IEEE NESCIR577-2014 en National Electrical Safety Code《国家电气安全规范》.pdf

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1、 1 Copyright 2014 IEEE. All rights reserved. Interpretation Section 23. Clearances Rule 232.A. Table 1 Vertical clearance of wires above ground or rails Basic clearances Minimum vertical clearance of wires above ground or rails (1961, 6th Edition; Volume 12, NESC Archives, pages 56-57) (9 December 2

2、014) IR577 Question: Does the language in the middle column of Table 232-1, entitled “Open supply line wires, arc wires and service drops” apply to all service drops or only open-wire drops? The language of the middle column is unclear regarding the clearances required by this Table. Specifically, c

3、larification of the minimum required clearance for a 120 V to ground triplex service drop (now known as a 230C3 cable) is requested, at point of attachment to the structure, above pedestrian-only areas. This becomes an issue when attempting to apply grandfathered status to the terms of the 1961 Edit

4、ion, to the service height clearance to an older home. The lack of clarity arises when trying to apply the footnotes for the clearances indicated for “Spaces or ways accessible to pedestrians only” One interpretation could be that the (middle column) language applies to all service drops and that, c

5、onsequently, Footnote 8(2) gives the flexibility to reduce that clearance to 8 ft, under certain conditions. Another interpretation is that the minimum clearance required by Table 232-1 is 10 ft, for what is now known as a 230C3 cable; that footnote 8(2) would apply only to open-wire services and th

6、en only when the form of the building will not permit 10 ft clearance. The second interpretation would also seem to indicate that, for the 230C3 cable described, the only avenue for reduction in the 15 ft clearance (stated in the Table) lies in application of footnote 7(4). 2 Copyright 2014 IEEE. Al

7、l rights reserved. Discussion: The language in this Table was changed significantly in this Edition, as was the language of Rule 230.C., describing “Supply Cables.” The verbatim inclusion of Rule 230.C. into the first column of Table 232-1, as well as into footnote 7(4), appears to be intentional an

8、d a clear indication that the committee recognized the differences between open-wire facilities and those described in Rule 230.C., and wanted to draw clear distinctions between the two types. Interpretation This Interpretation is limited to NESC 1961 Edition clearance requirements for service drops

9、 over spaces or ways accessible to pedestrians only, as detailed in Rule 232.A., Table 1. In answer to the question presented, the middle column of Table 1, “Open supply line wires, arc wires and service drops,” applies to open-wire service drops only; it does not apply to triplex service drops. Con

10、sequently, footnote 7 applies to triplex service drops and footnote 8 applies to open-wire service drops. In the heading of the Table 1 middle column, “Open” applies to all of the three designated types of conductors: supply line wires, arc wires and service drops. A semicolon would have been used a

11、fter “arc wires” if the middle column was intended to apply to all service drops. Rather, triplex service drops are covered in the first column under “insulated conductors supported on and cabled together with an effectively grounded messenger.” See also NESC IR 577a. _ National Electrical Safety Code and NESC are both registered trademarks and service marks of the Institute of Electrical and Electronics Engineers, Inc. The NESC is available from the Institute of Electrical and Electronics Engineers, Inc., 445 Hoes Lane, Piscataway, NJ 08854, USA (http:/standards.ieee.org/)