SOUTHWEST ELECTRIC COMPANY
Tulsa Service Center
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
INTRODUCTION
In this presentation we will be discussing:
• Why do we use Personal Protective
Grounds? (PPG)
• What are the purposes for using PPG?
• What makes up a PPG system?
• NFPA 70E requirements.
• Procedures for temporary grounding of
de-energized
• Isolated high-voltage equipment (over 600
volts) for the purpose of bare hand
contact.
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
WHY USE GROUNDING EQUIPMENT
•
•
•
•
Personal protective grounding (PPG)
techniques provide shock protection for
electrical workers working on de-energized
equipment.
PPG is by far the most effective means of
protecting workers from electrical shock.
In some cases PPG can precipitate arc flash
events of unimaginable magnitude.
PPG is especially important for high-voltage
(HV) electrical workers, because equipment
can become energized remote from the work
location due to switching errors or through
induction.
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
PURPOSE OF GROUNDING
• The main purpose of PPG is to expeditiously actuate overcurrent
protective devices (OCPDs) while simultaneously limiting voltage
to which workers are exposed to safe levels.
• When a circuit has been properly grounded for the protection of
workers — and it accidentally becomes energized — the voltage
on the system sags to near zero.
• Grounding cables cannot carry these massive amounts of
current for more than a fraction of a second. Therefore, the
workers' lives depend upon the OCPDs that protect the circuit (to
de-energize it) before the grounding cables melt open and
voltage levels return to unsafe levels.
Any changes to the OCPDs that would cause them to
retard fault clearing should be avoided. Delaying the
instantaneous trip setting could cause death!
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
GROUNDING EQUIPMENT
This type of equipment is actually a
system of components consisting of:
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•
•
•
Grounding heads
Grounding electrodes
Grounding mats
Grounding cables
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
GROUNDING EQUIPMENT (CONT.)
Grounding Heads
•
•
The grounding head is the only connection
between the grounding system and the
electrical circuit on which work is to be
performed.
Like grounding cables, the grounding
heads must be rated to withstand the
available fault current for the duration of
the fault event.
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
GROUNDING EQUIPMENT (CONT.)
Grounding Electrodes
• The grounding electrodes are the other end of the
grounding system in that the electrode provides the
physical contact with the earth.
• There are many different ways to connect to the
earth.
• On metal-enclosed power switchgear (MEPS) the
connection to the earth is usually through a
grounding bus, which is a metal bar that is, in turn,
connected to another grounding electrode.
• Care must be taken to ensure the grounding bus is
effectively connected to the earth via an effective
grounding electrode.
• Test your grounds!
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
GROUNDING EQUIPMENT (CONT.)
Grounding mats
• Grounding mats are used in PPG to place
workers at the same potential (i.e., voltage) as
the equipment on which they are working.
• The grounding mat is essentially a tarp with
aluminum strands braided into it in a
crosshatched pattern.
• The aluminum is connected to a “node” on the
edge of the mat, which allows for a connection
that is then connected to the grounding
conductors of the system on which work is to
be performed.
• The aluminum is only installed on one side of
the mat, so that side must obviously be facing
up — to ensure the worker is standing on the
aluminum grid.
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
GROUNDING EQUIPMENT (CONT.)
Grounding cables
• Grounding cables are responsible for
providing a low-impedance path for fault
current to flow on a properly grounded
circuit.
• The conductors must be made of multistranded copper and can be no smaller
than 2 AWG.
• The primary considerations when
selecting grounding cables is their
withstand rating for fault current and
their length.
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
GROUNDING EQUIPMENT (CONT.)
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
GROUNDING EQUIPMENT (CONT.)
Any changes to the OCPDs that would cause them to
retard fault clearing should be avoided. Delaying the
instantaneous trip setting could cause death!
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
NFPA 70E REQUIREMENTS (CONT.)
NFPA 70E Section 120.3(A) Placement
states, "Temporary protective grounds
(personal protective grounds) are to be
placed so that they do not expose
employees to hazardous differences in
potential. Grounds should not be placed
too close to the worksite and must be
placed or secured so they cannot come
into contact with people."
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
NFPA 70E REQUIREMENTS (CONT.)
Grounds must be placed close enough to protect
workers if ground is energized, but not so close that
they endanger the worker from:
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•
•
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Contact them causing electrical shock
Cables can swing violently
Cables could blow up causing shrapnel
Arc Blast could occur causing burns
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
NFPA 70E REQUIREMENTS (CONT.)
NFPA 70E Section 120.3(B)
Capacity states, "Temporary
protective grounding equipment
shall be capable of conducting
the maximum fault current that
could flow at the point of
grounding for the time necessary
to clear the fault."
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
NFPA 70E REQUIREMENTS (CONT.)
NFPA 70E Section 120.3(C)
Equipment Approval states,
"Personal protective grounding
equipment must meet the
requirements of ASTM F-855,
Standard Specification for
Temporary Protective Grounds to
be Used on De-energized Electric
Power Lines and Equipment."
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
NFPA 70E REQUIREMENTS (CONT.)
NFPA 70E Section 120.3(D)
Impedance states, "Temporary
protective grounding equipment
and connections shall have an
impedance low enough to cause
immediate operation of protective
devices in case of accidental
energizing of the electric
conductors or circuit parts."
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
ADDITIONAL INFORMATION
• If the system has a nominal voltage above 600V, grounding is a
mandatory requirement.
• However, grounding is not just for high-voltage systems. If there is any
danger of voltages appearing on the circuit or device, it must be
grounded.
• UPSs, VFDs, and similar types of equipment have large capacitors
that can store a lethal charge.
• Backfeeds
• Proper grounding and grounding equipment that meets ASTM F-2249
and ASTM F-855 specifications is necessary to provide a safe work
environment.
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
BACKFEEDING
Backfeed:
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Occurs when electric power is being induced into the local
power grid.
Power flows in the opposite direction from its usual flow.
Examples of Backfeeding:
• Light circuits
• CTs AND PTs during testing
• If there are de-energized cables run for long distances in
cable trays that contain energized cables, an induced
voltage can appear on them
• Rotating equipment such as fans
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
INSTALLING GROUNDS PROCEDURE
• De-energize the electrical equipment by isolating all
possible electrical sources to the equipment.
• For HV systems, it is a requirement to get a “visual
open” in the circuit, such that
• The worker can visualize an air-gap in the
switches used to isolate the circuit.
• This can be achieved either by opening a solidblade switch that can be visually inspected.
• Racking out a circuit breaker by removing it
from contact with an electrical bus.
• Any other means that positively separates the
electrical contacts in an energy isolating
device.
• Follow normal lockout/tagout (LOTO) procedures.
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
INSTALLING GROUNDS PROCEDURE (CONT.)
• It is required to perform a 3-point test with a sensitive voltage
testing devices to verify a zero energy state. A 3-point test
consists of:
1. Test the voltage tester on a known energized source to
verify it is working properly.
2. Test the circuit on which work is to be performed.
3. Test the voltage tester on the same energized source as
was used in No.1 to verify the tester is still working
properly.
4. Examples of sensitive voltage testing devices include
“proximity” testers, tic-tracers, or direct-reading HV
voltmeters.
NOTE: It is Southwest Electric Procedure to have two
independent voltage checks be performed and recorded on the
Safety Task Analysis (STA)
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
INSTALLING GROUNDS PROCEDURE (CONT.)
•
•
The most important step in the grounding process is to
properly clean the conductors before connecting to
them. The main point to remember is that you must
remove all oxidation on both the phase conductors and
grounding electrodes before attaching grounding cables
to them.
Grounding cables must be installed and removed in a
specific order:
1. Always connect the grounded end of the
grounding cables first.
2. Make connections to the phase conductors.
3. When finished with your work, remove the
grounding jumpers in the reverse order.
Caution: There have been fatalities when workers attempted
to move or remove the ground connections while the
jumpers were still connected to the phase conductors.
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SOUTHWEST
ELECTRIC
COMPANY
PERSONAL PROTECTIVE GROUNDS
FINAL THOUGHTS
Final Thoughts:
• Personal protective grounds are critical safety devices that require
care and skill when using them.
• Improperly sized or installed grounds will only provide a false sense of
security.
• Technicians often place personal protective grounds and don't give
much thought as to whether they would actually protect them if the
worst should happen.
• Once locked out and tagged, we have a tendency to consider electrical
circuits and equipment "safe."
• Electrical circuits and equipment cannot be considered safe until
tested and found absent of voltage.
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SOUTHWEST
ELECTRIC
COMPANY
There are a number of safety-related items that are not stated in either the OSHA regulations
PERSONAL PROTECTIVE GROUNDS
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