March-April 2026 Q&A
Q: Why does an EPZ pole connection need to be close to the worker’s feet?
A: In an equipotential arrangement, if the bus is inadvertently energized, the length of the bonding cable from the grounded conductors to the structure will affect the voltage across the worker. The worker is only exposed if they contact the phases and the structure at the same time. This is also the case with neutrals floating at a distribution pole and a static on an insulator or swinging clevis at the top of a transmission structure. If they are not electrically bonded to the pole or structure, lethal potential can exist between conductor and structure.
The bonding jumper has the same role when we mach out a system neutral. Two purposes are served by installing a mechanical jumper across the system neutral and then cutting the neutral. First, the system neutral’s current-carrying capability is continued through the mechanical jumper. Second, this creates a bond across the open in the cut neutral conductor, ensuring that no voltage appears in the open that could put the worker at risk.
Total resistance of the bonding jumper across its length will result in a measurable voltage drop across that length. Resistance is determined by conductor size and length and the amount of current flowing across the jumper. Since the bonding jumper is there to equalize potential across the open, the potential that exists across the open neutral will also be the potential across the mechanical jumper.
The same condition applies to the worker on the pole. The voltage that occurs across the length of the bonding jumper between the grounded conductors and the structure is the same voltage that the worker will be exposed to. This is why keeping the jumper as short as possible affects the total voltage that the worker can be exposed to.
Cable-length effect is one of two reasons why most procedures specify keeping the structure bond connection close to the work area. Length produces the resistance that determines the voltage drop across the cable and the worker. Cable whipping is the second reason. If a clamp located 10 feet down the pole is connected to a 20-foot cable, the cable will whip violently during the first few cycles of a fault. This can produce enough energy to pull apart connections and present just as much of a hazard to a nearby worker as poor grounding practices. It is good practice to tie down extra-long cable if you find it in your work area.
Q: Does the configuration matter when grounding three-phase?
A: Yes, but the extent to which it matters depends on the variables that could occur when a grounded circuit is unexpectedly energized. Review this comment published in Appendix C to OSHA 29 CFR 1910.269: “… if employees are working on a three-phase system, the grounding method must short circuit all three phases. Short circuiting all phases will ensure faster clearing and lower the current through the grounding cable connecting the deenergized line to ground, thereby lowering the voltage across that cable.”
Normal or fault current in a three-phase system is still electricity that behaves the same way normally operating three-phase currents do. In a three-phase grounded wye system, the current on the grounded neutral will be the imbalance between the conductor currents in the system. That is what the Appendix C statement above refers to. If we short circuit the three-phase system and it is suddenly hit by a current, the current will circulate within the three-phase system, causing the relay system to trip and open the feed. As with any three-phase system, while the current circulates within it, the imbalance will go to ground in that Y connection. In our case, that’s our ground connection, with – as per the Appendix C statement above – most of the current staying in the three-phase system, thereby limiting the current flowing into ground at the work area. This is an excellent reason to prioritize making the three-phase ground to the system neutral and the bonding connection to the pole between the neutral and pole. The current on the ground connection is distributed across the very low-resistance system neutral and every interconnected pole bond nearby.
Here, the ground cable three-phase current principle applies. The lower the current across the cable, the lower the voltage drop across the cable. Remember, the voltage drop across the cable is the voltage that the worker will be exposed to.
Phase to ground three times is the alternative configuration. A fault in that configuration is still short circuited but in a much longer pathway across the ground connection. The difference is that the short jumper short circuit limits the current to ground in the work area, while the phase-to-ground-three-times configuration passes the available fault current through the work area ground connections.
Q: I’ve noticed that some manual operators stand on grids when throwing substation gang switches while others do not. Are there any regulatory rules about this?
A: Switching grids are discussed as an additional protective method in Part 9.1.3 of IEEE 80, “IEEE Guide for Safety in AC Substation Grounding.” The grid below the surface of a substation creates an equipotential mat for workers. The switch handle is bonded to the structure, and the structure is bonded to the substation grid. Two modes of worker protection are available here. One is the layer of rock under the worker’s feet that creates an insulating buffer above the substation’s equipotential mat grid. For us, in terms of incidental versus intentional protection, there is a big difference between the grid below the substation rock and the visible grid that an operator stands on. The operator is incidentally protected by the substation grid and rock bed, but we can’t see the condition of the grid or the grid connections buried beneath our feet. Alternatively, we can install a conductive grid that is visibly bonded to the structure and handle.
Q: When working in substations, are we required to bond conductive lifts to grounded bus work?
A: Yes. Workers have been killed due to potential differences between bus work and unbonded lifts. OSHA addresses this in 1910.269(n)(3), “Equipotential zone,” which states the following: “Temporary protective grounds shall be placed at such locations and arranged in such a manner that the employer can demonstrate will prevent each employee from being exposed to hazardous differences in electric potential.”
There is almost always current flowing or circulating in a substation’s grounded bus. Raising a conductive lift to the bus extends a path to ground from the bus, down through the lift and into the earth. Insulating barriers to the pathway do exist, such as rubber tires and the substation rock layer, but their efficacy is not guaranteed. With current in the grounded bus and a ground path through the lift, there will be a potential difference between the bus and lift. If the potential is great enough to penetrate the worker’s skin, the circulating current will divide and flow through the worker into the lift. A bonding jumper connection between the grounded bus and the lift will bond out the potential difference, protecting the worker. The same rule applies to conductive lifts used in line construction, particularly where nearby energized lines present induction hazards. Bonding the lift to the new circuit conductors bonds out the potential difference between the bus and the lift path to ground.
Q: Can you explain the rule that requires utilities to install “High Voltage” signs on their jointly owned wood poles?
A: Utilities are required to post warning signs where unqualified individuals could access their facilities. Signage is mandatory where access points are located at or near ground level and could easily be breached (e.g., substations, vault doors, aerial banks on ground-level pads).
The ANSI Z535 standards don’t specifically call out when signs are required, but they do state that where a fenced-in facility contains exposed electrical equipment, signage must be legible at a safe distance from the hazard. So, no standard spacing exists. Compliant installation is based on an observer’s most likely angle as they approach the fence. For instance, signs every 50 feet would be noticeable where an observer approaches from an alley with a broad view of the fence. However, if the observer approaches through an ornamental hedge located 5 feet from the fence, there is a good chance they would not see the signs.
Section 110 of the National Electrical Code contains requirements for conspicuous signage on entrances to guarded rooms and other locations. The signage must warn unqualified individuals against entry. Part C of NEC Section 110 states the same criteria for high-voltage enclosures. The National Electrical Safety Code requires safety signs at substation gates and entrances and on the exterior lengths of substation fences and walls. NESC Part 217 addresses “readily climbable” structures, which include lattice with braces that can be used as steps and climbed by almost anyone. These structures require barriers, plus safety signs above the barriers that indicate the electrocution hazard.
Unless a utility pole has steps installed at ground level, it cannot be readily accessed by anyone other than individuals who have been trained to recognize the hazards noted above. For that reason, warning signs are not typically required on poles and similar structures. It is the owner’s responsibility to determine whether untrained individuals can access their facilities.
Do you have a question regarding best practices, work procedures or other utility safety-related topics? If so, please send your inquiries directly to kwade@utilitybusinessmedia.com. Questions submitted are reviewed and answered by the iP editorial advisory board and other subject matter experts.