Equipotential Grounding is the Law

I’ve written about equipotential grounding for Incident Prevention magazine dozens of times over the past 15 years, both in this column and in the Q&A. Those articles have had thousands of views on Incident Prevention’s website, which suggests that their messaging should be getting through to industry employers and lineworkers – but my experience says otherwise.

As I’ve mentioned in past articles, my consulting work includes serving as an expert witness in the litigation of both OSHA and civil cases. I’ve consulted on more than 40 cases overall; currently, I have 16 open fatality cases. These facts put me in a unique position to know exactly what is killing our lineworkers, no assumptions necessary. Most disturbing to me is that in more than half of my consulting cases, the lineworkers were killed by the grounding that they’d installed for their protection.

I want to take a moment here to repeat that: In more than half of my consulting cases, the lineworkers were killed by the grounding that they’d installed for their protection.

Yes, my colleagues and I at the Institute for Safety in Powerline Construction (ISPC) know why grounding caused these fatalities. The unfortunate reality is that we have clients – utilities and contractors – who still don’t use equipotential grounding, which is a violation of the law. You don’t have a choice whether to use bracket grounding or equipotential grounding. ISPC has never consulted on a case in which a worker using equipotential grounding was injured or killed. The law clearly and expressly states that grounding installed for personal protection must be arranged to ensure employees are not exposed to hazardous differences in potential. You can read the law’s full text at OSHA 29 CFR 1910.269(n)(3) and 1926.962(c). Additionally, Appendix C to 1910.269, “Protection From Hazardous Differences in Electric Potential,” is entirely dedicated to meeting OSHA’s equipotential grounding requirements.

So, why aren’t 100% of employers complying with the law?

Bracket Grounding Does Not Ensure Protection
Our industry has known for decades that bracket grounding does not ensure worker protection. In 1955, Bonneville Power Administration certified that bracket grounding does not ensure worker protection where an equipotential arrangement does. The value of using equipotential grounding was again demonstrated in a study of Puget Sound published by IEEE in 1988. Incident Prevention magazine has published articles written by Brian Erga, a now-retired principal engineer who worked on the Puget Sound study and was instrumental in establishing both the OSHA standards and industry consensus standards regarding equipotential grounding. Erga also facilitated educational sessions on grounding at past iP Utility Safety Conferences. The point here is that this information is available and easily accessible, so again, why do some employers continue to ignore the law?

The objections to equipotential grounding that I’ve heard over the years have primarily been based on fear that use of equipotential grounding would mean ending bracket grounding. That’s not the case; using brackets is fine so long as the structure you’re on is in an equipotential zone.

Still, why do so many people believe in bracket grounding to ensure worker protection?

It largely appears that the long history of brackets as protection makes it difficult for some employers to consider dropping their use. At ISPC, we’ve heard more than one client say something like this: “Every couple of years, somebody comes along with a new procedure, claiming that the old one was wrong. How long will it be until someone else tells us you were wrong and that they know better?”

I know there are numerous experts who are still getting it wrong because I frequently encounter them in my litigation consulting work. They author erroneous opinions – based on either incorrect interpretations of case documents or mixed assumptions about case details – that confuse the people reading or listening to their opinions.

With that said, let’s spend some time gaining a better understanding of grounding principles for worker protection.

The Electrocution Threshold
Here’s a relatively common question I receive: “I heard about an incident that happened while a crew was using brackets. Nobody got hurt, so how can you say that only equipotential grounding will ensure protection?”

My answer is that it’s entirely possible that no one was injured during that incident. “Ensure” is the key word here, and that’s where the electrocution threshold matters. That threshold varies with every exposure. We can’t even be precise as to how much voltage must be present to penetrate a worker’s bare skin and allow a deadly level of current to flow. This is essential knowledge: If voltage cannot penetrate the worker’s skin, current can’t flow, and the worker won’t be injured.

The natural resistance of a worker’s skin combined with their clothing and gloves increases impedance to voltage penetration. The same applies to potentials rising on a jobsite. We work in a multigrounded electrical environment. Neutrals, statics, pole bonds, wood and steel poles, and their ground rods are all bonded together, forming multiple pathways to ground as well as multiple circulating ground currents through varying resistances in the multiple pathways. These connections create a redundant grounding system for improved fault relay while also establishing a semblance of incidental bonding, which means that the interconnections may reduce potentials among the varying pathways – but not with any assumed assurance.

So, it’s possible that a bracket arrangement grounded to a system neutral one or more spans away – and where that system neutral is bonded to your work pole – could put the phase conductors at your pole close to the potential of the pole you’re on. But remember, both that system resistance and the fault current imposed upon it create a voltage drop across those grounds that’s the same voltage you’ll be exposed to in a fault. This is also essential knowledge: The voltage you’re exposed to is the voltage drop across the bonding path between your grounds and the pole you’re on. With brackets only, your voltage exposure is determined by the resistance of the neutral-to-pole connections; the distance from your pole to the brackets (conductor distance impedance raises the voltage); and the resistance of the phase grounding connections. “Crapshoot” is the technical term for this coincidental protection because you’re gambling that the incidental benefits of a 40-year-old grounding system will work in your favor.

A Better Plan
A better approach is to use a reliable, law-based plan. Here’s a third piece of essential knowledge: You must know the difference between incidental protection and intentional protection. Install an electrical bond between the neutral and the pole and ground at the work area. Avoid creating any risk to yourself or your co-workers by using the shortest ground length possible; this will limit ground impedances and keep voltage low across that intentionally installed protection.

Keep in mind that ground brackets serve to trip the circuit. The OSHA rule states that “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.” Note: Hazardous potential is potential great enough to penetrate an employee’s work gloves and skin, somewhere around 100 to 200 volts. Potential great enough to penetrate bare skin has been universally established at 50 volts.

A lawful equipotential zone can be accomplished in two ways. One approach is to hang properly arranged grounds at the pole you’re on. To ground on a nearby structure, you can create a “near” equipotential zone by adding the neutral connection at the pole you’re on. If you keep brackets a span away and only bond the neutral to the pole you’re on, you’re bonding in, but there will still be a voltage rise created by the conductor span length between the phases and the neutral bond below your feet. Your engineers must calculate how far away bracket grounds on your system can be while still providing low potential in your equipotential zone. The sketch below illustrates the use of remote grounds for old hands that don’t feel protected without them or to satisfy some state rules, such as California’s rule that still requires a bracket ground between the work location and every open point – but you still must bond your pole.

Additional Items of Note
Here are a few other tidbits. Your engineering study may suggest using a parallel set of 4/0 to manage high fault current. Two bracket grounds, one on either side of your work location, are equivalent to a parallel set. Electricity travels at the speed of light, so separation of a pole span or two would have little effect. On the other hand, if I parallel a set at the same location and don’t put the clamps within an inch of each other, a reactance occurs, resulting in an unequal division of current between the two paths. This can reach a high enough imbalance to cause thermal failure of the overloaded path. More than an inch or so of space between parallel clamps limits the performance of the parallel grounds set.

Sticking with brackets and grounding both bracket poles (phase to phase to grounded neutral) reduces the total combined resistance between the worker and the path to the equipotential zone at the work pole. This increases protection by lowering the total voltage drop across the combined pathways. However, you’ll get the same result if you establish an equipotential zone at the pole you’re working on and simply ground the phases to the neutral in the brackets. It’s the neutral connection to the working pole that creates the equipotential zone.

Lastly, when we ground three-phase, we must short-circuit the three-phase bus. Doing so causes a more reliable relay trip, but a good bus short-circuit using minimum-length ground cables keeps much of the fault current within the three-phase system, thereby limiting the current going to ground in your work area.

About the Author: After 25 years as a transmission-distribution lineman and foreman, Jim Vaughn, CUSP, has devoted the last 28 years to safety and training. A noted author, trainer and lecturer, he is a senior consultant for the Institute for Safety in Powerline Construction. He can be reached at jim@ispconline.com.