Best practices quiz: complete list of questions and answers

In the questions and answers below, "transmission" refers to installations on lines >100 kV and "distribution" refers to installation on lines < 100 kV. NESC refers to the National Electrical Safety Code which governs all electric utility installations in the U.S. (and any other jurisdictions that adopt it).

#1. (U.S.) Do you still meet NESC clearance requirements at your worst case wind storms and ice storms? Would your fiber survive these storms? (Back to top)

First, the code requires that you meet clearance requirements. Second, you can be sued if you don't meet code and there's a problem. Third, recent extensive research on ice storm historical data has indicated that in many areas, your fiber network may likely experience at least one ice storm exceeding NESC loading during the life of your fiber network (we've got a tech note on this). Finally, heavily sagging fiber cables blocking roads get cut by cleanup crews if they're in the way.

#2. Did you find any damaged (step attenuation increases of 0.1 dB or more?) fibers after your installation was complete? (Back to top)

It is reasonable to install hundreds of miles of ADSS or OPGW without one damaged fiber (let alone broken fibers). These cables contain either Kevlar (ADSS) or steel (OPGW) and are very strong -- theoretically, you could tow a trailer with this stuff and never damage a fiber.

We're defining "damaged" here as a step increase in attenuation of at least 0.1 dB.

While a step increase of just 0.1 dB is an insignificant amount of loss, it's an indication that something is pinching or stressing the fiber. That small step increase could easily become a break with a change in temperature or cable loading, depending on the cause of the step.

Furthermore, from our failure analysis consulting work, we've seen that certain types of installation damage can leave no external marks on the cable and yet still significantly damage long runs of the plastic (ADSS) or metal (OPGW) buffer tubes that protect the fibers inside the cable. Small changes in temperature and cable loading can cause the appearance (or disappearance) of attenuation steps all along these damaged stretches -- if you have an 'event' on one fiber, it may be a matter of time before you see more point defects on other fibers.

Some utilities and installation contractors have become used to a few damaged fibers during their installations and just shrug it off as "something that happens". That's absolutely wrong! Competent crews installing fiber cable under attentive supervision and following proper procedures routinely install fiber for years with no damaged fibers.

Depending on the circumstances behind a fiber fault, we may recommend an entire reel be replaced even if there's only a fault in one location.

#3. If you did, did you know how they were damaged? (Back to top)

This question is perhaps more important than the previous question. As noted, faults don't "just happen". And one fault may just be the tip of the iceberg -- if a long stretch of cable is damaged, many more may just be waiting to appear with a change in the weather.

If an installation crew used improper installation techniques on one reel of cable, we've found they were likely to have done it in many other places. It's critical to figure out exactly the reason for any failure so you can determine where similar damage was done.

Installation crews aren't the only possible culprits -- for instance, designers can specify the wrong cable or hardware and hardware manufacturers can ship the wrong cable attachments.

#4. Are you sure they were damaged and not just an OTDR misinterpretation? (Back to top)

We're big believers in the usefulness and accuracy of OTDRs (Optical Time Domain Reflectometers) -- two of us used to work for an OTDR manufacturer. We think any utility with fiber should own an OTDR (or mini-OTDR). Nevertheless, we've observed that the accuracy and power of modern OTDRs often exceeds the skill of the operator using it! Before "blowing the whistle" on fiber damage, the operator should make sure they've got their instrument set up correctly (we've got a tech note on proper OTDR setup). In particular, they need to ensure they have enough dynamic range and have selected the correct pulse width such that they're misinterpreting noise (static) in the display as a glitch in the fiber.

#5. Can you reconcile the differences between OTDR distances and actual locations (Back to top)

OTDRs are very accurate in determining the distance to a fault on a fiber -- typically within a few feet. More accurate, in fact, than the machine that prints the foot markings on the cable jacket (which may be off by as much as 1%) and more accurate than most utilities' as-built records. Finally, the OTDR operator needs to enter the correct index of refraction value. It's reasonable to expect an OTDR operator to nail the fault location within a few feet, but it doesn't happen without proper training ahead of time and good record-keeping. Otherwise, even with a properly-working OTDR, it's common for technicians to be off by 1% to 2% on fault locations -- that's 300 to 600 feet on a 6 mile run!

#6. Later, did any fibers start displaying damage for reasons other than obvious external causes (tornadoes, etc.)? (Back to top)

See the answer to the next question.

#7. If so, do you know why? (Back to top)

Most installation damage shows at least one fault during final acceptance testing, but for the reasons explained above, it could hide until a change in temperature or cable loading flexes a damaged buffer tube and breaks or pinches a fiber. It's important to aggressively track down the cause even for a minor fault to ensure it's not likely to happen elsewhere.

Cable manufacturing quality for the manufacturers on our approved list is exceptionally high -- fiber faults that occur are usually going to be due to a different cause, but it's still important to check each reel before ruling out manufacturing errors as a cause.

#8. Do you test incoming cable on the reel? If so, have you ever spotted a defective fiber? Why do you test incoming cable? Do you keep all the results? (Back to top)

As mentioned, cable quality is very, very high among our approved vendors. They ship tens of thousands of good ADSS reels without shipping a defective reel. All of the cable is 100% tested with OTDRs and documented at the factory before shipping. Incoming acceptance testing protects the cable purchaser from damage by the shipping company.

Some users don't test fiber cable on incoming inspection and we think that's a calculated risk to save time and money. We recommend taking this extra step and documenting the results; doing so protects the utility if a contractor subsequently damages the cable ("we didn't do that -- the trucker must have damaged it!")

If by some chance, you did receive a defective reel of cable on incoming inspection in the last 5 years, we'd be interested to hear about it and who the vendor was.

Finally, we should note that OTDRs are good at spotting point fiber defects on incoming reels. They are less accurate at measuring dB/km -- you may often find your measurement of dB/m varies from the factory's by 0.02 dB or so. Keep this in mind if you're trying to measure vendor performance against dB/km specifications.

#9. Do you know where all the long distance carriersÕ fiber cables serving your area cross your route and have you made provisions for potentially connecting to them in the future? (Back to top)

See the answer to the next question

#10. Have you identified additional corridors carriers might use in the future and made provision to run taps to them in the future? (Back to top)

Tying your network to long distance carriers' fiber may increase the potential revenues you can realize from dark fiber leases if you can then connect them to local businesses on your route and enable them to cut out the expense of going through the local carrier (usually Bell). It's important to identify where these carriers are crossing your route (or might in the future) and leave slack storage at those locations to facilitate splicing in taps to their fiber.

#11. Do you know where those carriers' POPs are and have you made provision to run taps to them in the future. (Back to top)

Some long distance carriers may prefer to tie to your fiber network at their local POP instead of making a direct fiber connection at a point where their fiber cable crosses your route. You'll want to know where their POPs are and make provision to runs taps to them.

#12. Have you identified the major potential business and institutional customers near your routes and made provisions to run fiber taps to them? (Back to top)

This is a common sense question that would seem to require no explanation, yet many utilities still overlook major opportunities. The key is to identify who's using lots of expensive bandwidth, not who has the tallest smokestacks.

Ironically, large investor-owned utilities, so good at developing business in big cities, are ignoring millions of dollars in potential revenue as they fight ever tougher battles in big cities saturated with fiber and competitors. They're not even entering the Tier 3 and Tier 4 markets in their service areas, where there's no competition besides Bell! Meanwhile, in adjacent small towns, municipal utilities are profitably connecting many of the local businesses.

#13. If building a network after September 11, 2001, have you talked to local homeland security and law enforcement personnel about possibly using your dark fiber for security video feeds? How about your own internal security department -- do they want fibers for video cameras at substations and other key assets? (Back to top)

September 11, 2001 changed the way we all look at security. Utility security personnel are looking to better secure key assets in their system. Local authorities are discovering new vulnerabilities and moving to secure them. Security staffing can only increase so quickly, so the demand for video surveillance systems and smart sensors is growing. Security officials are now installing cameras in new areas.

Additionally, a private fiber network is much more secure from intrusion than a wireless network or traffic moving over the public telecommunications network. Attackers can cut a fiber cable, but they're almost impossible to tap. Combine fiber with self-healing ring networks and utilities can offer local authorities increased data security.

Planning in these areas by security officials is evolving from day-to-day; perceived fiber needs may change from month to month. If your network designers aren't in regular touch with internal and external security personnel since 9-11, they should be.

#14. Do you have a dark fiber marketing plan? Is someone actually working it? (Back to top)

Again, another common sense question, but one that many utilities flunk. Some don't have a plan, some do but don't work it and others have a plan -- but don't work it very effectively.

Getting this going is hard for many utilities -- the skills and the thought processes just haven't been required before in the rest of the utility's business. This is an area where experienced outsiders can help.

#15. Do you require the cable vendor supply test reports from qualified independent test labs (such as Kinectrics -- formerly known as Ontario Hydro Technology) demonstrating compliance to IEEE standards for OPGW and ADSS? (Back to top)

Special IEEE standards apply to most of the fiber cables that utilities use; these are tailored to the special demands of power utilities, not phone or cable TV companies. Only a few independent labs worldwide have the facilities to perform these tests. Knowledgeable utilities require vendors provide test reports from such labs demonstrating successful performance on all of these tests. This is an absolute requirement of Fiber Planners before we approve any vendor's cable. (See our page on materials tests.)

(Such tests are expensive -- tens of thousands of dollars -- so they are usually done once for an entire family of related cables that share a common design. They're not done for every customer or every order.)

#16. Do you use any premium dispersion fibers (such as LEAF®, MetroCor™, AllWave®, or TrueWave®) in your network? If so, why? If not, why? (Back to top)

LEAF®, MetroCor™, AllWave®, and TrueWave® are "premium" single-mode fibers with special dispersion or attenuation characteristics to facilitate wavelength division multiplexing (WDM). Naturally, they're more expensive than traditional single-mode fiber. They offer no advantage when used in traditional optical networking applications but are valuable in WDM applications.

Some utility network routes use cables consisting mostly of premium fibers, others contain no premium fibers. Selecting the right fibers for your routes requires an understanding both of how these fibers work and what your future wavelength management needs may be. If you don't know what you're using or why, you'll want to go back to the books to learn more about current optical network design.

#17. Do you use any multimode fiber in your outside plant? If so, where and why? (Back to top)

Multimode fiber is used in corporate intra-building and campus local area networks (LANs). It's almost never used in utility fiber optic outside plant networks except occasionally in a few short links within a substation or office building. If you're running ADSS or OPGW with multimode in it, you need to ask why.

#18. Do you have an emergency restoration kit? Do you have an emergency restoration plan? Have you practiced it in the last 6 months? Last year? (Back to top)

Utility ADSS and OPGW networks are the most reliable fiber networks out there. As has often been said, "there are a lot more backhoes than tornados" -- buried telco cables get cut much more often than aerial power utility fiber cable systems.

Still, accidents can happen. Your own electric system and customers are counting on you to get service back up fast. Well-rehearsed restoration crews with pre-prepared restoration kits routinely restore fiber service in 4 hours or less -- can you?

If you don't have a kit, a plan and regular drills, you're in trouble. Routine OTDR checks (next question) are no substitute for drills, but they can supplement drills by reinforcing troubleshooting skills.

#19. How often do you check your lines with an OTDR once they're in service? (Back to top)

Checking at least your unused fibers periodically for attenuation changes can identify signs of future trouble before it gets out of hand. Having said that, those sorts of "creeping" problems are unusual in well-built systems.

Much more importantly, periodic OTDR checks keep your crews familiar with their OTDR, test access locations, as-built network records and any details of particular routes.

#20. What wavelengths do you test your fiber at? (Back to top)

You should have OTDR records of every fiber on every route and tested in each direction. Tests should be made at 1310 nm. and 1550 nm. Copies of these records should be kept both at a central location and at the test locations. If not, you're not ready.

What about 1625 nm. tests? It's still an open question whether to test at this new wavelength. Some networks will eventually carry traffic at or near this longer wavelength, which is much touchier for splicing mistakes. Many never will. What are your future wavelength management plans? If you may operate at 1625 nm. in the future, you should get these tests done now as part of your installation and splicing acceptance tests.

Even if you don't expect to operate at 1625 nm., it may still be worthwhile to test at 1625 nm., just to spot kinked fibers at splice cases, but it will add cost to your splicing contract, especially if your contractor doesn't have a 1625 nm. OTDR module. Industry opinions are divided on doing this.

#21. Does your design meet all appropriate NESC standards? Was your system built as specified or were things fudged? (Back to top)

If you can't answer yes to both questions, you're headed for trouble (see our litigation consulting page.)

Especially on distribution lines, it can be hard to squeeze in a fiber cable on to existing poles and still meet complex NESC requirements without replacing a pole. It's tempting for designers to either knowingly violate the code or, more commonly, specify an code-compliant installation on a pole that's impossible to actually install in the field.

Likewise, it's tempting for installers to install cable the easiest way, not necessarily the specified (and code-compliant) way.

The answer is careful planning for each pole, clear pole-by-pole instructions and attentive and careful project supervision.

#22. Have you set up a CLEC, hybrid fiber/coax CATV network or FTTH (fiber to the home) business or are you planning to? If so, did you get an outside feasibility study? If so, was it by a potential vendor? (Back to top)

Moving from dark fiber leasing to setting up a CLEC (competitive local exchange company) or a cable TV operation is potentially lucrative and we have clients already doing this successfully. And taking fiber to the home is the ultimate potential home run in fiber deployment.

All of these activities, however, call for greater financial risks and investments as well as major organizational changes and expansions at your utility -- think and plan carefully before undertaking them. Get an outside feasibility study as a second opinion (and be aware of the pitfalls in picking the wrong consultant -- see our page on feasibility studies.)

#23. If you are offering CATV services, did you hire someone out of that industry? If you've set up a CLEC, have you hired someone with telco experience? (Back to top)

Running a cable TV system or a competitive telephone company is sufficiently different from the power business that you need to bring in at least some good talent with strong backgrounds in the business you're entering -- yet we see utilities fail to do this. Conversely, we've seen utilities staff up a new division completely with outsiders -- yet it's important that at least some of the technical and managerial personnel have strong backgrounds in electric distribution design or construction.

#24. Do you always use sheaves at least the diameter required by the manufacturer? Do you know that diameter off the top of your head? Does someone check the crews - at every pole or tower - to make sure they're complying? (Back to top)

Never use a sheave smaller than that recommended in the cable manufacturer's procedures unless you have specific approval to do so from the vendors. Big sheaves are a real hassle, so line crews will sometimes try to take shortcuts and use smaller, lighter, easier-to-rig sheaves than approved by the manufacturer. Don't do this -- we'd rather be your designer than your failure analysis consultant! Undersized sheaves damage cable internally in ways that may not be obvious from the outside. They void your cable warranty, too. (We've got a tech note on sheaves.)

We'll ask one more time -- even if you say your installers don't use undersized sheaves -- are you sure of this?

#25. Do you ever use a cluster of smaller sheaves in order to get the bend radius required of a large sheave? (Back to top)

Installers may either rig their own cluster of undersized pulleys individually or use a "banana block" (also known as a "quadrant block" or "three-block"), a set of multiple small pulleys fixed in an arc. Using such methods ensures the manufacturer's minimum bend radius specification is met without having to struggle with heavy, full-sized sheaves. But it's still a bad choice -- these arrangements do maintain the correct bend radius, but they crush the cable by distributing the weight over a tiny area on each of several small sheaves.

#26. What fiber counts did you use? How did you pick those numbers? (Back to top)

Choosing fiber counts on different routes involves an understanding of who'll be using your fiber; expected future internal SCADA, video, voice and data needs; whether you might go offering additional services such as fiber to the home, CLEC services or cable TV in the future; and your future wavelength management needs. Fiber counts are also tied into your decision as to whether to use premium fibers (see the earlier question on this topic.)

In theory, it's possible to use time division multiplexing (TDM) and wavelength division multiplexing (WDM) to shoehorn all your traffic and your customers' traffic onto just several fibers -- the fiber by itself has that much bandwidth. In reality, the network equipment to do that much multiplexing is expensive and it's usually much cheaper and easier to add more fiber to the cable. We have small-town customers using 288-fiber cables in some areas.

#27. Does your designer have fiber experience? If not (for instance, they may be a staking engineer or transmission engineer), who trained them on designing utility fiber installations? Does your designer have utility line design experience? If not, who trained them on designing fiber installation for utilities? (Back to top)

Fiber optic networks require overlapping knowledge of both electric utility operations and fiber optics. Few people start out with both. How long have your designers been doing both?

Particularly with the recent slump in the cable TV and telephone businesses, many CATV and telco design firms have started going after the utility fiber business they ignored for many years. As a group, without getting extensive training in utility line design, they tend to produce designs on the surface that look inexpensive but rapidly go over budget as unforeseen make-ready expenses pile up. For instance, cable TV companies and telcos lash fiber cable to steel messenger wires in the communications space -- they're not allowed in the supply region. They use slightly less expensive fiber cable and hardware and much cheaper installation labor and equipment than power utilities use when installing ADSS in the supply zone.

So designers with telco and CATV backgrounds design the same way they always have, but this time the poles already have cable TV and telephone company cables on them. On many poles there's no room anymore for another lashed cable, so to meet NESC requirements the pole has to be replaced (including moving drops, transformers, etc.), driving make-ready costs through the roof. Since they have no background in working in the supply region, they avoid using ADSS in that area, even though with a little more upfront installation expense, the utility could cut pole replacements to under 2%. It usually only takes about 2 pole replacements per mile to make lashed aerial cable installations more expensive than ADSS installations.

Designers with powerline design backgrounds and no fiber experience usually don't specify the correct ADSS cable characteristics and create big sag and tension concerns for the future of the installation. ADSS has unique properties that must be understood in order to design a 40 year life span system.

#28. (Buried cable runs) Do you have a marker wire or marker balls to enable locating your cable in the future or do you rely on cable markers? (Back to top)

Most utility fiber cable is installed aerially, but there are still underground runs -- usually around substations and in downtown areas. It's good to use warning signs ("Do not dig -- fiber optic cable") but they're not enough, especially since they get knocked down and sometimes moved. An all-dielectric cable has to be detectable to cable locator crews, which means either burying a tracer wire with it or using electronic marker balls.

#29. (ADSS) Do you ever use the "moving reel method of installation"? (Back to top)

The moving reel method of aerial installation is typically used with messenger supported cables. First, a messenger must be installed on the aerial route using J-hooks at each structure. Then in a separate step, a truck with a spindle mounted on the rear of the truck or on a trailer is driven past each structure. As the truck drives the route, a "lashing machine" is pulled on the aerial line. The lashing machine can consist of a tie-wrap system or a wrapping system using mono-filament (fishing line) to wrap around the cable and messenger. There are a couple of complicated situations that might occur. First, the route may require the truck to oppose traffic or drive on the field side of the structure where a ditch would inhibit the path.

Secondly, the structures may be so crowded in the communication region that the operator has difficulty maneuvering the lashing machine past the structure. Thirdly, the sag requirements to match cables above and below may be so different that the new cable may clash with existing cables at installation.

The moving reel method is only acceptable when a messenger is used. The reason is that the structures are load balanced by the messenger since the ends of the route will terminate in downguys. If no messenger is used and ADSS is installed. The truck drives by a structure and attaches the cable but the truck can not balance the load on the structure since there is no backtension on the reel. This is not possible since the truck is moving and a reel brake would not be able to keep uniform pressure. The real danger is when a dead-end structure is tensioned and the first dead-end is applied. The uneven load is typically enough to bend a wood distribution pole and break power crossarms. Conductors drop and everyone is unhappy.

For these reasons, the moving reel method is never acceptable for ADSS installations.

#30. (ADSS) Do you use installation crews with cable TV or telephone fiber experience? Do you use crews with a power installation background? If they have a power background, who's trained them on installing fiber? (Back to top)

Fiber optic networks require overlapping knowledge of both electric utility operations and fiber optics. Installation crews with a firm understanding of both may not be available. So which do you use -- cable TV or telecommunications installers with years of fiber cable experience but none of it in the utility's "supply" space or traditional electric line construction personnel?

The answer is simple, go with the power-qualified line construction crews (either contractors or in-house crews) and train them on the specifics of fiber. Power utility fiber construction at the worker level is 95% good, safe utility line construction methods and 5% special fiber handling considerations.

We can train a good line construction crew that's new to fiber in one day, supervise them for a few days, then turn over supervision to our client (who we also train) with confidence they'll complete the installation with no major problems.

In contrast, cable TV or telephone contractor crews just don't have the equipment or the skills to work in the supply region. It's too big an undertaking to retrain and re-equip them for utility line construction just for your fiber project.

For Fiber Planners projects, we have an approved list of good contractors we've worked with. We are also open to working with other good installers our utility client likes and has worked with. (If you want to recommend a good power line construction crew to Fiber Planners, let us know.)

Finally, it may sound like we're down on line crews after our comments about sheaves, etc. We're not -- most linemen are conscientious. They work in a hazardous field where sloppiness can get them killed or fired. In our failure analysis consulting, we find installation problems usually involve lack of proper fiber installation training, inadequate supervision and poor designs (or inadequate instructions from the designer). Personnel turnover within crews after initial training and project briefings can also cause problems; new personnel should get the same training and be watched carefully initially to make sure they know what they're doing with fiber.

#31. (ADSS) What's the maximum line angle you use for tangents? Suspensions? (Back to top)

In designing for a 40 year life with little or no maintenance, it pays to be conservative in selecting attachment hardware.

The maximum line angle Fiber Planners recommends for tangents is 12 degrees, vertical or horizontal -- considerably more conservative than what the hardware suppliers specify. This limit is based on seeing others experience' using tangents for larger angles then having them chafe through hardware over time as cable moves back and forth to balance changes in cable loading.

The inside surface of a tangent has grit to increase the fiction so the cable doesn't easily slip until it has several hundred pounds of uneven tension to make it move. That friction and abrasion could damage the cable jacket and over time, damage the cable. (See the next question for an answer to avoid this condition)

Also, installers sometimes drill the attaching bolt into wood poles at something other than a 90 degree angle -- either by mistake or to avoid some obstruction. As a result, unless it's floated with a shackle (see the next question) the tangent may already effectively have a 10 to 15 degree on it before even considering the line angle on the pole.

Related to line angle limits are span length limitations when using tangents. Conservative designers usually avoid tangents on spans over 400 feet even if the vendor claims it can be used for longer spans. Above 400 feet, we recommend using Armor Grip Suspensions (AGS) and we limit their use to angles 25 degrees and under; for larger angles we use dead-ends.

#32. (ADSS) Do you "float" your tangents and suspensions with a shackle? (Back to top)

If you want a 40 year life with little or no maintenance, then Fiber Planners strongly recommends the use of an anchor shackle with each tangent and suspension to "float" the hardware. The anchor shackle allows the hardware to shift temporarily an inch or two to equalize uneven tensions at the pole, due to wind or ice. Once the external force is gone, the anchor shackle can shift back to balance the pole.

If the "fixed" tangent design is used, the cable physically moves from one side of the pole, through the hardware and into the longer span to equalize the load. Once the temporary weather condition is gone, someone must physically go to each piece of hardware and manually shift the cable back through the hardware. This is unrealistic when designing for a 40 year life with little or no maintenance, as we do. In most cases, the extra sag will stay in the longer span for years until it interferes with other cables or something on the ground.

Letting tangents and suspensions float also compensates for any bolt holes not drilled perpendicular to the pole (see the previous question.)

#33. (ADSS) WhatÕs the ratio of dead-ends to tangents in your system? Dead-ends to suspensions? (Back to top)

The ratio of dead-ends to tangents is not as critical as realizing that it takes many more dead-end structures to design an ADSS system than there are utility-labeled dead-end structures on your system. Fiber dead-ends are needed at storage loops, highway crossings, railroad crossings, windy valley crossings, vertical inclines and many more system features, even if these are not considered dead-end structures for the conductors. Experience and judgment are needed since the hardware manufacturer's instructions don't explain all the field conditions and their requirements.

If a tangent or suspension is installed where a dead-end is required, the cable will take the abuse of the friction or tension until failure starts. The bolt holding it to the structure may shear or the cable jacket may be rubbed enough to wear a hole in the material leading to later Kevlar® failure and a loss of the cable's tensile strength. Finally the cable will just fail and fall to the ground.

#34. (Distribution - U.S.) Do you always comply with the NESC requirements for clearances and for maintaining a 40" safety zone? (Back to top)

The NESC is complex and has a number of exceptions to the 40" safety zone for certain power utility equipment like streetlights. But except for limited situations where 30" may be permissible, 40" is the required spacing between any ADSS in the supply region and the highest communications cable. As long as that limit is met, the NESC gives considerable flexibility as to where to place the ADSS in the supply region -- above the neutral, below the neutral, on an extension arm, attached to a crossarm, etc. Also, a designer can sometimes shift around other power utility items on the pole such as streetlights to get enough room for a good attachment location.

Even then, it can be quite challenging to determine an NESC-compliant attachment point on a "fully loaded" pole (crowded safety zone, transformer, downguys, streetlight, etc.) that installers can actually install without damaging the cable. Also, there's the requirement for 4" bolt spacing. The designer still has to understand power distribution design and construction well enough to come up with designs that are not too dangerous for linemen to install and don't hamper future line maintenance, such as transformer change-outs. Inexperienced ADSS designers may end up with more pole replacements until they've designed a number of routes.

If the power utility uses fiber cable lashed to a steel messenger, it must stay in the communications region. If there's not that 40" space between this new lashed cable and the supply region, the utility can't attach to the pole without replacing it first. (Our understanding of the NESC is that the 30" exception is only available for supply region lines encroaching on the safety zone from above, not for communications cables encroaching on it from below.) Extension arms are not allowed. Pole replacements are more common in this situation than even with a totally inexperienced ADSS designer.

Our clients' experience is that pole replacement including moving over everything on the existing pole ranges from $500 (new simple pole) to $5000 (fully-loaded pole: telco and cable TV cables, transformer, multiple power circuits, etc.) Unfortunately, it's the more loaded poles that usually require replacement.

#35. (Distribution) What per cent of poles do you typically have to replace on ADSS projects in order to maintain NESC clearances? (Back to top)

Our own experience is a pole replacement rate under 1% to 2% on most projects.

#36. (Distribution) Do you run ADSS on any routes where you have a history of insulator contamination problems? If so, did you consider dry-band arcing in your design? (Back to top)

In North America, dry band arcing (DBA) is not normally a consideration on lines under 100 kV. In areas of heavy pollution, failures have occurred on lower voltage lines in this country in a few rare cases. If your existing distribution plant has insulator contamination problems in certain areas, you should consider analyzing the DBA potential more closely as you would for transmission lines. If warranted, you may want to install a tracking-resistant cable.

Outside North America, reports of failure in lower voltage environments are more common. We have a tech note that goes into electric field effects in detail.

#37. (Transmission) Do you sag your OPGW and ADSS with a dynamometer, sight lines or a stop watch? If an outside contractor installs your cable, does someone from your utility check the sags? (Back to top)

ADSS can't be sagged with a stopwatch. Depending on the particular designs, stopwatch sagging may be possible with most OPGW.

ADSS on transmission lines should always be sight-sagged using sight lines provided by the designer.

Dynamometers are useful installation tools but are subject to certain limitations: their accuracy in estimating tension on the actual section being sagged deteriorates if there are many spans between the dynamometer and the span being sagged. More importantly, ask your installer when he last sent his dynamometer to a certified calibration shop ("a certified what?"). We recently worked on a failure analysis study where 40 miles of ADSS was systematically installed using a dynamometer (but no sight sagging) at tensions 20% to 50% less than specified.

#38. (Transmission) Do you use OPGW or ADSS on your transmission lines? How did you pick which to use? (Back to top)

Both OPGW and ADSS have their place on utility transmission systems. Nevertheless, many utilities are either "OPGW bigots" or "ADSS zealots" because they're comfortable with one product and have either heard bad things or had a screwed up installation with the other product. Either way it's a mistake. For more information on the pros and cons of each, technology advisory subscribers can refer to our tech note on the subject.

#39. (Transmission - OPGW only) Have you had any OPGW failures due to lightning? If so, how many? How did you pick the fault-current rating for your cable? (Back to top)

OPGW, like traditional groundwire, occasionally suffers lighting damage to one or more wires in the outer layer; like traditional groundwire, these spots are repaired using armor rods. OPGW and regular groundwire are, after all, intentionally designed to be struck by lightning and to safely conduct the strikes to ground.

Recently, there's been an undercurrent of negative rumors about outright OPGW failures (not just damage) due to lighting. Yet actual reports are hard to pin down (if it's happened to you, we'd like to know more -- please contact us). We're only aware of 3 utilities where this occurred in the last decade but one of those utilities experienced multiple failures. Interestingly, we haven't heard of any in Florida, the state with both the highest incidence of lightning and the most installed OPGW. Were these failures a result of poor system design or bad luck?

In any event, even with these failures, OPGW's reliability track record remains outstanding.

#40. (Transmission - ADSS only) Do you use corona coils? If so, do your inspectors check to ensure that they've all been put on? Do you use vibration dampers? Again do you check that all get installed? (Back to top)

ADSS installed in high voltage environments can be damaged by corona effects occurring at the ends of the attach hardware. Corona coils prevent this.

Corona coils can be hard to install if bucket trucks aren't in use and the dead-ends are long, since the installer has to lean out far in the air to shove them over the end of the hardware. Vibration dampers also require similar skill to put on if the dead-ends are long. As a result, occasionally a damper or corona coil may be accidentally left off. System acceptance inspection should include a careful check of every span that neither has been left off.

Towers at the bottom of hills should be inspected after heavy ice storms to ensure melting ice has not slid down and knocked dampers off the line.

#41. (Transmission) Is your ADSS cable at or above the elevation of any conductors at any point on any span? If so did you do blow-out checks at your local worst case windstorm and worst case ice storm to ensure the ADSS would not collide with the conductors (and possibly wrap around them)? Did you do these checks at intermediate wind speeds and ice loads? Did you do icestorm blowout checks with both ice on and ice-off conditions for your conductors? (Note, these questions don't apply to OPGW in the normal high position; they do apply if you underbuilt with OPGW or a similar metallic cable) (Back to top)

See our page on transmission design page for more information -- all of these checks have to be made for each span to ensure cable to conductor collisions and entanglements do not occur as they have at some utilities.

#42. (Transmission) If you built with OPGW above your conductors, did you do OPGW to conductor clash studies for both ice on and ice off the conductors? (Back to top)

See our transmission design page for more information -- both conductor icing scenarios have to be checked since resistive heating may or may not keep the conductors warm enough to be ice free.

#43. (Transmission - ADSS only) Did you perform an electric field analysis on all ADSS installations over 100 kV to ensure you won't have dry band arcing problems? If so, did you use isovolt plots or jacket current models or both? Did you correct the isovolt plots for tower line angle and insulator swing angles? Did you use the correct phasing in your model? If it was on a double circuit transmission line, did you run studies with one side de-energized? If another transmission runs parallel to this one in the same corridor, did you check to see if it had an effect on your transmission line? (Back to top)

See our transmission design page. Isovolt plots at a minimum are required for all these scenarios and with the proper insulator and tower angle correction factors. Jacket current analysis is a new analytical technique we also use.

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