TESTING GROUNDING SYSTEMS

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TESTING GROUNDING SYSTEMS

• Originally Developed by
• RONALD J. RENOWDEN - CMSP
• Denver Field Office Supervisor, MNM MSHA
• Rocky Mountain District
• Denver, Colorado

Enhanced by Roy W. Milam Electrical
Engineer/Instructor National Mine Health and
Safety Academy Beckley, West Virginia
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TESTING GROUNDING SYSTEMS
As required by

• 30 CFR 56/57.12028

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56/57.12028 the REG.

• Continuity and resistance of grounding systems
  shall be tested immediately after installation,
  repair, and modification and annually
  thereafter. A record of the resistance measured
  during the most recent test shall be made
  available on request by the Secretary or his duly
  authorized representative.

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WHY DO WE TEST ?
Ensure that continuity resistance tests are
conducted on a specific schedule (at least
annually) Alert mine operators if there is a
problem in the grounding system Problem may not
allow the circuit protective devices to quickly
operate when faults occur
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WHY DO WE TEST?

• With exception of fixed installations - Numerous
  fatalities and injuries have occurred due to HIGH
  resistance or LACK of continuity in equipment
  grounding systems
• Proper testing and maintenance of grounding
  systems can prevent electrical accidents

This all sounds so good that we made it the
policy regarding 12028.
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56/57.12028 the POLICY
The intent of this standard is to ensure that
continuity and resistance tests of grounding
systems are conducted on a specific schedule.
These tests will alert the mine operator if a
problem exists in the grounding system which may
not allow the circuit protective devices to
quickly operate when faults occur. With the
exception of fixed installations, numerous
fatalities and injuries have occurred due to high
resistance or lack of continuity in equipment
grounding systems. These accidents could have
been prevented by proper testing and maintenance
of grounding systems.
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Grounding systems typically include the
following 1. equipment grounding conductors -
the conductors used to connect the metal frames
or enclosures of electrical equipment to the
grounding electrode conductor 2. grounding
electrode conductors - the conductors connecting
the grounding electrode to the equipment
grounding conductor and 3. grounding electrodes
- usually driven rods connected to each other by
suitable means, buried metal, or other effective
methods located at the source, to provide a low
resistance earth connection.
P O L I C Y
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Operators shall conduct the following tests 1.
equipment grounding conductors - continuity and
resistance must be tested immediately after
installation, repair, or modification, and
annually if conductors are subjected to
vibration, flexing or corrosive environments
2. grounding electrode conductors - continuity
and resistance must be tested immediately after
installation, repair, or modification, and
annually if conductors are subjected to
vibration, flexing or corrosive environments and
3. grounding electrodes - resistance must be
tested immediately after installation, repair, or
modification, and annually thereafter.
P O L I C Y
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56/57.12028 the POLICY
Conductors in fixed installations, such as rigid
conduit, armored cable, raceways, cable trays,
etc., that are not subjected to vibration,
flexing or corrosive environments may be examined
annually by visual observation to check for
damage in lieu of the annual resistance test.
When operators elect to conduct this visual
examination as a method of compliance with 30
CFR56/57.12028, MSHA will require that a record
be maintained of the most recent annual visual
examination.
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56/57.12028 the POLICY
Grounding conductors in trailing cables, power
cables, and cords that supply power to tools and
portable or mobile equipment must be tested as
prescribed in the regulation. This requirement
does not apply to double insulated tools or
circuits protected by ground-fault-circuit
interrupters that trip at 5 milli-amperes or
less.
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56/57.12028 the POLICY
Testing of equipment grounding conductors and
grounding electrode conductors is not required if
a fail-safe ground wire monitor is used to
continuously monitor the grounding circuit and
which will cause the circuit protective devices
to operate when the grounding conductor
continuity is broken.
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56/57.12028 the POLICY
A record of the most recent resistance tests
conducted must be kept and made available to the
Secretary or his authorized representative upon
request. When a record of testing is required by
the standard, MSHA intends that the test results
be recorded in resistance value in ohms.
Thats all the policy! But what does it all mean
?
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TYPICAL GROUNDING SYSTEMhas three parts
EQUIPMENT GROUNDING CONDUCTORS (the most
important part!!!) Grounding Electrode
Conductors Grounding Electrodes
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EQUIPMENT GROUNDING CONDUCTOR

• The conductors used to connect the metal frames
  or enclosures of electrical equipment to the
  grounding electrode conductor
• Life Wire Life Line
• Most important electrical safety item in the
  electrical system
• People protector

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• Equipment Grounding Conductors

GROUNDING BUS maybe in MCC
Motor 1
Motor 4
Motor 2
Motor 3
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GROUNDING ELECTRODE CONDUCTOR

• Conductor that connects the grounding electrode
  and the transformer to the equipment grounding
  conductor

Main Ground Bus maybe in the MCC
TRANSFORMER
Earth
Grounding Electrode
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GROUNDING ELECTRODES

• Usually driven rods connected to each other by
  suitable means, buried metal plates, or any other
  effective methods located at the power source to
  provide a low resistance earth connection.
• What is actually in contact with Earth.

Rod
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EQUIPMENT GROUNDING CONDUCTORS Test for
Continuity and Resistance
Immediately after - INSTALLATION, REPAIR,
OR MODIFICATION, AND ANNUALLY, IF conductors
are subjected to VIBRATION FLEXING CORR
OSIVE ENVIRONMENTS
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GROUNDING ELECTRODE CONDUCTOR Test for
Continuity and Resistance
Immediately after - INSTALLATION, REPAIR,
OR MODIFICATION, AND ANNUALLY, IF conductors
are subjected to VIBRATION FLEXING CORR
OSIVE ENVIRONMENTS
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GROUNDING ELECTRODESTesting
Test for Resistance (Earth)
Immediately after - INSTALLATION, REPAIR,
OR MODIFICATION, AND ANNUALLY thereafter.
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Are there EXCEPTIONS ?
YES !!!
In lieu of doing annual resistance tests, the
Grounds may be examined annually by visual
observation to check for damage.. BUT ONLY
IF The conductors are in fixed locations such
as RIGID CONDUIT ARMORED CABLE RACEWAYS CABLE
TRAYS, ETC (theres more)
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MORE EXCEPTIONS

• These FIXED LOCATIONS
• MUST NOT be SUBJECTED TO

Vibration
FLEXING
CORROSIVES
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HOW MUCH IS TOO MUCH ?
FLEXING
VIBRATION
CORROSIVES
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HOW MUCH IS TOO MUCH ?

• The inspector makes the final determination
  concerning areas acceptable to visual
  examinations

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IF VISUAL EXAMS ARE CONDUCTED

• MSHA policy requires that a WRITTEN RECORD
  be maintained of the most recent ANNUAL
  VISUAL EXAMINATION, can be electronic

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EQUIPMENT GROUNDING CONDUCTORS IN
Trailing cables Power cables Cords supplying
power to tools Cords and cables supplying power
to portable or mobile equipment MUST BE TESTED
AS PRESCRIBED IN THE REGULATION
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When Is Testing NOT Required?
IF a fail-safe ground wire monitor is used. The
monitor will cause the circuit protective device
to open when the grounding conductor continuity
is broken. It continuously monitors the
continuity of the grounding conductor. Double
insulated tools are used. There is no grounding
conductor to test. If the circuit used
incorporates a GFCI that trips at 5 milli-amps or
LESS. There are 110v and 220v devices now
available.
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RECORDS

• RESISTANCE VALUES IN OHMS
• Most recent tests
• Must be available for review by MSHA upon request
• No specific format required
• Be legible
• Visual exam records

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A little ADVICE ?

• Should have electrical knowledge
• Know how to test and use the instrument/PPE
• Know what kind of electrical system
• Check circuit protective device vs. Ohms test
• Check with power off
• Proper size ground wire
• Never let metal framework or earth be the primary
  grounding conductor
• Never use peg grounding

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NATIONAL ELECTRICAL CODE

• Section 250-51-EFFECTIVE GROUNDING PATH The path
  to ground from circuits, equipment, and metal
  enclosures for conductors shall
• Be permanent and electrically continuous
• Have capacity to conduct safely any fault
  current likely to be imposed on it, and
• Have sufficient low impedance to limit the
  voltage to ground and to facilitate the
  operation of the circuit protective devices.
• The earth SHALL NOT be used as the sole equipment
  grounding conductor

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OK, now that the operator has tested his
grounding circuit and recorded the results, what
do we do with them?
In other words
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How do you know if the ground wire resistance is
okay?

• Can apply good old OHMS LAW
• E IR E VOLTS I AMPS (current) R
  RESISTANCE (ohms) E
  I R

E
I
R
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BUT ..FIRST !

• Remember OHMS LAW ! ( E IR )
• Circuits are protected by fuses/breakers against
  SHORT CIRCUITS AND GROUND FAULTS
• IF GF occurs, we want the fuse/breaker to clear
  ASAP!
• Question? Where does the current go when a ground
  fault occurs?
• GROUNDING CONDUCTOR carries the fault current
  back to the SOURCE (current does not return to
  earth, but sometimes travels thru it).
• FAULT CURRENT takes paths of LEAST resistance?

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CONTINUED

• IF ground wire is missing or high resistance,
  current will flow in dangerous places to return
  to the source.
• TOUCH AND STEP POTENTIALS MAY EXIST ON THE FRAMES
  OF EQUIPMENT AND ON THE EARTH
• HAZARDOUS!!!!! SHOCK, BURNS, ELECTROCUTION..DE
  ATH

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EXAMPLE

• The operators record of resistance testing (in
  OHMS) shows the following
• Crusher motor 1 ohm
• Screen Deck .5 ohm
• Stacker main motor 1.5 ohm
• Conveyor 1 1 ohm

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ExampleWhats Next ?

• Need Circuit/System VOLTAGE
• Motors supplied with 3 phase, 460 volt AC
• Grounded WYE Service Ø-Ø460v Ø-grd265v
• Need Fuse/Circuit Breaker Size (for each)
• 100hp, 125amps, 3-fuses _at_ 300amps each (crusher
  motor)
• 40hp, 52amps, 3-fuses _at_ 100amps each (screen)
• 25hp, 34amps, 70 amp breaker (stacker)
• 10hp, 14amps, 30 amp breaker (conveyor 1)

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GROUNDED WYE

• Grounded WYE Service 460 V, 3-PHASE ØA-ØB460v
  ØA-grd265V ØA-ØC460v ØB-grd265V
  ØB-ØC460v ØC-grd265V
  

O A
B
A
O B
C
O C
Ground
Ground
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How good is the equipment grounding?

• CONVEYOR 1 1ohm, Ø-grd265v.
• How much FC will flow if GF at motor frame?
• To find current (ohms law) I E/R.
  265v I 265 amp FC On 30 amp 1ohm
  breaker
  
• 265a.(FC)/30a(bkr) 8.83...Whats this mean?
• Breaker will TRIP almost instantaneous level ASAP
• GOOD GROUNDING!

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LETS CHECK ANOTHER !

• SCREEN .5 ohms, Ø-grd265v 265v I
  530 amp FC On 100 amp
  .5ohm fuses
• 530a.(FC)/100a.(fu) 5.30...Whats this mean?
• Fuse will not TRIP near instantaneous level
  (ASAP)
• GOOD GROUNDING ? Questionable! Review trip curve
  chart for fuse to find trip time.
• ADVICE Check connections loose, dirty, wire
  size? CORRECT/ REPAIR! Screens- flexing and
  vibration!

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LETS CHECK ANOTHER !

• CRUSHER 1 ohm, Ø-grd265v 265v I
  265 amp FC 300 amp fuses
  1ohm
• 265a.(FC)/300a.(fu) .88 ...Whats this mean?
• Fuse will not BLOW (must see at least 125 to
  begin)
• DANGEROUS GROUNDING UNACCEPTABLE!
• ADVICE Check connections loose, dirty, wire
  size? CORRECT REPAIR! Crushers - flexing and
  vibration

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Lets make a small change!!!
CRUSHER 1 ohm, Ø-grd265v, but this time were
going to use a 100 Amp, Magnetic Trip Circuit
Breaker with a trip range of 150-480 amps, set on
LOW, as protection.

• 265v
• I 265 amp FC CB set 150 Amps
• 1ohm

• 265a.(FC)/150a.(Inst.) 1.77 ...Whats this mean?

• Breaker will TRIP instantaneously.

• GOOD GROUNDING!

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Corner Grounded Delta

• Corner Grounded Delta Service 460 V,
  3-PHASE ØA-ØB460v ØA-grd0V ØA-ØC460v
  ØB-grd460V ØB-ØC460v ØC-grd460V
  

O A
B
O B
C
O C
A
Ground
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Corner Grounded Delta

• CONVEYOR 1 1ohm, Ø-grd480v.
• How much FC will flow if GF at motor frame?
• To find current (ohms law) I E/R.
  480v I 480 amp FC On 30 amp
  breaker
  1ohm
• 480a.(FC)/30a(bkr) 16.0...Whats this mean?
• Breaker will TRIP at instantaneous level ASAP
• GOOD GROUNDING !

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Corner Grounded Delta

• SCREEN .5 ohms, Ø-grd480v 480v
• I .5ohm 960 amp FC On 100 amp
  fuses
  
• 960a.(FC)/100a.(fu) 9.60...Whats this mean?
• Fuse will TRIP near instantaneous level (ASAP)
• GOOD GROUNDING !

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Corner Grounded Delta

• CRUSHER 1 ohm, Ø-grd480v 480v I
  480 amp FC 300 amp fuses
  1ohm
• 480a.(FC)/300a.(fu) 1.6 ...Whats this mean?
• Fuse will start heating up. (must see at least
  125 to begin) Will blow on very long delay.
• DANGEROUS GROUNDING UNACCEPTABLE!
• ADVICE Check connections loose, dirty, wire
  size? CORRECT REPAIR! Crushers - flexing and
  vibration

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FLOATING or UNGROUNDED SYSTEMS
BE AWARE! HAZARDOUS- IF NOT MONITORED FOR
GROUNDS AND MAINTAINED ELECTRICAL SHOCK THERMAL
ARC FLASH BURNS ELECTROCUTION FIRES
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Now lets look at some of the test instruments
that can be used to test the grounding system
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Instruments used to test the grounding electrode
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This is a Biddle Earth Tester that is battery
powered. It uses 6 C cells. It is used to test
the grounding electrode resistance.
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This a type of Biddle Earth Tester that is
battery powered. It is powered by 4 C cells. It
is used to test the grounding electrode
resistance.
Measuring the resistance of the equipment
grounding conductor for this piece of equipment.
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This is a Biddle Earth Tester that is used to
test the resistance of the grounding electrode.
It is powered by the use of the hand crank on the
side of the device.
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This is the Field Kit that is used with an Earth
Tester to measure the resistance of the grounding
electrode. It contains 2 metal stakes, and 3
conductors of various lengths.
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Set-Up for Testing Grounding Electrode Resistance
C1 P1 G P2 C2
Earth
Test Rods
Grounding Electrode
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This person is driving a test rod to be used
while testing the grounding electrode resistance.
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This is the method used when testing the
grounding electrode resistance with a Biddle
Earth Tester.
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The results obtained during the testing of the
grounding electrode resistance are plotted on a
graph. The actual resistance of the electrode is
the flat part of the graph.
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Another method of testing the resistance of the
grounding electrode is using a voltage source,
such as a vehicle battery, a voltmeter and an
ammeter. We do not recommend this method as it
can be extremely dangerous.
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This is one possible set-up for testing the
grounding electrode resistance.
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This is the method used when testing the
grounding electrode resistance with a Biddle
Earth Tester.
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Use OHMS LAW to calculate the resistance values
your tests found. RE/I
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The results obtained during the testing of the
grounding electrode resistance are plotted on a
graph. The actual resistance of the electrode is
the flat part of the graph.
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This is the ECOS Pow-R-Mate Tester. It is used to
test the resistance and impedance of the
grounding electrode. It is both battery powered
and plug-and-cord connected.
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This is a Biddle Insulation Tester that is used
to test the insulation value of conductors,
motors, transformers, and cables. It is powered
by the hand crank on the side of the device. This
device should not be used to test the grounding
electrode nor the equipment grounding conductors.
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Instruments used to test the grounding electrode
conductor and the equipment grounding conductors
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This is a Fluke Graphics Multi-Meter which can be
used to measure the resistance of the equipment
grounding conductors.
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This is a Fluke Multi-Meter which can be used to
measure the resistance of the equipment grounding
conductors.
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This is a Simpson Multi-Meter which can be used
to measure the resistance of the equipment
grounding conductors. It is reading an open
conductor now.
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This is a Simpson Multi-Meter, with test leads
attached, which can be used to measure the
resistance of the equipment grounding conductors.
It is reading an open conductor now.
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This is a Simpson Multi-Meter, with test leads
attached, which can be used to measure the
resistance of the equipment grounding conductors.
It is reading Zero ohms resistance as the test
leads are contacting each other. The meter is
being zeroed.