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Insulator Strengths CP2829

NESC Rule 277 Today and in Past Editions:. Insulators shall withstand all applicable loads specified in Rules 250, 251, and 252 except those of Rules 250C and 250D without exceeding the percentages of their strength rating for the respective insulator type shown in Table 277-1. Proper allowance shou

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Insulator Strengths CP2829

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    2. NESC Rule 277 Today and in Past Editions: Insulators shall withstand all applicable loads specified in Rules 250, 251, and 252 except those of Rules 250C and 250D without exceeding the percentages of their strength rating for the respective insulator type shown in Table 277-1. Proper allowance should be made for the loads in Rules 250C and 250D. A Strength Factor is only specified for the un-factored, historic, NESC “District Loads” (Heavy. Medium and Light) Rules 250C and 250D are “Ultimate Loads” and Rule 277 does not specify a strength Factor; “Proper allowance should be made for the loads in Rules 250C and 250D”

    3. 2007 NESC

    4. Proposals for 2002 NESC Major revision to the 2002 NESC proposed a complete revision to Strength & Loadings, deleting district loads and replacing with Ultimate Loads (incorporated in 2007 NESC as Rules 250C and 250D). The 2002 proposal would have applied a strength factor of 70% to these Ultimate Loads

    5. Comments to 2002 Proposal In a formal comment to the 2002 CP, ANSI-C29 Committee (Insulators) stated: “Any load rating system for insulators that allows the service loads to exceed the current NESC loading limits is unacceptable to NEMA. Loads above these limits, no matter how short in duration, introduce a risk to the integrity of the insulators, and the possibility of either an immediate or delayed line failure.”

    6. CP2829 Submitted for 2007 NESC Submitted by a Working Group of NESC SC5 to address concerns stated in ANSI C29’s comments to 2002 NESC proposal. In October 2003, SC5 voted to reject CP2829 for the following reason: “Major changes to the insulators strength should be championed by ANSI C29.”

    7. Comments Received on CP2829 Comments were received from four utilities and utility organizations supporting the rejection of CP2829. No comment was received from the ANSI C29 Committee or NEMA.

    8. Final Status of CP2829 In the Fall of 2005, NESC SC5 voted to reconfirm the rejection of CP2829. NESC Working Group 5.6 was established by NESC SC5 to work with ANSI C29 to resolve issues relating to Insulator Loading.

    9. Proposals for 2012 NESC September 7 conference call between members of NESC SC5, the insulator manufacturers and a few additional members of the ANS C29 committee It was decided that ANSI C29 would be submitting a Change Proposal for the 2012 NESC to change NESC Rule 277 in a manner that reflects their desired mechanical loading limits. Insulator loading (working or ultimate load) should not exceed XX percent of insulators nameplate rating, with XX being percentages similar to those presently printed in the 2007 NESC.

    10. Proposals for 2012 NESC ANSI C29 has been advised that their Change Proposal will need to include technical information as to why the proposed changes need to be made.

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