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REA BULLETIN 160-2: MECHANICAL DESIGN MANUAL FOR OVERHEAD DISTRIBUTION LINES

REA BULLETIN 160-2: MECHANICAL DESIGN MANUAL FOR OVERHEAD DISTRIBUTION LINES
Overview on REA Bulletin 160-2 for overhead distribution line design guide

The engineering input to an overhead line project can be divided into three principal categories; system planning, electrical design of system components, and the mechanical design of the line. This overview for the design manual deals primarily with the last mentioned of these categories.

Preparation for an Overhead Distribution Line Project
This part involves coordination with system planning especially in the field of route selection and acquisition. This includes securing of rights of way and permits needed for the implementation. Preparing a line project also means preparing of staking aids as well as review of existing design guides or preparation of new ones.

The National Electrical Safety Code as a Basis for Distribution Line Design
The second part in implementing distribution line projects is insuring that appropriate standards are considered in preparing for the design. This may include preparation of NESC, interpretation and referring to applicable standards. Standards that are usually involved are the general discussions for clearance rules. Factors like basic clearance requirements, conditions, clearances above ground, rails, water, etc. must be considered.

Beside clearances, grades of construction, loading requirements, strength requirements, clearance from buildings and other objects, and miscellaneous clearance rules must be followed to avoid violations and design failures.

REA System of Unit Construction and Standard Construction Drawings
Third part of the manual focuses on project plans and drawings involved in the design. Chapter 1 discusses REA unit system of construction followed by REA standard overhead distribution construction drawings, pole top clearance limits, loads on pole top assemblies and strength of pole top assembly components where the loading limits are determined along with the strength of crossarms, crossarms bracing, suspension insulators assemblies and strength of pin and post type insulator assemblies.

Selection of Criteria for Line Design
The fourth part of the manual includes evaluation of existing design criteria and guides, development of design criteria for new line design, conductor design, conductor sag and tension calculations, ruling span, conductor sag-tensions and tension limits, controlling Aeolian vibration, conductor high operating temperature, coordination of conductor design as well as basic strength requirements.

Preparation of Staking Design Guides
The fifth part tackles topics which directly relates to staking design guides that includes preparation of stringing sag tables, staking tables, pole strength calculations and guides, guy and anchor calculation guides, and span limitation based on conductor separations.

Line Staking
The sixth part of the manual talks about the staking procedures, the use of staking tables, conductor uplift, span limitation and tangent structures, limitation at angles and dead-ends, guying and anchoring, special crossing requirements, and preparation of staking sheets.

Line Construction and Inspection
The last part of the manual is all about the line project implementation proper where actual installation occurs. Prior to construction, specifications for constructions should be secured. Chapter 2 of this part discusses the installation of construction assembly units, poles, guy and anchor installation, behaviour of conductor during stringing, conductor installation and lastly an efficient method for checking conductor sag.

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