October-November 2018 Q&A
Q: We were recently sticking distribution for a small utility when the utilities inspector stopped us for not having safety latches on our hot hoist. We have now been told that OSHA requires safety latches, but we can’t find a rule for that in the OSHA 1910.269 standard. What are we missing?
A: This answer will surprise and confuse some safety folks, so we want to remind you that we are not necessarily advocating the information we provide – we are educating readers on the rules and best practices. In response to your question, you are not missing anything; there is no OSHA rule for our industry that requires safety latches on hooks. Latches make sense. With a latch, connections do not unexpectedly separate. However, hooks under strain do not unexpectedly separate either. Most hooks for hoists have a tab for installing a latch. Many come with latches, and many do not. In hot-sticking applications, it often is difficult to open a latch and remove a hook from a sling. OSHA does, however, have safety latch requirements for some vertical standards that have no effect on utilities.
Q: When does OSHA consider a pole hole an excavation requiring a barricade?
A: It depends on whether or how long the pole hole is open and/or unattended. The preamble has a discussion on pole holes in which OSHA, in a fit of practicality, agreed that if the hole is bored and the pole is set within a reasonable time – being tens of minutes – there is very little practical reason to install fall protection. However, if the hole is large enough that a worker could fall in even with the pole in place, then some measures should be taken. As a contractor, we would ensure spoils were stable and lay 6 to 8 feet of 12-inch scaffold board across the holes between pole and spoils to ensure stable footing and no void large enough that a person could fall through. The other issue is, a hole for what pole? Distribution is not an issue. Transmission starts to need activities for protection like the above. Some transmission holes are 50 inches for a pole that’s only 36 inches to allow for concrete ballast. Those are excavations. We know many contractors that have used half of a round hay-bale feeder from Tractor Supply Co. as a guardrail.
Q: Does OSHA require brushing of a conductor before installing a temporary ground?
A: Strictly answering your question by the rule, no, OSHA does not require brushing the conductor before installing a ground clamp. What OSHA does require is grounding for the purpose of operating the circuit protective device and bonding for the protection of employees to prevent exposure to differences in electrical potential. If you can meet those requirements without brushing, then no, you don’t have to do it. For practical purposes, whether we are grounding or bonding, we are attempting to create a low-impedance path. The consensus standards describe cleaning the conductor, but they are not enforceable by OSHA. For all practical purposes, OSHA would have no reason to cite an employer who is not brushing if the employer could argue that the requirements are met. Electrically, we know that impedance in a circuit carrying current creates a voltage rise across the impedance, and impedance creates resistance to current flow. Both of the conditions raise risks. Lineworkers who understand that do opt to brush. Employers who understand the risks associated with not brushing make brushing a requirement and provide the tools and accountability to make sure brushing is done.
Q: We understand the value and reliability of equipotential bonding when working grounded circuits off the pole and even from buckets. We have a problem, though, during storm restoration when wire is down. Is there a best practice for EPZ on downed lines?
A: Unfortunately, there is no magical installation for equipotential that covers all installations. If we have wire down that is still connected to the system, there is always the possibility of unintended energizing. There are fatal events every year from backfeeds or energizing downed circuits. The problem is the difficulty of equalizing all of the paths when wire or poles are down. It’s pretty easy to create EPZs when wire is in the air. The only way to equalize on the ground is to drag shotguns, jumpers and equipotential mats with you and use insulating overshoes and rubber gloves. I think we would be fooling ourselves if we thought all lineworkers were going to do that, or do it well, under the pressure of restoration. That’s almost impractical. Isolation procedures are probably the best solution. Cut the conductors in the clear at the last standing pole, isolating the downed conductors from the system. That way no grounding is required. You do still have to pull meters and such to keep your innovative customers who use generators from backfeeding you. Once it’s all back up, reconnect in the air where you cut the downed system in the clear.
Q: I am a safety adviser for a mining company. We use a contractor to move and repair our 2400 delta system feeding our machines that use trailing cables. MSHA has no information regarding grounding of delta circuits, and our industrial contractor works these circuits out of conductive JLG lifts. How are they supposed to be grounding?
A: We think we can offer some guidelines, but there is no single procedure that is best for every situation. We find that most utilities with delta systems connect their three phases together and to a driven ground rod when installing temporary grounding. Installing the ground rod improves the operation speed and clearing time of the breaker protecting the feeder. That is important since the current in the lower voltage system often is high. If the fault does not clear quickly, the grounds can overload and fail before the circuit fault current clears. One other thing: When installing the lead down to the ground rod, tie off the cable about 6 to 7 feet above the ground. That 30 to 40 feet of cable connecting the phases to the ground rod will whip viciously in a fault. If not tied down, it will pull the ground rod right out of the ground when whipping. One tie-off will prevent that.
Regarding metal baskets, it’s not typical to use them on overhead distribution, but it’s also not illegal with the right precautions. Until a circuit is tested to be de-energized and grounded, it must be considered energized and worked as if it is energized. Once the circuit is grounded, and if crews are working the grounded circuit from the basket, the conductive basket should be bonded to the grounded circuit to protect the lineworker. Without the bonding jumper between the grounded phase and the basket, an air gap exists. That air gap is a resistance that will produce a voltage drop across the gap if current flows in the grounded circuit. A lineworker in the basket who is in contact with the phase would bridge that gap and likely be killed if the circuit should inadvertently be energized from any source, including induction.
Lastly, you didn’t ask, but there is no practical reason for grounding a lift working a grounded circuit. The phases are grounded by the ground cables. Grounding does not protect workers on the ground. It will simply lower the total impedance across the lift between the phase and earth, increasing the current that could flow in a fault, and raising risk to those in the basket – particularly to those near the lift on the ground. Lifts near conductor should be barricaded, and workers should stay away from the lift while the basket is in the air. Whether the lift is grounded or not, if workers are near to or accessing the lift while the basket is in the air, the lift access points should have equipotential mats or isolating rubber mats placed on the ground for safe access. Workers accessing the equipotential mats need an insulating transition from bare earth to the mat or insulating overshoes.
Q: In the past few years, our utility has begun converting some 15 kV to 23 kV. We have been sticking the 23 kV, but now we want to begin gloving like we do for our 15 kV. There is disagreement over the glove rating requirements from OSHA, minimum approach distance (MAD) and how the definition of multiphase exposure affects glove rating. We found an OSHA interpretation – www.osha.gov/laws-regs/standardinterpretations/2005-09-27 – that seems to say gloves should be rated for multiphase exposure. What are we missing?
A: Regarding the OSHA interpretation you referenced in your question, a key phrase in the text that I suspect is misunderstood is “breach the electrical component of the MAD” as opposed to the MAID. The electrical component is the MAID – or the minimum air insulation distance – and the MAID is the air gap of 1.7 inches for 15 kV. As to how MAD rules of OSHA affect gloves, they don’t per se. If you closely read rules 1910.269(l)(3), “Minimum approach distances,” and 1910.137, “Electrical Protective Equipment,” and the interpretation, you will see that none of the rules about multiphase exposure or the answers in the interpretation mentions gloves. All of the answers are about cover-up. Before cover is installed, there may be phase-to-phase exposure if a worker, conductive device, tool or material can breach the MAID of opposite phases simultaneously. That means if the phases were uncovered, a worker between the phases could touch both of them. For that reason, yes, the cover would be rated phase to phase. Almost all hose and hoods are Class 4. Orange blankets are Class 3 or 4. Plastics are Class 4.
Concerning gloves, once covered, there is no exposure. OSHA maintains that cover replaces the electrical component, thereby eliminating the exposure to gloves. The only way glove rating would be phase to phase is if the worker covered from a position between the phases where he could reach into the MAID – 1.7 inches for 15 kV – and we don’t work that way. If the worker is approaching from the street, and he can’t reach into the MAID from that outside position, there is no multiphase exposure. Class 2 gloves are exposure rated for 17,000 volts. That’s above the 12,470 (relative) phase-to-ground voltage for a 23-kV feeder.
Do you have a question regarding best practices, work procedures or other utility safety-related topics? If so, please send your inquiries directly to firstname.lastname@example.org. Questions submitted are reviewed and answered by the iP editorial advisory board and other subject matter experts.