Train the Trainer 101: Practical Recommendations for Wire Stringing
In the last installment of “Train the Trainer 101,” we discussed grounding when stringing in energized environments (see http://incident-prevention.com/blog/train-the-trainer-101-grounding-for-stringing-in-energized-environments). Many readers responded with questions regarding the myriad issues they have faced during stringing. I learned a lot about this type of work during my first 25 years in the trade. In stringing hundreds of miles of conductor, I am proud to say I never dropped wire. I also have to say it’s most likely I have that record because I learned a great deal from other workers’ accidents. In fact, I am seriously afraid of dropping wire. Stringing incidents are some of the most dangerous in the trade, not only risking the lives and limbs of line personnel, but creating a serious risk to the public. Over the years I have heard of or investigated every kind of incident, including one in which a phase dropped during clipping, shearing off 26 side-post insulators before the carnage ended. Wire ended up across school driveways, shopping center parking lots and intersections. More than 40 cars suffered damage and dozens of people reported injuries. I’ve seen wire dropped across interstates and rivers, and it always happens at the worst time. You’d be surprised how much damage 1272 can do to a luxury boat. So, the remainder of this installment of “Train the Trainer 101” will focus on some recognized issues and tips that might help prevent future disasters when stringing goes bad.
Training and Qualification
Every crew that pulls wire should be sure that workers are trained for the procedures to be employed and experienced with the pulling or tensioning equipment on the right-of-way. No lineworker wants to admit he or she has never run a bull-wheel tensioner, and learning by error does not go well with three miles of 1590 in the air.
Training was the topic of a panel discussion at the iP Utility Safety Conference & Expo, held earlier this year in Orlando, Fla. Many attendees told us that until they attended the discussion, they didn’t realize they had a problem, or at least a problem meeting the requirements of OSHA’s new rule. The agency now compels employers to witness an employee’s demonstrated skills related to the safety of assigned tasks before the employer can allow that employee to work. That’s not going to be easy to accomplish, but if it’s done right, there won’t be so many “He did what?” moments in the field.
For utilities, most lineworkers’ skills are understood because they are longtime employees. The employer knows who is best at operating that tugger or tensioner. In other words, if you, as a lineworker, have never been given the responsibility to run the tugger, that may not be a coincidence. For contractors, longtime employees are fewer in number. The employer must find a way to verify a new employee’s skills before they put millions of dollars in liability into the new employee’s hands.
Do not hesitate to seek the advice of your operators’ manuals in order to properly operate your tuggers and tensioners. There are now tensioners that are controlled by microprocessors and even sync to the reel stands, drag-feeding them for precise tensioning control. This is no place to try the “smoke test” training model. You know what I mean – the training during which the amount of smoke you generate tells you how far off your guess was.
Now, about stringing: IEEE 524, “IEEE Guide to the Installation of Overhead Transmission Line Conductors,” is a good place to begin if you are going to review your procedures. This consensus standard contains a collection of best practices developed from years of experience. As with all of the consensus standards, trainers and safety personnel should have a copy of IEEE 524 in their library and use it as both a reference and to develop training standards.
Although this article is not a synopsis of IEEE 524, I do want to recognize some key guidance necessary for success in pulling. As I mentioned earlier, the April 2016 installment of “Train the Trainer 101” focused on grounding and stringing in an energized environment. Section 5 of IEEE 524 contains some practical advice for installation of protective grounds. I want to use this opportunity to repeat and reinforce warnings and guidance about protecting workers from electrical hazards, but I also want to point out an important concept about the mechanical integrity of equipment. As Section 5 of IEEE 524 points out, it is important to inspect and maintain travelers for electrical protection. I have an additional practical observation: Poorly maintained travelers are subject to overheating. Heating of the traveler from current flow damages the axle pins by cooking out the grease. Damage to an axle adds drag. Adding drag increases pulling tension and creates fluctuation in pulling strains on all the devices in the pull. That raises risks.
I advocate a small shot of grease every time a traveler comes off a structure. More importantly, you should take the time to inspect every traveler when you take them down after a pull. True, you should inspect them before you hang them, but practical experience teaches this lesson: When you are four miles from the lay-down and find a traveler that makes a periodic grinding sound when you spin the sheave, it is probably going up on the structure instead of making the trip back for a replacement. If crews inspect travelers and tag them out for maintenance when crew members are stripping the pole, the traveler is more likely to get the maintenance it needs, which reduces risks.
Speaking of currents on sheaves, I sometimes see travelers suspended from steel using steel slings. This is a good way to eat up a sheave and sheave axle bearings, as the conductive path created by the rigging allows destructive currents across those mechanical surfaces. Ideally we hang travelers from the string, isolating them from induced currents. Sometimes clearances or pull dynamics prevent string supporting of travelers, so travelers get sling-supported off the grounded structure. The solution is to use a grounded traveler that will electrically shunt the current around the sheave, or insert a single bell in the rigging between the sling and sheave. Always take into account the electrical path being created by the traveler installation.
One last thing about traveler-related risks: In heavier weights, wire in a traveler for an extended period of time can damage bearing races, which produces drag. Any drag increase from bad bearings, too much angle over the sheave from low sag and bad sheave support at corners increase pressure on equipment. When wire bounces or over-tensions from excess drag, you increase risks for rigging failures.
Snatch blocks are typically used to adapt angles for pulling ropes to accommodate the lack of space at pulling setups. Generally at the break-over – which is usually the first pole away from the tugger (or tensioner) – the expectation is setting up 3:1. In other words, multiply the height of the traveler times three; that’s the distance the puller should be from the break-over pole. There are several reasons for this, and not knowing why 3:1 is important can get you in trouble. If you set up less than 3:1, you increase strains, including one that can lift the tugger off the ground or at least lighten the front end toward the pole, allowing it to move. Two other reasons that can be as risky are added weight on the break-over structure and stresses on the tugger’s level-wind.
If that angle can’t be made, you can sometimes do a reverse angle pull during which you set the puller out of line with the pull and accommodate the change in angle using a snatch block. Snatch blocks get more stress than travelers because of how they are rigged. Often the stress on the snatch block is overlooked or underestimated. Snatch blocks can be very expensive, usually running $600 to $1,000 dollars or more for transmission-rated loads. I know from performing root cause analyses that the cost, size and weight of snatch blocks affect selection. When cost or convenience affects selection, snatch blocks may not be right for the application. On more than one occasion, inappropriate rating for a snatch block has been the root cause for loss of rigging. The reason: It was smaller and lighter and “we thought it would work.” When you reduce the safety factor and then experience an unexpected condition, you have rigging failure.
A final comment about snatch blocks: I see lots of them in use far beyond the sell-by date, and often they are related to lost wire. As I mentioned earlier, snatch blocks often get overlooked. As with slings or hoists, they should be subject to a tracking program. It may be as simple as indicating the date the snatch block was put in service or adding a hash mark for every job during which it has been used, or it might be as detailed as cataloging and keeping a history. Whatever you choose to do, be sure to have a method of verifying integrity to reduce risks. Snatch blocks do fail, and they add drag and strain when they get worn. Get them off your job before they become a problem. When it comes to buying snatch blocks, $1,000 might seem like a lot, but it’s far less than the cost of losing wire in a pull when a snatch block fails.
I am a firm believer that nylon slings should not be used in rigging for stringing. Nylon is used to prevent scratching or damaging the weather coating or galvanizing on steel poles. Sleeving slings are a solution. There are several types available that will protect the surface you are wrapping, allowing you to use steel and not damage coatings.
In the utility industry, steel slings are used in numerous ways and often are wrapped on small-diameter points if choked. These rigging requirements kink slings. Kinked slings are supposed to be removed from service, but they still get used. I hear the excuse that they are new and hardly used, and that they are rated four times what the sling load will be during the pull. That is a risk. Slings are expensive and crews hate to throw them away. But – like snatch blocks – new slings are a lot less expensive than failed rigging. Begin every wire-pulling mobilization with a truck-by-truck sling inspection. Remove slings that show any damage.
Towers have come down when crews have chosen to snub off their pull on the lattice, and not all of those towers were old and fragile. The same thing has happened with poles. All structures are designed for a vertical load concentrated at the insulator anchorage and uniformly distributed through the structure. Thinking a steel structure will hold a lot of weight is an easy mistake to make. Snub weights for two miles of 795 can easily exceed 4,000 pounds. Imagine what three, three-bundle phases of 1590 can do to a poorly chosen snub. Snubs should be designed by a competent person. My preference is to build log anchor snubs. The anchor’s extensions are rated, basket-rigged steel slings trenched into a groove, keeping the wall of the log trench undisturbed. I have only heard of one coming up out of the ground. It was an economical design installed with one log used for both directions. Not surprisingly, when it rained overnight, the log pulled straight up out of the ground. Log snubs are still used today as anchors for permanent systems. Build snubs using new engineered components and they won’t let you down.
Grips and Socks
As with snatch blocks and slings, pulling socks may seem expensive, but they cost much less than dropped wire. I have found in the past that socks on strand seem to fail more than socks on wire. I also have seen a tendency for the sock to fail in the weave just below the braids at the eye. The issue may be the tendency for strand to curve. Strand is hard and cut edges are sharp. Strand is usually pulled on smaller travelers because it simply does not bend like aluminum wire. However, if strand is pulled too sharply, the end of the strand is pushed into a hard angle against the weave of the sock. This can promote damage to the weave from that sharp cut end on the strand. Curl is another likelihood. If there is any curl in the wire, it does not necessarily straighten out under the tension of the sock. Even the slightest bend at the leading end of the strand can poke a hole in the weave, and bumping against the sheaves entering the traveler can result in failure of the sock. Taping the end of the strand with friction tape softens it; this also may prevent damage and ultimately a failed sock.
Another issue with socks on strand is using the same size band on the strand sock as used on the conductor sock. Look closely at the length of the keeper on the banding. If it is wider than the strand, the keeper will not sufficiently tighten the sock on the strand and will not do its job, which is to drag the weave back and ensure it tightens and holds the strand.
Finally, do not succumb to the temptation to use preform guy grips for pulling strand. This is bound to fail for one big, unavoidable reason. Preforms are heat formed. The eye of the preform is twisted strands uniformly bent to match the head of an anchor. If you connect the preform with a swivel of narrow diameter, you will elongate the preform eye out of the designed dimension. Once the eye is deformed, the strands in the grip come out of alignment. When that happens, they are no longer in intimate contact with the wire strand and will fail. Dropping strand is just as risky as dropping wire. Using a preform as a pulling sock is a sure way to do it. It is important to mention that manufacturers don’t approve of using their preform grips for pulling.
Stringing and Communication Plans
A stringing plan and a communication plan are the last two things I recommend as keys to a successful pull. The stringing plan should take the crew through a systematic examination and verification of every element necessary for a successful pull. It should verify wire dimensions and grip numbers through crossing preparations and grounding preparations, structure by structure. A drive-through the length of the pull is the last thing that should be done; the stringing crew supervisors should perform this task using the stringing plan in order to visually confirm that the pull is ready.
The communication plan begins with a description of expected speed and pull pressures. If there are difficult sock passes, such as corners, the communication plan should include whether or not you are going to slow down as well as the language you will use to accomplish that slowdown. The communication plan also should include a discussion of the procedures following the sock, including the count into the structures and out of the sheave. Counting into the structure is important because the entry into the structure usually creates some bounce in the conductor. Counting into the structure helps observers to know when a bounce is expected or when the bounce is caused by some other difficulty. A complete communication plan is just as critical as the integrity and rigging of the pull’s mechanical components. I’ve seen pulls fail simply because a misinterpretation of radio traffic resulted in out-of-control conditions and lost wire.
These may seem like simple recommendations, but they are associated with mistakes commonly related to pulling accidents. Yes, implementation takes time and might cost a little money, but it will be less expensive and time-consuming than dealing with the aftermath of dropping wire across the interstate.
About the Author: After 25 years as a transmission-distribution lineman and foreman, Jim Vaughn has devoted the last 18 years to safety and training. A noted author, trainer and lecturer, he is senior safety manager for Global Energy Solutions Inc. in Baton Rouge, La. He can be reached at firstname.lastname@example.org.
Editor’s Note: “Train the Trainer 101” is a regular feature designed to assist trainers by making complex technical issues deliverable in a nontechnical format. If you have comments about this article or a topic idea for a future issue, please contact Kate Wade at email@example.com.