610 N. Whitney Way, Suite 160 Madison, WI 53705, U.S.A. Phone: (608) 238-2171, Fax: (608) 238-9241 Email: info@powline.com
Home Search News Products

Determining Structure and Wire Clearances

The advantage of using true 3-D software such as PLS-CADD is that the designer can see what will be built before the first structure is ordered. Clearances between conductors, conductors and structures, and even between conductors and communications cables can easily be checked for a variety of conditions to eliminate problems before they occur. This TechNote will briefly discuss how to use PLS-CADD and PLS-CADD/Lite to check clearances in a 3-D environment.

Wire Clearances

First, let's cover wire clearances. Wire clearances can be used in both the full PLS-CADD as well as PLS-CADD/Lite to check the clearances between any wires in a project, such as:

• Phase-to-phase clearances in a single circuit, such as a roll from a horizontal substation structure to a vertical transmission structure. (See video)
• Circuit-to-circuit clearances, such as in a double-circuit line or a transmission circuit over a distribution underbuild circuit. (See video)
• Energized wire to communications cable, such as ADSS, OPGW, coax, etc.

Many of these clearances need to be checked under a variety of possible line conditions. For example, that distribution underbuild or crossing may not always be energized when the transmission line is operating at its maximum temperature. The upper phase of a vertical circuit may have full ice on it while the middle phase may not. What could happen when one phase sheds the ice on it and then "jumps"? How do you check the NESC requirement that you must have different (larger) clearances at midspan? Or the different required clearances depending on whether or not the cables are attached to the same structures or different structures? PLS-CADD and PLS-CADD/Lite can check all of these conditions automatically for you.

Structure Clearances

Structure clearances are critical for obvious reasons. PLS-CADD or PLS-CADD/Lite can automatically check many different types of structure clearances for you. Would you rather catch an "overlooked" clearance with PLS-CADD while your project is still in the office or have it found by a lineman in the field? Clearances that can (and should) be checked are phase to:

• Shaft of pole or body of tower
• Crossarm or davit arm
• Guys
• Different structure
• Substation structures and rigid bus

See a video showing how PLS-CADD can be used to check structure and guy clearances.