Relationships of National Electrical Safety Code Vertical Clearances and Potentially Conflicting Activity

The development of the vertical clearance requirements of the National Electrical Safety Code (NESC) is briefly discussed and illustrated. Diagrams and tables are provided to summarize the clearances which generally apply in each land category and show the relationship of these clearances to the potential conflicting activities underneath the line. Comments on intended applications are included to aid engineers in understanding vertical clearance requirements and in developing special clearances for applications not specified in the NESC. Each category of Table 232-1 of the NESC is discussed and the vertical clearance requirements of Rules 232A and 232B are summarized in tables. Certain clearance values are shown to adhere to general relationships; others represent special cases which have been developed over the years from experience with actual construction. This work is the basis of a complete review of these relationships now being undertaken for use in simplifying the clearance rules in a future edition of the NESC.