A few years ago I came upon a crew using 6-inch chocks to hold back a 38-ton crane truck. I told the crew I was happy that they were making an effort at compliance, but I had to ask them, “Why do we place chocks under a truck’s wheels? Is it to comply with our safety rules or to keep the crane from running away?” It was obvious to me that the short chocks would not hold the crane. The driver proved my assumption true a few minutes later. From the cab, with the transmission in neutral, he released the parking brake. The crane easily bounced over the chocks and, unfortunately, hit my pickup truck.
Sometimes I ask similar questions about grounds installed during stringing. That’s because it seems we do not pay as much attention to the value of grounding as we do to the perceived value of an act of compliance. Grounding during stringing plays a very important role in protecting workers; however, that’s only the case if we know why we are grounding and then install grounding so it does what we want it to do.
A Change to the Rules
There was a change in the recent revision to OSHA 29 CFR 1910.269 that went largely unnoticed. The change to 1910.269(q)(2) removed language that dictated locations for temporary grounds used during stringing of conductors in an energized environment. Not only did OSHA remove the specific language that required grounds at break-overs, at energized crossings and no more than two miles apart, but the agency also removed all of the descriptive terms regarding placement of the grounded traveler, such as “either side of an energized crossing and both sides of a crossing that was de-energized and grounded.” Removing the specific language doesn’t mean you don’t have to ground. The industry recognizes that the use of temporary protective grounds prevents injury and loss of life during unanticipated incidents. The standard still has specific performance language that can only be met by the installation of temporary protective grounds. Rule 1910.269(q)(2)(ii) refers the employer to 1910.269(p)(4)(iii) for accepted methods used to protect employees. Rule (p)(4)(iii) is the grounding/barricading/insulating requirement for protection of personnel from equipment contacts.
It is most likely that part of the reason why the language was deleted was to stay within OSHA’s mission of using performance-based language to tell employers what they must accomplish, not how to accomplish it. In addition, OSHA probably realized that in the variety of conditions that exist in the utility world, there is no one simple formula sufficient to establish effective grounding for every scenario, although the agency’s old language was close.
OSHA’s former instructions for grounding were largely based on the consensus standard IEEE 524, “IEEE Guide to the Installation of Overhead Transmission Line Conductors.” IEEE 524 is listed as a reference document in Appendix G to 1910.269. Unlike adopted consensus standards, which have the weight of an enforceable OSHA standard, reference documents are tools an employer can use to develop compliance procedures. The introduction to Appendix G explains it this way: “The references contained in this appendix provide information that can be helpful in understanding and complying with the requirements contained in § 1910.269. The national consensus standards referenced in this appendix contain detailed specifications that employers may follow in complying with the more performance-based requirements of § 1910.269. Except as specifically noted in § 1910.269, however, the Occupational Safety and Health Administration will not necessarily deem compliance with the national consensus standards to be compliance with the provisions of § 1910.269.”
There is nothing complicated about reference standards. IEEE 524 is full of “may” and “should” recommendations. It is a useful tool, especially for individuals developing training and employers developing written work procedures to standardize operations. IEEE 524 is not a training program for employers new to the work. From the employer/compliance perspective, whether or not you use the IEEE standard, you should know what it says. And if you don’t follow the recommendations, you should have a reason why. That is because when OSHA is required to examine an employer’s operation – say, as part of an investigation – they will compare the consensus standard to your work practices and training. Any reference standard like IEEE 524, as a recognized standard published by the industry, is a basis for OSHA to cite an employer that lacks defensible training and procedures. If the agency decided the employer was negligent based on information they reviewed in IEEE 524, they would issue a General Duty Clause citation. In most cases when OSHA has done so, the agency has used language similar to the related standard, if not exactly.
There is an issue with the 1910.269(q)(2) rules for stringing in an energized environment. The rule applies to both transmission and distribution construction. However, accomplishing grounding for stringing in distribution construction is easier said than done. The grounding sheaves are easy to acquire for transmission construction but are not even manufactured in a size or dimension suitable for distribution construction. So first we will look at practical application of grounding and bonding for stringing, and then we will address the issues with distribution applications.
The Energized Environment
An energized environment is one in which an electrical exposure creates a hazard to workers either by induction or the possibility of contact between the conductors being installed and nearby energized systems. Where an energized environment presents a risk to employees, the employer must take steps to protect them by either grounding and/or bonding equipment and the conductors being installed, or by de-energizing, barricading (using guard structures) or isolating those nearby energized systems.
Where the risk is induction from nearby energized systems, the employer is required to estimate the level of induction exposure or to assume the induction level is hazardous (see 1910.269(q)(2)(iv)). The requirement to estimate the level of induction exposure is not difficult for a qualified engineer, but even with assurances that the level of induction could not inadvertently rise above the calculated level due to some unforeseen circumstance – like a transient from another utility’s nearby lines – most utilities and contractors simply provide the induction hazard protective measures. The good thing about the process is that the protections you provide for grounding of the conductors will also provide protections from induction.
The Purpose of Grounding
The purpose of grounding is to cause immediate operation of a circuit protective device. Grounding of travelers is done to ensure that the energized circuit will trip if the stringing conductor comes in contact with the energized phase. Energized circuits are required to have their automatic relay feature disabled so the circuit trips and stays off. The problem with the use of grounded travelers is that too often the connection of the ground lead is not taken seriously, thereby negating the real benefit provided. I have seen hundreds of travelers being connected, and rarely has it not been prudent to stop a crew and explain the importance of a good electrical connection through brushing the studs, clamps or termination point on the structure. This is when understanding what we are trying to accomplish is more important than merely hanging grounded travelers.
Let’s begin with the law of parallel paths. In parallel paths, current flows in every available path inversely proportional to the resistance of the path. Now think of the pull in its entirety. How many grounded travelers are up? In the event of a contact, every grounded traveler is a path and will carry some of the available current. There is also the path back to the tensioner, and in the case of hard-line pullers, that includes the path to the puller, too. When you think of the grounded system in its entirety, the value of properly installed grounds on those travelers begins to reveal the value of low-resistance connections. Those travelers can carry the majority of the fault current, minimizing the levels of current going back to the tugger and tensioner. In fact, I was once on a job when a helicoptered hard-line got into a three-phase distribution feeder. The workers at the tensioner site didn’t even know it had happened, which demonstrates the value of a well-installed grounded pull.
Fault and Induction Current
Grounded travelers provide a number of benefits depending on the conditions. As we already know, grounds help to control fault current. When induction is present, grounds aid in splitting and minimizing induction currents by bleeding current to ground and by producing opposing current loops between grounds. If an induction current is in a left-hand circulation in one loop, the adjacent loop at the intermediate traveler is flowing in the opposite direction at the traveler, canceling out all but the difference in current levels on either side of the grounded traveler. This benefit, of course, depends on the connection.
It is important to recognize that hanging grounds is not an end to all hazards. Whether fault current or induction current, that current creates another hazard along its path to ground. Those ground paths can create step and touch potential hazards at the point of grounding. I recently measured 695 volts and 100 amps on a lattice tower that had transmission phases grounded to it. Those areas on the ground at the base of the structure must be identified, flagged, barricaded or matted to protect workers.
It is obvious that fault currents can be high and a hazard, even if they only last a few cycles. Induction is just as dangerous or perhaps even more so. It will most likely be continuous depending on conditions. Over the years, I have taken dozens of measurements and collected information from colleagues that show induced voltages commonly in the 200- to 600-volt range. In the last few years we have seen voltages in the 2500-volt range. Currents measured are often in the 20- to 40-amp range but can be as high as 80 to 100 amps. When currents are that high, they can dry out the earth around grounds, melt insulation and even start grass fires. If currents like those are encountered, installing more grounding of the affected circuit will split those cells between grounded travelers, lowering the current and usually the open-circuit voltage as well.
By the way, you are going to find induction in crowded corridors. When conductors get in those travelers, they are going to pass current unless the traveler is suspended from insulators. If you steel-sling travelers on conductive structures, those currents will eat through sheaves and bearings. Grounded travelers prevent that damage by providing an electrical shunt around the bearings, preserving those expensive travelers.
Grounding Stringing Equipment
Now let’s take the law of parallel paths to one more level. Bonding of pulling, tensioning and snubbing sites is being taken more seriously by an increasing number of employers. Myriad employers now require a conducting grid, assembled from hog-fence panels, reinforcing panels or chain-link fencing, to be laid out. At the very least, many follow the traditional choice to install a temporary ground rod and ground everything to it, and they install equipotential mats at the access points to equipment.
Employers that understand how a well-installed, good grounding plan can minimize fault currents are taking that electrical path planning one step further. Earlier I described building an equipotential mat upon which all of the equipment sits. The mat is barricaded with designated points of entry that are insulated bridges between the surrounding earth and the mat.
The mat itself consists of conductive panels that are overlapped and clipped. There are various methods employed to assemble the mat, but common among all of the methods is that the mats are in fairly intimate contact with the earth. What is different with many installations is the absence of driven grounds. At first that may sound illegal, but in reality there is no rule that requires them. In fact, as the standard states, it is up to the employer to show that the system employed protects all employees, and if they can’t show that, then they must meet the requirements of rule 1910.269(p)(4)(iii)(C)(1), which mandates “[u]sing the best available ground to minimize the time the lines or electric equipment remain energized.” This rule is usually cited as a requirement to ground equipment and the mat. However, the ground required is the grounded travelers out on the line, doing just that – minimizing the amount of time the equipment or lines remain energized. As for the rest of that rule, bonding equipment together, and using mats and barricades are all met in the installation of the grid as previously described.
The reason we might choose to float the mat makes sense if you go back to thinking about the electrical characteristics of the pull as one large electrical system. In your system, you have several efficient grounding points out on the line. These are grounds designed to handle fault current or induction current. The last path is to the equipment equipotential pad. That path at a high resistance without the installation of driven grounds is a floating plane of equipotential. The mat and equipment, all bonded together, will perform equally well whether grounded or not. Electrically, the floating plane is expected to be a higher-resistance path with less dangerous current on it in case of a fault, since the majority of that fault current will be managed out on the line.
Ultimately there is no single plan that will fit every scenario. The employer must train and equip personnel to be able to anticipate risks and design and install the appropriate system to protect all workers.
Grounding for Distribution Stringing
As I mentioned at the beginning of this article, the rules for stringing in an energized environment are the same whether you are building transmission or distribution. In distribution, the risks are almost the opposite of transmission. In transmission, we usually see more risks from induction as most new transmission stringing occurs in existing rights-of-way. With distribution, the greater risk is contact with existing circuits. In both cases we install guard structures, isolate or insulate, barricade and ground. The difficulty in distribution is that there are no manufacturers that provide grounded travelers in the most popular distribution traveler size. As I understand it, the tension necessary to provide a contact surface for the ground shunt for a distribution traveler is not practical, as it would lift most wire from the traveler sheave. And despite what an OSHA compliance officer once told me, you can use traveling grounds out on the line in place of grounded travelers. The clamp and roller systems used in traveling grounds will not allow passing of socks.
Grounded travelers do not have a specific manufacturing or performance standard. I have been told by manufacturers that they use the fault capacity criteria of ASTM F855 – a standard for grounds – to determine suitable performance for travelers. Manufacturers that build distribution-size travelers have been producing grounding studs for years that are usually installed in the bearing axle shaft. These manufacturers have exposed their devices to fault currents to establish a level of performance that indicates they will trip a circuit in a fault. Once exposed, the traveler is no longer usable, but that is a small price to pay. Employers should recognize that the accessory stud’s absence of compliance with a standard, not to mention a standard that does not apply to travelers, does not make use of the grounding accessory for distribution travelers impractical or illegal.
So let’s ask the question: Why are we grounding? Are we doing it to comply with a rule or to protect employees? Even if your old answer was “to comply with a rule,” kick it up a notch. If you are not grounding, start. If you are grounding, take a look at your process and determine if it needs to be improved so you get the best value out of the task. Be careful out there.
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