Presentation on theme: "1 Grounding and Jumpering. 2 Temporary Grounding Why is it so important? De-energized Circuits become energized accidentally –Human Error –Contact with."— Presentation transcript:
1 Grounding and Jumpering
2 Temporary Grounding Why is it so important? De-energized Circuits become energized accidentally –Human Error –Contact with energized circuits –Induced Voltage –Lightning –Faults on adjacent circuits
3 The “A” Approach Aware--see everything-What if? Adapt--What is this situation,no standard approach. What if? Attack—Don’t violate MY zone, I am responsible for me!
4 What Conditions Justify Reviewing Grounding & Jumpering Practices Increased Fault Current Levels Increased Conductors per Structure Increased Conductors per Right-of-Way Age of Protective Grounding Equipment Accidents Continue to happen
OSHA 29 CFR Guidelines Equipotential Zone (EPZ): –“Temporary protective grounds shall be placed at such locations and arranged in such a manner as to prevent each employee from being exposed to hazardous differences in electrical potential.” (n)(3) Grounding for the Protection of Employees Question: Is there a difference between: TRIPPING OR BRACKET GROUNDS PERSONAL PROTECTION GROUNDING (EPZ) 5
Grounding for the Protection of Employees PERSONAL PROTECTION GROUNDING – EQUIPOTENTIAL ZONE GROUNDING (EPZ) A COMBINATION of tripping grounds AND personal grounds installed in a method that BONDS the de-energized cables and equipment with ALL other conductive objects within the work site, limiting the VOLTAGE DIFFERENTIAL (Electrical Potential) exposure to a safe value. From page 11-5 of Encyclopedia of Grounding 6
7 OSHA 29 CFR Guidelines Equipotential Zone Protective Grounding Equipment Testing Order of Connection Order of Removal Grounding for the Protection of Employees
8 Equipotential Zone: –“Temporary protective grounds shall be placed at such locations and arranged in such a manner as to prevent each employee from being exposed to hazardous differences in electrical potential.” (n)(3) OSHA 29 CFR Guidelines Grounding for the Protection of Employees
9 Protective Grounding Equipment: –“Protective grounding equipment shall be capable of conducting the maximum fault current that could flow at the point of grounding for the time necessary to clear the fault. This equipment shall have an ampacity greater than or equal to that of No. 2 AWG copper. –Protective grounds shall have an impedance low enough to cause immediate operation of protective devices in case of accidental energizing of the lines or equipment.” (n)(4) OSHA 29 CFR Guidelines Grounding for the Protection of Employees
10 OSHA 29 CFR Guidelines Testing: –“Before any ground is installed, lines and equipment shall be tested and found absent of nominal voltage, unless a previously installed ground is present.” (n)(5) Grounding for the Protection of Employees
12 OSHA 29 CFR Guidelines Order of Connection: –“When a ground is to be attached to a line or to equipment, the ground-end connection shall be attached first, and then the other end shall be attached by means of a live-line tool.” (n)(6) Grounding for the Protection of Employees
® OSHA 29 CFR Guidelines Order of Connection: –“When a ground is to be attached to a line or to equipment, the ground-end connection shall be attached first, and then the other end shall be attached by means of a live-line tool.” (n)(6) Grounding for the Protection of Employees IMPORTANT ! - Rubber Gloves are NOT live-line tools 13
14 Order of Removal: –“When a ground is to be removed, the grounding device shall be removed from the line or equipment using a live-line tool before the ground-end connection is removed. ” (n)(7) OSHA 29 CFR Guidelines Grounding for the Protection of Employees
® Note: All grounding clamps, ferrules and cable meet ASTM F 855 (For the latest information, please reference ASTM F 855 Standard) “Type” – refers to the means of installing a ground clamp (i.e. eyescrew, tee handle, permanent hot stick). Type I Clamps for installation on de-energized conductors are equipped with eyescrews for installation with removable hot sticks. Type II Clamps for installation on de-energized conductors have permanently mounted hot sticks. Type IIII Clamps for installation on permanently grounded conductors or metal structures have tee handles and eyes or square or hexagon head screw(s), or both. “Class” – refers to the clamp jaw surface (i.e. smooth or serrated). Class AClamp jaws with smooth contact surfaces. Class B Clamp jaws with serrations, or cross hatching, or other mean intended to abrade or bite through corrosion products on the surfaces of the conductor being clamped. “Grade” - refers to the withstand rating for the ground clamp (e.g. "Grade 5" Clamp is rated at 43 kA for 15 cycles). Grade Withstand Rating, Symmetrical kA RMS, 60Hz 15 cycles (250MS) 30 cycles (500MS) (b). ASTM F 855 DESIGNATION SUMMARY 15
16 Support Studs Visually and functionally identifies order of removal
17 Effects of Current on Man *Short shock values for 165 lbs. person C. F. Dalziel & W. R. Lee, "Lethal Electric Currents“ 1969
, Nikola Tesla invents the “Tesla coil”, a transformer that changes electricity from low voltage to high voltage making it easier to transport over long distances. The transformer was an important part of Tesla’s alternating current (AC) system, still used to deliver electricity today. 1884, Nikola Tesla arrives in America and starts work with Edison’s Electric Light Company. During this year, Nikola Tesla invents the electric alternator, an electric generator that produces alternating current (AC). 1885, After improving upon Edison’s DC dynamo, Tesla leaves Edison’s company and forms partnership with George Westinghouse after Edison refuses to pay him for his work. 1886, William Stanley develops the induction coil transformer and an alternating current electric system. 1888, Nikola Tesla demonstrated the first “polyphase” alternating current (AC) electrical system. His AC system includes everything needed for electricity production and use such as the electric generator, transformer, transmission system, motors and lights. 1890, War of Currents between Thomas Edison/JP Morgan and Nikola Tesla/George Westinghouse and continues through the 1890’s and early 1900’s. 1892, Anticipating AC to become the dominant form of electric power, JP Morgan gains control of the Edison Electric Light Company and forms General Electric. GE invests heavily into AC power. 1893, The Westinghouse Electric Company used an alternating current (AC) system to light the Chicago World’s Fair. George Westinghouse and Nikola Tesla also win contract to build the first hydro electric power plant at Niagara Falls. Niagara Falls Power Co opens in 1896 and supplies power to Buffalo NY.
22 Each Phase Connected to a Driven Ground Rod Problems –Resistance between grounds. –Does not limit voltage drop across the worker. –Different potentials present. –Long cable lengths. –Does not protect against “step” potential.
23 Equivalent Circuit Diagram Each Phase Connected to a Driven Ground Rod R J is the equivalent resistance of the ground leads. R W is the equivalent resistance of the worker on the structure. R E is the equivalent resistance of the earth between driven grounds. RJRJ RJRJ RJRJ RwRw RERE RERE RERE
24 Phases Connected to a Common Ground Improvements –Reduced resistance between phases. –Results in faster system reaction time. Problems –Ground resistance in parallel with the work area. –Does not limit voltage drop across the worker. –Does not protect against “step” potential
25 Equivalent Circuit Diagram Phases Connected to a Common Ground R J is the equivalent resistance of the ground leads. R W is the equivalent resistance of the worker on the structure. R E is the equivalent resistance of the earth between driven grounds. RJRJ RJRJ RJRJ RwRw RERE
26 Jumpering from Phase to Phase Improvements –Reduced number of leads to ground. –Eliminates violent reaction of multiple leads to ground. –Minimum resistance between phases, rapid fault clearing. Problems –Does not limit voltage drop across the worker –Does not protect against “step” potential –Does not create an equi- potential work zone
27 Equivalent Circuit Diagram Jumpering from Phase to Phase R J is the equivalent resistance of the ground leads. R W is the equivalent resistance of the worker on the structure. R E is the equivalent resistance of the earth between driven grounds. RJRJ RJRJ RJRJ RwRw RERE
28 Equi-Potential Configuration Improvements –Reduced number of leads to ground. –Eliminates long leads to ground. –Puts conductor, work area, and lineman at the same potential. Creates an Equi-Potential work area. Problems –Does not protect against “step” potential. Connect to neutral when available
29 Equivalent Circuit Diagram Equi-Potential Configuration Example Cable 1/0 AWG Copper, 12’ Long R J = (12 X.098 mΩ) +.32 mΩ = mΩ R W = 1000 Ω Fault Current, i F = 12,000 A Current through the worker by Kirchoff’s Law i W = (R J )/(R J +R W ) X i F = 18 mA 1.49/(1.49+1,000)x12,000 =18mA 100 mA: Fibrillation can occur 23 mA: Painful & Severe shock RJRJ RJRJ RJRJ RwRw
30 Equivalent Circuit Diagram Equi-Potential Configuration Example Cable 1/0 AWG Copper, 8’ Long R J = (8 X.098 mΩ) +.32 mΩ = 1.10 mΩ R W = 1000 Ω Fault Current, i F = 12,000 A Current through the worker by Kirchoff’s Law i W = (R J )/(R J +R W ) X i F = 13 mA 1.10/(1.10+1,000)x12,000 =13mA 100 mA: Fibrillation occurs Reducing the cable length 4’ reduced the current through the workers body by 26% RJRJ RJRJ RJRJ RwRw
31 HPS Ground Clamp Ratings
32 Double Point Grounding Jumpers connect all three phases together on each side of the work site. Jumper connects cluster bar to phases on each side of the work site. Jumper connects cluster bar to system neutral or a ground rod if a neutral is not available. Provides additional capacity for larger fault currents, (fault current is divided by Ohm’s Law). If the job requires breaking the circuit at the work site, double-point grounding must be used. Phase Conductor Jumpers Ground Jumper Neutral Jumper Cluster Bar (chain binder) below working position
33 Single Point Grounding Jumpers connect all three phases together. Jumper connects cluster bar to phases. Jumper connects cluster bar to system neutral or a ground rod if a neutral is not available. Phase Conductor Jumpers Ground Jumper Neutral Jumper Cluster Bar (chain binder) below working position
34 Step & Touch Potential Ground rod test at A.B. Chance Research Center, Centralia, MO
35 Step Potential (Unprotected) Dependent upon resistance between “system” ground and workman on the “Earth” ground. Hazardous voltage potential exists across the workman on the ground. Solution: Create a zone of Equi-Potential for the workman on the ground. R1R1 R2R2 R0R0 RFRF RKRK RFRF I FAULT
36 Step Potential (Protected) R K =resistance across the worker. R 0 =ground resistance R 1 =structure resistance R 2 =ground grid resistance E STEP =voltage drop across worker I K =current through the worker The closer the worker is to the structure the greater the potential rise. Voltage drop across the worker on the ground is limited by the ground grid. Unprotected workers should stay clear of the work area around the structure ground. R1R1 R2R2 R0R0 RKRK R1R1 R2R2 R0R0 E STEP RKRK I FAULT IKIK Potential rise above remote earth during short circuit
37 Equi-Mat ® Ground Grid Protection against step potential. Portable ground grid provides Equi- Potential work zone for groundman. Limits hazardous voltage drop across the person due to voltage gradient at the ground site. Meets or exceeds (New) ASTM F2715
38 Touch Potential (Protected) R K =resistance across the worker. R 0 =ground resistance R 1 =ground grid resistance E TOUCH =voltage drop across worker I K =current through the worker The closer the worker is to the structure the greater the potential rise. Voltage drop across the worker on the ground is limited by the ground grid. Unprotected workers should stay clear of the work area around the structure ground. R1R1 R0R0 RKRK R1R1 R0R0 E TOUCH RKRK I FAULT IKIK Potential rise above remote earth during short circuit
Tested to ASTM Standard in Hubbell Short Circuit Lab Results meet or exceeded ASTM Standards for HPS/Chance Equi-Mat. Test Duration – 14.5 cycles Ground fault measured at 1132A at 7680V at ground rod. 3 volts & 3mA measured across man when tested grid up, 4 volts & 4.3mA measured across man when tested grid down. Mat is designed for grid up use only.
40 Equi-Mat ® Ground Grid Portable ground grid provides Equi-potential work zone for worker. Protection against step and touch potential. Limits hazardous voltage drop across the person due to voltage gradient at the work site. Now available in Slip Resistant material (Black)
41 Touch & Step Potential Protection at Truck Work Site
43 OHSA 1926 Subpart E OHSA § , Mechanical Equipment (iii) Each employee shall be protected from hazards that might arise from equipment contact with the energized lines. The measures used shall ensure that employees will not be exposed to hazardous differences in potential. Unless the employer can demonstrate that the methods in use protect each employee from the hazards that might arise if the equipment contacts the energized line, the measures used shall include all of the following techniques: (A) Using the best available ground to minimize the time the lines remain energized, (B) Bonding equipment together to minimize potential differences, (C) Providing ground mats to extend areas of Equi- potential, and (D) Employing insulating protective equipment or barricades to guard against any remaining hazardous potential differences. Meets or Exceeds ASTM F2715
44 General Worksite Schematic
45 Voltage vs. Distance from Ground Point
46 Protection at Truck Worksite If equipment is grounded, is it safe? How do we limit a hazardous voltage in the event the equipment becomes energized?
47 Temporary Grounding Equipment Selection & Location Choose ground cable with adequate capacity. Choose ground clamps with adequate current capacity. Verify system is de-energized. Clean connections. Locate clamps for jumpering. Minimize cable slack.
48 Grounding Cable Selection Size / Fault Current Withstand Capacity. Ratings at 15 and 30 cycles per ASTM F855 Jacket Color –Yellow, Clear, or Black(Personal preference) Ferrules –Shrouded or UnShrouded (Depends upon type of stress relief) –Threaded or Smooth (Match to ground clamp terminal) –Copper or Aluminum(Match with the clamp material) Cable Size15 Cycles30 CyclesASTM Grade #214 kA10 kA1 1/021 kA15 kA2 2/027 kA20 kA3 4/043 kA30 kA5
49 Fault Current Withstand Rating
50 Temporary Grounding Cable #2, 1/0, 2/0, & 4/0 Copper Cable. Yellow, Black, & Clear Jacket. Threaded and Plug Type Compression Ferrules (ASTM F855 recommendation). –Copper Ferrules: Use with bronze body clamps. –Aluminum Ferrules: Use with Aluminum body clamps.
TAP CLAMPS ARE NOT GROUNDING CLAMPS!! Oversized Tap Bolt Extra clamp for ground cable to help withstand high mechanical forces of a fault current Larger Diameter Eyescrew with fine threads for additional clamping force Oversized main area provides larger contact area Key Differences: Much Larger Clamp Mass 51
52 Ground Clamp Selection Type: “C” Type, Duckbill, Flat Faced, Tower Type, Ball & Socket. Fault Current Capacity. Eye Screw or “T” Handle. ACME or Fine Thread. Body: Aluminum or Bronze. Jaws: Serrated or Smooth. Terminals: Threaded, Smooth, Pressure Type
53 “C” Type Ground Clamps Designed for use on wide range of conductor and tubular bus. Up to Grade 5 rating (43kA) Available with pressure type or threaded terminals. Available with serrated jaws or smooth jaws. –Serrated jaws are better able to penetrate corrosion. –Can provide a lower resistance connection when cleaning is impractical. –Tighten the clamp, slightly rotate it, then securely tighten.
54 Flat Face Ground Clamps Designed for connection to flat surfaces. Utilizes “set” screw to assist electrical connection. Available with eye screw or “T” Handle. Threaded, smooth, or pressure type terminals.
55 Tower Ground Clamps Designed for making low resistance connection to galvanized steel. Special “self-cleaning” cutting edges. Tighten clamp, slightly rotate, then securely tighten. Pressure - Type Terminal “T” Handle Screw
56 Duckbill Ground Clamps Quick installation on range of conductor. Large “Spring-loaded” Duckbill makes it easy to install. Available with pressure type or threaded terminals. Up to Grade 5 rated 15 cycles).
57 Ball and Socket Ground Clamps Unique design for substations, switchgear, and industrial applications. Permits installation at various angles. Available with eyescrew or “T” handle. Pressure type or threaded type terminals. Rated up to Grade 5 15 cycles).
58 All Angle Ground Clamps Ideal for substation and transmission applications. Installs at a wide range of angles. Maximum opening of 2.88”. Rated Grade 5, 15 cycles). Pressure type or threaded type terminals. Eye screw or stick mounted.
59 Cutout Grounding Clamps Ideal for grounding at open points. Provides physical barrier to prevent accidental closing. Fits a wide variety of cutout designs. Rated 30 cycles.
60 Verify system is de-energized Check meter for continuity Use appropriate length of stick
62 Underground Distribution Ground Set Provides high visibility ground elbow. Ground elbow mounts directly to a ground bushing or feed through bushing. Rated 10 cycles. Available in single phase and three phase sets.
63 Minimize Cable Length Demonstrates the violent reaction of the ground clamp and cable during fault currents.
64 Pole Type Ground Set Includes pre- assembled jumpers with aluminum body clamps and ferrules. Bottom left is the cluster bracket.
65 Testing Personal Protective Ground Sets
66 15 kV Vertical Running Corner Cluster bar mounted below the work area. Jumper Cluster Bar to neutral. Jumper neutral to outside phase. Jumpers connect all three phases together.
67 15 kV Vertical Deadend Cluster bar mounted below the work area. Jumper Cluster Bar to neutral. Jumper neutral to outside phase. Jumpers connect all three phases together.
68 15 kV Crossarm Application Cluster bar mounted below the work area. Jumper connects Cluster Bar to neutral. Jumper connects neutral to outside phase. Jumpers connect all three phases together.
69 Equi-Potential Grounding Why is it Important? Mandated by OSHA Section “N” Federal law since 1994 Provides employee protection Provides a Zone of Equi-potential Provides a path to ground w/ low voltage drop across worker Requires a Minimum cable size #2 Copper or equivalent Grounding sets must have low impedance
70 Equi-Potential Grounding Why is it Important? Recommend periodical testing per ASTM F2249- In Service Test Methods for Grounding Jumper Assemblies Allows for Single or Double point Eliminates differences in potential Backed up by field tests and actual use for over 20 years Accepted by most utilities and contractors
72 Ground Set Tester Information Uses D.C. low current test No need to measure ground leads up to 25 ft Adapters available for testing all types of grounding components Will test aluminum as well as copper ferrules Probing capability to find high resistance areas Not affected by coiling of the cables Cable Inductance does not affect readings Not affected by placement on metal table or on concrete floors
73 Ground Set Tester Comparison Can test sets w/ spring protectors around ferrules D.C. designed to give accurate, easy test method 5 volts across set compared to.5 volts for other testers No need to disassemble elbow grounds or grounded parking stand to test Two indications of high resistant area, one by digital readout, other red or green pass/fail light Non Destructive test No specific cable orientation
74 Why Use Grounding Cable? Finer stranding makes cable more flexible Cable tested to carry fault currents Preferred by ASTM F Rubber jacket also important for flexibility Clear jacket offers easy visual inspection of cable Yellow cable more visible than black