This report presents information for transmission owners on best practices regarding the analysis and administration of underbuilt and ancillary facility attachments to existing transmission line structures. A literature review of existing codes, industry guides and other research documents was conducted to identify the existing standards as pertaining to loading and analysis considerations, clearances and safety, and construction and maintenance. An industry survey was also conducted to determine current practices in these areas.
The research findings relevant to structure loading on the basis of minimum code requirements are catalogued, and best practice recommendations developed. Structure and foundation analysis considerations relevant to increased loading due to underbuilt and ancillary attachments are discussed by structure and foundation type. The research findings relevant to clearances, safety, construction and maintenance are presented for each North American code document.
The following three design examples are included in an Appendix to the report:
1. The installation of a cellular antenna array on a 138kV transmission tower in the United States.
2. The installation of optical ground wire (OPGW) as a replacement for existing overhead ground wire (OHGW) on a wood H-frame transmission line in Canada.
3. An evaluation of electric space potential for a 230kV double circuit steel pole for the installation of an underbuilt all dielectric self-supported (ADSS) cable.
The examples are designed to illustrate the analysis and decision process involved for each design. Example 1 utilizes the National Electrical Safety Code (NESC)  and Telecommunications Industry Association (TIA) 222-G , and Example 2 utilizes Canadian Standards Association (CSA) 22.3 No. 1-10  and CSA 22.3 No. 60826-10 . Example 3 is code independent. Each example utilizes the unit system most commonly associated with the referenced code, but the process illustrated is relevant for use with any requirements or standards.
Transmission line, underbuilt utilities, analysis of appurtenances, North American transmission industry codes, foundation analysis, clearance, construction safety, maintenance