IEEE NESCIR576-2014 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 235C1b Clearance for wires, conductors, or cables carried on the same supporting structureVertical clearance between conductors at the supportBasic clearance for conductors of same or different circuitsBetween su

2、pply lines and communication lines (2012 Edition, pp. 145-148) (9 September 2014) IR576 Question: Do the clearances listed in Table 235-5 for vertical clearance between communication and supply circuits at the support extend to situations in which supply conductors are run below communication conduc

3、tors and do not meet the requirements of Note ? Discussion: Rule 239G1 creates confusion as to what the vertical clearance between communication and supply circuits at the support should be when supply conductors are run below communication conductors and do not meet the requirements of Note . The p

4、ortion of Rule 239G1 that requires guarding of vertical supply conductors from 40 in above the highest communication line does align with the 40 in required by Table 235-5. However, the portion of 239G1 that requires guarding of vertical supply conductors to 6 ft below the lowest communication attac

5、hment creates confusion as to what the vertical clearance at the support between supply conductors run below communication conductors should be. Rule 239G1 suggests that the vertical clearance at the support between supply conductors run below and communication conductors should be 6 ft, while Table

6、 235-5 suggests that when the requirements of Note are not met, the clearance should be 40 in. This question specifically relates to trolley conductors which by Rule 220B1 EXCEPTION may be run below communication conductors. Interpretation The simple answer to your question is “yes.” Rule 235C appli

7、es to vertical clearances between conductors and cables located at different levels on the same support. Table 235-5 specifies the required clearance between the attachment points. Note that Rule 235C, Table 235-5 does not apply to vertical runs of conductors or cables attached to the same supportin

8、g structure. 2 Copyright 2014 IEEE. All rights reserved. Conversely, Rule 239G applies to vertical runs of supply conductors and cables passing through the communication space of jointly-used structures. Rule 239G1 specifies requirements for guarding such construction that is attached to the structu

9、re. Note that Rule 239G does not apply to vertical clearance between communication and supply circuits. The guarding requirements of Rule 239G1 are intended to limit the likelihood of communication workers: Gaffing a supply cable attached to the structure. Being exposed to an energized supply cable.

10、 See also: Rule 239G3 that is specific regarding protection near trolley attachments. Table 238-2 for vertical clearance requirements between trolley and communication construction. _ 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/)