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Grounding Equipment – 3000
Page 3002
July 2012
Phone: 573-682-5521 Email: hpsliterature@hubbell.com Web: hubbellpowersystems.com
To indicate energized conditions on overhead lines, (from left) Chance Auto Ranging Voltage Indicator, Digital
Voltage Detector and Multi-Range Voltage Detector. At far right, Energized Cable Sensor performs the same function
on URD cable with an exposed concentric neutral and elbows without test points.
See Catalog Section 2450, “Instruments and Meters,” for details and ordering information.
General Practices
• On de-energized distribution lines, Chance recommends Double-Point grounding
• This grounding is at both structures adjacent to worksite: Connect all three phases via ground set, then connect to
ground rod.
• Plus a personal ground at the worksite, from any one phase to a cluster bar well below the worker’s feet
• On a system without a neutral, Chance recommends connecting down leads to screw ground rods installed at least
20 feet from all structures and barricaded
• Only for maintenance tasks during which grounds need not be replaced does Chance find acceptable the Single-
Point grounding method (at only the worksite: Connect all phases together and grounding plus personal ground,
as above)
• Where adequate phase-to-phase clearances permit, Chance accepts the practice of grounding only the phase being
worked (in the same manner as personal ground, above)
Temporary Grounding Equipment
Safe Working Practices
There are many reasons for temporary grounding to
protect personnel working on de-energized circuits,
including:
1. Induced voltage from adjacent energized lines
2. Fault-current feedover from adjacent lines
3. Lightning strikes anywhere on the circuit
4. Switching-equipment malfunction or human error
5. Accident-initiated contact with adjacent lines
Since any one of the above could result in re-energizing
the circuit, most utilities treat these potential dangers
as ever-present and impose strict temporary-grounding
work rules. Their crews’ experience often voices these
watchwords for the wise to heed:
“If you can’t see both ends, it’s hot” and “If it isn't
grounded, it isn’t dead.“
Vital Procedure Recommendations
Step One: Testing
• With a test instrument, confirm the circuit to be worked
has been de-energized intentionally before ground sets
are applied
Step Two: Cleaning
• For a good connection, scrub oxides and contaminants
from conductor, buswork or lattice contact points
• Chance universal wire brushes make this easy
• Serrated-jaw clamps also aid by penetrating surface
contaminants
Step Three: Connecting
• Chance insulated Grip-All clampsticks are the proper
tools to apply grounding clamps
• Various clampstick lengths and styles are available in
Catalog Section 2100, “Insulated Hand Tools”
Reference:
Derived from
ASTM F 855,
Standard
Specifications
for Temporary
Protective
Grounds to be
Used on De-
energized Electric
Power Lines and
Equipment
Copyright ASTM
Reprinted with
permission.
Grounding Set Ratings
Grade
Short Circuit Properties
A
Continuous
Current
Rating, A
RMS,
60 Hz
Minimum
Cable Size
with Ferrule
Installed
Equal or
Larger Than
Withstand Rating,
Symmetrical kA RMS, 60 Hz
Ultimate Rating/Capacity,
B
Symmetrical kA RMS, 60 Hz
15
cycles
(250
MS)
30
cycles
(500
MS)
Copper Cable
Size
6
cycles
(100
MS)
15
cycles
(250
MS)
30
cycles
(500
MS)
60
cycles
(1 S)
1
14
10
#2
 29
 18
13
9
200
#2
2
21
15
1/0
 48
 30
21
15
250
1/0
3
27
20
2/0
 61
 38
27
19
300
2/0
4
34
25
3/0
 76
 48
34
24
350
3/0
5
43
30
4/0
 96
 60
43
30
400
4/0
6
54
39
250 kcmil or
two 2/0
114
 72
51
36
450
250 kcmil
or two 2/0
7
74
54
350 kcmil or
two 4/0
159
101
71
50
550
350 kcmil
or two 4/0
A
Withstand and ultimate short circuit properties are based on performance with surges not exceeding 20% asymmetry factor
(see Appendices X3 and X4, ASTM F 855).
B
Ultimate rating represents a symmetrical current which the clamp shall carry for the specified time.