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Topic: Testing earth fault resistance

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  Three-phase testing - Wikipedia, the free encyclopedia
Where the supply is fed froma delta connected transformer, the line to earth ground voltage may not be balanced but phase-to-phase voltages must be balanced for proper motor operation.
Tests should be made between A and B, A and C, B and C. If the supply has a neutral, A and earth, B and earth, and C and earth.
Topics including testing motor coil resistance and testing earth fault resistance are covered separately.
en.wikipedia.org /wiki/Three-phase_testing   (441 words)

 Testing earth fault resistance - Wikipedia, the free encyclopedia
The human body conducts electricity, especially where moisture is present, such as in kitchens and bathrooms, and for that reason it is very important that any parts of electricity-using appliances have a high resistance/impedance to the outside case, and/or to any other parts that could get to be in contact with any person's skin.
In a typical three phase induction motor circuit, an appropriate place to test is at the load side of the direct-on-line motor starter.
If the motor system has satisfactory motor coil resistance, the test should be made between A, B, or C and Earth.
en.wikipedia.org /wiki/Testing_earth_fault_resistance   (294 words)

 Class Definition for Class 324 - ELECTRICITY: MEASURING AND TESTING
For example, a patent claiming means for automatically testing a circuit for an "open circuit" caused by the failure of a circuit element, followed automatically by a test to determine the input/output characteristics of the circuit is classifiable as an "original" in subclasses 500+.
For example, a patent claiming a testing apparatus consisting of a combination of means to determine frequency, means to compare phase, and means to permit a human operator to switch from one means to another is classifiable as an "original" in subclasses 78+.
Testing means of this subclass type produce a distinct indication for each of the plural tests, Hence, testing means comprising plural transducers or detectors, each of outputs are combined to produce only on indication is not classifiable in this subclass unless the whole test is automatically repeated.
www.uspto.gov /go/classification/uspc324/defs324.htm   (4110 words)

 Hipot Testing FAQ - Introduction to Hipot Testing
In dielectric withstand testing you are trying to answer the question "Will this cable withstand a required voltage for a required time?" You apply the voltage for the amount of time and watch the current that flows.
In insulation resistance testing you are trying to answer the question "Is the resistance of the insulation high enough?" You apply a voltage and very carefully measure the current.
Resistance, capacitance, arcs, electrochemical effects, and corona are all effects that describe current flow.
www.cirris.com /testing/guidelines/hipot_testing.html   (1345 words)

 Ground Resistance Article
Each layer offers a resistance to the passing current, which is proportional to the ground resistivity and to the layer thickness (resistance length in Figure 1), and inversely proportional to the layer's area, according to eq.1.
When a grounding system resistance of an energized installation is measured, a significant voltage of industrial frequency and possible harmonics between the earth electrode E and the potential electrode S appears due to the existence of an earth fault current.
The greatest challenge that a good Earth tester faces is to be able to distinguish the potential drop in earth resistance due to the test current from the interfering voltages (which may have a substantially greater magnitude).
www.duncaninstr.com /Gr_article.htm   (2399 words)

 LECTURE NOTES   (Site not responding. Last check: 2007-10-13)
Physical geology examines the materials composing the Earth and seeks to understand the processes that operate beneath and upon the surface.
Biosphere includes all life on Earth and is concentrated near the surface in a zone that extends from the ocean floor upward for several kilometers into the atmosphere.
Leaching is defined as the process of dissolving washing or draining earth material by percolation of ground water or other liquids occurs in the A horizon and moves clay and other material such as iron and calcium to the B horizon.
www.accd.edu /pac/earthscience/hefner/1403/LECT.HTM   (4368 words)

 [No title]
Tests must be carried out at the origin of the installation, at each distribution board, at all fixed equipment, at all socket outlets, at 10% of all lighting outlets (choosing points farthest from the supply) and at the furthest point of every radial circuit.
This effect is difficult to calculate, and a practical alternative is to ensure that the measured values of earth fault loop impedance do not exceed three quarters of the maximum values shown in {Tables 5.1, 5.2 or 5.4} as appropriate.
The effect of supply voltage on the calculation of earth fault loop impedance is considered in {5.3.4}.
www.tlc-direct.co.uk /Book/8.6.2.htm   (986 words)

For de-energized circuit analysis, modern high voltage testing is used to detect: incipient cable faults, winding faults, both to earth and turn to turn, winding contamination and partial discharge’s between turns and to earth.
This means the tests are capable of detecting and locating incipient: cable faults, winding faults, insulation to ground faults, motor contamination and other problems such as leaking check valves located in the driven load.
When the surge test was used to diagnose insulation integrity in a 5 HP electric motor, the numerical difference percentages obtained against weak insulation was approximately 20%, clearly a much larger error value.
www.reliabilityweb.com /art04/modern_testing.htm   (2866 words)

 May-June 2005: Preventing Electrical Shocks with Proper Grounding Techniques
The earth ground could be a single ground rod, multiple ground rods, a mat or a grid system, or various other conducting elements that establish a connection to the earth.
While testing the resistance of the ground electrode of the rod, pipe, or plate types after installation will satisfy NEC requirements in 250.56, it is not always enough to ensure protection of personnel or electronic equipment.
A ground resistance clamp meter enables electricians to measure the resistance of the ground electrode in a fraction of the time required using the traditional three-point fall of potential test.
www.iaei.org /subscriber/magazine/05_c/gregorec.htm   (2366 words)

 Product Safety: New Developments in Hipot Testing
In fact, hipot testing is not a measurement, but rather a procedure that aims to illustrate whether a product remains safe when subjected to high voltage and whether the user is protected from danger.
Hipot testing of Class II equipment involves much higher voltage levels, typically between 2500 and 4200 V. A common problem, particularly on new equipment, is that failure can be detected on the primary insulation that is undetectable by a hipot test on the outer surface, which tests the secondary insulation only.
This test may be practical for laboratory situations, but it is impractical for production testing, because of both the complexity in test setup and time required and because the outer surfaces of the product must be easily marked.
www.ce-mag.com /archive/02/Spring/jansen.html   (2249 words)

 Production-Line Testing:A 100% Solution to Product Safety
It should be noted that the three main tests required to ensure product safety are high-current earth bond (ground) measurement, high-voltage flash (hipot or dielectric strength) test, and insulation-resistance measurement.
For example, comprehensive test stations are available that can apply all three basic safety tests in cycles of as little as 2–3 seconds per product.
Because the earth bond test is conducted to ensure the proper and secure connection of the metal case to the mains earth reference using test probes, each external metal surface must be tested—a process rendered nearly impossible by the polyester resin coating.
www.ce-mag.com /archive/02/03/jansen.html   (1403 words)

 LEM Instruments, Inc. - Electrical Grounding Techniques - Ground Electrodes
A) The resistance of the ground electrode and it's connection is generally very low, ground rods are generally made of highly conductive/low resistance material such as copper of copper clad.
B) The contact resistance of the earth to the electrode: The Bureau of Standards has shown this resistance to be almost negligible providing that the ground electrode is free form paint, grease etc. and that the ground electrode is in firm contact with the earth.
Because the earth is in layers resistivity changes and varies considerably on the layer and the depth within that layer.
www.leminstruments.com /online-store/scstore/an-ground-04.html   (578 words)

 Power Quality - Lightning Protection, Earthing - South Africa
The objectives of good earthing practice are therefore to achieve at minimum cost, safe voltages, with the neutral close to zero potential, and to assist in detecting and disconnecting faults.
The target resistance is a calculated figure based on the surface resistivity, the fault current of the system, and the trip time of the protection equipment.
The resistance of an earth mat should be tested on a regular basis as part of the planned maintenance system.
home.intekom.com /powerquality/Testing.htm   (362 words)

 PAT Testing information on RCD's
Short circuit current flow to earth via an installation's earthing system causes the circuit breaker to trip, or fuse to blow, disconnecting the electricity from the faulty circuit.
However, if the electrical resistance in the earth fault current path is too high to allow a circuit breaker to trip (or fuse to blow), electricity can continue to flow to earth for an extended time.
On a circuit protected by an RCD, if a fault causes electricity to flow from the Active conductor to earth through a person's body, the RCD will automatically disconnect the electricity supply, avoiding the risk of a potentially fatal shock.
www.pat-testing.info /rcd.htm   (557 words)

 MEM Fall 2002 - Automating Complex Electrical Safety Testing of Medical Devices
For the hipot test, the requirement in most medical standards is to apply a test voltage that is two times the normal operating voltage plus 1000 V (1250–1500 V ac, depending on whether the product is to be operated from 115 or 240 V).
Another leakage test is enclosure leakage (or touch/chassis leakage), which is essentially the leakage to ground that a person would be subjected to if they were to touch non-earth-protected exposed parts of the device.
Like the other leakage tests, this test measures the leakage current that a patient would be subjected to between two patient leads that are in contact with the patient.
www.devicelink.com /mem/archive/02/10/richards.html   (2225 words)

 Ground Resistance Tester
AEMC Ground- Earth Resistance Meter Model 3620 features three-terminal operation for fall-of-potential earth-ground resistance testing, and may also be used for 2-Point test.
AEMC 3620 - Ground Resistance Tester is also available in complete kit form, which includes the meter to measure earth resistance, 16 ft lead, two 150 ft leads on spools, two wind-up handles, two auxiliary ground electrodes and soft carrying bag.
This direct reading meter measures earth resistance and or soil resistivity from 10MΩ to 1999Ω, and is auto-ranging, so it automatically seeks out the optimum measurement range.
www.valuetesters.com /Ground-Resistance-Tester.php   (536 words)

 ESD Journal - The ESD & Electrostatics Magazine
A frequent alternative to using the system ground for ESD is a separate earth ground rod installed near the workstation for ESD use, and this is indeed effective in draining away static charges.
It should also be capable of testing equipment-ground impedance by injecting AC current into the equipment ground conductor and measuring between it and the neutral conductor.
Using a specialized ground resistance tester, measure the earth's resistance between your auxiliary earth ground and the AX system's ground conductor.
www.esdjournal.com /eosesd/static/sgscw.htm   (1107 words)

 September-October 1998: The Grounding Electrode
Fault current flows as indicated by the dashed line in the figure, but the impedance of the grounding electrode system limits the magnitude of the fault current.
A person in contact with the earth and any conductive part connected to a grounding conductor of equipment plugged in or permanently wired anywhere in the building while the fault current flows could experience an electric shock, if the voltage dropped across the grounding electrode system is high enough.
The grounding electrode contributes in part to this total value, and therefore, the resistance to earth of the grounding electrode system alone might have to be significantly lower than 5.5 Ohms.
www.iaei.org /subscriber/magazine/98_e/boden.htm   (2127 words)

The resistance of the rod was plotted on a depth vs. resistance graph as shown in Figure 1.
The earth resistance of an electrode is dependent on several factors including: soil resistance, contact resistance of the electrode to the earth and resistance of the rod(s), couplers, and connections.
Due to high earth resistance, the typical shallow electrode is unable to maintain an electrical system at earth potential during transient voltage conditions and lightning surges.
www.cpccorp.com /deep.htm   (3364 words)

 Fluke 1625 GEO Earth Ground Tester Fluke 1625
The Fluke 1623 and 1625 are distinctive earth ground testers that can perform all four types of earth ground measurement.
This method doesn’t require the use of earth ground stakes or the disconnection of ground rods.
Selective testing — without disconnecting ground rods, a technician can measure ground resistance using a combination of stakes and a clamp.
www.tequipment.net /Fluke1625.html   (188 words)

Low resistance earth grounding is essential for safety and protection of sensitive electronic equipment.
This paper will demonstrate that deep driven electrodes provide low earth resistance, are economical to install, maintain low resistance over lime, are maintenance free, and do not have environmental concerns.
This low resistance is required due to the high potential to earth of the electrical system.
www.groundperfect.com /DeepEarthPaper.htm   (1144 words)

The POWER LINE FAULT LOCATOR SYSTEMS, used for fault detection and maintenance of EHT Power lines is one and only of i its kind in the world today, becomes a born for Electric supply Undertakings as it eliminates completely the tedious process of visual line patrolling thereby reducing the line down time.
FREQUENCY OF TRANSMISSION 12 HZ This equipment is used to find the resistance to Earth of the various Electrical appliances in the station.It is immune to all 50 cycle interference in the station and could be used to Earth under enerized condition.
TESTING FREQUENCY 120 HZ This equipment is used for testing of various electrical appliances and cables.
www.indiansources.com /mksystems.htm   (754 words)

 Who Cares About 25 Ohms or Less?
250-54, which requires the resistance to ground of a single-made electrode (e.g., ground rod) to be 25 ohms or less.
You should measure the resistance of an electrode with respect to the surrounding soil in the area.
Spend less time on the testing and qualification of the GES resistance and more time checking the bonding between locations and the equipment-grounding conductor impedance.
www.ecmweb.com /mag/electric_cares_ohms_less/index.html   (719 words)

 Joe Tate: Ambient Power Module
Tesla actually calculated the resonant frequency of the Earth, and proposed that electromagnetic waves of this frequency (6-8 Hz) should be generated by the planet from the action of lightning.
Beginning with blocks 100 and 102, the system is continually tested (hourly) for the occurrence of a SD of the hourly averages of greater than 0.3.
In lieu of testing the antenna's output reception of the area's AM stations, a special, dedicated transmitter with a special, dedicated frequency and a specially-tuned matching receiver can be used to avoid dependence on stations which are not under the control of the earthquake prediction system and its personnel.
www.rexresearch.com /tate/tate.htm   (8409 words)

 277/299 Medical Device Safety Analyers for Patient Leakage Testing - QuadTech   (Site not responding. Last check: 2007-10-13)
Test currents of 0.1, 1, 10 or 25A can be applied and resistance measured over a range from 0 to 20 ohms.
Earth and Enclosure Leakage: Measures earth and enclosure leakage current under normal, reverse, or single fault test conditions using IEC60601 or ANSI body models.
All tests are automatically performed in sequence under normal, reverse, or single fault test conditions.
www.quadtech.com /products/products.asp?familyid=73   (528 words)

 LEM Instruments, Inc. - Electrical Grounding Techniques - What Is A Ground?   (Site not responding. Last check: 2007-10-13)
The NEC, National Electrical Code defines a ground as: "a conducting connection, whether intentional or accidental between an electrical circuit or equipment and the earth, or to some conducting body that serves in place of the earth." When talking about grounding it is actually two different subjects, earth grounding and equipment grounding.
Earth grounding is an intentional connection from a circuit conductor usually the neutral to a ground electrode placed in the earth.
These two grounding systems are required to be kept separate except for a connection between the two systems to prevent differences in potential from a possible flashover from a lightning strike.
www.leminstruments.com /online-store/scstore/an-ground-02.html   (210 words)

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