line construction specs ?

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Part 77

Member
Location
WA state
This may not fit in Mike's forum, so moderators feel free to tell me. Part of my job duty is building 34.5 KV distribution lines (jack of all trades...). When exceeding a standard span of 150' to 200' spacing (standard 9' wood arm, 45' class 3 pole, 3 phases of 336 mcm ACSR (Merlin) 2 on the arm and 1 on a pole top insulator with raptor safe spacing, 4/0 ACSR ground (Penguin) 7'6" below the arm on a spool bolt; what are some specs for longer spans using heavy arms, double arms, taller poles etc.? I may need to span 300-400' due to terrain and want to know some maximum specs for single pole construction with the above referenced conductors before going to H-structures. TIA
 

MJJBEE

Member
Generally on a long run like that you would have an engineer take a look and see what you can do. The thing that makes the most difference is the average and maximum wind velocities. Another thing to look at is the expected sag of the conductors I don't do line design but there is a minimum height for conductors. Also are you passing over a road ect... This is a design problem which takes some thought.
 

bob

Senior Member
Location
Alabama
MJ brings out some good points. You need to calculate the wind and ice loading on the poles. This load will dictate the class of pole you need to use. It varies with the area you are in. I think you can span 300 ft with 336 AL with no problem. You should be able to use a pole top pin and insulator together with a 48" fiberglass 2 phase bracket that is able to support this size conductor. Ground clearance is also required depending on what you are crossing. A 45 ft pole will provide ground clearance in most all situations. Using a longer arm will spread the phases and keep them from making contact during high wind. You should not need to use any H frame construction.
Consider installing lightning arresters and grounds at some given interval.
 

jtester

Senior Member
Location
Las Cruces N.M.
In addition to pole loading, you may need additional conductor separation due to sag allowing conductors to get together. You will also need to consider vertical loading on equipment including arms, etc. I have designed a lot of feeders with 336 ACSR, and 300' never was a problem, 400 feet is a different situation.

It is likely that you can't use standard arms for deadends, or even tangent poles on 336 construction except for the shortest of spans. I don't have an NESC handy, but I believe you will overload standard arms with just about anything larger than 4/0 ACSR. We always resorted to manufactured deadends by Hughes or others to withstnd the extra tension of the 336.

Jim T
 
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