Q: Why do some experts say ground rods won’t work to trip a circuit?
A: The experts say this because they are right depending on the conditions, which we’ll soon discuss. But let’s start with a definition of the idea of “remote ground” as the point at which we connect a protective system to earth. The lower the resistance of that remote ground connection to earth, the more current flows and the faster a fault clears. So, what we should be doing as a rule is using the best available ground to remote earth. The problem is that we often overlook a key element in this debate, which is that the ground source is not what protects the worker. The ground path trips the circuit. Bonding the worker into the ground scheme – the path between the fault and ground – is what provides reliable protection for workers using personal protective grounds. For example, if you ground to a system neutral, you have connected to a very low-resistance path, but you also are connecting to a current-carrying conductor. If workers are not bonded into the ground scheme, they can be exposed to current from the neutral that can result in voltage rises across the ground scheme, especially if a fault current rises on the neutral from some remote event on the system. If you are on a delta primary system at a transformer bank, that neutral on the secondary side is derived from the ground rod at the foot of the pole. Nobody would take their truck ground up to the neutral bushing of a 300-kVA 277/480 bank, but that’s no different than connecting to the ground rod bonding that 480-VAC neutral to earth. That is why delta system workers use ground rods, and to good effect if the conditions are right.
Regarding conditions, a ground rod’s performance is very much related to earth conductivity and earth density when the rod is initially installed. If the earth is clay and not too dense, vibration during an impact install of the rod creates air gaps along the rod, affecting the connection. One reason some utilities turn down those auger-tipped temporary rods is to overcome that problem. The next condition is voltage and current needed for relaying. If we have an idea of the resistance of the rod, we can estimate the current that will initially flow in a fault. Let’s use some pretend numbers to explain the limits of the ground rod. If a feeder relay scheme is based on a load characteristic, the load fluctuations affect the programmed speed of relaying and trip. A 12-kV circuit where several sawmills have high-current load shifts may have long time-over-current (TOC) settings. A truck in a phase connected to a ground rod might only result in a 180-amp current rise on the phase. The circuit may not even trip but at the very least may result in a delay due to the TOC setting. On the other hand, a sudden rise of 180 amps on a 138-kV would likely trip any transmission circuit. We have never seen a pole butt pulled that didn’t have moisture at the bottom, so we have always used the pole ground rod to ground a truck. Incident Prevention’s Q&A consultants agree that we know of many examples of ground rods tripping circuits, especially in those delta primary utilities. However, the best connection is the one that will trip the circuit quickly. That’s why OSHA explains in Appendix C to 29 CFR 1910.269 that the system neutral, if available, is the preferred ground connection. But don’t forget, grounds trip circuits. It’s the bonding in of the worker that protects them during the fault while the ground trips the breaker, making the circuit safe.
Q: We have been grounding two-bundle transmission phases, with one ground jumper on each phase to the ground point. We have been advised that it’s not a good idea, something about asymmetrical current and spacing of the cables. Can you explain?
A: It’s not a good idea, and asymmetrical current is a large part of that. Almost all utility faults are asymmetrical because of the different values of phase impedances in the typical utility circuit. This asymmetrical period of the fault lasts less than a few cycles, but that time period can result in much higher currents than calculated in a straight steady-state Ohm’s formula. The industry has learned that this asymmetrical current divides radically across parallel conductors when the connections are spaced apart from each other. According to some high-current research we have seen, the offset of current can be as high as 90% if the ground clamps are spaced 10 inches apart. That alone would result in a thermal failure of one of the cables in a high-current fault. Yes, we know that subconductors are bonded together through common hanger and dead-end yokes and through spacers, but those are mechanical interfaces with no known electrical rating, and often they are far from the work site. Bond the subconductors together and then attach your ground or grounds to one of the subconductors. If you use parallel grounding sets, make sure they are the same length and conductor size and built the same. Most importantly, shoulder the clamps side by side on the phase connection. For more information on asymmetrical phenomena, paralleling, thermal and mechanical dynamics, and derating of ground cables, see the appendices to ASTM 855-20, particularly Appendix X5. You can purchase the 855 standard at www.astm.org/Standards/F855.htm.
Q: As an old transmission lineman, I really appreciated the great cover photo of the crew spreading phases on hot sticks. Where do you get your photos from?
A: Thanks for the comment. The photo on the cover of the December 2020-January 2021 issue of iP was from a live-line hot-stick methods recertification session for the linemen at Southern Electric Corporation of Mississippi, who were working on the Entergy system. The photo came from trainers Tony Boyd and Jim Vaughn of the Institute for Safety in Powerline Construction in Alexandria, Louisiana. All of the photos used on iP’s covers are original photos from our writers, editorial advisory board members and other contributors. iP uses high-resolution images that are vertical in orientation and have enough space to include headlines. All of the photos used must be original art owned by the submitter, and they must be approved for publication if any company names, copyrighted logos or individuals are identifiable.
Q: Thanks to iP for the article on arc flash, COVID-19 and face masks. Is there an issue with us wearing cotton masks on the job?
A: In our industry, we can’t just hear that masks are required and don them. We have to examine the work environment and identify the risks. There are now face masks, face shields and balaclavas rated for flame resistance, but part of the issue with masks is whether they will melt or continue to burn if exposed to flame. The data that is currently available regarding the efficacy of masks is so controversial that we tend to look at the problem from a practical perspective. We think that it probably depends on the nature of other protection being used that might reduce the exposure. For instance, if you are wearing a face shield that is arc-rated, you probably are wearing an arc-rated balaclava, so there isn’t much point in wearing a mask. If you are outdoors, the exposure numbers we have seen indicate that work-environment exposures are very low without workers in face masks. From that perspective, if wearing a mask in an energized environment creates a greater injury risk than not wearing the mask, you may need to look at your policies. Certainly, a balaclava is not rated like a mask, but according to the data on effectiveness that we’ve seen for masks, the balaclava must have some protective value. If you are not in a face shield, a face shield is not required by 1910.269(l)(8)(v)(C) if the open-air exposure is less than 9 cal/cm2, which is below arc flash category 2. If your employer says you must wear a mask, then your choice is limited to arc-rated if you consider your mask to be clothing; that’s because of rule 1910.269(l)(8)(iv), which requires the employer to ensure that the outer layer of clothing worn by an employee, except for clothing not required to be arc-rated under paragraphs (l)(8)(v)(A) through (l)(8)(v)(E), is flame-resistant.
Q: We have a work situation that requires us to lift certain materials over a feeder to get the materials from the street into the work area. We have an easy 30 feet of clearance over the feeder between the load and the conductor. Is it permitted to lift over the energized line?
A: There is no reason that you cannot lift materials over a feeder. The only standard is clearance between the load, load line and the crane itself, and in our industry, that is further defined as an operator who is qualified versus an unqualified operator. An electrically qualified operator meeting the requirements of OSHA 1910.269(a)(2) can lift a load with the circuit voltage minimum approach distance as minimum clearance. A non-electrically qualified operator who is not trained to the (a)(2) standard has the 1926 Subpart CC “Cranes and Derricks in Construction” clearances to maintain. Per 1926.1408, Option 2 ((a)(2)(ii)) is to maintain 20 feet and Option 3 ((a)(2)(iii)) from Table A is to maintain 10 feet with several other requirements. If you have 30 feet of clearance, appropriate rigging, and a lift plan that clearly defines the pick, path and location for the set, and all are outside the 20-foot clearance of any part of the load, hook and load line, there is no reason not to proceed.
Q: Do you have any updates regarding COVID-related OSHA citations?
A: In December 2020, OSHA issued over $7 million in fines to employers over COVID-19 infections of employees. More than 99% of those have been in major cities and were mostly to hospitals, care centers and nursing homes – but not all of them. The citations were based on:
The outcomes against employers are not settled, and many will contest the OSHA charges. Employers need to understand that they have a duty to evaluate workplace exposures, and that includes communicable diseases in the workplace. There are two modes of exposure recognized by OSHA that are treated differently. One is where the workplace requires workers to be in exposure contact with COVID-19-positive patients. The utility industry falls under a coincidental exposure brought into the workplace from outside, such as through family or other social exposures. Exposure is exposure. The COVID-19 threat is real, and contagion could be engendered as a result of the workplace exposure if the employer takes no action to protect employees from the relative hazard.
The likelihood is that if the utility employer is following Centers for Disease Control and Prevention guidelines, as recommended by OSHA, any workplace exposure is likely to be from outside the workplace. The OSHA test for workplace exposure that makes it a recordable is the assumption that a person sick at work was sickened by the workplace. The presumption is, as OSHA writes, “rebuttable” when symptoms merely surface on the employer's premises, where the symptoms are the result of a non-work-related event or exposure off premises. Since all employees have more time away from work in family and social exposures, the assumption is rebuttable and therefore not recordable, especially if the employer orders and enforces CDC protective measures of hygiene, disinfecting public surfaces, social distancing, limited intrapersonal contact, and covering the nose and mouth.
Employers also should write and publish an assessment of the COVID-19 transmission hazards in the workplace and protocols and practices to be employed. The employer should publish and erect poster-type signs or reminders in public access areas. Lastly, the employer must strictly enforce the policies. Several of the high-dollar fines went to employers who had policies but clearly failed to enforce them. There also must be assessment protocols and mandatory and enforced off-work policies for anyone who shows symptoms of COVID-19.
If your workforce has an infection rate equal to or, even better, lower than the per-capita infection rate of the local area, your program is working. There are generous resources available at www.astm.org/READINGLIBRARY, where ASTM has made all of their COVID-19 PPE standards free to the public. Take advantage of those resources and do thank ASTM.
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