Overview of 2017 NESC Updates - GDS Associates

Overview of 2017 NESC Updates

AnthonyH   |    Sep 28, 2016    |    Hi-Line: Seminars & Testing


EUCI 2017 NESC Webinar Oct 5th: In-Service Wood Poles
Kevin Mara is presenting a special webinar on Inspection of In-Service Wood Poles, October 5th for the Electric Utility Consultants, Inc., (EUCI). REGISTER FOR THIS WEBINAR.

The 2017 National Electrical Safety Code was released August 1, 2016. There are hundreds of proposed changes or additions to the NESC, most directly affecting distribution systems, learning these changes is imperative for personnel responsible for the safe design, construction and operations of an electric utility system. Below is an overview of some of these changes.

Add/Modify Rules for Solar Panels


  • Reason for electric supply equipment change

    • Communication equipment can be in the communication space
    • Communication space is below the communication attachment
  • A driving factor was the placement of solar panels in the communication worker safety zone or the communication space

    • Which is a violation of 2012 and 2017 NESC


Multi-Grounded Systems


  • Neutral connected to electrode at each transformer plus

    • A sufficient number of additional points
    • Total of 4 grounds per mile
    • Do not include grounds at individual services
    • Recognizes some intervals may be longer than 1/4 mile
  • Exceptions (one existing + two new exceptions)

    • Cable crossing underwater
    • Buried cable in conditions where meeting the rule would be difficult
    • River crossings or mountainous terrain
  • Exception 2: For cables or cables in duct where meeting the Rule would be difficult

    • No need to meet 4 grounds per mile
  • Without the 4 grounds per mile, neutral does not meet the definition of effectively grounded neutral.

    • May need additional grounding system
  • Exception 3: River crossing/Mountainous Terrain

    • Where terrain (river crossings or mountainous areas) limits the installation of supporting structures every 1/4 mile or less
    • Requirement for 4 per mile does not apply for THIS portion of the line
    • ALL available structures should be grounded


Clearance Over Driveways


  • Table 232-1, footnote 7 – 2012 NESC

    • Where residential building does not permit service drops to meet thse values (16 feet) the clearance over residential drive ways only may be reduced as follows: 12 feet for triplex conductors 150v phase to ground
  • New text for 2017 NESC Footnote 7:

    • Where vehicles exceeding 8 feet in height are not normally encountered nor reasonably anticipated, the clearance over residential driveways only may be reduced to the following
  • Driveway may limit big trucks
  • Now very subjective for designer


Swimming Pools


  • Added the words “in-ground” or permanently installed above ground” to clarify the type of pool.
  • 2017 added new diagrams to apply for above ground swimming pools.


Extreme Ice with Concurrent Wind Loading


  • ASCE 7 updated their weather loading maps for extreme ice in 2010

    • Now incorporated into the 2017 NESC
    • Ice loading areas are generally the same as in 2012
    • Wind loading has changed


Tension Limits


  • Major change in 2017 regarding tension limits

  • Underlying reason is the need to control Aeolian vibration

    • Wind induced vibration causes fatigue of the conductor
  • Now have 3 tension load factors to consider

    • 261H1a – Maximum design tensions
    • 261H1b – Aeolian vibration tension limits
    • 261H1c – Tension limits when used to control Aeolian vibration


Vibration Tension Limits


  • Potential damage from Aeolian vibration shall be considered

  • Aeolian vibration is usually low amplitude & high frequency

    • Causes fatigue or possible failure of conductors or attachment hardware near the supports
    • Generally more of an issue for transmission


For more information, please contact:

Transactions 115 Pic 4Kevin Mara, Vice President Hi-Line Engineering | CONTACT
GDS Associates, Inc. – Marietta, GA