System Grounding for Worker Protection Against Induced Voltages
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- System Grounding for Worker Protection Against Induced Voltages
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In the last installment of “Voice of Experience,” we reviewed OSHA’s rules for transmission and
distribution (T&D) equipment grounding. This time around, we are going to discuss where and
how induced voltages occur and, more importantly, how to protect employees from hazards
associated with induced voltages via proper system grounding.
“It’s not dead until it’s grounded” is one of the oldest and most inaccurate statements made in
our industry. It’s also one of the first things I was ever told when I started working for Georgia
Power in 1967 as a helper on a line crew. Many years passed before I learned the true meaning of
Back then, induced voltages were called “static” and primarily found when de-energizing T&D
lines in a corridor with other transmission lines. Even reconductoring a distribution line – by
reframing and using layout arms to spread phase conductors to allow the installation of new
conductors – will involve voltages on new, not-yet-energized conductors once they are in the air,
isolated and insulated. That’s the reason grounds should be installed after new conductors are
installed and in the process of “clipping in” to insulators.
The number of induced voltages is determined by three factors: the distance between the de-
energized and energized conductors in the corridor; the voltage of the energized line; and the
distance that the energized and de-energized lines run parallel in the corridor. The higher the
voltage of the energized line, the closer the circuits are together, and the total distance the lines
run parallel, the higher the amount of induced voltage. Voltage on the de-energized line is a form
of capacitance coupling from the de-energized to the energized conductors. It is common to have
several thousand volts of induced voltage on de-energized circuits in corridors with multiple
circuits. Several of my customers working on 345-kV or 500-kV circuits have discovered as
much as 10 kV on de-energized conductors. Everyone must remember, 115-kV lines can easily
induce enough voltage to be deadly. Without checking for the presence of voltage with an
approved voltage meter, it is extremely easy to be deceived if you do not see an arc while
applying grounds. When de-energized circuits cross over or under energized circuits, there can
still be enough induced voltage to be hazardous to humans. As few as 50 volts entering the body
and 50 milliamps crossing the heart can create atrial fibrillation, a potentially deadly condition.
Another Important Consideration
Another fact workers must understand is that the work location may be the only circuit present,
but several miles down the line, the circuit may run parallel to other circuits that are energized.
Even though the energized circuits cannot be seen from the work location, the danger of induced
voltage exists when working on de-energized lines near energized conductors. Employees must
always expect that induced voltage is possible even when other circuits are not visible.
The induced voltage is truly in a static condition because the conductors are insulated and
isolated. However, this is not the traditional static voltage resulting from a positive charge that is
discharged one time and cannot be built back up with a physical action, like scuffing your shoes
on carpet and shocking someone else by touching them.
Induced voltages are the result of coupling through air from the energized conductors. The magic
of physics occurs when we ground the conductors with the induced voltages. If you install a
voltmeter on de-energized lines, there will be a measurable amount of AC voltage indicated prior
to installing system grounds. As soon as grounds are installed, the voltage will immediately
collapse to almost zero. Now, if you had an amp meter on grounds, there would be an immediate
rise in current flow on the grounds. The application of grounds could result in a visible arc when
a clamp contacts a conductor. One myth from days gone by is that if there was no arc, there was
not enough static to be hazardous. That is not true. There could be significant current flow with
no visible arc.
Many of us were told that when you ground, you “bleed the static” from the de-energized line.
This is another inaccurate statement. When grounds are removed from grounded lines, the amp
meter will indicate zero current flow, but the voltmeter will immediately see the voltage return to
ungrounded conductors. That voltage is the result of the capacitance coupling from energized
lines. If you are working on de-energized lines in a corridor with energized lines, there will
always be induced voltages on ungrounded, de-energized conductors. These voltages can be
hazardous to utility workers. The good news is that the hazards can be controlled by proper
system grounding and never getting in series with an ungrounded conductor and a different
Grounds Do Not Save Lives
My good friend Jim Vaughn and I present system grounding and the principles of grounding to
companies all over the U.S. During these presentations, we often say one thing that gets a lot of
attention: Grounds do not save lives. Bonding saves lives, and grounds operate systems. When
reading the OSHA maintenance and construction standards regarding distribution and
transmission, the message is the same. The intent of system grounding is to create a faulted
condition that generates enough fault current to trigger system protection and clear the fault.
Bonding in the work area creates an equipotential work zone so that all equipment and system
conductors are at the same potential. If the potential is the same, employees do not face
hazardous differences of potential. Further, even if the line becomes energized accidentally or by
a faulted condition near the work area, the voltage will rise in the work location, but if all points
of contact in the work zone are equal, the employee probably won’t know if the area was
OSHA states in 29 CFR 1910.269(n)(3) that 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.” I try to remind everyone that
OSHA standards are the whats and whys – they do not instruct readers on how to accomplish the
performance standard requirements.
Grounds also shall be properly sized, placed and installed according to the amount of available
fault current. They are required to meet the ASTM and IEEE consensus standards regarding the
construction of clamps and proper maintenance to meet the intent of the OSHA standards.
In almost every class I teach, I ask this question: Electricity takes the path of __________? Most
of the time, attendees will respond with, “Least resistance.” That is not true. Ohm’s law states
that electricity will take all conductive paths, and Kirchhoff’s law of current division states that
the amount of current flow is determined by resistance and impedance on the voltage path. If
grounds are applied, the circuit will not remain energized as long as system protection works as
it should. What employees must consider is this: If an equal potential zone is not installed with
bonding, will enough voltage be sustained in the two to 10 cycles it takes to clear the fault that it
could be harmful if an employee is in contact with differences of potential in the work zone?
In closing, it’s no wonder that system grounding is one of the most misunderstood and hazardous
tasks performed by lineworkers in our industry. We’ll tackle another related topic – neutral
return currents and lightning – in a future edition of “Voice of Experience.”
About the Author: Danny Raines, CUSP, safety consultant, distribution and transmission,
retired from Georgia Power after 40 years of service and opened Raines Utility Safety Solutions
LLC, providing compliance training, risk assessments and safety observation programs. He also
is an affiliate instructor at Georgia Tech Research Center OSHA Outreach in Atlanta.
Learn more from Danny Raines on the Utility Safety Podcast series. Visit https://incident-
prevention.com/podcasts to listen now!