The tension of attached wires to structures are the major loads they are required to support, under a variety of load cases. As such, any deviation from expected norms for tensions will have a significant effect on calculated single and multi-structure analysis results. Their resulting sags under various load cases are also key in meeting clearance to ground requirements in the respective code and utility standards. So both Sags and Tensions should be evaluated in a comparable manner under a very wide range of scenarios. To meet code and utility standard requirements, each span of wires attached to a structure needs to be assessed under any load case that may have an impact. All wires are assumed to have nonlinear material characteristics. Wire states such as birdcaging, will also come into play for wires composed of more than one material.


Average day temperature for creep and installation shall be 10%RTS @ 10C. Additional creep temperatures of 0C and 20C shall be tested. 


Evaluation tests should include:

  1. Values for:
    1. Tension at both support structures
    2. Horizontal tension
    3. Line of sight sag
    4. Vertical sag (sag below lowest attachment support)
    5. Horizontal and vertical loads per meter on the wire.
  2. Weather loads that test wire 
    1. stretching behavior with different possible loads in the vertical and transverse planes. 
      1. 400 pascals wind pressure
      2. 12.5mm radial ice accretion
    2. Line of Sight and Vertical Sags will be collected for sag comparisons
    3. Thermal condition (50C for steel wires and 100C for all others)
  3. Level spans of varied typical lengths, plus additional amounts for extreme tests
    1. 20m
    2. 40m
    3. 60m
    4. 80m
    5. 100m
    6. 120m
    7. 140m
    8. 160m
    9. 180m
    10. 200m
  4. Unlevel spans
    1. varied lengths as above
    2. varied elevation changes up to 60 degree incline
      1. 5 degrees
      2. 10 degrees
      3. 20 degrees
      4. 30 degrees
      5. 40 degrees
      6. 50 degrees
      7. 60 degrees
    3. measure both upper and lower attachment point tensions plus sags described above
  5. Observance of any birdcaging effects for multi-material wires and what temperature they occurred. Increments of 10C temperature increments are recommended.
  6. Wire types:
    1. All aluminum
      1. 566.5 Dahlia AAC
      2. 336.4 Tulip ASC
      3. 4/0 Oxlip AAC
      4. 1/0 Poppy AAC
    2. Aluminum and Steel
      1. 795 Drake ACSR
      2. 4/0 Penguin ACSR
      3. 3/0 Pigeon ACSR
      4. 1/0 Raven ACSR
      5. #2 Sparrow AW 6/1
    3. Copper
      1. 750 kcmil 37 strands
      2. 4/0 7 strands
      3. 1/0 7 strands
      4. #6 7 strands
    4. Steel
      1. 3/4 inch Grade 180
      2. 1/2 inch Grade 180
      3. 3/8 inch Grade 180
      4. 1/4 inch Grade 180
      5. 3/16 inch Grade 180
    5. Dielectric cables with a fiberglass core messenger
      1. ADSS cable from AFL AE2889CO31BA5
        1. Wire mass=0.393kg/m
        2. Strength=24225N
        3. Diameter=22.61mm
        4. Cross sectional area=401.16mm2
        5. Thermal exp. 2.9069e-3
        6. Stress polynomials= 0.0, 29.83, 0.0,0.0,0.0
        7. Creep Polynomials=0.0,24.86,0.0,0.0,0.0
  7. Wire states:
    1. Initial
    2. Final after Creep
    3. Final after Load


To properly evaluate Sag & Tension calculations, some details need to be taken into account. Softwares need to model all wires/messengers in a way that they are typically installed, assuming new material. When wires are installed and sagged in one operation in a line section of several equal or unequal, level or unlevel spans, the structures between the dead-ends of the stringing section support the wire with stringing sheaves or blocks, that permits the conductor to move freely between spans. Once the wire’s tension is set to the desired value, the conductor is secured to its supporting insulator or connection hardware. This fixes the amount of wire used between the structure supports under initial stringing conditions. In PLS CADD’s terminology this means that the wires are “clipped”. Under initial stringing conditions there is no longitudinal imbalance, but under other load cases there may be. For PLS CADD specifically and possibly other software, the cable condition needs to be set to Initial FE and the wires need to be clipped at the insulators to properly compare. 


For sag-tension calculation for communication cables, the exact same procedure needs to be followed as for conductors, for the messenger alone. After the messenger conductor is clipped, allowing the messenger to fix its length, the communication cables get lashed onto the messenger. All loadcases are calculated, and wire stretch scenarios are calculated using this additional cable weight and larger bundle diameter. This is representative of how communication cables are strung in the field. The equivalent can be done in PLS CADD and other software by 1) stringing the messenger, 2) clipping the insulator letting the messenger to fix its length and 3) replacing the messenger cable file for the final cable file – messenger plus communication cables. 


This methodology is the most accurate, but can cause some inconsistencies when comparing results between line design programs that use only the ruling span for calculations.