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EEI Occupational Safety & EEI Occupational Safety & H lth C itt C fH lth C itt C fHealth Committee ConferenceHealth Committee Conference
Brian ErgaBrian ErgaESCI, Inc.ESCI, Inc.SC , c.SC , c.
October 2, 2007October 2, 2007
Protective Grounding MethodsProtective Grounding Methods Tests
-Keith Wallace, P.E.
O P j t fOur Project focus:
Comparing Methods ofComparing Methods of Grounding
• worksite grounding with pole bands (cluster bars)pole bands (cluster bars)
• worksite grounding without pole bands (cluster bar)
OSHA RequirementsqOSHA 29 CFR1910 269( )(3)1910.269(n)(3)
"E i t ti l " T t ti"Equipotential zone." Temporary protective grounds shall be placed at such locations
d d i h t tand arranged in such a manner as to prevent each employee from being exposed to h d diff i l t i l t ti lhazardous differences in electrical potential.
Fault TestingFault TestingTransformers
3 x 333 kVA, 4.3% Z7200 / 480V
Vacuum BreakerLine Regulators(set at 10% raise)Generator
Breaker
2.5 MVAMotor-Generator
5kV output
MG PhaseConnection
NeutralConnection
Fault TestingNEETRAC Project No. 05-035
Not to scale
Seven (7) Spans - 1084.5 feet (330.6 meters)
Pole 6
127'
327 Ohms
Pole 5 Pole 3
196' 178'
106 Ohms53 Ohms282 Ohms
Pole 4 - Midspan
Pole 2
180'
238 Ohms
Pole 2
148.5'
176 Ohms
Pole 1
Fault TestinggThree grounding configurations
Fault Testing ResultsgThree pole categories
•No pole ground wireNo pole ground wire
•Insulated pole ground wire
•Bare pole ground wire
Worker in contact with Neutral
MMan
Fault TestingFault TestingNo pole ground wire
Case N b
Worker l i
Type worksite di h d
V Ф N
If (mA)Number location grounding method Ф-N
NB1 On neutral No pole band 20.3 20.3
NB2 On neutral Pole band 1 25.2 25.2
NB3 On neutral Pole band 2 20.5 20.5
Fault TestingFault Testingbare ground wire
Case N b
Worker l i
Type worksite di h d
V Ф N
If (mA)Number location grounding method Ф-N
B1 On neutral No pole band 17.4 17.4
B2 On neutral Pole band 1 21.4 21.4
B3 On neutral Pole band 2 17.6 17.6
Fault TestingFault TestingInsulated ground wire
Case N b
Worker l i
Type worksite di h d
V Ф N
If (mA)Number location grounding method Ф-N
IB1 On neutral No pole band 19.3 19.3
IB2 On neutral Pole band 1 24.7 24.7
Pole band 2 -- --
Worker Circuit – worker onWorker Circuit worker on pole
Man
Fault TestingFault TestingNo pole ground wire
Case Number
Worker location
Type worksite grounding method
V Ф-N*
If (mA)dry
If (mA)wet
N1 On A2 No pole band 448 .047 --
N2 On A2 Pole band 1 at A1 448 056 495N2 On A2 Pole band 1 at A1 448 .056 .495
* - removed Ф-N jumpers to increase current through worker - removed Ф-N jumpers to increase current through worker to measurable value
Fault TestingFault TestingInsulated ground wire
Case Number
Worker location
Type worksite grounding method
V Ф-N*
If (mA)dry
If (mA)wet
I1 On A2 No pole band 450 .037 .19
I5 On A2 Pole band 1 at A1 450 080 2 3I5 On A2 Pole band 1 at A1 450 .080 2.3
* - removed Ф-N jumpers to increase current through worker to measurable value
Fault TestingFault TestingBare ground wire
Case Number
Worker location
Type worksite grounding method
V Ф-N*
If (mA)dry
If (mA)wet
B1 On A2 No pole band 443 .039 .78
B5 On A2 Pole band 1 at A1 443 045 57B5 On A2 Pole band 1 at A1 443 .045 .57
* - removed Ф-N jumpers to increase current through worker to measurable value
Element TestinggPole resistivity
R=ρ*LVoltage sourceTest Resistor
R=ρ*LA
Wooden poleContact resistance
Contact resistanceWooden poleresistance
significantresistance significant
Element TestinggPole band contact resistance
R=ρ*L +R(band)ρ ( )A
Element TestinggStaple contact resistance
R=ρ*L +R(staple)ρ ( p )A
Element Testing Resultsg
Wooden pole resistances - from 500Ω -700kΩ /ft.Pole bands - from 4kΩ to 800kΩStaples/nails - from 10kΩ to 100kΩ
Pole band and staple resistance are a function of pole resistivity and surface moisture.
Fault TestingFault TestingResults
Pole band contact resistances are large and greatly reduce the theoretical effectivenessgreatly reduce the theoretical effectiveness of the pole band.
Worksite grounding provides as much or more protection than pole bands
Critical Factors The current through the worker is a function of:
•Fault current at jumper location
•Impedance of grounding jumpers
•Resistance of worker circuit (worker, pole, contact resistances)
•Pole resistivities
•Location of grounds relative to workers
NEETRAC Project 05-161Evaluation of Direct Neutral vs.
Pole Band Grounding
-Keith Wallace, P.E.
Types of Tests
1 - High current tests with temporary grounds Φ-G (2000 3500 A t 480 lt )(2000-3500 A at 480 volts)
2 - High voltage tests on dry pole without temporary grounds Φ-G (6650 Volts)
3 - High voltage tests on wet pole without g g ptemporary grounds Φ-G (6650 Volts)
4 – High voltage tests on wet pole with temporary4 – High voltage tests on wet pole with temporary grounds (6650 Volts)
Conclusions
1 – If pole band is used, bond phases to neutral, th t l t l b d ( id dditi l jthen neutral to pole band (avoid additional jumper impedance).
Conclusions
2 – In the case of a metal pole, the pole must be b d d t th t l C t t i t dbonded to the neutral. Contact resistances, and pole resistances are minimal.
Conclusions 3 – A worker located between the source and the temporary grounds will be exposed to a higher
lt d t ki th l d id fvoltage compared to working on the load side of the temporary grounds. (The extra conductor is in series with jumper impedance)in series with jumper impedance)
Larger exposure voltage
source
Ifault
Ifault source
Ifault
Ifault
Ifault Ifault
Conclusions 4 – The exposure voltage will reduce in direct proportion to the length of the temporary ground. I i th di t i f th tIncreasing the diameter size of the temporary ground also reduces the exposure voltage, but to a lesser extenta lesser extent.
Example: 10 ft Copper temporary groundExample: 10 ft Copper temporary ground
1/0 2/0 4/01/0 2/0 4/01.59Ω 1.57Ω 1.11Ω
Conclusions5 – Bracket grounding on adjacent poles will develop less Φ-N exposure voltage compared to p p g pgrounding at the worksite.
source 15 1mAsource 15.1mA
source 6.7mA
Developed following “man on the pole” models:
ΦA (3P3, 3P3G)
R =1 kΩ
ZTPG=0.9+j1.27 mΩ(10’, 2/0 TPG, Table 3)
R ff R= 260.5 kΩ
Rworker =1 kΩ
Gaff (3P3F)
ZN-R by WinIGS0 542+j0 366 Ω
(3P3 N)
Rgaff-R 260.5 kΩ
Downlead and Ground Rod (150 Ω)0.542+j0.366 Ω
T t lt did ’t h
Figure 12: Workpole Model for
Test results didn’t show much difference between bare pole ground and insulated pole groundDirect Grounding Method on
Wet CCA Wood Poleinsulated pole ground
Developed following “man on the pole” models:
ΦA (3P3, 3P3G)
ZTPG=0.9+j1.27 mΩ(10’, 2/0 TPG, Table 3)
Gaff (3P3F)
Rworker =1 kΩ
R =71 3
(3P3 N)
Rgafft-PB/N =71.3 kΩ
ZN R by WinIGSZN-R by WinIGS0.0344+j0.024 Ω Downlead & Ground
Rod (150Ω)
Figure 13: Workpole Model for Pole Band Grounding Method on gWet CCA Wood Pole
Computer Modeling
1Ph1Ph
1Ph
Modeled distribution line with four 150Ω grounds per mile to maximize neutral system
G
1Ph 1Ph 1Ph
1Ph
1Ph1Ph
3-Ph, 2.2 mi, 4 grounds/mi @ 150 Ohms
Ph-A line, customer loads & grounds
SUB 3P2 3P33P3G3P45 3P67 3P8 3P10 3P11 ST1 ST2 ST3
ST3A
ST4
ST4A
ST3BST3CST3Dy
impedance.
G
1Ph
1Ph1Ph1Ph 1Ph 1Ph 1Ph
Ph-A line, customer loads & groundsConductor Sizes Ph (N): 1/0 (#2) ACSR
SUB 3P2 3P33P3G3P45 3P67 3P8 3P10 3P11 ST1 ST2 ST3 ST4
ST5ST6ST7ST8ST9ST10ST11ST12Moved the1Ph 1Ph 1Ph 1Ph
1Ph
1Ph
1Ph
Ph-A line, customer loads & grounds
ST8AST8BST8CST8DST5A
ST5B
Moved the “man on the pole” model everywhere on
1Ph
1Ph
Ph-A line, customer loads & grounds ST5TST5B
ST5C
ST5D
everywhere on the distribution line to look for the worst case
1Ph
1Ph ST5D
ST5E
the worst case.
Conclusions
For these models, the worst case location for the pole band case on a wet pole is a function of the maximum fault current – i.e. near the substation.
For these models, the worst case location for the no pole band case on a wet pole is a function of p pthe maximum phase-to-remote earth – i.e. one half mile from the substation.
Conclusions
10kA
e kV
8kA 4kV
ent k
A
h vo
ltage
6kA
4kA
3kV
2kVult C
urre
ote
earth
2kA 1kV
Fau
e to
rem
421 3 Pha
se
Distance from the substation - milesDistance from the substation miles
Table 7Computed Exposure Currents for Wet CCA Wood Pole, Phase to Pole Contact (Figures 10, 12 and 13)
L-L SystemV lt
ΦA-NFault Current
I
Temporary Protective Ground (TPG) Connection
* ΦA -PB-N or ΦA-N-PB (Cases with Pole Band) $ ΦA-N (Cases with No Pole Band)VoltagekV
InSubstation
A
( ) $ ( )
TPG CurrentA
ΦA-Remote Earth
Voltage@ Work pole
V
Exposure Current
mA
TPG Current
A
ΦA-Remote Earth
Voltage@ Work pole
V
Exposure Current
mA
V V
12 5322 5092 230 0.24 2726 1785 6.8
11161 10180 461 0.48 3566 2335 8.9
24728 20250 916 0.96 4153 2720 10.4
25 5152 5049 228 0.24 3662 2398 9.17
10685 10250 463 0.48 5601 3668 14.0
21854 20060 908 0.95 7318 4793 18.3
35 5112 5038 228 0.24 3990 2613 10.0
10354 10060 455 0.48 6445 4221 16.1
21252 20020 906 0.95 9092 5954 22.8
* Representing a worse case, the work pole is located 150’ from the substation.$ Representing a worse case the work pole is located 0 565 miles from the substation$ Representing a worse case, the work pole is located 0.565 miles from the substation.General Note for All Cases: Presence or absence of a downlead with a ground rod has insignificant influence on computed exposure current.
Table 8Computed Exposure Currents on Steel Pole Connected to Neutral (Phase to Pole Contact), on Wood or Concrete Pole (Contact
between Phase and Hardware Connected to Neutral)
L-L SystemVoltage
kV
ΦA-NFault Current
in SubA
Temporary Protective Ground (TPG) Connection
* ΦA–PB-N or ΦA–N-PB or ΦA-N (Neutral Connected t St l P l N t l C t d t H d W dto Steel Pole or Neutral Connected to Hardware on Wood
or Concrete Pole )
TPG CurrentA
ΦA-Remote Earth
Voltage
Exposure CurrentmA
@ Work poleV
12 5322 5092 230 17
11161 10180 461 35
24728 20250 916 69
25 5152 5049 228 17
10685 10250 463 35
21854 20060 908 69
35 5112 5038 228 17
10354 10060 455 34
21252 20020 906 69
* Work pole is located 150’ from the substation.General Notes for All Cases: 1) Presence or absence of a downlead with ground rod has insignificant influence on computed exposure current. 2) Resistance of the (steel) pole base to remote earth is assumed to be 200 Ω.
Where do we go from here?•Need more accurate model of wooden poles (3 dimensional) surface potentials) p
•Need more accurate model of contact resistance
N d th d f d li f t ti l•Need method for modeling surface potentials on poles
•Perform parametric analysis varying types of wooden poles, grounding methods, voltage l l d f lt t l l
Keith Wallace P E
levels, and fault current levels
-Keith Wallace, P.E.
Incorrect Simple Model –wooden pole with no pole ground and pole bandwooden pole with no pole ground and pole band
voltage 1000 Ω.002 Ωjumper manSource
Rneutral
It is a common misconception that the pole band holds the voltage on the pole above the g ppole band at the same potential as the neutral.
Common MisconceptionIf the pole band held the voltage on the pole above
Equipotential Zone
voltage on the pole above the pole band at the same potential as the neutral, pthe current through the man would not change
h th h i th l man
whether he is on the pole or touching the pole band.
m
No published test data support this idea.support this idea.
Better Simple Model
1000 Ωman
Source impedance
voltage
1000 Ω+footing resistanceR+jXΩ
Source
SmallNeutral system network
Small section of pole
Pole Band Contact ResistanceSource Resistance
Pole Resistance/
pole groundGround
Better Models – insulated pole ground wire
contact resistance(conductor to hand)
source impedance
body resistance
contact resistance(f t t l )
jumper impedancesource voltage
(foot to pole)
pole resistance(one foot)
neutral impedance(multi-grounded) contact resistance
(pole to poleband)
nds
pole resistance(~35 feet)
pole groundwire
pole
gro
un
contact resistance(pole to earth)
contact resistance(pole to electrode)
electroderesistance
Better Models – bare pole ground wiresource impedance
contact resistance(conductor to hand)
body resistancejumper impedancesource voltage
contact resistance(foot to pole)
pole resistance(one foot)
neutral impedance(multi-grounded)
contact resistance(pole to pole band)
pole groundwire pole resistance
(one-three feet)contact resistance
(pole to staple)
pole groundwire
pole resistance(one-three foot)contact resistance
(pole to staple)
pole g
roun
ds
contact resistance(pole to staple)
(p p )
pole resistance(~2 feet)
l t th
contact resistance(pole to electrode)
electrode
pole groundwire
pole to earthresistance
electrodeto earth
resistance
Wooden Pole ResistivityPole Length Avg Treatment R(total) R ρPole Length.
(m.)Avgdia
(cm.)
Treatment ( )(kΩ)
R(Ω/m)
ρ(Ω-m)
1 11.6 12.7 Creosote 52 4475 227
2 9 2 14 0 CCA 161 17579 10812 9.2 14.0 CCA –dry
161 17579 1081
3 9.2 8.3 CCA –dry
193 20984 449
4 12.3 11.6 CCA –dry
139 9968 478
5 12.3 13.0 CCA –dry
178 14472 764
6 9.2 11.3 No treatment
40 4432 178
7 9.2 11.9 No treatment
56 6129 275
8 9.2 11.8 No treatment
52 5663 249
9 12.28 12.7 CCA –damp
36.5 2972 151da p
10 12.28 12.7 CCA –damp
36.9 2972 153
Pole Band Contact ResistanceSample Length of Pole
(m.)Avg. dia.
(cm.)Pole Description Pole ρ
(Ω-m)Pole Band (kΩ)
1 11.64 14.6 No treatment
178 886.3
2 9.20 15.4 No 275 610.79. 0 5. Notreatment
75 6 0.7
3 9.24 15.4 No treatment
275 558.6
4 12.28 15.4 No treatment
275 34.5
5 12.31 15.3 No treatment – damp
249 4.3treatment damp
6 9.20 15.3 No treatment – damp
249 15.4
7 9 20 16 4 CCA damp 151 602 37 9.20 16.4 CCA – damp 151 602.3
8 9.24 16.4 CCA – damp 151 631.1
Jumper Impedance Table 4TPG Impedance Test Data (Tests Performed on Pole 3, NEETRAC/SOCO Project 05035)
NEETRA ∗TPG Description Polar $Current Phase Angle TPG ImpedancesC
Test IDmΩ in TPGs
AmpsBetween
Voltage and Current∠°
φC -φB
φB -φA
φA - N Total TPG
LengthFt
Total TPG Imp
PolarmΩ
PU TPG Impedance
RectangularmΩ
1b One One One 6.2 (φA – N) 3463 ∠34.6° 10 1.79 ∠34.6° 0.179 ∠34.6° 0.147+j0.1010’
1/0 CU10’
1/0 CU10’
1/0 CU2a 18.8 (φC – N) 3791 ∠23.8° 30 4.96 ∠23.8° 0.165 ∠23.8° 0.151+j0.07
3a 6.1 (φC –φB) 3530 ∠30.2° 10 1.73 ∠30.2° 0.173 ∠30.2° 0.149+j0.09
4a One 6’2/0 CU
One 10’
2/0 CU
One 6’
2/0 CU
3.46 (φC –φB) 3587 ∠34.6° 6 0.97 ∠34.6° 0.162 ∠34.6° 0.133+j0.09
5a 12.3 (φC – N) 3564 ∠23.3° 22 3.45 ∠23.3° 0.157 ∠23.3° 0.144+j0.06/0 CU /0 CU6a 3.32 (φA – N) 3564 ∠38.7° 6 0.93 ∠38.7° 0.155 ∠38.7° 0.122+j0.09
7a One 25’
4/0 CU
One 25’
4/0 CU
One 25’
4/0 CU
10.2 (φA – N) 3564 ∠45.4° 25 2.86 ∠45.4° 0.114 ∠45.4° 0.080+j0.08
8a 30.0 (φC – N) 3610 ∠47.5° 75 8.30 ∠47.5° 0.110 ∠47.5° 0.074+j0.08
9a 11.0 (φC –φB) 3587 ∠51.8° 25 3.10 ∠51.8° 0.123 ∠51.8° 0.076+j0.10
∗ TPGs are connected from φC- φB - φA – N on Pole 3 and voltage applied between φC and N.$ Current duration = 0.217 seconds (13 cycles).
Staple Contact Resistance
Sample Length of Avg Pole Description Pole ρ (Ω- StaplesSample Length of Pole (m.)
Avg. dia.
(cm.)
Pole Description Pole ρ (Ω-m)
Staples(kΩ)
1 9 78 12 7 Creosote 227 11 01 9.78 12.7 Creosote 227 11.0
2 8.60 12.7 Creosote 227 24.0
3 3.44 13.7 CCA 3097 36.5
4 2.56 13.7 CCA 3097 42.8
Jumper Impedance Testing
Includes resistance of conductors,of conductors, ferrules and clamps, and inductance of conductors.
Jumper Impedance –E l 1/0 CUExample 1/0 CU
a b c
Z V /I Z=18 08V/3791A at 23 8 degrees
n
Z=Van/I Z=18.08V/3791A, at 23.8 degrees
Z= 4.77 mΩ, at 23.8 degrees (.159 mΩ/ft.)
Z= 4.36 + j1.93 mΩ (X=.064 mΩ/ft.)Ground jumpers are Z= R + jX mΩj p1/0 CU, each ten ft. in length for a
R= Rcable +Rconnections
Rconnections= R – Rcable = 4.36 – 3.15 mΩlength for a 30 ft. total
Rconnections R Rcable 4.36 3.15 mΩ
Rconnections= 1.21 m Ω
Jumper Impedance –E l 2/0 CUExample 2/0 CU
a b cZ=V /I Z=12 3V/3564A at 34 6 degrees
n
Z=Van/I Z=12.3V/3564A, at 34.6 degrees
Z= 3.45 mΩ, at 34.6 degrees (.157mΩ/ft.)
Z= 2.84 + j1.96 mΩ (X=.089 mΩ/ft)
Z= R + jX mΩGround jumpers are
R= Rcable +Rconnections
Rconnections= R – Rcable = 2.84 – 1.83 mΩ
j p2/0 CU, 22 ft. total
connections
Rconnections= 1.01 m Ω
Jumper Impedance –E l 4/0 CUExample 4/0 CU
a b c
Z V /I Z=30V/3610A at 47 5degrees
n
Z=Van/I Z=30V/3610A, at 47.5degrees
Z= 5 61 + j6 13 mΩ (X= 082 mΩ/ft)
Z= 8.31 mΩ, at 47.5 degrees (.111m Ω/ft.)
Z= 5.61 + j6.13 mΩ (X=.082 mΩ/ft)
Z= R + jX mΩGround jumpers are
R= Rcable +Rconnections
Rconnections= R – Rcable = 5.61 – 3.95 mΩ
j p4/0 CU, each 25 ft. in length for a
Rconnections= 1.66 m Ω
length for a 75 ft. total
Test 1Ifault ~2000-3000kA
TestNo
NEETRA
CTest ID
*Grounding Method/Configuration
Worker Between
WorkerExposure Voltage
(V) or Current (ma)
ΦA to Remote Earth Voltage
(V)
Neutral to Remote Earth
Voltage(V)
Current in TPGsAmps
ZTPGs Across the Worker
Tests with Pole Band
1 1 Worksite grounds on Pole 2ΦA- ΦB- ΦC-N-PB
ΦA & PBΦA & N (Pole 2)
9.28.9
153 147 2105 Z3TPGs=4.4 mΩZ3TPGs=4.2 mΩ
2 2 Worksite grounds on Pole 2ΦA- ΦB- ΦC-PB-N
ΦA & PBΦA & N
8.911 95
157 145 2172 Z3TPGs=4.1 mΩZ =5 5 mΩΦA ΦB ΦC PB N ΦA & N
(Pole 2)11.95 Z4TPGs 5.5 mΩ
3 5 Worksite grounds on Pole 2 ΦA- ΦB- ΦC-PB-N
ΦA & N (10’ on source side of Pole 2)
21.22 154 139 2104 Z4TPGs=10 mΩ (Includes imp. of 10’ of phase and
neutral conductors)
4 6 Worksite grounds on Pole 2ΦA ΦB ΦC PB N
ΦA & N (10’ on load side of
12 154 142 2138 Z4TPGs=5.6 mΩΦA- ΦB- ΦC-PB-N on load side of
Pole 2)
Tests without Pole Band
5 3 Worksite grounds on Pole 2ΦA- ΦB- ΦC-N
ΦA & N(Pole 2)
9.3 156 146 2206 Z3TPGs=4.2 mΩ
6 4 Worksite grounds on Pole 2 ΦA & N 5 9 154 143 2150 Z =2 74 mΩ6 4 Worksite grounds on Pole 2ΦA- ΦB- ΦC & ΦB-N
ΦA & N(Pole 2)
5.9 154 143 2150 Z2TPGs=2.74 mΩ
7 7 Worksite grounds on Pole 2ΦA- ΦB- ΦC-N
ΦA & N (10’ on source side of Pole 2)
18.9 157 141 2195 Z3TPGs=8.6 mΩ (Includes imp. of 10’ of phase and neutral conductors)
8 8 Worksite grounds on Pole 2ΦA ΦB ΦC N
ΦA & N (10’ L d Sid
9.4 153 143 2105 Z3TPGs=4.5 mΩΦA- ΦB- ΦC-N on Load Side
of Pole 2)
9 9 Grounds on Pole 3ΦA- ΦB- ΦC-N
ΦA & N( Pole 2)
15.1 129 112 3417 Z3TPGs=4.4 mΩ
10 10 Grounds on Pole 3ΦA- ΦB- ΦC-N
ΦA & N ( Pole 1)
15.1 - - 3417 Z3TPGs=4.4 mΩ
11 11 Bracket Grounds on Poles 1 & 3 (ΦA- ΦB- ΦC-N on each pole)
ΦA & N on Pole 2
6.72 123 115 3259 (Pole 3)104 (Pole 1)
-
*Voltage applied between φA and N
Test 2 (dry) & Test 3 (wet)Test 3 (wet)
Pole Band with bare pole groundbare pole ground conductor
Tests 2 & 3
bare pole ground conductor with no pole groundpole ground
Tests 2 & 3
Pole band with no pole ground
Tests 2 & 3
no pole ground with no pole band
Test No
NEETRACTestID
VΦA-NkV
Downlead Connected to Neutral
Pole Band
Grounding Connection Reference
I1013ΩmA
$I5.67ΩmA
*RΦA-neutral or RΦA-remote earth
kΩ
156.65 With
Figure 5A0.217
~ 6 30645
1 Insulated
2
146.65 Without
Figure 5B0.182
~ 6 36538
16 Figure 5C 0 30504
3
166.65
None
WithFigure 5C
0.2180 30504
4
176.65 Without
Figure 5D0.179
Not applicable
37151
5
12C6.65
Bare
WithFigure 5A
0.196~ 6 33928
6
136.65 Without
Figure 5B0.181
~ 6 36740
6
Table 5High Voltage Tests without TPGs on Dry Pole, Pole 5 (Category 2 Tests)$ Capacitively coupled ambient current* RΦA-neutral or RΦA-remote earth = (VΦA-N)/ (I1013Ω)
Table 6High Voltage Tests without TPGs on Wet Pole 5 (Category 3 Tests)
Test
NEETRAC VΦA Downlead
Grounding Connectio
I5.67ΩmA
*RΦA-neutralor RΦA remote
Commentst
NoC
TestID
VΦA-
NkV
Downlead Connected to Neutral
Pole Band
Connection
Reference I1013ΩmA
mA or RΦA-remote
earthkΩ
1 18
6.8 With
Figure 5A
94 44
72.34 ~ 8mA capacitively coupled ambient
current in the I5.67Ω
Insulated circuit
2 19
6.8 Without
Figure 5B
39 17
174.36 ~ 6mA capacitively coupled ambient
current in the I5.67Ωcircuit
3 20
6.8
None
With
Figure 5C
89 44
154.54 ~ 0mA capacitively coupled ambient
current in the I5.67Ωcircuit
4 21 Figure 5D Not 261.546.8 Without 26 applicabl
e
5 22
6.8 With
Figure 5A
90 37
75.56 ~ 5mA capacitively coupled ambient
current in the I5.67Ωcircuit
Barecircuit
6 23
6.8 Without
Figure 5B
38 12
178.95 ~ 6mA capacitively coupled ambient
current in the I5.67Ωcircuit
* RΦA-neutral or RΦA-remote earth = (VΦA-N)/ (I1013Ω)
Test 1Ifault ~2000-3000kA
TestNo
NEETRA
CTest ID
*Grounding Method/Configuration
Worker Between
WorkerExposure Voltage
(V) or Current (ma)
ΦA to Remote Earth Voltage
(V)
Neutral to Remote Earth
Voltage(V)
Current in TPGsAmps
ZTPGs Across the Worker
Tests with Pole Band
1 1 Worksite grounds on Pole 2ΦA- ΦB- ΦC-N-PB
ΦA & PBΦA & N (Pole 2)
9.28.9
153 147 2105 Z3TPGs=4.4 mΩZ3TPGs=4.2 mΩ
2 2 Worksite grounds on Pole 2ΦA- ΦB- ΦC-PB-N
ΦA & PBΦA & N
8.911 95
157 145 2172 Z3TPGs=4.1 mΩZ =5 5 mΩΦA ΦB ΦC PB N ΦA & N
(Pole 2)11.95 Z4TPGs 5.5 mΩ
3 5 Worksite grounds on Pole 2 ΦA- ΦB- ΦC-PB-N
ΦA & N (10’ on source side of Pole 2)
21.22 154 139 2104 Z4TPGs=10 mΩ (Includes imp. of 10’ of phase and
neutral conductors)
4 6 Worksite grounds on Pole 2ΦA ΦB ΦC PB N
ΦA & N (10’ on load side of
12 154 142 2138 Z4TPGs=5.6 mΩΦA- ΦB- ΦC-PB-N on load side of
Pole 2)
Tests without Pole Band
5 3 Worksite grounds on Pole 2ΦA- ΦB- ΦC-N
ΦA & N(Pole 2)
9.3 156 146 2206 Z3TPGs=4.2 mΩ
6 4 Worksite grounds on Pole 2 ΦA & N 5 9 154 143 2150 Z =2 74 mΩ6 4 Worksite grounds on Pole 2ΦA- ΦB- ΦC & ΦB-N
ΦA & N(Pole 2)
5.9 154 143 2150 Z2TPGs=2.74 mΩ
7 7 Worksite grounds on Pole 2ΦA- ΦB- ΦC-N
ΦA & N (10’ on source side of Pole 2)
18.9 157 141 2195 Z3TPGs=8.6 mΩ (Includes imp. of 10’ of phase and neutral conductors)
8 8 Worksite grounds on Pole 2ΦA ΦB ΦC N
ΦA & N (10’ L d Sid
9.4 153 143 2105 Z3TPGs=4.5 mΩΦA- ΦB- ΦC-N on Load Side
of Pole 2)
9 9 Grounds on Pole 3ΦA- ΦB- ΦC-N
ΦA & N( Pole 2)
15.1 129 112 3417 Z3TPGs=4.4 mΩ
10 10 Grounds on Pole 3ΦA- ΦB- ΦC-N
ΦA & N ( Pole 1)
15.1 - - 3417 Z3TPGs=4.4 mΩ
11 11 Bracket Grounds on Poles 1 & 3 (ΦA- ΦB- ΦC-N on each pole)
ΦA & N on Pole 2
6.72 123 115 3259 (Pole 3)104 (Pole 1)
-
*Voltage applied between φA and N
AEP Wood Pole DistributionJobsite Grounding Tests
Preliminary Resultsy
EEI Occupational Safety and Health Committee ConferenceConference
Grounding – Industry PanelTucson, AZ
October 2, 2007John M. Schneider, Dr. Eng.John M. Schneider, Dr. Eng.Technology ConsultantDistribution Engineering [email protected]
Di l iDisclaimerThe procedures, methods and results presented herein are for e p ocedu es, et ods a d esu ts p ese ted e e a e o
informational purposes only and do not represent an endorsement by American Electric Power Company of any particular
grounding practices.
American Electric Power Company and its affiliates, expressly disclaims all liability, both direct and indirect, arising from the use or
application of any of the information, methods, or procedures found i thi t tiin this presentation.
Additionally, American Electric Power Company and its affiliates, disclaim any and all warranties with respect to the accuracy or usedisclaim any and all warranties with respect to the accuracy or use
of the information, methods, or procedures found in this presentation, whether expressed or implied, including the implied warranties of merchantability and fitness for a particular purpose.
2
E i t ti l G diEquipotential GroundingOSHA 1910.269 (n)(3) “Equipotential Zone”OSHA 1910.269 (n)(3) Equipotential Zone
Safe PotentialDifference?
3
‘E ga Pape ’‘Erga Paper’Discussions with various cluster ground barDiscussions with various cluster ground bar manufacturers, consultants and users revealed that the ‘Erga Paper’ forms the basis of its g peffectiveness in equipotential grounding applications. J T Bonne B E g W W Gibb V MJ. T. Bonner, B. Erga, W. W. Gibbs, V. M. Gregorius, “Test Results of Personal Protective Grounding on Distribution Line Wood Pole gConstruction,” IEEE Transactions on Power Delivery,Vol. 4, No. 1, January 1989.
4
EPRI T i i T i i VidEPRI Transmission Training Video
Phase
ClusterBar
© 2005 EPRI
Ground
5
CEA R t 101 d 876CEA Report 101 d 876
“Safety Grounding Practices for Personnel Working on Distribution Systems Up to 50kV,” CEA December 1997CEA, December 1997. Review of published wood pole measurement data & extensive computer simulations.data & extensive computer simulations.
“Equipotential Bonding…the effectiveness of this practice can range from nil to order-of-magnitude reductions in the resulting body currents, depending on the relative values of the f ll i k i bl l l it di l i t itfollowing key variables:…pole longitudinal resistance per unit length.”Pole longitudinal resistance is strongly dependent upon wood moisture content and distribution, which is
6
indeterminate.
‘Utility A’ Wood Pole Cluster G dGround Bar Test
In early 1970’s ‘Utility A’ field tested theIn early 1970 s, Utility A field tested the effectiveness of cluster ground bar:
S t t d t d j i tl ith l tSome tests conducted jointly with a cluster ground bar manufacturer.Ground bar did not provide consistentGround bar did not provide consistent protection.Concluded that ground bar should not beConcluded that ground bar should not be adopted.
7
‘Utility B’ Wood Pole Cluster G d B TGround Bar Tests
Recently commissioned series of testsRecently commissioned series of tests conducted at an independent laboratory
Contact resistance between cluster groundContact resistance between cluster ground bar and wood pole too high to be effective.Currently, leaning towards recommendingCurrently, leaning towards recommending installation of full pole ground, before maintenance on ungrounded structures.
8
‘I iti l’ W d P l R i t T t‘Initial’ Wood Pole Resistance TestCreosote (aged), CCA (new), Penta (new)Creosote (aged), CCA (new), Penta (new)Both dry & wet (tap water) poles tested.Aged creosote pole produced the worst case g p presult (best conductor of electricity), it was selected for the subsequent high voltage testingtesting.
T kΩ/ftType kΩ/ft(Worst case)
Creosote 0.66
CCA 7 1
9
CCA 7.1
Penta 15.5
AEP Test Set pAEP Test Setup
Recloser Test Pole7620 V
19.9 kV7620 V
2400/480 V
BixbySubstation
0.175Ω
10
Simulated Line MechanicSimulated Line MechanicHV Probe
Line-ground voltage500 Ω Body Impedance
10 Ω ShuntLine mechanic current
SimulatedGaff
Many standards (IEEE Std 80 2000) typically use
SimulatedHand130 cm2
Many standards (IEEE Std 80-2000) typically use 1000Ω body impedance.Neglects insulation provided by work boots, gloves &
11
clothing.Simulated gaff’s penetrated ~3/4”.
AEP Sh k C it iAEP Shock Criteria60 Hz Threshold ReactionCurrent (mA) Reaction
1 Perception level
3 Painful shock*
10 Let Go
E t i i t t30 Extreme pain, respiratory arrest, severe muscular contraction
157 ** Ventricular fibrillationLimiting Criteria
* Startle response may result in a fall, dropped tool, … .
** Hand to foot path, 1 second duration, 99.5% probability of no ventricular fibrillation for 154 lbs. person (Dalziel).
12
A o d of ca tionA word of caution…Distribution system design, service history, y g , y,operating procedures and environmental factors present a wide range of variability. Key variables are unknown or indeterminate.Cannot test every conceivable ‘real world’ scenario.Tests are intended to be representative of worst case conditions.Hence, caution must be exercised in the
li ti f th lt t d13
application of the results presented.
Nomenclature:Li M h i G ffLine Mechanic on Gaffs
GroundingJumper
PhaseWire
Insulator
Hands
NeutralWire
Bare Pole Ground w/Staples Line
Mechanic
304/116 mA1’
MoldingExtrapolated to
34.5/12 kV
H i ht
Gaffs
Ground Rod
Height
14
Cluster Ground Bar‘D ’ A d C t P l‘Dry,’ Aged, Creosote Pole
219/79 A221/80 A* 219/79 mA
ClusterG d
17.5’
221/80 mA*19.5’
18.5’
GroundBar
* l d / k
9/3 mA
* Extrapolated to 34.5/12 kV
27/10 mA
Bare Pole Ground w/Clips & Nails
15
Major OutcomeMajor OutcomeThe cluster ground bar does not consistentlyThe cluster ground bar does not consistently achieve a sufficiently low resistance contact with the wood, to provide an effective equipotential zone for a line mechanic working on the pole.
High Contact
Resistance
16
‘Wet ’ Aged Creosote Pole TestsWet, Aged, Creosote Pole Tests33/12 mA343/129 mA*
23/9 mA19.5’
227/85 mA
Isolated
* Extrapolated to 34.5/12 kV
39/15 mA 46/18 mA
17.5’14.5’
-11.5’
-8.5’
26/10 mA 17.5’227/87 mA
15.5’
17.5’
17
‘Wet ’ Aged Penta Pole TestsWet, Aged, Penta Pole Tests684/231 mA*
19 5’19.5’
165/63 mA3’
15/1 mA10’
* Extrapolated to 34.5/12 kV
286/110 mA8’
42/16 mA13’10’ Ground
18
S mmaSummaryThe presence of a ground rod, eitherThe presence of a ground rod, either permanent or temporary, does not adequately reduce the line mechanicadequately reduce the line mechanic current.The equipotential zone established with aThe equipotential zone established with a single lag screw (spike) does not protect the line mechanic in all positions on thethe line mechanic in all positions on the pole.
19
S mma Cont’dSummary Cont’d.Current through the line mechanic can be greduced substantially by:
Applying a single-point or bracket ground at the jobsitejobsite … Insuring the integrity of the neutral conductor and connections in the vicinity…Creating an equipotential zone (EZ) by bonding the neutral to either:
A full, uninsulated pole ground nailed/stapled to the pole., p g / p pA partial (10’), uninsulated pole ground nailed/stapled to the pole. (Must be disconnected from neutral when not in use.)
20
S mma Cont’dSummary Cont’d.The effective EZ extends from the midpoint of the pole ground length to the highest attachment on the structure.
In some circumstances, steps must be taken to protect the line , p pmechanic when entering or exiting the EZ.
EZ*10’
5’EZ*
PoleGround
d
d/2Molding
21Partial Pole GroundFull Pole Ground
Questions?Questions?
22
Single-Point Ground Radial Distribution LinePotential Distributions & Current Paths
PhasePotential
CurrentPath
Vs
ØØ
N N
G
Neutral
G
23
Potential
AEP Wood Pole DistributionJobsite Grounding Tests
Preliminary Resultsy
EEI Occupational Safety and Health Committee ConferenceConference
Grounding – Industry PanelTucson, AZ
October 2, 2007John M. Schneider, Dr. Eng.John M. Schneider, Dr. Eng.Technology ConsultantDistribution Engineering [email protected]
Di l iDisclaimerThe procedures, methods and results presented herein are for e p ocedu es, et ods a d esu ts p ese ted e e a e o
informational purposes only and do not represent an endorsement by American Electric Power Company of any particular
grounding practices.
American Electric Power Company and its affiliates, expressly disclaims all liability, both direct and indirect, arising from the use or
application of any of the information, methods, or procedures found i thi t tiin this presentation.
Additionally, American Electric Power Company and its affiliates, disclaim any and all warranties with respect to the accuracy or usedisclaim any and all warranties with respect to the accuracy or use
of the information, methods, or procedures found in this presentation, whether expressed or implied, including the implied warranties of merchantability and fitness for a particular purpose.
2
E i t ti l G diEquipotential GroundingOSHA 1910.269 (n)(3) “Equipotential Zone”OSHA 1910.269 (n)(3) Equipotential Zone
Safe PotentialDifference?
3
‘E ga Pape ’‘Erga Paper’Discussions with various cluster ground barDiscussions with various cluster ground bar manufacturers, consultants and users revealed that the ‘Erga Paper’ forms the basis of its g peffectiveness in equipotential grounding applications. J T Bonne B E g W W Gibb V MJ. T. Bonner, B. Erga, W. W. Gibbs, V. M. Gregorius, “Test Results of Personal Protective Grounding on Distribution Line Wood Pole gConstruction,” IEEE Transactions on Power Delivery,Vol. 4, No. 1, January 1989.
4
EPRI T i i T i i VidEPRI Transmission Training Video
Phase
ClusterBar
© 2005 EPRI
Ground
5
CEA R t 101 d 876CEA Report 101 d 876
“Safety Grounding Practices for Personnel Working on Distribution Systems Up to 50kV,” CEA December 1997CEA, December 1997. Review of published wood pole measurement data & extensive computer simulations.data & extensive computer simulations.
“Equipotential Bonding…the effectiveness of this practice can range from nil to order-of-magnitude reductions in the resulting body currents, depending on the relative values of the f ll i k i bl l l it di l i t itfollowing key variables:…pole longitudinal resistance per unit length.”Pole longitudinal resistance is strongly dependent upon wood moisture content and distribution, which is
6
indeterminate.
‘Utility A’ Wood Pole Cluster G dGround Bar Test
In early 1970’s ‘Utility A’ field tested theIn early 1970 s, Utility A field tested the effectiveness of cluster ground bar:
S t t d t d j i tl ith l tSome tests conducted jointly with a cluster ground bar manufacturer.Ground bar did not provide consistentGround bar did not provide consistent protection.Concluded that ground bar should not beConcluded that ground bar should not be adopted.
7
‘Utility B’ Wood Pole Cluster G d B TGround Bar Tests
Recently commissioned series of testsRecently commissioned series of tests conducted at an independent laboratory
Contact resistance between cluster groundContact resistance between cluster ground bar and wood pole too high to be effective.Currently, leaning towards recommendingCurrently, leaning towards recommending installation of full pole ground, before maintenance on ungrounded structures.
8
‘I iti l’ W d P l R i t T t‘Initial’ Wood Pole Resistance TestCreosote (aged), CCA (new), Penta (new)Creosote (aged), CCA (new), Penta (new)Both dry & wet (tap water) poles tested.Aged creosote pole produced the worst case g p presult (best conductor of electricity), it was selected for the subsequent high voltage testingtesting.
T kΩ/ftType kΩ/ft(Worst case)
Creosote 0.66
CCA 7 1
9
CCA 7.1
Penta 15.5
AEP Test Set pAEP Test Setup
Recloser Test Pole7620 V
19.9 kV7620 V
2400/480 V
BixbySubstation
0.175Ω
10
Simulated Line MechanicSimulated Line MechanicHV Probe
Line-ground voltage500 Ω Body Impedance
10 Ω ShuntLine mechanic current
SimulatedGaff
Many standards (IEEE Std 80 2000) typically use
SimulatedHand130 cm2
Many standards (IEEE Std 80-2000) typically use 1000Ω body impedance.Neglects insulation provided by work boots, gloves &
11
clothing.Simulated gaff’s penetrated ~3/4”.
AEP Sh k C it iAEP Shock Criteria60 Hz Threshold ReactionCurrent (mA) Reaction
1 Perception level
3 Painful shock*
10 Let Go
E t i i t t30 Extreme pain, respiratory arrest, severe muscular contraction
157 ** Ventricular fibrillationLimiting Criteria
* Startle response may result in a fall, dropped tool, … .
** Hand to foot path, 1 second duration, 99.5% probability of no ventricular fibrillation for 154 lbs. person (Dalziel).
12
A o d of ca tionA word of caution…Distribution system design, service history, y g , y,operating procedures and environmental factors present a wide range of variability. Key variables are unknown or indeterminate.Cannot test every conceivable ‘real world’ scenario.Tests are intended to be representative of worst case conditions.Hence, caution must be exercised in the
li ti f th lt t d13
application of the results presented.
Nomenclature:Li M h i G ffLine Mechanic on Gaffs
GroundingJumper
PhaseWire
Insulator
Hands
NeutralWire
Bare Pole Ground w/Staples Line
Mechanic
304/116 mA1’
MoldingExtrapolated to
34.5/12 kV
H i ht
Gaffs
Ground Rod
Height
14
Cluster Ground Bar‘D ’ A d C t P l‘Dry,’ Aged, Creosote Pole
219/79 A221/80 A* 219/79 mA
ClusterG d
17.5’
221/80 mA*19.5’
18.5’
GroundBar
* l d / k
9/3 mA
* Extrapolated to 34.5/12 kV
27/10 mA
Bare Pole Ground w/Clips & Nails
15
Major OutcomeMajor OutcomeThe cluster ground bar does not consistentlyThe cluster ground bar does not consistently achieve a sufficiently low resistance contact with the wood, to provide an effective equipotential zone for a line mechanic working on the pole.
High Contact
Resistance
16
‘Wet ’ Aged Creosote Pole TestsWet, Aged, Creosote Pole Tests33/12 mA343/129 mA*
23/9 mA19.5’
227/85 mA
Isolated
* Extrapolated to 34.5/12 kV
39/15 mA 46/18 mA
17.5’14.5’
-11.5’
-8.5’
26/10 mA 17.5’227/87 mA
15.5’
17.5’
17
‘Wet ’ Aged Penta Pole TestsWet, Aged, Penta Pole Tests684/231 mA*
19 5’19.5’
165/63 mA3’
15/1 mA10’
* Extrapolated to 34.5/12 kV
286/110 mA8’
42/16 mA13’10’ Ground
18
S mmaSummaryThe presence of a ground rod, eitherThe presence of a ground rod, either permanent or temporary, does not adequately reduce the line mechanicadequately reduce the line mechanic current.The equipotential zone established with aThe equipotential zone established with a single lag screw (spike) does not protect the line mechanic in all positions on thethe line mechanic in all positions on the pole.
19
S mma Cont’dSummary Cont’d.Current through the line mechanic can be greduced substantially by:
Applying a single-point or bracket ground at the jobsitejobsite … Insuring the integrity of the neutral conductor and connections in the vicinity…Creating an equipotential zone (EZ) by bonding the neutral to either:
A full, uninsulated pole ground nailed/stapled to the pole., p g / p pA partial (10’), uninsulated pole ground nailed/stapled to the pole. (Must be disconnected from neutral when not in use.)
20
S mma Cont’dSummary Cont’d.The effective EZ extends from the midpoint of the pole ground length to the highest attachment on the structure.
In some circumstances, steps must be taken to protect the line , p pmechanic when entering or exiting the EZ.
EZ*10’
5’EZ*
PoleGround
d
d/2Molding
21Partial Pole GroundFull Pole Ground
Questions?Questions?
22
Single-Point Ground Radial Distribution LinePotential Distributions & Current Paths
PhasePotential
CurrentPath
Vs
ØØ
N N
G
Neutral
G
23
Potential
OSHA 1910 269 (n)(3)OSHA 1910 269 (n)(3)OSHA 1910.269 (n)(3)OSHA 1910.269 (n)(3)“Equipotential Zone. Temporary “Equipotential Zone. Temporary q p p yq p p y
protective grounds SHALL be protective grounds SHALL be placed at such locations andplaced at such locations andplaced at such locations and placed at such locations and arranged in such a manner as to arranged in such a manner as to prevent each employee from prevent each employee from being exposed to hazardousbeing exposed to hazardousbeing exposed to hazardous being exposed to hazardous differences in electrical differences in electrical
t ti l ”t ti l ”potential.”potential.”
OSHA does not distinguish OSHA does not distinguish ggbetween overhead distribution between overhead distribution and transmission when it come and transmission when it come to grounding for employeeto grounding for employeeto grounding for employee to grounding for employee protection.protection.pp
OSHA 1910 269 (n)(3) CoversOSHA 1910 269 (n)(3) CoversOSHA 1910.269 (n)(3) CoversOSHA 1910.269 (n)(3) Covers
Overhead DistributionOverhead DistributionOverhead DistributionOverhead DistributionOverhead TransmissionOverhead TransmissionUnderground DistributionUnderground DistributionUnderground TransmissionUnderground TransmissionSubstationsSubstationsSubstationsSubstationsNetworksNetworks
1926 Subpart V Preamble1926 Subpart V Preamblepp
“Grounding practices that do“Grounding practices that doGrounding practices that do Grounding practices that do not provide an equipotential not provide an equipotential p q pp q pzone in which the employee zone in which the employee i f d d f lti f d d f ltis safeguarded from voltage is safeguarded from voltage differences do not providedifferences do not providedifferences do not provide differences do not provide complete protection.”complete protection.”
““Th i ti t d d iTh i ti t d d i““The existing standard requires The existing standard requires grounds to be placed betweengrounds to be placed betweengrounds to be placed between grounds to be placed between the work location and all the work location and all sources of energy, and as sources of energy, and as close as practicable to theclose as practicable to theclose as practicable to the close as practicable to the work location. Alternatively, work location. Alternatively, grounds could be placed at the grounds could be placed at the work location ”work location ”work location.work location.
“Although these requirements “Although these requirements g qg qare intended to protect are intended to protect employees in case the line onemployees in case the line onemployees in case the line on employees in case the line on which they are working is which they are working is
id t llid t ll i d thi d thaccidentally reaccidentally re--energized, the energized, the existing provisionsexisting provisions do notdo notexisting provisions existing provisions do notdo notensure the grounding practices ensure the grounding practices and equipment are adequateand equipment are adequateand equipment are adequate and equipment are adequate to provide this protection.”to provide this protection.”
Dalziel’s ForumlaDalziel’s ForumlaDalziel s ForumlaDalziel s Forumla
Perception LevelPerception LevelPerception LevelPerception Level1 1 –– 3 mA, or 0.001 A3 mA, or 0.001 A
Let Go Threshold:Let Go Threshold:99 25 mA or 0 009 A25 mA or 0 009 A9 9 –– 25 mA, or 0.009 A25 mA, or 0.009 A
Ventricular Fibulation Ventricular Fibulation Threshold:Threshold:
164 mA or 0 164 A164 mA or 0 164 A164 mA, or 0.164 A164 mA, or 0.164 A
How Much Can A Worker How Much Can A Worker Take ?Take ?
V = I RV = I R= (0.164A) X (500 ohm)= (0.164A) X (500 ohm)= 82 Volts= 82 Volts
Phase
1 ohm
500 ohm Person
Ground
V 7200 V
5 ohm
V 7200 VI = = = 14.23 Amps
R 506 ohmsR 506 ohms
500 ohm 1 ohm
Phase
Person
63 x 10 ohm pole
Ground
5 ohm
V 7200 VI = = = 2.4 mA
R 3 000 506 hR 3,000,506 ohms
Speed of LightSpeed of LightSpeed of LightSpeed of Light
186,000 miles/second186,000 miles/second
77 1/2 times around1/2 times around77--1/2 times around 1/2 times around earth/secondearth/secondearth/secondearth/second
Current Takes All Paths to Current Takes All Paths to G dG dGroundGround
Current Likes the LeastCurrent Likes the LeastCurrent Likes the Least Current Likes the Least Resistive Path to GroundResistive Path to Ground
300’300
300’300’
500 ohm personI.002 ohm1 ohm
500 ohm person
7 000 h l
I1
I2
1 ohm 7,000 ohm pole
5 ohm
V 7,200 VI = = = 3,607 Amps
5 ohm
I 3,607 Amps1 R 2.002 ohm
V 3 607 VV 3,607 VI = = = 480 mA = 0.5 Amp2 R 7 506 ohm2 R 7,506 ohm
• PolePole
Rm=500 VmRj 0 002Ij ImI ohm
Rm=500 VmRj=0.002
1 h1 ohm
Vm = It x Rp5 ohm
Vm = It x Rp
Vm = 3924 (0.002) = 7.84 VIm = Vm = 7.84 = 15 mA
Rm 500Rm 500
7200 volts
G Remote grounding
7200 volts
grounding elbow
Vault
500 ohm personI.002 ohm1 ohm
500 ohm person
100 h V lt
I1
I2
1 ohm 100 ohm Vault
5 ohm
V 7,200 VI = = = 3,607 Amps
5 ohm
I 3,607 Amps1 R 2.002 ohm
V 3 607 VV 3,607 VI = = = 5.95 A2 R 606 ohm2 R 606 ohm
7200 volts
G Remote grounding
7200 volts
grounding elbow
Vault
Equipotential Grounding7200 volts
Equipotential Grounding
G Remote grounding
7200 volts
grounding elbow
UG Grounding
G Touch Volts = 2121 volts
SS
• UG TESTS
G Touch Volts= 28 volts
SS