 76.0 87.2 1.316
The ratio column in the table above shows:
=
Where:
= 7 − 10
= 7 − 05

This ratio serves as a conversion between the ASCE Standards because the velocities
of the wind are the only change in the wind speed pressure equation. The largest ratio
from the tabulated values is 1.675 which is from Eureka, CA and Portland, OR. The
ratio from Madison, WI is 1.633. All three areas will be examined because each area
represents an NESC Loading District (Light, Medium, and Heavy respectively).
ELECTRICAL TRANSMISSION AND SUBSTATION STRUCTURES 2012 © ASCE 2013 429

Theese three areeas would alsso see the most drastic change to dessign if the A ASCE 7-10
mapps were adop pted. One innteresting th
hing to note iis that the larrger values oof this ratio
are not governeed by areas of
o high wind d speed but innstead areas of lower wiind speed.

Figure
F 1 Extreme Wind Speed Map (ASC
CE 7-10) mph- (m/s) (MRI = 700 Years, Caategory II)

2.2 Results of
o Load Calculations

Tabble 2 Wind Pressures for Exxtreme Wind

Eurek
ka, CA Portland, OR
R Madisoon, WI
(NESCC Light) (NNESC Medium m) (NESC Heavy)
Go
overning Windd Load Wind Load Wind Load
Body/Gu
uide/Standard
d (P
Pa) (Pa) (P
Pa)
AS
SCE 7-10 14
480 1480 1620
AS
SCE 7-05 890
8 890 9990
NESC – Rule 250C 890
8 890 9990
ASCE Manual
M No. 74 890
8 890 9990

Tabble 2 above shows

s what the differentt wind pressuures are for each Governning Body,
Guiide, or Standdard. The GRF and KZ faactors will m modify the baase wind preessures
bassed on the strructure heigh
ht and span length
l so thee numbers inn Table 2 wiill be
slig
ghtly modifieed.

Forr the purposees of this papper a span off 122 m (Shoort Span) and 274 m (Loong Span)
will be looked at a with 336.44 kcmil “Lin nnet” and 10033.5 kcmil ““Curlew” coonductor.
Aloong with the different span lengths, twot differentt structure tyypes will be looked at.
Thee first will bee a double ciircuit tangen
nt pole with ttwo shield w
wires (3/8” E
EHS) and
the other will be a 90° dead d-end single circuit struccture with onne shield wirre (3/8”
EHHS).
ELECTRICAL TRANSMISSION AND SUBSTATION STRUCTURES 2012 © ASCE 2013 430

2.3 PLS-CADD Analysis

NESC District Load cases will be evaluated as well to compare against the wind
loading.

Table 3 PLS-CADD Analysis of Different Loading Scenarios for Tangent Example

Ground-Line Reaction (N-m)
Wind Load Short Span (122 m) Long Span (274 m)
Load Case
(m/s) Factor(s) Linnet Curlew Linnet Curlew
17.9
NESC Heavy1 (1.27 cm NESC 475 580 1020 1300
ice)
Extreme Wind -
40.2 1.0 390 550 680 1020
20051
Extreme Wind -
51.4 1.0 640 900 1100 1660
20101
17.9
NESC Medium2 (0.64 cm NESC 340 440 710 960
ice)
Extreme Wind -
38.0 1.0 350 495 600 910
20052
Extreme Wind -
49.2 1.0 590 830 1010 1520
20102

NESC Light3 26.8 NESC 490 700 930 1440

Extreme Wind -
38.0 1.0 350 500 600 910
20053
Extreme Wind -
49.2 1.0 590 830 1010 1520
20103
Notes:
1
Stringing Condition is NESC Heavy at 40% of ultimate tension (Creep)
2
Stringing Condition is NESC Medium at 40% of ultimate tension (Creep)
3
Stringing Condition is NESC Light at 40% of ultimate tension (Creep)

The analysis in table 3 shows that the only change was the wind speed and removal of
the load factor. It should be noted that table 3 shows the ASCE 7-2010 Extreme
Wind Loads do govern when compared to the NESC District Loads.
ELECTRICAL TRANSMISSION AND SUBSTATION STRUCTURES 2012 © ASCE 2013 431

Table 4 PLS-CADD Analysis of Different Loading Scenarios for Dead-End (90°) Example
Ground-Line Reaction (N-m)
Wind Load Short Span (122 m) Long Span (274 m)
Load Case
(m/s) Factor(s) Linnet Curlew Linnet Curlew
17.9
NESC Heavy1 (1.27 cm NESC 4240 8480 4410 8730
ice)
Extreme Wind -
40.2 1.0 1920 4300 2000 4430
20051
Extreme Wind -
51.4 1.0 1590 5000 2600 5210
20101
17.9
NESC Medium2 (0.64 cm NESC 4320 8930 4440 9120
ice)
Extreme Wind -
38.0 1.0 2320 5090 2390 5220
20052
Extreme Wind -
49.2 1.0 2790 5610 2910 5810
20102

NESC Light3 26.8 NESC 4570 9390 4690 9600

Extreme Wind -
38.0 1.0 2620 5670 2690 5800
20053
Extreme Wind -
49.2 1.0 3030 6100 3150 6300
20103
Notes:
1
Stringing Condition is NESC Heavy at 40% of ultimate tension (Creep)
2
Stringing Condition is NESC Medium at 40% of ultimate tension (Creep)
3
Stringing Condition is NESC Light at 40% of ultimate tension (Creep)

Table 4 above for the 90° dead-end case shows even with the increased wind speed
on a dead-end type structure the NESC district loads (Heavy, Medium, and Light)
will still govern the design of the pole. This is true for other angles in the dead-end
case. It is important to note that large angle and dead-end structures are typically the
most expensive structures on a transmission line and would not be affected if the
ASCE 7-10 maps were adopted by ASCE Manual No. 74 and the NESC.

2.4 Turning the 700-year Mean Recurrence Interval (MRI) map into a 50-year
MRI map

Turning the 700-year MRI map values into lower MRI values is necessary since
Transmission Lines are traditionally designed for a 50 year life. An equation similar
to C26.5-2 in the ASCE 7-10 commentary can be derived from known values. Take
for example the Midwestern United States in Table 5 below:
ELECTRICAL TRANSMISSION AND SUBSTATION STRUCTURES 2012 © ASCE 2013 432

Table 5 Return Period Values for the Midwestern United States

Midwestern United States

Return Period, T Wind Velocity, VT
VT/V700
(yrs) (m/s)
50 40.2 0.783
100 42.9 0.835
300 46.9 0.913
700 51.4 1.000
1700 53.6 1.043

Return Period vs. Velocity Ratio

1.10
1.00
0.90
VT/V700

0.80
0.70
0.60
0.50
0 500 1000 1500 2000
y = 0.0763ln(x) + 0.4841 Return Period, T (yrs)

Figure 2 Graph of Return Period vs. Velocity Ratio

The equation below can be used to determine the velocity of wind based on a desired
return period. In the case of Transmission Line Design, 50 years is often the desired
value.
= × (0.484 + 0.0763 ( ))

It should be noted that a 50-year MRI map is published in the ASCE 7-10 standard
however it is not exactly the same as the 50-year MRI map from ASCE 7-05 (the
ASCE 7-10 50-year MRI map is intended to be used for serviceability analysis). The
reason for the difference is that the ASCE 7-05 maps were actually a 700-year MRI
map divided by √1.6 (1.6 was the wind load factor). The commentary of ASCE 7-10
states “The task committee (Wind Load Subcommittee) reasoned that the annual
probability of exceeding the strength design wind load in the hurricane and non-
hurricane regions of the United States should be the same” (p. 509).

In table C6-7 (p. 318) of ASCE 7-05 there is a footnote that states in reference to
hurricane velocities, “For the MRI = 50 as shown, the actual return period, as
represented by the design wind speed map in Fig. 6-1, varies from 50 to
approximately 90 years.” The result was that the ASCE 7-05 maps resulted in a true
50-year event for non-hurricane regions, but in hurricane regions the event was
slightly larger than a 50-year event. This means that current transmission line designs
involving extreme wind events are not designed based on a consistent recurrence
ELECTRICAL TRANSMISSION AND SUBSTATION STRUCTURES 2012 © ASCE 2013 433

interval because the ASCE 74 and the NESC reference the ASCE 7-05 maps without
the load factor.

This adds to the complexity of the decision for the ASCE 74 and the NESC
committees. If ASCE 74 and the NESC want to continue using the same variable
recurrence interval then they will need to continue using the ASCE 7-05 maps,
however trying to justify this approach may not agree with good engineering practice.
The author believes the most logical choice is to specify a minimum recurrence
interval and use the appropriate map from ASCE 7-10. The MRI maps available in
ASCE 7-10 are 10, 25, 50, 100, 300, 700, and 1700. Depending on which map is
chosen to be referenced the committees could choose to include a formula based on
that map to adjust the wind speed to a desired recurrence interval.

2.5 Conclusion of Extreme Wind

It is at this point that the author would like to propose a change (in bold) to the wind
pressure formula so that the ASCE 7-10 maps could be adopted into ASCE Manual
No. 74 and eventually the NESC.

: = 0.613 × × × × ×

: = 0.613 × × × × ×

ℎ : =
=
= −
=
=
= ℎ

: =
= (700 )
=
= × (0.484 + 0.0763 ( ))

: 50 700 :
= 51.4 / × (0.484 + 0.0763 (50))~ 40.2 /

By introducing the VRI term the new ASCE 7-10 maps will be able to be used by
ASCE Manual No. 74 and the NESC. With these changes, the NESC for example
would be able to dictate what minimum recurrence interval Transmission Lines
should be designed to. Currently a minimum of 50 years for most of the United
States is the recurrence interval in the NESC.

If the ASCE 7-10 700-year MRI maps are adopted as is then the increased wind loads
would govern the design of the tangent structures. It is possible that ASCE Manual
No. 74 could adopt the ASCE 7-10 maps and methodology with modifications after
benchmarking across the United States. The NESC would then be encouraged to
follow as their maps are traditionally adopted from ASCE 7. By using the modified
ELECTRICAL TRANSMISSION AND SUBSTATION STRUCTURES 2012 © ASCE 2013 434

nd pressure formula,
win f designers may be
b encouraged to think aabout the retturn
he line more so than befoore. The oveerload factorrs could
period/reliabilitty need of th
rem
main at 1.0 annd this woulld align the ASCE
A Manuual No. 74 annd the NESC C
metthodology with
w the ASC CE 7-10 standdard (use a cconsistent reecurrence intterval).

3 EXTREM
ME ICE WIT
TH CONCU
URRENT W
WIND LOAD
DING
REQUIRE
EMENTS

3.1 Compariison of ASC

CE 7-05 to ASCE
A 7-10 E
Extreme Icee and Concu
urrent
Wind

Thee values in th
he table belo
ow were tabu
ulated using the ASCE 77-05 and ASCE 7-10
Exttreme Ice and Concurren nt Wind mapps.

Table 6 AS
SCE 7-05 and ASCE
A 7-10 Exxtreme Ice an d Concurrentt Wind Speed Values
ASCE 7-005 ASC CE 7-10
Area of NESC
Interest Zone Ice Wind
W Icce Wind d Tempeerature
(cm) (m
m/s) (cmm) (m/s)) (°C
C)
Northern
Heavy 1.27 17.9 1.227 22.44 -200.6
Wisconsin
W
Eastern
Medium 0.64 22.4
2 1.227 22.44 -266.1
Montana
Lake
Superior, Heavy 3.18 26.8
2 1.991 22.44 -200.6
Minnesota
M
Northern
Medium 2.54 13.4 2.554 13.44 -155.0
Missouri

Thee new Extrem me Ice and Concurrent

C Wind
W Speed maps have cchanged sligghtly.
ASCE 7-10 also o introduced
d a temperatu ure map for the Extremee Ice and Concurrent
Winnd loading condition.
c The
T ASCE 7--05 cases willl use -9.4°C C and the AS SCE 7-10
cases will use th
he new temp perature map p. Some areeas have incrreased the ammount of
ice on the wiress while otherrs have adjusted the winnd speed andd some have adjusted
both. Four areaas have beenn chosen for analysis whhich are Nortthern Wisconnsin
(changed wind speed), Easttern Montan na (changed aamount of raadial ice), Laake
Supperior area in
n Minnesotaa (changed bo oth), and Noorthern Misssouri (no chaange).

Fig
gure 3 Extrem
me Ice and Con
ncurrent Wind d Map (ASCE E 7-10); Figuree 10-3 of ASCE
E 7 is also of
interest for this paper (MRI = 50 Years)
ELECTRICAL TRANSMISSION AND SUBSTATION STRUCTURES 2012 © ASCE 2013 435

3.2 PLS-CADD Analysis

NESC District Load cases will be evaluated as well to compare against the Extreme
Ice and Concurrent Wind loading.

Table 7 PLS-CADD Analysis of Different Loading Scenarios for Tangent Example

Ground-Line Reaction (N-m)
Wind Ice Load Short Span (122 m) Long Span (274 m)
Load Case
(m/s) (cm) Factor(s) Linnet Curlew Linnet Curlew

NESC Heavy1 17.9 1.27 NESC 475 580 1020 1300

Extreme Ice and Wind –

17.9 1.27 1.0 190 230 400 500
Wisconsin – 2005 1
Extreme Ice and Wind –
22.4 1.27 1.0 290 350 620 770
Wisconsin – 2010 1

NESC Heavy1 17.9 1.27 NESC 475 580 1020 1300

Extreme Ice and Wind –

26.8 3.18 1.0 790 890 1820 2130
Lake Superior – 2005 1
Extreme Ice and Wind –
22.4 1.91 1.0 370 440 820 990
Lake Superior – 2010 1

NESC Medium2 17.9 0.64 NESC 340 440 710 960

Extreme Ice and Wind –

22.4 0.64 1.0 210 270 430 580
Montana – 2005 2
Extreme Ice and Wind –
22.4 1.27 1.0 290 350 620 770
Montana – 2010 2

NESC Medium2 17.9 0.64 NESC 340 440 710 960

Extreme Ice and Wind –

13.4 2.54 1.0 160 190 370 440
Missouri – 2005 2
Extreme Ice and Wind –
13.4 2.54 1.0 160 190 370 440
Missouri – 2010 2
Notes:
1
Stringing Condition is NESC Heavy at 40% of ultimate tension (Creep RS)
2
Stringing Condition is NESC Medium at 40% of ultimate tension (Creep RS)

In table 6 above, the calculations show that the 2010 Extreme Ice and Wind ground-
line reactions increased from the 2005 Extreme Ice and Wind in Wisconsin and
Montana, but the NESC District Loads still continue to govern the design. However,
one area of interest is the Lake Superior region where the loads actually decreased
along some parts of the lake. There was no change in ground-line moment for the
region in Northern Missouri.
ELECTRICAL TRANSMISSION AND SUBSTATION STRUCTURES 2012 © ASCE 2013 436

Table 8 PLS-CADD Analysis of Different Loading Scenarios for Dead-End (90°) Example
Ground-Line Reaction (N-m)
Wind Ice Load Short Span (122 m) Long Span (274 m)
Load Case
(m/s) (cm) Factor(s) Linnet Curlew Linnet Curlew

NESC Heavy1 17.9 1.27 NESC 3130 6260 3250 6440

Extreme Ice and Wind –

17.9 1.27 1.0 1660 3650 1710 3730
Wisconsin – 2005 1
Extreme Ice and Wind –
22.4 1.27 1.0 1840 3910 1920 4020
Wisconsin – 2010 1

NESC Heavy1 17.9 1.27 NESC 3130 6260 3250 6440

Extreme Ice and Wind –

26.8 3.18 1.0 3140 5210 3390 5520
Lake Superior – 2005 1
Extreme Ice and Wind –
22.4 1.91 1.0 2210 4280 2310 4810
Lake Superior – 2010 1

NESC Medium2 17.9 0.64 NESC 3370 6930 3460 7080

Extreme Ice and Wind –

22.4 0.64 1.0 1850 4110 1900 4190
Montana – 2005 2
Extreme Ice and Wind –
22.4 1.27 1.0 2220 4580 2300 4700
Montana – 2010 2

NESC Medium2 17.9 0.64 NESC 3370 6930 3460 7080

Extreme Ice and Wind –

13.4 2.54 1.0 3530 6560 3630 6740
Missouri – 2005 2
Extreme Ice and Wind –
13.4 2.54 1.0 3560 6640 3660 6820
Missouri – 2010 2
Notes:
1
Stringing Condition is NESC Heavy at 40% of ultimate tension (Creep RS)
2
Stringing Condition is NESC Medium at 40% of ultimate tension (Creep RS)

Table 7 above for the 90° dead-end case shows that even with the increased ice and
wind speed on a dead-end type structure the district loads will still govern the design
of the pole except in Missouri for small conductor sizes.

3.3 Conclusion of Extreme Ice and Concurrent Wind

The analysis for Extreme Ice and Concurrent Wind shows that even though the
loadings for some cases have increased, the NESC District loads still govern (a few
special areas will still dictate the design but there was no increase in ice and wind
loads in those areas). ASCE Manual No. 74 and the NESC can adopt the Extreme Ice
and Concurrent Wind loading maps without a drastic change to current design
practice. The temperature maps from ASCE 7-10 do not necessarily need to be
ELECTRICAL TRANSMISSION AND SUBSTATION STRUCTURES 2012 © ASCE 2013 437

adopted by ASCE Manual No. 74 and the NESC because the calculations show the
differences to be negligible – Less than 1.5% increase in the analysis for Missouri.

4 CONCLUSIONS

Currently, there is a lot of dialogue in the construction industry to create

infrastructure that is more sustainable and exhibits a longer life. Transmission lines
are no exception and are just as important as a road or a building is to our everyday
lives. As mentioned in this paper, the NESC (2007 and 2012) currently requires a 50
year return period (minimum) on extreme events in most areas of the United States.
The author is aware of several transmission lines that have been in service for well
over 50 years, so maybe it is time to examine increasing the return period on extreme
events if we intend to keep these lines in service for longer periods.

The author believes that overall the ASCE 7-10 maps could be adopted by ASCE
Manual No. 74 and eventually the NESC if modifications are implemented to use a
more applicable return period for transmission line design. In some areas the
loadings have increased and structures may need to be designed to be more robust.
Since the data shows that the loading conditions for different areas of the United
States have changed, or we have refined our methods, then we as engineers should
not be hesitant to adjust either. In the end, ensuring our electric grid is more
structurally reliable based on new data as it becomes available is a step in the right
direction.

REFERENCES

1. ASCE/SEI 7-05. (2006). Minimum Design Loads for Buildings and Other
Structures Wind Loads.
2. ASCE/SEI 7-10. (2011). Minimum Design Loads for Buildings and Other
Structures Wind Loads.
3. National Electric Safety Code. (2012). Section 25 – Loadings for Grades B
and C.
4. ASCE Manual No. 74 (3rd Edition). Guidelines for Electrical Transmission
Line Structural Loading, Reston, VA, USA, 2006.
5. PLS-CADD, A Computer Program for the Analysis and Design of Overhead
Electric Lines. Power Line Systems, Madison, WI, USA.
6. Microsoft Excel 2010. Microsoft Corp.
7. Applied Technology Council. (2011). Windspeed by Location. Retrieved
from http://www.atcouncil.org/windspeed/
ELECTRICAL TRANSMISSION AND SUBSTATION STRUCTURES 2012 © ASCE 2013 438

PPENDIX
AP

Tan ngent Exammple: Deaad-End Exam mple:

Stru ucture Descrription – Dou
uble circuit Struucture Descriiption – Singgle circuit
and d self-supporrting and self-supportting
Rulling Span – 213
2 m Ruliing Span – 2213 m
Min n Span – 1222m Minn Span – 1222 m
Maax Span – 274 m Maxx Span – 2744 m
Win nd to Weighht Span – 1.0
0 Winnd to Weightt Span – 1.0
Shiield Wire 1 – 3/8” EHS Shieeld Wire – 3//8” EHS
Shiield Wire 2 – 3/8” EHS Connductor
Con nductor 336..4 kcmil “Liinnet” ACSR R and
336 6.4 kcmil “L
Linnet” ACSR R and 10333.5 kcmil “CCurlew” ACS SR
103 33.5 kcmil “CCurlew” AC CSR Linee Angle – 900°
1
Linne Angle – 0° Sagg Condition – NESC Heavy
1
Saag Condition
n – NESC Heeavy Disttrict Loads (440% UBS)
2
Disstrict Loads (40%
( UBS) Sagg Condition – NESC Meedium
2
Saag Condition
n – NESC Meedium Disttrict Loads (440% UBS)
3
Disstrict Loads (40%
( UBS) Sagg Condition – NESC Ligght District
3
Saag Condition
n – NESC Lig ght District Loadds (40% UB BS)
Loaads (40% UB BS)