Transcript basics_of_clamp_grou..

Basics Clamp-on Ground
Resistance Tester
© 2007 Ideal Industries
www.idealindustries.com
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Integrity of the Ground
• Three key components of
the single ground
Electrode
– Resistance between
Ground Electrode and
Clamp, Bonding in multirod applications
– Resistance of contact
between soil and rod(s)
– Resistance of Concentric
Shells of earth
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Integrity of the Ground
• Effect of the Soil on Electrode resistance
– Soil conditions, and soil types
• Sandy soil have higher resistance that clay or
loam
– Seasonal Environmental conditions which
effect both moisture and temperature
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Integrity of the Ground
• Ground Electrode
– Typically measured only at installation
• In truth very seldom tested by installers.
• Only one out of 10 said they test single point
ground Electrodes, in an informal survey
– Methods of testing the ground electrode
• Fall potential test, and Slope method
• Ground resistance clamps
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Test Equipment
Clamp-On Ground
resistance tester.
• The Resistance of the
total ground network is
now measured.
• This is a loop tester and
requires the utility
return to act in simples
terms as the aux rods.
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Test Equipment
Clamp-On Ground
resistance tester.
• Make sure you have a clean,
clear connection of the clamp
around the ground.
• Select and measure the current,
if current is > 5 (this my very
from manufacture) resistance
can’t be measured using the
ground clamp tester.
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Test Equipment
Clamp-On Ground
resistance tester.
• If voltage (E) is applied to any
measured grounding probe
R(X) through a special
transformer , current (I) flows
through the circuit and can be
measured , thereby
establishing an equation which
can be used to calculate R(x)
– E/I=RX. If E is kept constant, then
through the use of a CT current can
be detected and the resistance of the
ground electrode circuit my be
achieved.
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Clamp-On Ground Resistance
Measurement
• R1, R2, ---Rn can be considered as a large parallel
resistive circuit. As we know, a large number of
resistors in parallel with each other effectively create a
resistance value which is lower than the value of the
least resistive path.
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Here is an easy to understand example of parallel resistance.
Simple equation, 1/R = 1/R1 + 1/R2 + 1/R3 + 1/R4.
If R1=3.5, R2 =4, R3 = 4.5 and R4= 5,
then 1/R=0.285 +0.25 + 0.22 + 0.2, or R= 1.04 ohms.
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Clamp-On Ground Resistance
Test
• Advantage is that the
ground electrode
doesn’t need to be
disconnected from the
electrical system.
• The jaws of the clamp
must be placed in the
electrical path of the
systems grounding wire
to the ground rod
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Clamp-On Ground Resistance
Test
• This is an example the Clamp-On Ground tester is being used to
measure the ground resistance in a street light application
• Note in this application the tester is place between the ground
conductor and the ground electrode. The loop is between the ground
conductor and the parallel path of R1, R2 ---Rn back through the earth
resistance.
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www.idealindustries.com
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Earth Testers
• Ideal/Megger 61-788
– 3 pole Testers
• IDEAL/Megger 61-789
– 4 pole Testers
– Self powered - no need
for hand crank
– Low power
consumption
Compact and
lightweight
– Quick battery check
– Limited lifetime
warranty
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www.idealindustries.com
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Earth Testers
• Ideal 61-920 Ground
resistance Clamp
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Ground Resistance
Ground Leakage Current
Auto ranging
Audible indication < 40 ohms
Open jaw indication
Data hold
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