Q: We have a group reviewing our personal protective grounding procedures, and they are asking if we should be grinding the galvanized coating off towers when we install the phase grounding connections. What are your thoughts?
A: In addition to your question, we also recently received another question about connecting to steel for bonding, so we’ll address both questions in this installment of the Q&A. Your question is about the effectiveness of grounding to towers, and the other question is about the effectiveness of EPZs created on steel towers. We’ll discuss the grounding question first and then move on to the EPZ question.
As to grounding effectiveness, we have two thoughts here – one simple and one that likely will raise more questions than we can resolve in these pages.
The simple thought is this: Consider grounding to the circuit static. It’s difficult to reach but doing so makes it easier to create an electrical connection. Using the system static shares current with adjacent structures and reduces current on the structure being worked. Dividing current among adjacent structures also reduces ground potential’s risks to workers at the foot of the tower. See the following Q&A regarding EPZ if you are grounding to the static.
As to connecting to the tower, grinding off the galvanized coating opens the underlying steel to corrosion and would need to be replaced after the operation. We have asked how utilities make connections and found that most use a flat clamp to a brushed plate or insulator bracket, or a C-clamp to a brushed bolt or step. Either method is a good one. Others follow one of the recommendations in IEEE 1048, “IEEE Guide for Protective Grounding of Power Lines,” 22.214.171.124 for lattice using a ground cluster. The cluster serves two purposes: providing a clamping connection and keeping the clamps close together.
Fortunately, the structure connection can be installed by hand, making the cleaning and mechanical security of the connection pretty reliable. There are several considerations to discuss that should be part of the training provided to lineworkers who make these connections.
The first consideration is that every ohm of resistance built into the grounding scheme increases heat in the circuit, voltage divisions where parallel cables are used and voltage drops across resistances that can cause electrical shock to workers. From a practical standpoint, control what you can to reduce potential issues. What we can control is the integrity of the grounds we use, and we can ensure that paralleled sets are built with exactly the same components, are the same length, have the same resistance and are clamped closely together at the terminal points. Now all we have to deal with is the ground path of the tower.
The only way to remove resistances between mechanical interfaces on a tower or steel pole is to install a jumper parallel to the pole to overcome those resistances. Lately we have been seeing new designs that install bonds across slip joints and between tower and arm interfaces. Installing a parallel temporary bond can create its own issues in extreme cases, such as a current division between the higher-resistance tower and parallel ground, voltage drops between the tower and ground electrodes, and step potential hazards. These can be reduced by connecting each end to the tower, but that won’t remove the voltage difference that may develop between tower and cable, since ground cables are not insulated for voltages that may develop in a fault.
We agree with IEEE 1048 126.96.36.199 that in most cases, the tower’s steel mass can overcome the issues of current flow across those resistances. The assumption is that the mass of steel and number of connections, even if not electrical, are sufficient for conducting fault current that can be coupled to the tower through the grounding connections. Still, IEEE 1048 188.8.131.52 suggests periodically measuring resistance between slip joints to assess resistance-created risks. We are not aware of any utilities that do this, but we do know many have consulted with steel pole manufacturers who have performed weathered resistance measurements as part of their design criteria.
To wrap it all up:
• Experience from utilities indicates that most assume steel structures are sufficiently conductive to be used as a grounding connection, but it is worth measuring resistances across joints to calculate voltage drops.
• Construct, test and connect grounds to maintain the least resistance possible in the grounding connections.
• Consider when ground connections to a static would be preferable over connections to the tower.
• Conduct training on the limitations of each possible connection and the hazards created by grounding for workers in the air and on the ground.
Q: How effective can an EPZ be if phases are bonded to a steel lattice when the tower has resistances between the galvanized mechanical connections of the lattice itself?
A: In most cases, an EPZ connection to a steel structure will not be affected by the continuity of the tower’s mechanical interfaces. There are some considerations that need to be addressed depending on how the grounding scheme affects the EPZ scheme. Remembering that the grounding scheme is for the purpose of tripping circuit protective devices (tripping grounds), and the EPZ is for the purpose of protecting workers from differences in electrical potentials (personal bonding), how you mix the two makes a difference. If the grounds are installed in an arrangement to also create a zone of equipotential, then size, manner of connection and location of cable and connections should be assessed for hazards created. We addressed these issues above in our answer to a question about grounding on towers, so we won’t repeat them here. Now, if the tripping grounds, sized to effectively handle the maximum available fault current, are installed more remotely – such as to the system static – the bonding cable connections for creating an equipotential zone are less problematic. The difference is the current-carrying capacity of the tripping grounds in the near vicinity of the EPZ, as well as what happens in a fault to the cables and connections resulting from the tower connections.
If tripping grounds and the EPZ bond are in separate connections, there will be a division of current between the tripping grounds and the EPZ bond. The desired case is that the tripping grounds manage the greater part of the current than the bond connection. Ultimately, this lowers the current available in the bonding connection, and that is a good thing. The work area itself will have some resistances between mechanical interfaces, but that current is going around and away from the work area. The purposes of the bond are to ensure the phase voltages and tower voltages are equal, and the series of resistances represented in the mechanical interfaces between the EPZ and remote earth are not affected. In that way, any voltage potentials within the EPZ would be very low so as not to create a risk to workers.
Q: We still can’t determine when digger derrick operators must be licensed crane operators in accordance with OSHA’s “Cranes & Derricks in Construction” exceptions. Is there any change in the utilities exemption status? We have heard conflicting things.
A: There is no change in the OSHA rules for crane operators under the federal rules found in 29 CFR 1926.1400. November 10, 2017, is the effective date for all crane operators to be third-party licensed. Under the federal plan, digger derrick operators for utilities and communications are exempt as long as they are setting poles with a digger derrick and hanging appurtenances that are normally attached to those poles. That is not the case for many state plans that still require digger derrick operators to be licensed just as crane operators. If you are under a state plan, it is important that you find out if your digger derrick operators are exempt.
Now, there are limits to the exemption under the federal rule. Paragraph 1926.1400(c)(4) clearly states that the subpart does not cover the following: “Digger derricks when used for augering holes for poles carrying electric or telecommunication lines, placing and removing the poles, and for handling associated materials for installation on, or removal from, the poles, or when used for any other work subject to subpart V of this part. To be eligible for this exclusion, digger-derrick use in work subject to subpart V of this part must comply with all of the provisions of that subpart, and digger-derrick use in construction work for telecommunication service (as defined at Sec. 1910.268(s)(40)) must comply with all of the provisions of Sec. 1910.268.” We have often heard the claim that the portion of the rule that states “or when used for any other work subject to subpart V of this part” is an exemption for structural steel and foundations in substations because substations are included in subpart V. That’s true, there is a title for substations in subpart V, but the substation section does not cover structural steel or foundations, so it is not part of the exemption. In the preamble to the final rule, OSHA clearly spelled out their intent for the use of the digger derrick exemption. In 2013, OSHA directly answered the industry’s request to exempt all digger derrick use from the cranes and derricks standards with a well-explained “denied.” To read the discussion for yourself, go to Federal Register Vol. 78, No. 103, Wednesday, May 29, 2013, “C. Agency Decision to Issue a Final Rule.”
As OSHA has stated, using a digger derrick to lift items other than poles and related equipment is work normally performed using cranes and does not entitle the operator to the licensing exemption. OSHA did expand the exemption in 2013 to include padmount transformers, but the agency maintained that substation work, normally handled by cranes, would not be included in the exemption. OSHA also warned that if they found that utilities and contractors were expanding the use of digger derricks to do work previously and normally performed by cranes, they would revisit the exemption. Be assured that OSHA’s warning to revisit is not to further expand the exemption. The agency’s intent is to provide a limited exemption for poles and underground padmount transformers. If we cheat, they are warning us that they will rethink and remove that exemption.
Q: What is the safest way to open substation gates if it appears that the grounding has been stolen?
A: That depends on whether the grid below the gates has been pulled up or if the thieves only removed the leads from the gates to the grid. If they only removed the leads, the problem might be solved by installing a bonding jumper across the gate opening before you open it. Doing so will bring both gates to an equal potential. If there is concern that the ground grid below the gate is gone, you need to accommodate the possible step potentials that might occur. There is no standard or official guidance on how to do that, but one of our consultants made an interesting recommendation. Keep in mind that you have to make a determination for yourself if this is a solution. This is not a solution offered by Incident Prevention, only a discussion in principle. The suggestion is to create a temporary equipotential grid using what many use to build equipotential grids for pulling sites. Hog panels are 16 feet by 50 inches and constructed of #4 steel welded in 2-inch-by-3-inch mesh. Attach jumpers to the side that will be at the gates. Drop the panel in place and access the panel as you would any EPZ mat. Use a shotgun to attach the jumpers to the fence. When you first access the grid, it will be a floating plane of equipotential. Once connected to the fence, it will now be at the same potential as the fence and gate and likely earth as well. Any solution needs to be well thought out against the identified risk. There are a number of things that can be used as a system of protection in such a scenario, including rubber gloves and insulating overshoes.