Sag and tension measurement

The LineSmarts overhead power line tension measurement function enables the use of android tablet or smartphone devices to safely and efficiently measure:

  • Conductor tension, catenary constant, horizontal tension and axial tension at supports
  • Conductor vertical force at supports
  • Sag at the maximum position in span
  • Conductor mechanical utilisation
  • All of the above under a range of user defined limit state load cases.
  • Conductor blowout distance under relevant user defined limit state load cases
  • Identification of critical design load cases and maximum values for the above parameters

Measurement accuracy is a function of how well LineSmarts is calibrated. Instruction on how to calibrate LineSmarts can be found here.

Conductor tension

Conductor tension is arguably the most fundamental and important parameter for the design of overhead lines. Discrepancy between actual line tensions and the tension used for calculation leads to errors which touch on almost every facet of line design, including:

  • Support design – longitudinal, transverse and vertical loads on poles, stay and footing loads.
  • Conductor and fittings mechanical design – design for fatigue endurance and strength under extreme loading events.
  • Electrical design – phase to phase and circuit to circuit internal clearances, ground clearances and blow-out clearances to buildings, trees and easement boundaries.
  • Maintenance and construction design – for hazard identification and the specification of appropriate methods and equipment

LineSmarts provides users with a tool to measure the catenary constant of a wire. Once the user identifies the conductor type, and therefore the wire’s mass per unit of length, the catenary constant can be used to identify wire tension.

The capability to measure conductor tension might be used:

  • as part of a condition inspection programme
  • to provide input information for design
  • to review the tensions at a damaged, repaired or newly installed structure or section of line
  • to assist with works planning and works method development by assessing actual loads on a structure
  • to identify whether out of balance in-line loading or extreme side loading might be a factor at a leaning structure
  • diagnose vibration issues and the need for vibration protection

For detailed instructions on how to calculate conductor tension please watch the following video.


In many cases the reason designers wish to know the conductor sag is to understand the tension in the conductor. Sometimes conductor stringing tensions are supplied as mid-span sags since before the advent of LineSmarts sag was easier to measure than tension. As part of the tension calculation the sag is also calculated.

Conductor tension under alternative load conditions

As well as allowing users to measure the conductor tension at the time of survey, LineSmarts also allows users to calculate conductor tensions for alternative load cases. For example users may wish to calculate conductor tension for a maximum temperature, snow or wind load case.

The load case tension calculator might be used to:

  • Identify whether conductor or conductor fittings are susceptible to overloading under extreme loading events
  • Identify whether conductor is susceptible to vibration damage
  • Assessing how much a conductor is likely to blow out or sag under extreme loading events
  • Assess support structure loading under various load cases

Advantages of LineSmarts tension calculation over conventional line design software include:

  • calculated tensions are based on directly measured line tensions, not guessed or assumed tensions, or tensions from potentially out-of date or incorrect records.
  • calculations can be performed in the field
  • calculations can be performed quickly