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National Electrical Safety Code 1997 Edition | PDF Free Download.
This publication consists of the parts of the National Electrical Safety Code® (NESC®) currently in effect. The fonner practice of designating parts by editions has not been practical for some time. In the 1977 Edition, Parts 1 and 4 were 6th Editions; Part 2 was a 7th Edition.
Part 3, a revision of the 6th Edition; Part 2, Section 29, did not cover the same subject matter as the 5th Edition; and Part 3 had been withdrawn in 1970.
In the 1987 Edition, revisions were made in all parts and revisions to all parts have been made in subsequent editions.
It is therefore recommended that reference to the NESC be made solely by the year of the published volume and desired part number.
Separate copies of the individual parts are not available. Work on the NESC started in 1913 at the National Bureau of Standards (NBS), resulting in the publication of NBS Circular 49.
The last complete edition of the Code (the 5th Edition, NBS Handbook H30) was issued in 1948, although separate portions had been available at various times starting in 1938.
Part 2-Definitions, and the Grounding Rules, 6th Edition, were issued as NBS Handbook H81, ANSI C2.2-1960, in November 1961, but work on other parts was not actively in process again until 1970.
In 1970 the C2 Committee decided to delete the Rules for the Installation and Maintenance of Electric Utilization Equipment (Part 3 of the 5th Edition), now largely covered by the National Electrical Code (ANSIINFPA 70), and the Rules for Radio Installations (Part 5 of the 5th Edition) from future editions.
The Discussion of the NESC, issued as NBS Handbook H4 (1928 Edition) for the 4th Edition of the NESC, and as NBS Handbook H39 for Part 2 of the Grounding Rules of the 5th Edition, was not published for the 6th Edition.
The 1981 Edition included major changes in Parts 1,2, and 3, minor changes in Part 4, and the incorporation of the rules common to all parts into Section 1.
The 1984 Edition was revised to update all references and to list those references in a new Section 3. Rounded metric values, for information only, were added.
Gender-related terminology was deleted. Sections I-Introduction, 2-Definitions, 3-References, and 9- Grounding Methods, were made applicable to each of the Parts 1, 2, 3, and 4.
The 1987 Edition was revised extensively. Definitions were changed or added. Requirements affecting grounding methods, electric supply stations, overhead line clearances and loading, underground lines, and work rules were revised.
The 1990 Edition included several major changes. General rules were revised.
A significant change to the method for specifying overhead line clearances was made and the rationale added as Appendix A. Requirements for clearances of overhead lines from grain bins and an alternate method for determining the strength requirements for wood structures were added.
Rules covering grounding methods, electric supply stations, underground lines, and work rules were changed.
In the 1993 Edition, changes were made in the rules applicable to emergency and temporary installations. In Section 9 and Parts 1, 2, and 3, rules were extended or clarified to include HVDC systems.
The requirements for random separation of direct-buried supply and communication systems were modified for consistency and clarity, as was the rule in Part 4 on tagging electric supply circuits.
For 1997, several changes were made that affected all or several parts of the Code.
The most significant of these, which is stated in Section 1, is to show numerical values in the metric (SI) system first, with the customary inch-foot-pound values (inside parentheses) following.
The second general change was the addition of NOTES referring to several ANSI standards on safety signs. Finally, in order to reduce the probability of misinterpretation, words such as "minimize the possibility" or "prevent" were changed to "limit the likelihood" or similar language.
One exception to this type of change is Part 4. In Section 2, definitions of several items related to worker safety, and a definition of limited access highways, were added.
The definition of a generating station was changed and relocated as one type of an electric supply station. The list of references in Section 3 was reorganized and revised so as to include only documents referred to in one or more sections of the Code.
In Section 9-Grounding Methods, changes were made in rules affecting the grounding offences so as to state only the methods of grounding to be used when the grounding of fences is required by other parts of the Code.
The wording of rules affecting Ampacity and Strength Underground Installations, Separation of Grounding Conductors, and Communication Apparatus was changed for clarity. In Section 9 and Parts I and 2, rules were extended or clarified to include HVDC Systems.
In Part I-Electric Supply Stations, requirements for a safety clearance zone for fences relative to exposed live parts were added.
In most cases, requirements copied from the National Electrical Code®, NFP A 70 were replaced by direct references to the applicable rules of the NEC document. A requirement for short circuit protection of power transformers was added.
In Part 2-0verhead Lines, changes were made to the clearance rules applicable to emergency and temporary installations to allow for the proper choice of methods for assuring safety.
Footnotes to several tables regarding the requirements applicable to ungrounded guys and ungrounded portions of span guys were added, as were clearance requirements for unguarded rigid live parts over or near swimming pools.
Clearance requirements between different facilities located on the same structure were changed. Strength requirements contained in Sections 24, 25, and 26 were revised completely.
In Part 3-Underground Lines, the requirements for random separation of direct-buried supply and communication cables were modified with respect to sequential marking of the identification symbol with other data on the cable.
A requirement for a continuous metallic shield for some communication cables was added. In Part 4-Work Rules, a requirement that warning signs and tags comply with the provisions of applicable ANSI standards, and extensive requirements for fall protection were added.
The rule on tagging electric supply circuits was revised to clarify its application to Supervisory Control and Data Acquisition (SCADA) Systems.
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