Transcript Equipotential Grounding

Equipotential
Grounding
Engineering & Operations Technical Conference
April 13-18,2007
Jim McGrail
City of Naperville
Safety &Training
Instructor
Introduction
• Definition - Equipotential Grounding
• Regulatory Agencies
• Some benefits of Equipotential
Grounding
• Other considerations…
What is equipotential ?
An identical state of electrical
potential for two or more items.
For the purposes of protective
grounding a near identical state of
electrical potential-*
*IEEE Guide for Protective Grounding of Power lines IEEE STD 1048-2003
OSHA says…
“General.” For the employee to work
lines or equipment deenergized, the
lines or equipment shall be
deenergized under the provisions of
paragraph (m) of this section and shall
be grounded as specified in
paragraphs (n) (3) through (n)(9) of
this section.*
*OSHA 1910.269(n)(2)
OSHA - 1910.269(n)(3)
continued
“Equipotential zone.” Temporary
protective grounds shall be
arraigned in such a manner as to
prevent each employee from
being exposed to hazardous
differences in electrical potential.*
*OSHA 1910.269(n)(2)
National Electrical Safety
Code C2-2007
444D Employee’s protective grounds
…”Grounds shall be placed at each
side of the work location and as close
as practical to the work location ,or a
worksite ground shall be placed at the
work location.”
IEEE Std.1048-2003
6.2.4 Worksite versus bracket
grounding sets
In general ,the use of worksite
grounding sets will result in the
minimum obtainable impedance path
in parallel with the workers body, and
thus , the minimum body intercept
voltage for the worker.
APPA Safety Manual
Rev.13,2004
615 Grounding—General
(f) Grounds shall be placed between
work location and all sources of energy
and as close as practicable to the work
location ,or grounds shall be placed at
the work location…Temporary
protective grounds shall be placed at
equipotential zones and arranged in a
manner to prevent exposure to
hazardous differences in electrical
potential.
APPA safety manual -
continued
616 Equal Potential Grounding
(f) When it is not practical to use
single point grounding at the pole
where work is to be performed
,such as when wires are down
,grounds shall be installed on both
sides of the work location but not
further than adjacent structures.
Definitions Bracket Grounding: A grounding
method where temporary ground sets
are installed on both sides of the
worksite. Syn. adjacent structure
grounding.
IEEE Guide for Protective Grounding of Power lines IEEE STD 1048-2003
Definitions -
continued
Worksite grounds: A technique where
either the ground set is installed at the
structure where the work is to be
performed. Syn. personal ground;
working ground; ground stick; personal
protective ground.*
IEEE Guide for Protective Grounding of Power lines IEEE STD 1048-2003
Reasons For Grounding • Circuit is accidentally energized
from source
• Energized from another circuit
(Top circuit contacts lower circuit)
• Induction
• Lightning Strikes
Unintended Induced Current Loop
Energized 138 Kv.
Source Circuit
Induced
circuit
12.7 Kv
Bracket Grounds
Neutral
Equal Potential Grounding per “APPA Safety Manual”
a) A chain binder ,with provisions
for attaching a personal
protective ground, shall be
tightened around the pole at a
position below where the
lineman place his feet
Equal Potential Grounding per “APPA Safety Manual”
b) A personal protective ground shall be
attached to the chain binder and
extended to the system neutral. If the
neutral is not present or cannot be
approached safely ,refer to
Paragraphs 615-h and 615-I for
alternate grounding
Equal Potential Grounding per “APPA Safety Manual”
c) Personal protective grounds shall
be extended from the chain binder
to each phase conductor or from
the chain binder to a single phase,
and from that phase to the other
phases.
Equal Potential Grounding per “APPA Safety Manual”
d) When work is completed ,the
personal protective grounds shall
be removed in reverse order of
installation.
Equal Potential Grounding per “APPA Safety Manual”
e) When a circuit is to be opened (e.g.,
opening jumpers at a junction pole or
cutting slack), a temporary jumper
shall be installed across the open
point.
Other Considerations
Start with fundamentals…
1.
Verify equipment is de-energized
2.
Grounding equipment is in good condition
(proper size and style)
3.
Install and remove in correct order
4.
Make sure connection points are clean and
tight
Other Considerations -
continued
Ground personnel should be
aware if there is fault current on
the system a possibility for step
and touch potential could be
present at the base of the
structure.
Conclusion:
 OSHA 1910.269(n)(3) Refers to
establishing a “Equipotential zone”
 IEEE Std.1048-2003 talks about worksite
grounding and the minimum body
intercept voltage for the worker.
 APPA Safety Manual also supports the
use of Equal potential grounding.
Resources
 OSHA 29 CFR 1910.269
 IEEE Guide for Protective Grounding of
Power lines IEEE STD 1048-2003
 APPA Safety Manual
 National Electrical Safety Code C2-2007
 “Why Single- Point Grounding Works”
by Jim Vaughn, iP Volume 2 Issue 3
May/June 2005