Overhead Distribution Line Specifications

Jim Bohlk and Stephen Jones, Electrical Engineers,

Distribution Branch, RUS

1

New Features in RUS Bulletin 1728F-803

(25 kV Construction Standards)

The 1963 version of Rural Utilities Service (RUS) Bulletin 50-5, “Specifications and

Drawings for 14.4/24.9 kV Line Construction” was updated and revised so that the

newest requirements of the National Electrical Safety Code (NESC) would be applied to

RUS standard construction as required by RUS regulations. Also, some material and

older assemblies, no longer accepted as RUS standards, needed to be replaced by newer

materials and assemblies.

New Bulletin 1728F-803 (same title as old Bulletin 50-5) contains a total of 222

assembly and guide drawings. 89 of the drawings are of new assemblies or construction

guides; 133 are drawings of old assemblies of which 52 have been modified.

Bulletin 1728F-803 incorporates the following new “general” construction standards:

♦ The use of post type insulators;

♦ Square washers placed under the shoulder of 15 kV crossarm pins;

♦ The use of anti-split bolts whenever double pole-top pins are installed; and,

♦ The use of neutral assemblies, matched in strength to their corresponding primary

assemblies, for holding transverse conductor loads.

Each of the above factors allows greater line angles than previous, similar assemblies.

The new standard use of 3 inch, square, curved washers for all downguys, primary and

neutral deadends attached to the pole allows greater longitudinal loads than the previous

construction assemblies. Also, Bulletin 1728F-803 permits the use of stirrups under

certain conditions without additional RUS approval.

Included on the assembly drawings, when applicable, are new “design parameters” which

define or limit the allowable loading or line angles. Several new tables are included in

the new bulletin which define the maximum line angles for pole-top assemblies given the

NESC loading district, wind span, conductor size and transverse loads. These tables help

assure the proper application of pole-top assemblies and will eliminate future, redundant

engineering calculations.
2

New numbers were assigned to each assembly, and the new bulletin was reformatted so

that assemblies are arranged in more logical order and easier to find. Pole-top assemblies

for all possible line angles are so numbered and arranged order of increasing angles in the

new bulletin.

Immediately after finalizing the new bulletin in December, 1998, some borrowers

informed RUS of difficulties in changing to the new assembly numbers in their computer

software. In order to assist borrowers in their changeovers, RUS delayed the effective

date of Bulletin 1728F-803 until July 1, 2001. RUS also prepared a conversion table

which matches the new assembly numbers with the old numbers (where applicable) and

also list the material changes, if any, of the old assemblies whose use has been continued.

Central Area Data Processing Cooperative and Daffron & Associates, Inc., suppliers of

computer software to approximately 375 RUS borrowers have both told RUS that they

estimate that it will take approximately 25 man-hours for each cooperative to make the

assembly number changes in the software purchased from them.

As 1728F-803 was being revised, RUS identified certain problems with the numbers

assigned to existing and new construction assembly units. First, 17 new assemblies were

added and 39 new guide drawings were developed which needed new numbers.

Secondly, 52 of the old assemblies were modified and therefore needed new numbers.

Lastly, the 97 “M” (miscellaneous) assemblies and guide drawings were hard to find in

the old Bulletin 50-5. RUS realized advantages to standardizing the format based on the

original REA numbering scheme. In the revised new bulletin 803 many of the “M”

drawings were removed, and others were placed in categories that were more specific

which makes them easier to find.

RUS developed and documented the new assembly number system in new guide bulletin

1728F-800, “Assembly Unit Numbers and Standard Format.” This bulletin explains the

RUS system of defining and numbering standard construction assembly units. The

bulletin explains in detail the format and meanings of assembly numbers. For your

convenience, Bulletin 1728F-800 can be downloaded from the internet at

www.usda.gov/rus/electric/bulletins.htm .

The 1728F-800 includes the standard assembly format which is PL1N1N2S1S2.

Where,

“P” denotes voltage or type of use,

“L1” denotes the assembly category,

“N1” denotes the subcategory,

“N2” denotes the assembly identification number,

“S1 and S2” denote variations from the same assembly number without the suffix.

The effect of the new numbering system on new bulletin 803 is that it is now easier to

find assemblies. This is accomplished by the elimination of the “M” numbers, creating 19

sections which are grouped by category (type of unit), and covering line angles in

ascending order.
3

As with the bulletin 803, RUS plans to format the 12.47/7.2 kV Drawings and

Specifications, Bulletin 1728F-804, similarly and with the same numbering system.

Many of the assemblies, such as all of the “E” (guy) drawings, will be the same in

Bulletin 804 as presently in Bulletin 803.
4

BIOGRAPHICAL SKETCH

JIM BOHLK

Jim grew up in northwestern lower Michigan. He was graduated from Michigan State

University in 1969 with a BSEE degree.

After college, Jim worked for 10 years at Ohio Edison Company in Akron. For the first 3

years he engineered distribution lines and facilities. Next he worked as an Industrial

Sales Engineer. His last 4 years he performed short-ranged and long-ranged plans in the

Planning Division.

Jim then accepted the position of System Engineer at Cherryland Electric Cooperative in

Michigan. For 7 years he supervised the Engineering Department and performed all of

the system’s planning and special studies. He was then promoted to Operations Manager

where he supervised both the Engineering and Line Departments.

Since coming to work at RUS in the Distribution Branch of the Electric Staff Division in

1990, Jim had updated the Construction Work Plan bulletin, the Long-Range System

Planning bulletin, and the Specifications and Drawings for 24.9/14.4 kV overhead

construction. He has made several presentations, including workshops, on various topics

regarding distribution line design and planning. He serves on various NESC, NRECA,

and ANSI/IEEE committees.

STEPHEN JONES

Born and raised in Richmond, Virginia

Graduated from North Carolina State University as a BSEE in 1993

Engineer for HC Yu Consulting Engineers located in Richmond, VA, 1994

Engineer for the City of Manassas (Virginia), Municipal Electric Department, 1995

Engineer, Distribution Branch, ESD, RUS, 1997
New Features in

RUS Bulletin 1728F-803

Jim Bohlk

Electric Staff Division

Old Bulletin 50-5 Was

Updated Because ...

➨ Last Updated in 1963

➨ Changes in NESC

➨ Needed Neater (AutoCAD)

 Drawings

➨ Eliminate Non-Standard

 Assemblies and Materials

➨ Add New Assemblies
Larger Allowable Line Angles

Now Possible Because of ...

➨ Use of Post Type Insulators

➨ Washer Under Shoulder of

 Crossarm Pins

➨ Use of Anti-Split Bolts

➨ Neutral Assembly Properly

 Matched to Pole-Top Assembly

More Improvements

	











➨ Proper Application of Assemblies

➨ Fewer Required Engineering

 Calculations
Additional Features

➨ More Modern Now With 4 - 1⁄4 Inch

 Deadend Insulators Assemblies

➨ 3 Inch Square Curved Washers at

 All Deadends for More Strength

and

➨ Stirrups Allowed Without RUS

 Permission !

To Help Implement, We ...

➨ Delayed Effective Date Until 7/1/2001

➨ Wrote Guide Bulletin 1728F-800

➨ Prepared New Retirement Unit Tables

➨ Prepared Listing of Material Changes

 (in 1999 Items of Engineering Interest)
Assembly Numbers Were

Changed Because

➨ 17 New Assemblies + 39 New Guide

Drawings Needed New Numbers

➨ 52 Old Assemblies Modified - Needed

New Numbers

➨ 97 Old “M’ (miscellaneous) Assemblies

and Guide Drawings Were Hard to Find

Guide Bulletin 1728F-800

➨ “Assembly Unit Number and

 Standard Format”

➨ Explains Format & Meanings

 of Assembly Numbers

➨ www.usda.gov/rus/electric/

 bulletins.htm
Standard Assembly Format

PL1N1.N2S1S2

P = Voltage or Type of Use

L1 = Assembly Category

N1 = Subcategory

N2 = Assembly Identification No.

S1 =Variation of Similar Assembly

S2 = “ “ “ “

Example of Standard Format

PL1N1.N2S1S2 = VC4.1LG

P (Voltage): V = 24.9/14.4 kV

L1 (Category): C=3-Phase Primary

N1 (Subcategory): 4 = Large Angle

N2 (Assembly No.): 1 = First Drawing

S1 (Variation): L = Large Wires

S2 (Variation): G = Guide Drawing
Now Easier to Find

Assemblies Because ...

➨ Elimination of the “M” numbers

➨ 19 Sections by Category

 (type of unit)

➨ All Line Angles are Covered

 and in Ascending Order

New Bulletin 1728F-804

12.47/7.2 kV Drawings and Specifications

➨ Same Format and Assembly

 Numbering as 1728F-803

➨ Possible Additions

➨ Raptor Protection Drawings

➨ Narrow Profile Assemblies

➨ Steel Pole Assemblies

➨ Extra Large Conductors