Future New 15 KV Construction Standards

The Rural Utilities Service (RUS) is working on updating and revising Bulletin 50-3 (Standard D 804, April 1983,) "Specifications and Drawings for 12.5/7.2 kV Line Construction." The updated bulletin would be renumbered as Bulletin 1728F-804 and incorporate the requirements of the 2002 edition of the National Electrical Safety Code (NESC). A draft of the revised bulletin is nearly complete. The bulletin is expected to be published as a proposed rule in the Federal Register in the fall of 2002.

The new bulletin will be very similar in appearance and content as Bulletin 1728F-803 "Specifications and Drawings for 24.9/14.4 kV Line Construction," dated December, 1998. As such, it would contain the following significant changes.

• Assembly categories, like "anchors," are groups of assemblies that fulfill the same function. In the new bulletin, the "A" through "K" categories will remain essentially unchanged. Nine new categories would be created from the "M" (miscellaneous) subcategories as shown in the following table. (Miscellaneous assemblies not shown in the table will either be moved to another specific category or discontinued.)

Category Description	Old Designation	New Designation
Grounds	M2	H
Pole (and Line) Protection	M2	P
Reclosers	M3	R
Poles, Crossarms	M5, M19, M20	W
Sectionalizing	M3, M5	S
Voltage Regulation	M7	Y
Metering	M8	Q
Services	M8, M24	K
Tying Guides	M41-M43	L
Neutrals	- - -	N (new category)

• The addition of new assembly categories and the reorganization of the bulletin will make it easier to find specific assemblies. The specifications for each category will be conveniently located in the same section as the drawings for the assembly category. Also, all of the pole-top primary assemblies will be arranged in ascending order of permitted line angles. All of the possible line angles will also be included.
• New assemblies will be given numbers that conform to RUS’ updated standard assembly numbering format explained in Bulletin 1728F-800 "Assembly Unit Numbers and Standard Format." For the 127 assemblies expected to be reused from Bulletin 50-3, borrowers would be able to continue to use the existing numbers or may choose to use new numbers in the standard format.
• The new pole-top primary deadend assembly drawings will show the use of 4-1/4 inch suspension insulators instead of 6-inch suspension insulators. This is only a drawing revision and would not require borrowers to make any changes in their present construction practices or material lists.
• RUS will specify (now recommends) the installation of a 2-1/4 inch square washer under the shoulder of all 7.2 kV crossarm pins. Likewise, RUS will specify (now recommends) the installation of a 3-inch square, curved washer abutting the pole on all primary, neutral and guy deadends. These changes will allow larger line angles and greater longitudinal loading (tension) for conductors and guys. The larger surface area of the washers mitigates the crushing of wood fibers, which is the limiting strength factor in these types of pole-top assembly units.
• The drawings will have "design parameters" that show each assembly’s permitted loading and maximum line angles when applicable. New maximum line angle and permitted crossarm longitudinal loading tables will appear in appendixes at the end of the bulletin. The use of these tables will save engineering time (no calculations required) and assure greater accuracy and conformance to the NESC.
• The new construction standards would allow the conditional use of stirrups without further approval from RUS.
• The new bulletin will have a coordinated set of new standard narrow profile assemblies.
• The number of assemblies and guide drawings proposed for change are shown below:

Construction personnel, engineers and others will eventually need to become familiar with approximately 43 new assemblies, some new assembly numbers and slight material changes on 54 existing assemblies.

Moreover, most borrowers will need to modify computer software and databases for engineering, accounting, and work order procedure programs to accommodate any assembly changes. Making these changes might be relatively easy and straightforward for some borrowers. Making needed software changes may cause problems to those borrowers who do not have enough flexibility in their software or do not reserve enough time to make changes. The required changes are: removing 115 old assemblies; slight material changes (mostly washers) to 54 assemblies; and adding some of the new assemblies as needed.

When the Proposed Rule is published in the Federal Register, we recommend that you obtain a copy of the proposed bulletin and scrutinize its drawings and specifications. Please send us your comments, suggestions, and error corrections. Our goal is to make the bulletin error free and as user friendly as possible.

We recommend that you examine all existing (and potential new) engineering and accounting software linked to RUS standard construction assemblies to ascertain that they can easily be utilized to add, delete and change construction assembly numbers and materials. Make modifications as may be necessary. Thus, you may be able to avoid extensive and time-consuming problems when Bulletin 1728F-804 becomes effective.

If you would like more information or have any questions, please contact Jim Bohlk, Electrical Engineer, Distribution Branch, at 202-720-1967 or at jbohlk@rus.usda.gov.