This paper presents result of research on the application of a Portable Protective Gap (PPG) to live work on a compact 550 kV steel lattice tower. The objective of the research was to provide experimental evidence which confirms the needed coordination of the PPG sparkover characteristics with the sparkover characteristics of the worksite on the compact tower during live work. Sparkover characteristics of the worksite are strongly affected by the presence of the worker, the live working tools, and damaged insulators.

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Research was conducted to determine the minimum number of healthy insulator units needed to ensure worker safety in live working on a compact 550 kV steel lattice tower, A large variety of worksite conditions was investigated. Test results confirm the conservative nature of the CIGRE formula for defective insulator units, and modifications to the formula are suggested. The recommended number of healthy units is 12 in a string of 24 units for the case of live work on the compact 550 kV tower, when the Portable Protective Gap (PPG) is used. Adjustment for altitude should be made above 900 m (3000').

This paper was created to provide the public with the background data for the derivation of the National Electrical Safety Code (NESC) 1993 Edition Minimum Approach Distances. Subc-ittee 8 (SC8). Working Rules, used the reasoning and methods o f calculation presented here to obtain the published minimum approach distances for NESC-1993. Values in this paper reflect the changes to the Tables and the supporting paragraphs contained in the Tentative Interia Amendment (TIA) to be issued in 1993. W u e s t o be re flected i n the TZA amear i n j t a l i c underlined as shown here, The Institute o f Electrical and Electronics Engineers (IEEE) Engineering in the Safety, Maintenance, and Operation of Lines (ESMOL) Subcocnittee and the NESC-SC8 agreed to use IEEE Std 4-1978 and Std 516-1987 as the basis for its calculations so that one set of numbers will appear in all documents. These numbers were proposed to OSHA for inclusion in OSHA 1910.269 during the public hearings on that regul at i on. The reader is furnished with sufficient data to verify the minimum approach distances. Patience is required to follow the progression for Table 441-1, especially for voltages of 72.5 kV and below. The data was amassed by using six decimal places on the calculator, rounding each calculation in accordance with the principles of Rules 441ASa(l) and 441A5a(2), and reentering the rounded number before performing the next calculation. The respective NESC table appears before the derivation of each table. Technical assistance was provided by Fred Ooering, Jim Gillies, Charley Gross. and Joe VanMaine. Calculations were made by Hank Kientz and verified by Vivian Kientz. This document was peer reviewed by the IEEE/ESNOL Uorking Group on Coordinating ESMOL Revisions to the NESC. U.S. Government work not protected by U.S. copyright 4-1 Voltage QP For single phase systems, use the voltage t o ground.