Grounding and bonding testing
- 1. Grounding and Bonding Testing Presented by Mike Lewis Senior Application Engineer Meggergg
- 2. ObjectiveObjective • Review Proper soil resistivity techniques Id tif d l t d t• Identify ground electrode system components and bonding materials • Ensure proper installation • Measure the effectiveness of the groundg electrode and bonding system by means of ground testingg g
- 3. Simply PutSimply Put… • Step 1 Earth (Soil) Testp ( ) • Step 2 Install System • Step 3 Test System• Step 3 Test System
- 4. I. Earth (Soil) Resistivity TestingI. Earth (Soil) Resistivity Testing Wh i E h R i ? • Earth’s resistance to current flow from the ground electrode What is Earth Resistance? • Largest factor influencing ground system effectiveness What Affects Earth Resistance? • Type of soil • Amount of moisture/presence of salts • Temperature
- 5. Resistivities of Different SoilsResistivities of Different Soils
- 6. Why Earth (Soil) Test?Why Earth (Soil) Test? Tells you how “good” (conductive) your soil issoil is Good indication on whether or not generic ground specification designg g p g will work Helps reduce “surprises” at the end ofp p the installation
- 7. 5 Ohm Requirements5 Ohm Requirements Soil Resistivity ranges: 100 - 15,000 Ohms cm – Standard Design Ok 15 000 25 000 Oh M b15,000- 25,000 Ohms cm- Maybe 25 000 - 50 000 Ohms cm- Special25,000 - 50,000 Ohms cm- Special 50,000 + - Very Special; maybe not practical50,000 y Sp a ; ayb o p a a
- 8. Earth (Soil) Resistivity TestingEarth (Soil) Resistivity Testing • How do we test the soil?• How do we test the soil? 4 P W T• 4 Part Wenner Test
- 9. Measuring Earth ResistivityMeasuring Earth Resistivity Use a 4 terminal gro nd testerUse a 4-terminal ground tester. Space the electrodes an equal distance “a” aparta apart. Insert the electrodes a distance of a/20 into the groundinto the ground. Measures the average soil resistivity to a depth equal to the electrode separationdepth equal to the electrode separation.
- 10. Measuring Earth ResistivityMeasuring Earth Resistivity a a a a/20 C2P2P1C1 C2P2P1C1 C2 P2 C1P1 DET2/2
- 11. M i E h R i i iMeasuring Earth Resistivity a a a C2P2P1C1 X C2P2P1C1 a
- 12. Actual Site Testing ProceduresActual Site Testing Procedures Test at Multiple locations across the site Motorola R56 2000 Test at Multiple locations across the site
- 13. Actual Site Testing ProceduresActual Site Testing Procedures Soil is not Homogenous; test at various soil depths as well Motorola R56 2000
- 14. Soil Resistivity Test SummarySoil Resistivity Test Summary • If the Results of the Soil Test are in the 15,000 Ohm-cm range or less, it is prudent to go with the generic ground system specified • If the Results of the Soil Test areIf the Results of the Soil Test are substantially above 15,000 Ohm-cm; contact the carrier owner and thecontact the carrier, owner and the engineering firm.
- 15. Ground Electrode System Components • Ground Electrodes • Ground ConductorsGround Conductors • Ground Bars • Bonding Connectors Mechanical–Mechanical –Compression –Exothermic
- 16. Ground ElectrodesGround Electrodes 1. Ground Electrodes Types -yp Ground Rods: Copper Clad Steel Solid Copper GalvanizedGalvanized Stainless Steel Enhanced Ground PlatesGround Plates Copper Ground Mesh
- 17. Ground Electrodes… ConsiderationsGround Electrodes… Considerations Soil Resistivity - Some soils, (such as sandy soils), have such high resistivities that conventional ground rods or ground electrode Ground Electrodes… ConsiderationsGround Electrodes… Considerations g g systems may be unable to attain the desired ground resistance requirement. Enhanced ground electrodes or ground enhancement materials may be required to meet the groundingenhancement materials may be required to meet the grounding specification. /Soil PH/type - PH a factor in choosing. Some ground rod types work better in different soils. Soil Characteristics - Some sites may have only a few inches of soil (or none) sitting on top of bedrock. In this case, ground mesh is the preferred electrode (Never drill into bedrock)mesh is the preferred electrode. (Never drill into bedrock).
- 18. Ground Mesh
- 19. Ground Electrodes… Considerations Ground Rod Diameter - Doubling diameter of ground rod reduces resistance only 10%. Using larger diameter ground rods is mainly a strength issue (ie. In rocky conditions, a largerrods is mainly a strength issue (ie. In rocky conditions, a larger diameter ground rod might be advantageous). G d R d L th D bli l th th ti ll dGround Rod Length - Doubling length theoretically reduces resistance 40%, actual reduction depends on soil resistivities encountered in multi- layered soils. Ground Rod Spacing - Approximately twice the length (inGround Rod Spacing Approximately twice the length (in good soil).
- 20. Ground Rod Driving TipGround Rod Driving Tip • Don’t do this!
- 21. Ground Rod Spacing Rule of ThumbGround Rod Spacing Rule of Thumb Proper Spacing 1x length Too Close
- 22. Ground Electrodes… ConsiderationsGround Electrodes… Considerations Ufer Grounds - Concrete encased electrode. Forencased electrode. For example, tying into the tower footing rebar or building pad rebar provides a Ufer ground. Ufer grounds should b d th lnever be used as the sole ground electrode.
- 23. Enhanced Grounding Materialg Should be > 95%95% pure carbon Should not contain concrete or bentonite fillers
- 24. ApplicationsApplications Vertical Application Horizontal Application
- 25. Enhanced Ground RodsEnhanced Ground Rods Contain electrolytic salts that lower ground resistivity over time
- 26. Grounding ConductorsGrounding ConductorsGrounding ConductorsGrounding Conductors Types - Grounding: Solid Stranded Flat Strap Lightning: Rope Lay
- 27. Inductance Flat strap conductors have less inductance than their similarly Conductors... ConsiderationsConductors... Considerations Inductance - Flat strap conductors have less inductance than their similarly sized round conductor counterparts. Strength/Durability - Round conductors whether solid or stranded are muchStrength/Durability Round conductors whether solid or stranded are much stronger than a 24 or 26 gauge flat strap conductor. This should be a consideration when backfilling trenches. Exothermic Connections - The preferred type of connection for underground uses. Availability as well as ease of connection is better for the round conductors than the flat strap conductors. Cost Effectiveness - Although the inductance may be less for the flat strap conductors, their cost is much higher. It may be more cost effective to use lti l d d t th l i ll d t i d thmultiple round conductors, thus lowering overall ground system impedance than single flat strap conductors.
- 28. Lightning Tra els on the o tside s rface of a Conductors…ConsiderationsConductors…Considerations Lightning Travels on the outside surface of a conductor, the so called “skin affect”. Therefore, the larger the surface area of a conductor, the betterlarger the surface area of a conductor, the better path it makes. Remember, multiple parallel paths are very important. The fewer paths you have the larger the f di h d dsurface area or diameter the conductor needs to have. Remember, a Tower is the down conductor.
- 29. Conductor…ConsiderationsConductor…Considerations - Selection of Proper Size I h b f S f d R- In the absence of a Specified Requirement… - No Standards exist in Wireless Telecommunications. (ANSI J Std 607)J-Std 607) - LP Standards state if building height is equal or greaterg g q g than >75’ use class II - Size Should be Dependent on the length and number of- Size Should be Dependent on the length and number of paths
- 30. Conductor… ConsiderationsConductor… Considerations Conductor Routing and PlacementConductor Routing and Placement General Rules of Thumb for Placement: As far as possible from communications cable (12” minimum for a ground conductor. Reference NEC 800(12 minimum for a ground conductor. Reference NEC 800 for Power lines). Lightning conductors must be 6’ away from power &Lightning conductors must be 6 away from power & communications cable. (Reference NEC 800 & NEC 250). C i di l f hi if d dCross in a perpendicular fashion if needed.
- 31. Not Good….Not Good…. Pl tPl tPlacement….Placement….
- 33. A little Better….A little Better…. Placement….Placement….
- 35. C d C id iC d C id iConductor…ConsiderationsConductor…Considerations Routing and Placement General Rules of Thumb for Routing: M i t i d d l i th t d ( i t ti lMaintain downward sloping path to ground (equipotential bonds exception) Do not run conductors uphill (1/4 rise acceptable to a point) Maintain at least an 8” radius of bend
- 36. - Uphill path to ground - Radius of bend less than 8” - Bonding issue - Water pipe?
- 37. Not bonded to conduit….Not bonded to conduit…. Harger Lightning & Grounding © 2006
- 38. Conductor…ConsiderationsConductor…Considerations Routing in conduit… - Sometimes required by local codes If i t lli d it it t b b d d- If run in metallic conduit, it must be bonded on both ends - Might be beneficial if run in metallic conduit
- 39. - Conduit on left a little better…. - Needs to be bonded as close to the opening as possible... - Two conduits on right t b d d t d itnot bonded to conduit
- 41. - A really good idea !!!idea !!! - Used “romex” style fittings
- 43. Ground BarGround Bar • What is a Ground Bar? – Simply a connection point • What does it do?What does it do? – Facilitates ease of bonding connections • Issues• Issues – Theft Tamper resistantTamper resistant – Galvanized Bad idea, galvanic coupleg p
- 44. Grounding/Bonding ConnectionsGrounding/Bonding Connections Three Types of Connectionsy MechanicalMechanical Compression Exothermic
- 45. Mechanical ConnectionsMechanical Connections • Use StandardUse Standard Tools & Hardware
- 46. Mechanical ConnectionsMechanical Connections • Used when compression or exothermic connections are not practical/feasible • Surface preparation essentialp p • Use appropriate hardware • Tighten to proper torque rating• Tighten to proper torque rating
- 47. Mechanical ConnectionsMechanical Connections • Advantagesg – Can be removed – Use common tools – Lower material Cost • Disadvantagesg – Can be removed – Loosen over time – Require more maintenance
- 50. Hardware RequirementsHardware Requirements • Stainless Steel• Stainless Steel or • Silicon Bronze• Silicon Bronze • No Zinc!
- 51. Galvanic SeriesGalvanic Series • Galvanic SeriesGalvanic Series – >.3 volts difference in potential can causep corrosion – Use stainless steel hardware instead of zinc
- 53. Proper Torque
- 55. More MechanicalsMore Mechanicals • Possible “burn h h” ithrough” issues
- 56. More MechanicalsMore Mechanicals Motorola R56 2000
- 58. More MechanicalsMore Mechanicals • Dissimilar metals
- 59. Compression ConnectionsCompression Connections • Used when it is desirable to make an irreversible electrical connectionirreversible electrical connection • Less maintenance than a mechanical connection • Not a molecular bond, (Not recommended for underground use)
- 60. Compression ConnectionsCompression Connections • Specialized tools/dies requiredSpecialized tools/dies required – Generate, 2, 6 and 13 tons of crimping forcep g
- 61. Compression ConnectionsCompression Connections AdvantagesAdvantages Irreversible UL listedUL listed Low/no maintenance Di dDisadvantages Expensive tooling Sometimes hard to make, (location) Not a molecular bond
- 62. Compression LugsCompression Lugs Long Barrel Inspection Port g p 2-Hole
- 63. Connection ProcessConnection Process Trim insulation back so that b d d t i li htlbared conductor is slightly longer than barrel.
- 64. Connection ProcessConnection Process Insert conductor so that it butts up against end of barrel. View this thru inspection portView this thru inspection port.
- 65. Connection ProcessConnection Process 2 crimp minimum2 crimp minimum Make sure end of conductor i t d f b lremains at end of barrel; Make first crimp Repeat crimping process
- 66. Connection ProcessConnection Process 2 Crimp Minimum
- 67. More CompressionMore Compression • H-TapsH Taps • C-Taps
- 68. Bad ExamplesBad Examples Poor Mechanical ConnectionsConnections Poor Compression Connections
- 70. Exothermic ConnectionsExothermic Connections What is an exothermic connection? An exothermic connection is used to form a molecular bond between two metals such as copper and steel.pp
- 71. Exothermic Connections Provides a Molecular Bond Ampacity exceeds that of conductors Connections will not loosenConnections will not loosen Connections never increase in resistance Does not deteriorate with age Maintenance free
- 72. Compression vs. Exothermicp Molecular BondPoint-to-Point Contact Molecular BondPoint-to-Point Contact
- 73. The Exothermic ProcessThe Exothermic Process Tools Required
- 75. Exothermic Connection ProcessExothermic Connection Process Safety First Protective Glasses Gloves C ACover Arms
- 76. Connection Process Step 1 – Connection Process Step 1 – Torch dry the mold to eliminate moisture! (First connection and…) torch
- 77. Connection Process Step 2 –Step 2 • Dry conductors Cl d t f• Clean conductor surfaces • Position conductors in mold • Close mold CCBRSH1 CCBRSH2
- 78. Connection Process Step 3 – Position the disk in the mold evenly, concave side upside up
- 79. Connection Process Step 4 – P ld t l i t ld• Pour weld metal into mold • Sprinkle 2/3 of starting material over the weld metal • Close mold lid
- 80. Connection ProcessConnection Process Step 5 – P i i t ti• Pour remaining starting material into ignition pocket on top of the mold lid. TOPTOP LIGHTLIGHT LIDLID
- 81. Connection ProcessConnection Process Step 6 – • Stand to the side of the mold• Stand to the side of the mold • Ignite the starting material with a flint igniter
- 82. Connection Process Step 7 – • Allow 15-20 seconds to complete the process • Open mold and remove the finished connection. • Clean mold to prepare for the next connection. Spade Brush
- 84. General Indicators:General Indicators: Si N d i h ld b dSize - No conductor portion should be exposed Color - bright gold to bronzeColor - bright gold to bronze Surface Finish - smooth; free of slag depositsg p Porosity - few pinholes acceptable
- 85. Exothermic Inspection CriteriaExothermic Inspection CriteriaExothermic Inspection CriteriaExothermic Inspection Criteria Good connection Bright, shiny & free from porosity
- 86. Exothermic Inspection CriteriaExothermic Inspection CriteriaExothermic Inspection CriteriaExothermic Inspection Criteria Unacceptable connection Slag > 20% Leakage - Mold not t d lseated properly
- 87. Exothermic Inspection CriteriaExothermic Inspection CriteriaExothermic Inspection CriteriaExothermic Inspection Criteria UnacceptableUnacceptable connection Not enough weld metalweld metal
- 88. C P blCommon Problems Connection not sticking to Ground BarConnection not sticking to Ground Bar Connection not sticking to Tower LegConnection not sticking to Tower Leg Burn thru on Fence Post Melt thru on Cable to Ground Rod
- 89. Ground Electrode System Testing • Ok, So the System is installed • Let’s Test!
- 90. Choose the Proper Instruments:Choose the Proper Instruments: • Use a dedicated ground tester (designed to make this measurement)(designed to make this measurement). • Don’t make the measurement with a generalized ohmmeter or multimetergeneralized ohmmeter or multimeter - results will be erroneous. Don’t use an insulation tester• Don t use an insulation tester.
- 91. 3-Terminal Earth Tester3 Terminal Earth Tester Current SupplyCurrent Supply Ammeter (I)Ammeter (I) Voltmeter (E) P C Current Probe Potential Probe Ground Electrode Under Test P C EarthEarth Probe X
- 92. 4-Terminal Earth Tester Current Supply Ammeter (I)( ) G d Voltmeter (E) P2 C2 C1 P1 Auxiliary Current ElectrodeAuxiliary Potential Electrode Ground Electrode Under Test 2 2 EarthEarth X
- 93. Theoretical BackgroundTheoretical Background Ground Rod Sphere of Influence I Current I Current
- 94. Theoretical BackgroundTheoretical Background Current Probe Sphere of Influence Auxiliary Current Auxiliary Potential Ground Electrode Under Test (X) Current Probe (C) Potential Probe (P) ( )
- 95. Theoretical Background - Resistance Curve Ohmsistancein True Resistance Resi Current Probe Distance of Potential Probe from X (dp) Ground El t d X C Probe Position Electrode Position
- 96. Theoretical Backgroundg Insufficient Probe Spacing Ground Current Probe (C) Potential Probe (P) Ground Electrode Under Test (X) nOhmssistancein Distance of Potential Probe from X (dp) Res
- 97. Test Methods Serve Two Primary Purposes:Purposes: Verify that correct spacing is being used to assure reliable results. Provide specific shortcuts to reduce testing time.
- 98. Ground Testing Methodsg Fall of Potential Method 61 8% R l /M th d61.8% Rule/Method Four Potential Method I i C M h dIntersecting Curves Method Slope Method Dead Earth Method Star-Delta Method
- 99. Fall of Potential Method Advantage: Extremely reliableAdvantage: Extremely reliable. Disadvantage: Extremely time consuming and labor intensivelabor intensive.
- 100. Theoretical Background - Fall of Potential Current Probe (C) Potential Probe (P) Positions Ground Electrode Under Test (X) Probe (C)Test (X) stanceinOhm Current Probe Distance of Potential Probe from X (dp) Ground El d X C Resist Probe Position Electrode Position
- 101. Site Testing Fall of Potential Method 1. Determine size of ground grid system and calculate length of test leads required. (Pythagorean theorem). Lead Length CriticalCritical. 2. Make sure that the ground system under test is non connected to the Utility ground system grid. (Telephone as well). 3. Starting at 50’, record readings every 50’ t bt i d i t (Oto obtain a ground resistance curve. (Or enough points to ensure a good graph. 4.The point where curve flattens out is the4.The point where curve flattens out is the system’s ground resistance. (62%)
- 102. 3 Point Test Format Distance Readings Readings I F t i Oh i Oh 10 In Feet in Ohms, in Ohms, Easterly Northerly Direction Direction 25 50 75 6 8 East Direction 75 100 1.16 0.84 125 1.39 1.1 150 1.67 1.27 175 1.8 1.46 200 2.18 1.67 0 2 4 North Direction225 2.59 1.99 250 3.04 2.49 275 3.47 2.95 300 3.67 3.17 325 3.86 3.35 350 3 97 3 51 0 100 150 200 250 300 350 400 350 3.97 3.51 375 4.25 3.62 400 4.68 4.02 425 5.4 4.92 450 6.52 5.91 475 8 08 7 79475 8.08 7.79 500
- 103. Advantages of Fall of Potentialg Testing Conforms to IEEE 81 onl appro ed• Conforms to IEEE 81; only approved method. • Operator has complete control of the test set-up.p • Far more accurate: - 4-wire configuration/no additional loop- 4 wire configuration/no additional loop resistances included. - Significant for low resistance (1-2Ω) grounds
- 104. Simplified Fall of Potential Method Based on the theory behind the full Fall of Potential method. k hTake measurements at three points. Advantage: Much faster than full Fall of Potential th dmethod. Disadvantage: Less reliable since fewer measurements being mademeasurements being made.
- 105. Simplified Fall of Potential Methodp dc C2P2X 50% 60%40% 50% C2 P2 C1P1 DET2/2
- 106. Simplified Fall of Potential Methodp • RA = R1 + R2 + R3 33 • RMax Deviation = RA - RX (RX is furthest R value from RA)( X A) • % deviation = (RMax Deviation )*100 RARA • If (% deviation)*1.2 > 10%; C2 must be moved further awaymoved further away
- 107. 61.8% Rule/Method Based on the theory behind the full Fall of P t ti l th dPotential method. Take measurement at only one point. Ad E l i k dAdvantage: Extremely quick and easy. Disadvantage: Assumes that conditions are f t ( d t b i d ilperfect (adequate probe spacing and soil homogeneity).
- 108. 61 8% R l /M th d61.8% Rule/Method dcdc dp = 61.8%dc CPX C2 P2 C1P1 DET2/2
- 109. Theoretical Background - 61 8% RuleTheoretical Background - 61.8% Rule Ground Electrode Current Probe (C) Potential Probe (P) Under Test (X) anceinOhms Current Probe Resistance Resista 61.8% Ground Electrode Resistance Distance of Potential Probe from X (dp) X C
- 110. The Problem of LimitedThe Problem of Limited Distance/Space Ground Current Probe (C) Potential Probe (P) Ground Electrode Under Test (X) sanceinOhms Distance of Potential Probe from X (dp) Resist
- 112. Di d tDisadvantages Stakeless/Clamp-On Method • Effective only in situations with multiple grounds in parallel (pole grounds)grounds in parallel (pole grounds). • Cannot be used on isolated grounds. - no return path- no return path • Cannot be used if an alternate lower resistance return exists not involving theresistance return exists not involving the soil. Cellular towers- Cellular towers - Substations
- 113. DisadvantagesDisadvantages Stakeless/Clamp-On Method • Subject to influence if another part of the ground system is in “resistance area”. • Test is less representative of a fault at power frequency.power frequency. • Accuracies are greatly reduced.
- 114. Disadvantagesg Stakeless/Clamp-On Method • Requires a good return path. • Connection must be on the correct part of the loop.p p • Susceptible to noise from nearby substations and transformers (nosubstations and transformers (no reading).
- 115. Clamp-on Applicationp pp Motorola R56 2000
- 116. Ground Testing SummaryGround Testing Summary • 3 Point Fall of Potential Method most accurate – Must disconnect from Utility Grid – Testing Area often an issue • Clamp-On Style has limited Applications L t ti l f i– Large potential for misuse – Not as accurate as 3 point method • Testing must be done correctly to determine if theTesting must be done correctly to determine if the desired ground resistance specification is met
- 117. SummarySummary • Proper Testing and Installation methods are often over-lookedare often over-looked. • Following these guidelines will help l f t i ith di dlessen future issues with grounding and bonding related events. • For more information please contact BICSI or Megger.gg