User Manual - Chauvin Arnoux Group
Contents
1. 9 3 1 Electrical Specifications 9 9 4 10 3 3 Table of Influencing Parameters 11 3 4 Influence of Stray 12 3 5 Influence of Auxiliary Resistances 12 3 6 Mechanical 13 3 7 Safety Specifications 14 4 OPERATION 15 4 1 Grounding Electrode Resistance 15 4 1 1 Effect of Electrode Size Depth 17 4 1 2 Effects of Soil Resistivity on Electrode Resistance 18 4 1 3 Factors Affecting Soil 18 4 1 4 Effect of Ground Electrode Depth on Resistance 21 4 2 Ground Resistance Values 22 4 3 Ground Resistance Testing Principle 24 4 3 1 Position of Auxiliary Electrodes in Measurements 25 4 4 Measuring Resistance of Ground Electrodes 26 4 4 1 Auxiliary Electrode 28 4 5 Ground Resistance Measurement Procedures 29 4 5 1 Over ran2. DIGITAL GROUND RESISTANCE TESTER 4500 230V ll 30V 50 60 400 Hz 110V 2 k gt 20V A BLINK DISPLAY Powe H BATTERY En pm H E Q9 cust RESISTAN INDICATES DIGITAL GROUND RESISTANCE TESTER MODEL 4500 TEST CURRENT INSTRUMENTS AEMC ENGLISH User Manual INSTRUMENTS Owner s Record The serial number for the Model 4500 is located on the front of the instru ment Please record this number and purchase date for your records GROUND RESISTANCE TESTER MODEL 4500 CATALOG 450 100 SERIAL PURCHASE DATE DISTRIBUTOR Table of Contents 1 INTRODUCTION 3 1 1 International Electrical 4 1 2 Receiving Your 4 1 3 Ordering 4 1 3 1 Accessories and Replacement Parts 4 2 PRODUCT FEATURES 4 c 6 24 m 6 2 2 Detaching the 7 2 3 Control Features 8 3 SPECIFICATIONS
3. 42 5 4 Storage ee 42 Repair and Calibration sse 43 Technical and Sales Assistance 43 Limited Warranty 2 c cT 44 Warranty REPalrs em 44 CHAPTER 1 INTRODUCTION A Warning It should be impressed on all personnel that lethal potential can exist between the station ground and a remote ground if a system fault involving the station ground occurs while tests are being made Since one of the objects of tests on a station ground is the establishment of the location of an effectively remote point for both current and potential electrodes the leads to the electrodes must be treated as though a possible potential could exist between these test leads and any point on the station ground grid excerpted from IEEE Std 81 1962 These safety warnings are provided to ensure the safety of per sonnel and proper operation of the instrument The instrument must not be operated beyond its specified operating range Safety is the responsibility of the operator All metal objects or wires connected to the electrical system should be assumed to be lethal until tested Grounding systems are no exception Use extreme caution when using the instrument around energized electrical equipment Never attempt to use the instrument to twist or pry the ground electrode or ground wire away from the equipment being grounded AEMC Instruments considers the use of rubber gloves to be an e
4. Chassis Ribbon Cable Kf Figure 22 Remove the wing nuts the spacers and the protective cover to gain access to the two 12V DC battery See Figure 23 Digital Ground Resistance Tester Model 4500 39 act Nuts Stress Relief Plate 12 V DC Lengthwise Shock Absorbing Layer Power Supply Board Figure 23 Disconnect the two wires which connect the battery to the power supply board Replace the worn battery Connect the new 12V DC battery to the power supply board Pay close attention to the polarities printed on the power supply board Source Voltage Selection Switch 110V AC 220V AC Power Supply Board Figure 24 5 2 6 Changing the Supply Voltage 110 220Vac e Open up the Model 4500 Position the selector switch on the power supply board See Figure 24 Set the plate 11 in Figure which indicates 220V AC on one side and 110V AC on the other to the selected voltage Reassemble the Model 4500 40 Digital Ground Resistance Tester Model 4500 WARNING If the supply switch is set to 110V AC and the instrument is connected to 220V AC the battery charge indicator see Figure 3 will turn on for several seconds but will then turn off The fuse will blow Do not continue to run the instrument fthe supply switch is set to 220V AC position and the instrument is connected to 110V AC the indicat
5. Impact Resistance Shock and vibration according to MIL T 28800D class 3 Environmental O ring sealed faceplate against water and dust sealed cover when closed IEC529 DIN 0470 T1 EN 61010 1 A2 ed 95 Double Insulation 30V Cat Il for measurement 230V Cat Il for battery charger 12V Cat Il for auxiliary supply EN 61557 Electromagnetic Compatibility Emmission and Immunity IEC 61326 1 ed 98 14 Digital Ground Resistance Tester Model 4500 CHAPTER 4 OPERATION 4 1 Grounding Electrode Resistance Figure 4 illustrates a grounding rod The resistance of the electrode has the following components the resistance of the metal and that of the connection to it the contact resistance of the surrounding earth to the electrode the resistance in the surrounding earth More specifically A Grounding electrodes are usually made of a very conductive metal copper with adequate cross sections so that overall resistance is negligible B The National Institute of Standard and Technology N I S T has demonstrated that the resistance between the electrode and the surrounding earth is negligible if the electrode is free of paint grease or other coating and if the earth is firmly packed D Ground Rod E zi and Clamp l Resistance l Between Rod l and Soil Shells of 7 22 1 Earth Satan A 1 VN bct 2 VN CO ee uw i he oN ues we it S
6. Digital Ground Resistance Tester Model 4500 7 2 3 Control Features um eX oN 14 15 16 308 CAT Il GROUND VOLTAGE BLINKING DISPLAY AND POINTER INDICATE EXCESSIVE TRANSIENT NOISE ELECTRODE RESISTANCE Figure 3 Test button Input Terminal Z C2 Input Terminal Y P2 Input Terminal Xv P1 Shorting strip Input Terminal X C1 Incorrect measurement indicator Low battery indicator Display Battery charge indicator Supply voltage indicator Jack for power supply cord 12VDc Range selector switch Test Current selector switch BATTERY CHARGE DIGITAL GROUND RESISTANCE TESTER MODEL 4500 Connecting terminals for power supply from external battery Adhesive label C 1 P 1 P 2 C 2 supplied with each instrument Digital Ground Resistance Tester Model 4500 CHAPTER 3 SPECIFICATIONS 3 1 Electrical Specifications Reference Conditions 23 C 3K 30 to 50 RH power supply 12V 0 2V no electrical or magnetic field no auxiliary rod resistance no noise voltage NOTE Specifications given for 60Hz distribution systems if 50Hz consult factory Recommended 10mA or 2mA 10mA 2mA or 2mA or Current Ranges 50mA or 50mA 10mA 10mA Maximum Output Voltage 38Vrms Accuracy see chart on following page 2 of Reading 1ct from 10 to 100 of range Test Current Ranges 2mA 10mA 5
7. iLL 7 7 lt a lc MN ae Figure 4 Digital Ground Resistance Tester Model 4500 15 C The only component remaining is the resistance of the surround ing earth The electrode can be thought of as being surrounded by concentric shells of earth or soil all of the same thickness The closer the shell to the electrode the smaller its surface hence the greater its resistance The farther away the shells are from the electrode the greater the surface of the shell hence the lower the resistance Eventually adding shells at a distance from the grounding electrode will no longer noticeably affect the overall earth resistance surrounding the electrode The distance at which this effect occurs is referred to as the effective resistance area and is directly dependent on the depth of the grounding electrode In theory the ground resistance may be derived from the general for mula Length Resistivit Resistance Resistivity x rem r This formula clearly illustrates why the shells of concentric earth decrease in resistance the farther they are from the ground rod Thickness of Shell R Resistivity of Soil x y Area In the case of ground resistance uniform earth or soil resistivity through out the volume is assumed although this is seldom the case in nature The equations for systems of electrodes are very complex and often expressed only as approximations The most commonly used formula for single ground ele
8. Calibration To ensure that your instrument meets factory specifications we recommend that it be scheduled back to our factory Service Center at one year intervals for recalibration or as required by other standards or internal procedures For instrument repair and calibration You must contact our Service Center for a Customer Service Authorization Number CSA This will ensure that when your instrument arrives it will be tracked and processed promptly Please write the CSA on the outside of the shipping container If the instrument is returned for calibration we need to know if you want a standard calibration or a calibration traceable to N I S T Includes calibration certificate plus recorded calibration data Ship To Chauvin Arnoux Inc d b a AEMC Instruments 15 Faraday Drive Dover NH 03820 USA Phone 800 945 2362 Ext 360 603 749 6434 Ext 360 Fax 603 742 2346 or 603 749 6309 E mail repair aemc com Or contact your authorized distributor Costs for repair standard calibration and calibration traceable to N I S T are available NOTE You must obtain a CSA before returning any instrument Technical and Sales Assistance If you are experiencing any technical problems or require any assistance with the proper operation or application of your instrument please call mail fax or e mail our technical support team Chauvin Arnoux Inc d b a AEMC Instruments 200 Foxborough Boulevard Foxborou
9. orate grounding system In such situations it may be economical to use a ground rod system of limited size and to reduce the ground resistivity by periodically increasing the soluble chemical content of the soil Table 8 shows the substantial reduction in resistivity of sandy loam brought about by an increase in chemical salt content The Effect of Salt Content on the Resistivity of Soil sandy loam moisture content 15 by weight temperature 17 C Added Salt Resistivity by weight of moisture Ohm centimeters 10 700 Table 8 20 Digital Ground Resistance Tester Model 4500 Chemically treated soil is also subject to considerable variation of resistiv ity with changes in temperature as shown in Table 9 on the next page If salt treatment is employed it is of course necessary to use ground rods which will resist chemical corrosion The Effect of Temperature on the Resistivity of Soil Contining Salt sandy loam 20 moisture salt 5 of weight of moisture Temperature Resistivity Onm centimeters 20 10 5 Table 9 Such as copper sulfate sodium carbonate and others Salts must be EPA or local ordinance approved prior to use 4 1 4 Effect of Ground Electrode Depth on Resistance To assist the engineer in determining the approximate ground rod depth required to obtain a desired resistance a device called the Grounding Nomograph may be used The Nomograph shown on the following page indicates that to ob
10. required by the NEC When these situations develop several methods of lowering the ground resis tance can be employed These include parallel rod systems deep driven rod systems utilizing sectional rods and chemical treatment of the soil Additional methods discussed in other published data are buried plates buried conductors counterpoise electrically connected building steel and electrically connected concrete reinforced steel Electrically connecting to existing water and gas distribution systems was often considered to yield low ground resistance however recent design changes utilizing non metallic pipes and insulating joints have made this method of obtaining a low resistance ground questionable and in many instances unreliable Ground rods of course will be required in high voltage transmission lines where maximum resistance of 150 is recommended and in distribution lines where maximum resistance of 25Q is preferred All electrical sys tems constructed in accordance with the National Electrical Code should not exceed 250 Digital Ground Resistance Tester Model 4500 23 The measurement of ground resistances may only be accomplished with specially designed test equipment Most instruments use the Fall of Potential principle of alternating current AC circulating between an auxiliary electrode and the ground electrode under test the reading will be given in ohms and represents the resistance of the ground electrode to
11. 0mA Maximum Auxiliary Electrode Resistance Ry 50kQ on 200 2000 20000 and 20kQ ranges 5 on 20 range Rz 2mArange 15 10mA range 30000 50mA range 4000 Noise Influence on Accuracy 0 596 of range max to 20V peak to peak 20 x peak Operating Frequency 128Hz square wave Dielectric Test 2000Vrms 50 60Hz between four interconnected mea suring terminals and any external metal ground between line input and measuring terminals on front panel Power Supply One built in rechargeable 12V battery or external 12VDc Battery Life 4 hrs on 50mA test current 800 15 second measurements 7 hrs on 2mA and 10mA test currents 1500 15 second measurements Digital Ground Resistance Tester Model 4500 9 Charging Time 14 hours typical Charging Supply Voltage Internally selectable 110 220V 45 to 450Hz Low Battery Indication Battery can be recharged with built in dual volt age charging unit 94 to 127V or 187 to 253V 47 to 450Hz A WARNING Do not fully discharge batteries Fuse Protection 250Vrms measurement circuit via 3 15A 250V fuse 3 2 Accuracy Maximum Value of Accuracy Y and Z Electrodes Resolution Test in of Having Influence lt 1 5kQ 5mQ 1ct 2 30mQ 1 5kQ 2 3mQ ict 2 1 6002 to 204 to be selected in relation to the test 2 1ct of 10 to 100 of full scale No accuracy specification do not use See Table III for maxi
12. 2 C2 hex key spare fuse and user manual 1 3 1 Accessories and Replacement Parts Test Kit for Model 4500 te Cat 100 525 Includes Canvas Bag 2 500 ft Color coded Leads on Reels 1 30 ft Color coded Lead 2 T shaped Auxiliary Ground Electrodes Test Kit for 3 Point Testing Supplemental for 4 Point testing Cat 2130 61 Includes Carrying Bag 2 100 ft Color coded Leads 1 16 ft Lead and 2 16 T shaped Auxiliary Ground Electrodes Battery Replacement 12V Cat 2960 10 Fuse Set of 3 3 15A 250V 6 x 32mm charger board Cat 100 357 Fuse Set of 5 0 1A 380V 6 x 32mm measure board Cat 2970 12 4 Digital Ground Resistance Tester Model 4500 Set of 2 T shaped Auxiliary Ground Electrodes Cat 100 335 Ground Tester Video Workbook Cat 2130 64 250 Calibration Checker Cat 2130 59 Tape Measure AEMC 100 Cat 2130 60 NEW Order Accessories and Replacement Parts Directly Online Check our Storefront at www aemc com for availability Digital Ground Resistance Tester Model 4500 5 CHAPTER 2 PRODUCT FEATURES 2 1 Description The Digital Ground Resistance Tester Model 4500 is a rugged easy to use tester which is specifically designed for measuring very low resistance on large g
13. al length For example a square having a side of 20 ft will have a diagonal of approximately 28 ft Figure 21 36 Digital Ground Resistance Tester Model 4500 Digital Ground Resistance Tester Model 4500 37 CHAPTER 5 MAINTENANCE 5 1 Warning Please make sure that you have already read and fully understand the WARNING section on page 3 To avoid electrical shock do not attempt to perform any servicing unless you are qualified to do so To avoid electrical shock and or damage to the instrument do not get water or other foreign agents into the case Turn the Instrument OFF and disconnect the unit from all circuits before opening the case 5 2 Power Supply 5 2 1 Testing Battery Voltage e Short circuit the X and Z terminals Turn the current selector see Figure 3 to 50 mA Turn the range selector to 200 Pressthe Test button If the colon 8 in Figure 3 lights up recharge the batteries If the colon does not light the batteries are charged 5 2 2 Average Operating Time Ahrs on 50mA test current 800 15 second measurements on 2mA and 10mA test currents 1500 15 second measure ments If the colon lights up the battery has lost power Thereafter the available operating time remaining is approximately 100 15 second measurements When this situation arises recharge the battery at once or obtain power from an external battery see the following paragraphs 38 Digital Grou
14. and Xv terminals Arrange the electrodes in a straight line Be sure that distances between electrodes are identical e g 3 meters between each electrode See Figure 18 The distance between poles is proportional to the average depth of the soil sample you wish to make The electrodes should be placed at a depth of approximately 6 0 15m so that the depth is approximately 1 20th of the distance between electrodes Useleads to connect the X Xv Y and Z electrodes to the respec tive terminals on the Digital Ground Resistance Tester e Itis preferable to place the selector a range position which varies inversely in relation to the distance identified as A in other words the farther apart the four electrodes the lower the test current should be Press the TEST button Read the resistance level R indicated on the display nthe event of difficulties in performing measurements consult the previous instructions concerning ground resistance measure ments Apply the following formula in order to determine resistivity p 27 x 2250 x 3m 4350 Example After inspection the area to be investigated has been narrowed down to a plot of ground approximately 75 square feet 22 5m Assume that you need to determine the resistivity at a depth of 15ft 450cm The distance A between the electrodes must then be equivalent to the depth at which average resistivity is to be determined 15 ft o
15. and expressed as a percent of the initial reading 2 5 10 etc Ground Auxiliary Auxiliary Electrode Potential Current Under Test Electrode Electrode X Y Effective Resistance Areas Do Not Overlap Resistance of 1 Auxiliary Current Electrode Resistance Resistance of Earth Electrode Distance from Y to Ground Electrode Figure 14 4 4 1 Auxiliary Electrode Spacing No definite distance between X and Z can be given since this distance is relative to the diameter of the electrode tested its length the homogeneity of the soil tested and particularly the effective resistance areas However an approximate distance may be determined from the following chart which is given for a homogeneous soil and an electrode of 1 in diameter For a diameter of 1 2 reduce the distance by 10 for a diameter of 2 increase the distance by 10 Approximate distance to auxiliary electrodes using the 62 method Depth Driven Distance to Y Distance to Z 6 ft 45 ft 72 ft 8 ft 50 ft 80 ft 10 ft 55 ft 88 ft 12 ft 60 ft 96 ft 18 ft 71 ft 115 ft 20 ft 74 ft 120 ft 30 ft 86 ft 140 ft 28 Digital Ground Resistance Tester Model 4500 4 5 Ground Resistance Measurement Procedures 3 Point Ground 4 Strip Z Electrode Y Electrode So Alligator Clips Ground Rod 10 3rd Measurement 7 TU Measurement Sa Ground R
16. ch measurements can be performed where 40V 50 60Hz peak to peak stray voltage is present without obtaining error levels representing more than 0 596 of the measurement range 3 5 Influence of Auxiliary Resistances In the absence of stray signals the maximum values for Rx Rz which will allow measurements to be performed are those indicated within Table 3 Range 2000 20 kQ 50 6000 Rz 6002 max Rx Rz 40002 max Do not use Table 3 Even if auxiliary resistance of Rz 0 the maximum reading is lt 2000 counts on these three ranges voltage limiting circuit at output terminals 12 Digital Ground Resistance Tester Model 4500 Table 4 shows the maximum resistance of the current circuit Rx Rz for stray voltage of 10V peak to peak Range Rx Rz 400Q max Rx Rz 30002 max Rx Rz 15 kQ max Do not use Table 4 3 6 Mechanical Specifications Display 2000 count 7 segment LCD 71 3 1 2 digit Connection Via terminals wires forked lugs with min gap of 6mm banana jacks with 4mm Operating Temperature 14 to 122 F 10 to 50 C Case Heavy duty plastic with detachable cover and carrying handle Colors Case Safety yellow Front Panel Brown Dimensions 15 75 x 10 2 x 9 8 400 x 260 x 250mm Weight 14 Ibs 6 5 kg approximate Digital Ground Resistance Tester Model 4500 13 3 7 Safety Specifications
17. ctrode systems developed by Professor H R Dwight of the Massachusetts Institute of Technology follows R P In 4L 1 2nL r R resistance in ohms of the ground rod to the earth or soil L grounding electrode length r grounding electrode radius average resistivity in ohms cm 16 Digital Ground Resistance Tester Model 4500 4 1 1 Effect of Ground Electrode Size and Depth Resistance Size Increasing the diameter of the rod does not materially reduce its resistance Doubling the diameter reduces resistance by less than 10 100 75 50 25 0 1 2 5 8 3 4 1 1 1 4 1 1 2 1 3 4 Resistance in Rod Diameter inches Figure 5 Depth As a ground rod is driven deeper into the earth its resistance is substantially reduced In general doubling the rod length reduces the resistance by an additional 40 200 100 80 60 40 30 1 2 dia Resistance in Ohms 5 15 25 35 40 50 60 70 Driven Depth in Feet Ground Resistance Versus Ground Rod Depth Figure 6 Digital Ground Resistance Tester Model 4500 17 NEC 2014 250 52 A 5 requires a minimum of 8 ft 2 4m of the elec trode to be in contact with the soil The most common of electrode is a 10 ft 3m cylindrical rod which meets the NEC code which requires a minimum diameter of 5 8 1 59cm 4 1 2 Effects of Soil Resistivity on Ground Electrode Re
18. d be completely buried if possible e If stray currents are suspected one solution to reduce their influ ence is to move both Y and Z electrodes in and arc relative to the X electrode e g try a 90 shift and test again 4 6 2 Measurement Simplified Measurement This is an alternative method to three point measurement when an excel lent ground is already available In congested areas where finding room to drive the two auxiliary rods may be a problem the two point measurement method may be applied The reading obtained will be that of the two grounds in series Therefore the water pipe or other ground must be very low in resistance so that it will be negligible in the final measurement The lead resistances will also be measured and should be deducted from the final measurement This method is not as accurate as three point methods 6296 method as it is particularly affected by the distance between the tested electrode and the dead ground or water pipe This method should not be used as a stan dard procedure but rather as a backup in tight areas See Figure 16 30 Digital Ground Resistance Tester Model 4500 Procedure Short X and Xv C1 P1 Short Y and Z P2 C2 Connect X to ground rod to be measured Connect Z to an electrode Measure as in the three point method Grounding conductor Terminals shorted Auxiliary rod Y Z shorted Utility p
19. esistance areas of both the ground electrode and the auxiliary current electrode The best way to find out if the auxiliary potential rod Y is outside the effective resistance areas is to move it between X and Z and to take a reading at each location If the auxiliary potential rod Y is in an effective resistance area or in both if they overlap by displacing it the readings taken will vary noticeably in value Under these conditions no exact value for the resistance to ground may be determined Digital Ground Resistance Tester Model 4500 25 Effective Resistance Areas Overlapping Reading Variation Resistance 1 1 1 X Y Distance Figure 10 On the other hand if the auxiliary potential rod Y is located outside of the effective resistance areas as Y is moved back and forth the reading variation is minimal The readings taken should be relatively close to each other and are the best values for the resistance to ground of the ground X The readings should be plotted to ensure that they lie in a plateau region as shown in Figure 11 X Z 27 Effective Resistance Areas No Overlap Resistance X Y Distance Figure 11 4 4 Measuring Resistance of Ground Electrodes 62 Method The 62 method has been adopted after graphical consideration and after actual test It is the most accurate method but is limited by the fact that the ground tested is a single unit This method applies
20. ge 30 4 5 2 Incorrect 30 4 6 2 Point Measurement Simplified Measurement 30 4 7 Continuity 31 4 8 Soil Resistivity 2 2 32 4 9 Soil Resistivity Measurement Procedure 4 1 33 4 10 Multiple Electrode System 36 5 38 5 1 38 5 2 Power Supply ise tee te d eet es 38 5 2 1 Testing Battery 38 5 2 2 Average Operating 38 5 2 3 Recharging Built In Battery 39 5 2 4 Power Supply from External Battery 39 5 2 9 Replacing Battery iiie iacu cete teilt ee decas 39 5 2 6 Changing the Supply Voltage 110 220VAC 40 5 2 7 Replacing the Supply Fuse 41 5 2 8 Replacing the Safety Fuse 41 5 3 51
21. gh MA 02035 USA Phone 800 343 1391 508 698 2115 Fax 508 698 2118 E mail techsupport aemc com www aemc com NOTE Do not ship Instruments to our Foxborough MA address Digital Ground Resistance Tester Model 4500 43 Limited Warranty The Model 4500 is warranted to the owner for a period of one year from the date of original purchase against defects in manufacture This limited warranty is given by AEMC Instruments not by the distributor from whom it was pur chased This warranty is void if the unit has been tampered with abused or if the defect is related to service not performed by AEMC Instruments For full and detailed warranty coverage please read the Warranty Coverage Information which is attached to the Warranty Registration Card if enclosed or is available at www aemc com Please keep the Warranty Coverage Information with your records What AEMC Instruments will do If a malfunction occurs within the one year period you may return the instrument to us for repair provided we have your warranty registration information on file or a proof of purchase AEMC Instruments will at its option repair or replace the faulty material REGISTER ONLINE AT www aemc com Warranty Repairs What you must do to return an Instrument for Warranty Repair First request a Customer Service Authorization Number CSA by phone or by fax from our Service Department see address below then return the instrument al
22. is improved by spacing greater than 6 feet apart The National Electrical Code states that the resistance to ground shall not exceed 250 This is an upper limit and guideline since much lower resistance is required in many instances How low in resistance should a ground be An arbitrary answer to this in ohms is difficult The lower the ground resis tance the safer and for positive protection of personnel and equipment it is worth the effort to aim for less than one ohm It is generally impractical to reach such a low resistance along a distribution system or a transmis sion line or in small substations In some regions resistances of 5Q or less may be obtained without much trouble In others it may be difficult to bring resistance of driven grounds below 1000 Accepted industry standards stipulate that transmission substations should be designed not to exceed one ohm resistance In distribution sub stations the maximum recommended resistance is 5Q In most cases the buried grid system of any substation will provide the desired resistance In light industrial or in telecommunications central offices 5Q is often the accepted value For lightning protection the arresters should be coupled with a maximum ground resistance of 10 These parameters can usually be met with the proper application of basic grounding theory There will always exist circumstances which will make it difficult to obtain the ground resistance
23. mum auxiliary resistance 10 Digital Ground Resistance Tester Model 4500 3 3 Table of Influencing Parameters Reference Operating of Measurement Conditions Conditions Typical Maximum Supply Voltage 12V 0 2V 11to 14V DC 0 2 volt 0 3 volt 73 F 437F 23 F to122 F 0 5 50F 1 50 FO Temperature 23 C 3 C 5 Cto50C 05 10 C 1 10 C Auxiliary Electrode 0 0 to 0 5 10kQ 196 10kQ Resistance Ry 0 2 0 1 10kQ 2mA 0 3 10kQ 10mA 0 1 3kQ 10mA 0 3 3kQ 0 1 1kQ 50mA 0 3 1kQ or 5 cts Ry Influence of Auxiliary Electrode Resistance Rz Rz See Table 3 in Relation to Test Current N DC Voltage in AC 60 Hz Stray Voltage Influence in Series with See Table 3 Rx Ry or Rz Table 1 1 For the 2Q range 2mA and 10mA test currents maximum Ry is Influence will typically be 0 5 5kQ with a maximum of 1 max 5kQ or 3cts 2 Presence of DC voltage may tend to limit the maximum Rx Rz level indicated within Table 3 3 From 10 to 100 of measuring scale interval It is necessary to add the following quantities to those indicated with Table 1 10mQ for 20 2mA range 3mQ for 20 10mA range 1 count for other ranges Digital Ground Resistance Tester Model 4500 11 3 4 Influence of Stray Voltage Test Current 50 mA 10 mA 2 20 200 2kQ 20kQ2 Range Table 2 Shaded areas indicate the ranges in whi
24. nd Resistance Tester Model 4500 5 2 3 Recharging Built In Battery Use the power cord stored inside the compartment within the cover Plug the power cord into the female input jack Connect the other end of the cord to a power outlet voltage must be the same as voltage indicated on the plate identified as 11 The red light will turn on and remain lit while the battery is recharging Charging time is 14hrs minimum for a discharged battery NOTE 1 The battery may be charged for more than 14 hours without damaging the instrument internal protection NOTE 2 Do not allow the battery to remain discharged for more than several days NOTE 3 If an instrument is not used frequently the battery should be recharged regularly three month intervals are recommended 5 2 4 Power Supply from External Battery The external battery should be directly connected to the appropriate terminals Be sure to observe the proper polarities The external battery does not charge the internal battery NOTE It is not necessary to remove the battery supplied with the instru ment when using an external battery or supply 5 2 5 Replacing Battery Use the hex key to unscrew the six fastening screws from the chas sis which are located on the bottom of the case e Pull out the chassis Figure 22 Remember to unplug the ribbon cable which connects the power supply board in the bottom of the case to the boards mounted in the chassis
25. od Y Electrode Z Electrode X Y 0 52 62 72 100 of distance between X and Z Figure 15 A Warning Do not disconnect the ground of a live circuit Xand Xv C1 P1 are shorted Connect X to the ground rod to be tested Connect Y P2 to the central electrode Connect Z C2 to the farther electrode Use the range selector switch and select a range with a measurement capability between 2 and 20000 Using the test current selector switch select the highest current for which you observe a stable reading and for which the display is not blinking or use the following guidelines Recommended 10mA or 2mA 10mA 2mA or 2mA or Current Ranges 50mA or 50mA 10mA 10mA Digital Ground Resistance Tester Model 4500 29 4 5 1 Over range Indication Over range is indicated when the display reads 1 or when the display is blinking and the indicator is lit 4 5 2 Incorrect Measurements The incorrect measurement indicator shows excessive electrode resis tance and excessive transient noise and stray current it also indicates when the selected test current is too high In the event of an incorrect measurement indication Select the next lowest test current mprove the quality of the auxiliary ground electrodes Y and Z Z is the most likely source of problems with excessive resistance Check connections for continuity between leads and electrodes Be sure that electrodes are properly inserted they shoul
26. ole Ground level Ground rod Butt plate Figure 16 4 7 Continuity Measurement After the shorting strip has been properly positioned between X and Xv C1 P1 connect the Y P2 and Z C2 terminals together as well Continuity measurement is made with two leads one from X Xv the other from Y Z P2 C2 push the TEST button to measure Digital Ground Resistance Tester Model 4500 31 Loma f 202092 D TEST CURRENT RANGE Figure 17 4 8 Resistivity Measurements Why make soil resistivity measurements Soil resistivity measurements have a threefold purpose First such data are used to make sub surface geophysical surveys as an aid in identifying ore locations depth to bed rock and other geological phenomena Second resistivity has a direct impact on the degree of corrosion in underground pipelines A decrease in resistivity relates to in increase in corrosion activ ity and therefore dictates the protective treatment to be used Third soil resistivity directly affects the design of a grounding system and it is to that task that this discussion is directed When designing an extensive ground ing system it is advisable to locate the area of lowest soil resistivity in order to achieve the most economical grounding installation Resistivity measurements are of two types the 2 point and the 4 point method The 2 point method is simply the resistance measured between t
27. ong with the signed CSA Form Please write the CSA on the outside of the shipping container Return the instrument postage or shipment pre paid to Ship To Chauvin Arnoux Inc d b a AEMC Instruments 15 Faraday Drive Dover 03820 USA Phone 800 945 2362 Ext 360 603 749 6434 Ext 360 Fax 603 742 2346 or 603 749 6309 E mail repair aemc com Caution To protect yourself against in transit loss we recommend you insure your returned material NOTE You must obtain a CSA before returning any instrument 44 Digital Ground Resistance Tester Model 4500 GJ AEMC INSTRUMENTS 11 15 99 MAN 100033 v11 Chauvin Arnoux Inc d b a AEMC Instruments 15 Faraday Drive Dover 03820 USA Phone 603 749 6434 Fax 603 742 2346 www aemc com
28. only when all three electrodes are in a straight line and the ground is a single electrode pipe or plate etc as in Figure 12 26 Digital Ground Resistance Tester Model 4500 Y Electrode Z Electrode N Alligator Clips Ground Rod Figure 12 Consider Figure 13 which shows the effective resistance areas concentric shells of the ground electrode X and of the auxiliary current electrode Z The resistance areas overlap If readings were taken by moving the auxiliary potential electrode Y towards either X or Z the reading differentials would be great and one could not obtain a reading within a reasonable band of tolerance The sensitive areas overlap and act constantly to increase resistance as Y is moved away from X Ground Auxiliary Auxiliary Electrode Potential Current Under Test Electrode Electrode X Z UNO Overlapping Effective Resistance Areas Resistance Distance from Y to Ground Electrode Figure 13 Now consider Figure 14 where the X and Z electrodes are sufficiently spaced so that the areas of effective resistance do not overlap If we plot the resistance measured we find that the measurements level off when Y is placed at 62 of the distance from X to Z and that the readings on Digital Ground Resistance Tester Model 4500 27 either side of the initial Y setting are most likely to be within the established tolerance band This tolerance band is defined by the user
29. or will not turn on The instrument will not recharge or operate NOTE For either situation errors in completing connections will not endanger the instrument 5 2 7 Replacing the Supply Fuse An internal fuse is used to protect the instrument against an improperly selected supply voltage To replace this fuse Remove the six hex screws from the bottom of the case see Figure 22 and lift the chassis from the case housing Replace the fuse Figure 24 and reassemble the instrument 5 2 8 Replacing the Safety Fuse An internal fuse which provides protection for up to 500V AC is used to protect the instrument against voltages into the test leads To replace this fuse Remove the six hex screws from the bottom of the case see Figure 22 and lift the chassis from the case housing Turn the chassis over Replace the fuse Figure 25 and reassemble the instrument Digital Ground Resistance Tester Model 4500 41 Replacement Fuse Installed Safety Fuse Figure 25 5 3 Cleaning A Disconnect the instrument from any source of electricity Use a soft cloth lightly dampened with soapy water Rinse with a damp cloth and then dry with a dry cloth Do not use alcohol solvents or hydrocarbons 5 4 Storage If the instrument is not used for an extended time period the battery should be recharged regularly Three month intervals are recommended 42 Digital Ground Resistance Tester Model 4500 Repair and
30. r 450cm Using the more simplified Wenner formula p 27 AR the electrode depth must then be 1 20th of the electrode spacing or 8 7 8 22 5cm Lay out the electrodes in a grid pattern Figure 20 and connect to the Model 4500 as shown in Figure 19 Proceed as follows Remove the shorting strip between X and Xv Connect all four auxiliary rods 34 Digital Ground Resistance Tester Model 4500 For example if the reading is R 15 resistivity 22x R xA A distance between electrodes 450cm p 6 28 x 15 x 450 42 390 Q cm Fue 1 yrr Frrr prr Figure 20 Digital Ground Resistance Tester Model 4500 35 4 10 Multiple Electrode System A single driven ground electrode is an economical and simple means of making a good ground system But sometimes a single rod will not provide sufficient low resistance and several ground electrodes will be driven and connected in parallel by a cable Very often when two three or four ground electrodes are used they are driven in a straight line when four or more are used a hollow square configuration is used and the ground electrodes are still connected in parallel and equally spaced Figure 21 In multiple electrode systems the 62 method electrode spacing may no longer be applied directly The distance of the auxiliary electrodes is now based on the maximum grid distance e g in a square the diagonal in a line the tot
31. rounding systems ground grids ground mats even under diffi cult conditions such as high stray currents or excessive auxiliary electrode resistance This high performance instrument is capable of measuring up to 20kQ and direct reading with a resolution of 1 milliohm is possible The extra large 3 digit LCD display minimizes the possibility of operator reading error and dual indicators blinking display and arrow warn the operator when excess stray current or auxiliary electrode resistance is present or when there is a lack of continuity between leads and electrodes A beeper notifies the user if a voltage greater than 20V peak is present between the terminals X and Y or X and Z when the ground leads are connected The Model 4500 can be used to perform soil resistivity measurements with the four point method by using the high 20kQ range and is designed in a sturdy dust and water resistant carrying case with a detachable cover Protective Cover Case for Compartment for Leads and Hex Key Carrying Handle Snaps for Closing Cover Figure 1 6 Digital Ground Resistance Tester Model 4500 2 2 Detaching the Cover To detach the cover from the case apply downward pressure to the rear portion of the cover while gripping it firmly To re attach the cover fit the hinges into the respective housings and apply strong rear to front pressure to the cover until it snaps into place Unhinging Supporting Point Figure 2
32. sistance Dwight s formula cited previously shows that the resistance to earth of grounding electrodes depends not only on the depth and surface area of grounding electrodes but on soil resistivity as well Soil resistivity is the key factor that determines what the resistance of a grounding electrode will be and to what depth it must be driven to obtain low ground resistance The resistivity of the soil varies widely throughout the world and changes sea sonally Soil resistivity is determined largely by its content of electrolytes consisting of moisture minerals and dissolved salts A dry soil has high resistivity if it contains no soluble salts sor minimum average Maximum Same with varying proportions 1020 15 800 135 000 Gravel sand stones with little clay or loam 59 000 94 000 458 000 Table 5 4 1 3 Factors Affecting Soil Resistivity Two samples of soil when thoroughly dried may become in fact very good insulators having a resistivity in excess of 109 ohm centimeters The resistivity of the soil sample is seen to change quite rapidly until approxi mately twenty percent or greater moisture content is reached 18 Digital Ground Resistance Tester Model 4500 Moisture content Resistivity Q cm by weight Top Soil Sandy Loam to Table 6 The resistivity of the soil is also influenced by temperature Table 7 shows the variation of the resistivity of sandy loam con
33. tain a grounding resistance of 20 ohms in a soil with a resistivity of 10 000 ohm centimeters a 5 8 OD rod must be driven 20 feet NOTE that the values indicated on the Nomograph are based on the assumption that the soil is homogeneous and therefore has uniform resistivity Figure 8 The Nomograph value is an approximation Digital Ground Resistance Tester Model 4500 21 Grounding Nomograph Ground Rod Soil Resistivity Rod Depth Rod Diameter Resistance Ohms Ohm centimeters Feet Inches D joo R 100 80 DIA 80 60 60 40 Figure 8 Select required resistance on R scale 2 Select apparent resistivity on P scale Lay straightedge on R and P scale and allow to intersect with K scale Mark K scale point Lay straightedge on K scale point and DlA scale and allow to intersect with D scale 6 Point on D scale will be rod depth required for resistance on scale 4 2 Ground Resistance Values NEC 2008 article 250 56 regarding the resistance of rod pipe and plate electrodes states that if the rod pipe or plate does not have a resistance of 25Q or less to ground shall be augmented by one additional electrode of any of the types specified by 250 52 A 4 through A 8 Where multiple rod pipe or plate electrodes are installed to meet the requirements of the section they shall not be less than 6 feet apart 22 Digital Ground Resistance Tester Model 4500 FPN The paralleling efficiency of rods longer than 8 feet
34. taining 15 2 moisture with temperature changes from 20 to 15 C In this temperature range the resistivity is seen to vary from 7200 to 330 000 ohm centimeters Resistivity Q cm 66 720 9 900 32 2 0 32 ice 30 000 79 000 Table 7 18 800 0 Because soil resistivity directly relates to moisture content tem perature it is reasonable to assume that the resistance of any grounding system will vary throughout the different seasons of the year Such varia tions are shown in Figure 7 below Since both temperature and moisture content become more stable at greater distances below the surface of the Digital Ground Resistance Tester Model 4500 19 earth it follows that a grounding system to be most effective at all times should be constructed with the ground rod driven down a considerable distance below the surface of the earth Best results are obtained if the ground rod reaches the water table 80 60 40 Curve 1 20 1 Curve 2 c 2 E G zm 35323383 3 85 5 Figure 7 Seasonal variation of earth resistance with an electrode of 3 4 pipe in rather stony clay soil Depth of electrode in earth is 3 ft for Curve 1 and 10 ft for Curve 2 In some locations the resistivity of the earth is so high that low resistance grounding can be obtained only at considerable expense and with an elab
35. the surrounding earth AEMC Instruments has also recently introduced a clamp on ground resistance tester NOTE The National Electrical Code and NEC are registered trademarks of the National Fire Protection Association 4 3 Ground Resistance Testing Principle Fall of Potential 3 Point Measurement Three point measurement is used to measure resistance to ground of ground rods and grids The potential difference between rods X and Y is measured by a voltmeter and the current flow between rods X and Z is measured by an ammeter By Ohm s Law RI or we may obtain the ground electrode resistance R If E 20V and 1 then It is not necessary to carry out all the measurements when using a ground tester The ground tester will measure directly by generating its own cur rent and displaying the resistance of the ground electrode 24 Digital Ground Resistance Tester Model 4500 CURRENT SUPPLY 5 H H AMMETER I VOLTMETER E GROUND AUXILIARY AUXILIARY ELECTRODE POTENTIAL CURRENT UNDER TEST ELECTRODE ELECTRODE Figure 9 NOTE Terminals X and Xv are shorted together in three point measure ment 4 3 1 Position of the Auxiliary Electrodes in Measurements The goal in precisely measuring the resistance to ground is to place the auxiliary current electrode Z far enough from the ground electrode under test so that the auxiliary potential electrode Y will be outside of the effec tive r
36. wo points For most applications the most accurate method is the 4 point method which is used in the Model 4500 Ground Tester The 4 point method as the name implies requires the insertion of four equally spaced and in line electrodes into the test area A known current from a constant current generator is passed between the outermost electrodes The potential drop a function of the resistance is then measured across the two innermost electrodes Model 4500 is calibrated to read directly in ohms 1000A x 1 32 Digital Ground Resistance Tester Model 4500 Where distance between the electrodes in centimeters B electrode depth in centimeters If A gt 20 B the formula becomes 2x AR with A in cm p 191 5 AR with A in feet p Soil resistivity ohm cm This value is the average resistivity of the ground at a depth equivalent to the distance A between two electrodes nao Feces Z electrode Figure 18 4 9 Resistivity Measurement Procedure 4 Point Given a sizeable tract of land in which to determine the optimum soil resis tivity some intuition is in order Assuming that the objective is low resis tivity preference should be given to an area containing moist loam as opposed to a dry sandy area Consideration must also be given to the depth at which resistivity is required Digital Ground Resistance Tester Model 4500 33 Disconnect the shorting strip from the X
37. xcellent safety practice even if the equipment is properly operated and correctly grounded Always inspect the instrument and leads prior to use Replace any defective parts immediately Digital Ground Resistance Tester Model 4500 3 1 1 International Electrical Symbols E This symbol signifies that the instrument is protected by double or reinforced insulation Use only specified replacement parts when servicing the instrument This symbol on the instrument indicates WARNING and that the operator must refer to the user manual for instructions before operating the instrument In this manual the symbol preceding instructions indicates that if the instructions are not followed bodily injury installation sample and product damage may result A Risk of electric shock The voltage at the parts marked with this symbol may be dangerous 1 2 Receiving Your Shipment Upon receiving your shipment make sure that the contents are consistent with the packing list Notify your distributor of any missing items If the equip ment appears to be damaged file a claim immediately with the carrier and notify your distributor at once giving a detailed description of any damage Save the damaged packing container to substantiate your claim 1 3 Ordering Information Ground Resistance Tester Model 4500 Cat 450 100 Includes AC power supply cord 12V nickel cadmium battery installed adhesive label C1 P1 P
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