Q: We experienced an event that has caused some confusion among crew and supervisors about what we thought we knew about grounding. We were working midspan on a de-energized 345-kV circuit. We drove a ground rod, grounded our trucks to it and grounded the phases to it. Almost immediately, we smelled hot rubber, and then tires started to smoke. Can you help us understand why this happened?
A: That was likely much more serious than hot tires. For the benefit of readers, we spoke with you on the phone, got details and shared opinions. Here is what happened: Your crew was in a right-of-way with very high induction. The ground rod you drove was very high resistance. When you connected your trucks, essentially you made a radial connection from phase to truck through the ground rod connection. In doing so, you loaded very high induction current onto the truck, which passed into the earth across the tires and outriggers. Many utilities by procedure use ground rods at midspans, and often it goes without problems. This is why we stress learning the principles of current flow in grounded systems. If you can ground phases to the very low-resistance static, the induction load is handled without much risk to workers on the ground. If you do have to ground your truck, and there is high induction, a well-driven rod isolated from the phase grounds might be a good choice. If grounding to the same ground electrode as the phases can energize the truck, as happened in your case, dangerous gradients can occur around the truck, and touch potentials between earth and truck can be deadly.
This is why it is important to understand what is meant by OSHA 29 CFR 1910.269(p)(4)(iii)(C)(1) through (4). If a vehicle exposes employees to shock hazards, rules (1) through (4) require grounding, bonding together of trucks, and use of equipotential mats, barricades, and insulation or isolation to ensure workers are protected from touch and step potentials around the equipment. Yes, 1910.269(p)(4)(iii)(C)(1) requires grounding but not without also requiring bonding, matting, barricades, and isolation or insulation. The lesson is, grounding alone does not provide protection for workers. Equalizing potentials and isolation do.
In your scenario, the best option we see is grounding the phases to the system static and positioning the truck so that no conductive part of the boom can come into contact with the phases. Use an observer to ensure boom-to-phase clearances, and if you are required by policy to ground your truck, use an isolated ground rod system.
Q: As we were reviewing our distribution grounding practices, we found a reference from Appendix C to OSHA 1910.269 establishing the system neutral as the definition of “best available ground” to satisfy 1910.269(p)(4)(iii)(C)(1). That sounds like a conflict since we see the system neutral as a current-carrying conductor. What do you think?
A: Your question fits in nicely with the previous inquiry regarding transmission grounding and will allow us to fill in some blanks. OSHA is right and you are right. You also are using the right rule to address the issue. Let’s define the “conflict” for readers before we get to the answer to your question. The system neutral – as you correctly pointed out – is a current-carrying conductor. Under normal operation, a system neutral on a three-phase circuit carries a current equal to the imbalance of the three individual phase currents. On a single-phase line, the system neutral carries the same current as the phase current, less that part of the current that finds its way to earth via pole bonds. Under normal conditions, these currents are pretty low in most cases. Still, many utilities that ground to neutrals have rules prohibiting bare-hand contact with the system neutral, but they don’t have rules prohibiting contact with a truck grounded to the system neutral. That could be a problem, especially in a system fault. In system faults, the neutral often is the sole route back to the substation and is subject to very high currents. A truck connected to the system neutral could experience a high-current charge, creating a high enough voltage between the truck and the surrounding earth to generate a deadly shock hazard.
OSHA was not wrong in the guidance you referenced regarding the definition of “best available ground,” but let’s clarify what OSHA was addressing. You referenced Appendix C to 1910.269, the title of which is “Protection From Hazardous Differences in Electric Potential.” Good for you for reading it; everyone in the industry should do so as the appendix clearly explains OSHA’s intent for the rules in the standard regarding grounding and bonding. You referred to OSHA’s statement defining the system neutral as the best available ground. Look closely at the title to that section: “Ensuring that the circuit opens in the fastest available clearing time.” Here, OSHA is describing the system neutral as the best connection to ensure fast operation and clearing of a circuit that inadvertently energizes a grounded conductor. And OSHA is right. The purpose of grounding is tripping the offending circuit. If you read further, the very next paragraph is entitled “Ensuring that the potential differences between conductive objects in the employee's work area are as low as possible.” In this paragraph, OSHA explains the difference between tripping the circuit with a good ground connected to the system neutral and the requirement to protect workers by bonding in to prevent hazardous differences in potentials. The bottom line is that in every rule regarding grounding for the protection of employees, the grounding rule is immediately followed by language that requires bonding or isolation of employees to ensure their safety.
Q: Our policymakers have a difference of opinion as to when minimum approach distance applies to insulated conductors and using rubber sleeves and when rubber gloves are to be used for workers outside the MAD. Can you help us sort this out?
A: If you are a contractor and a member of the Electrical Transmission & Distribution Partnership, your rules are different than the minimum OSHA requirements for sleeves. The partnership adopted a partnership-wide requirement to wear sleeves when wearing gloves, with a couple of exceptions. The OSHA standard has a pretty broad exception found in 1910.269(l)(4), “Type of insulation.” Sleeves are not required if conductors not being worked on are covered and insulation is installed from a position that does not expose the worker’s upper arms. In addition, the partnership rules are cradle to cradle, whereas OSHA’s minimum requirement is gloves and – if required – sleeves, which are to be put on before the employee can reach into the MAD. Likewise, if the employee is removing gloves and/or sleeves, they must do so from a position where the employee cannot reach into the MAD.
If you are not a partnership employee, you may not know that the partnership adopted the mandatory sleeve rule because of the high frequency of upper arm contacts. Since the partnership established those rules and other best practices also based on high incident rates, they have reported a significant reduction of incidents in those best practices categories. You can find more information on the Electrical Transmission & Distribution Partnership and their best practices at www.powerlinesafety.org.
Q: We recently had a series of knife incidents that has resulted in a call for an across-the-board ban of pocketknives. I have heard this is an OSHA requirement, but I can’t find the rule. Can you point me in the right direction?
A: The rule you refer to does not specifically address pocketknives. It does address the employer’s responsibility to perform a hazard assessment of the workplace and mitigate as much as possible any hazardous conditions that are found. The requirements for hazard assessments are found in 1910.132(d)(1), which states: “The employer shall assess the workplace to determine if hazards are present, or are likely to be present, which necessitate the use of personal protective equipment (PPE). If such hazards are present, or likely to be present, the employer shall …” The paragraph is followed by references and direction to Appendix B on assessments and actions required by the employer. The section on hand protection found at 1910.138 specifically requires actions by the employer if cuts and lacerations are hazards associated with tasks.
Your knife experience and the proposal to prohibit them are not that uncommon. Ultimately, banning personal knives doesn’t solve the problem as much as training reduces incidents and still allows the use of pocketknives. We have found that most utilities that suddenly wanted to ban knives could not point to any specific training they had previously done to educate workers on knife use. An argument against banning knives is the high expense of the myriad types of strippers and safe cutters the employer will need to provide to perform routine work. Still, some utilities have successfully prohibited knives, and workers finally got used to working without them.
Banning knives is a choice requiring re-engineering of tooling to accomplish tasks. In our experience, we don’t see eliminating knives as practical for the reasons above, so when we are faced with an increase of hand injuries – primarily cuts – we recommend a hand protection emphasis program. Train workers, address hazards and proper knife usage, audit crews and hold workers accountable for safe procedures. Get the message out and keep the reminders flowing to the field to support safe practices that will result in a reduction of knife-related injuries.
Q: We have line crews setting laminate poles in holes 5-1/2 feet in diameter and 17 feet deep. Is there an OSHA rule that requires a lineman to wear fall protection while backfilling a hole with material?
A: There is nothing in the 1910.269 or 1926 Subpart V standard that addresses pole holes except 1926.964(a)(3)(iii), which states: “To protect employees from falling into holes used for placing poles, the employer shall physically guard the holes, or ensure that employees attend the holes, whenever anyone is working nearby.” The rule does not specify size of the poles, but we assume OSHA was thinking of wood distribution and transmission poles.
Generally, it’s not practical to use fall protection while backfilling. In most cases, our justification for no fall protection is that there are too many moving parts in the process that could cause trips and falls or ropes getting hooked on moving equipment. I have seen crews use ropes tied off to body belts and truck bumpers to limit travel (shortened so you can’t fall in) as well as portable concrete slabs. Sometimes those ropes are a hazard depending on space, how many people there are and what types of power equipment are being moved around. It also is not practical to have fall protection between the time an auger is removed and a pole is set; OSHA has spoken to that (using observers) and recognizes that as an industry, we have practically no incidents of falls into pole holes. If you are using a large-bit pressure digger, you may need some protection for whomever measures depth. We are aware of crews that went to a Tractor Supply store and got a hay-roll feeder – the kind that farmers put around hay bales in the field so that the bales stay together while cows are eating them. The feeder comes in two parts and is separable and made of lightweight inch-and-a-half tubing. Use a half-section to encircle the pole hole like a guardrail. It’s not too much of a concern on distribution as the holes aren’t much bigger than the poles and you can’t bodily fall in. Transmission typically has a big enough gap that you might fall in, and it would hurt and be difficult to get out, so prevention is the best practice. For all practical purposes, train workers, keep them aware and use an observer who reminds workers to keep off the edge.
Here is another tip we also have seen and used: To stabilize the edge, diagonally overlap 8-foot-long 2x12 boards or scaffold boards across the hole’s edge. Doing so supports the edge so that no one can fall in even if the edge collapses. It takes a little planning with excavated material, but it works.
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