G157LT99 Grounding Book COVER 9/10/1999 2:40 PM Page 1 $28.95 U.S. Practical Guide To Electrical Grounding An First Printing, First Edition, August 1999 Publication W.
Grounding Book 4/14/99 10/5/99 6:01 PM Page IFC1 (Black plate) Practical Guide to Electrical Grounding Library Of Congress Catalog Card Number: 99-72910 Electrical Protection Products 34600 Solon Road Solon, Ohio 44139 W. Keith Switzer, Senior Staff Engineer Phone: (440) 248-0100 Fax: (800) 677-8131 E-mail: kswitzer@erico.com Copyright © 1999 ERICO, Inc. All rights reserved.
Grounding Book 4/14/99 10/5/99 6:01 PM Page i (Black plate) Practical Guide To Electrical Grounding An Publication First Printing, First Edition, August 1999 W.
Grounding Book 4/14/99 ii 10/5/99 6:01 PM Page ii (Black plate) Practical Guide to Electrical Grounding Table of Contents Chapter Description Page 1 Building and Service Entrance Grounding The grounding of buildings and facilities where people work. Building Grounding Ground Resistance Electrical Service Grounding Ufer Grounding 1 2 Building Lightning Protection - A critical extension of grounding.
Grounding Book 4/14/99 10/5/99 6:01 PM Page iii (Black plate) Preface WHY DO WE NEED ANOTHER BOOK ON GROUNDING? This book is designed for the contractor who finds that installing grounding systems, which are in compliance with all relevant codes and standards, is a complex and somewhat mystifying assignment.
Grounding Book 4/14/99 iv 10/5/99 6:01 PM Page iv (Black plate) Practical Guide to Electrical Grounding essential to provide a reference function. Another suitable conductive body may be used instead. The function of a grounding electrode system and a ground terminal is to provide a system of conductors which ensures electrical contact with the earth.
Grounding Book 4/14/99 10/5/99 6:01 PM Page v (Black plate) Preface are some of the best, long lasting and cost effective products available. Here we combine these with our knowledge of methods to assist the industry professional in sound choices. It is most often an electrician or electrical worker who is affected by poorly designed ground systems. All of the drawings (non shaded versions) in this book are available in AutoCAD® .DWG files. These are available through the ERICO CAD-Club™.
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Grounding Book 4/14/99 10/5/99 6:01 PM Page 1 (Black plate) Chapter 1: Building and Service Entrance Grounding 1 Chapter 1 Building and Service Entrance Grounding Building Grounding Ground Resistance Electrical Service Grounding Ufer Grounding
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Grounding Book 4/14/99 10/5/99 6:01 PM Page 3 (Black plate) Chapter 1: Building and Service Entrance Grounding BUILDING GROUNDING — AN OVERVIEW Despite the electrical designers’ best efforts, electrical ground faults, short circuits, lightning and other transients can and often do occur in building electrical distribution systems.
Grounding Book 4/14/99 4 10/5/99 6:01 PM Page 4 (Black plate) Practical Guide to Electrical Grounding BUILDING GROUNDING Typical Installation Weld At Column Base. Electrical design and installation professionals need to consider several different building grounding systems for any building or structure on which they may work.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 5 (Black plate) Chapter 1: Building and Service Entrance Grounding When “inspection wells” are required to expose points from which to measure system resistance, several methods are available. Inspection wells are usually placed over a ground rod.
Grounding Book 4/14/99 6 10/5/99 6:01 PM Page 6 (Black plate) Practical Guide to Electrical Grounding When the required resistance is not achieved using the usual grounding layouts, ERICO prefabricated wire mesh can be added to lower the overall grounding impedance (Fig. 1-8). ERICO offers a complete line of prefabricated wire mesh products in sizes ranging from No. 6 to No. 12 AWG solid conductors.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 7 (Black plate) Chapter 1: Building and Service Entrance Grounding 2. If a conducting gate is used, a buried bonding jumper must be installed across the opening (Fig. 1-11). 3. Where gates are installed, they shall be bonded to the fence, grounding conductor or other bonding jumper (Fig. 1-12). 4. If the fence posts consist of a conducting material, the grounding conductor must be connected to the fence posts with a suitable connecting means (Fig. 1-13).
Grounding Book 4/14/99 8 10/5/99 6:01 PM Page 8 (Black plate) Practical Guide to Electrical Grounding Other items that are located on the outside of the building that should be considered are lighting fixture standards, pull box covers and rails. Handhole, manhole and pull box covers, if conductive, should be bonded to the grounding system using a flexible grounding conductor (Fig. 1-17).
Grounding Book 4/14/99 10/5/99 6:01 PM Page 9 (Black plate) Chapter 1: Building and Service Entrance Grounding Grounding conductors shall be protected against physical damage wherever they are accessible (Fig. 1-21). Grounding conductors installed as separate conductors in metal raceways always must be bonded at both ends to ensure that current flow is not choked off by the inductive element of the circuit. See page 15 for a discussion of how to accomplish the required bonding.
Grounding Book 4/14/99 10 10/5/99 6:01 PM Page 10 (Black plate) Practical Guide to Electrical Grounding The grounding electrode system is designed to provide multiple electrical paths into the earth. As stated in the Preface, grounding of electrical systems helps to ensure personnel safety, provide equipment and building protection and achieve electrical noise reduction. Section 250-81 requires that four components, if available, be bonded together to form the grounding electrode system.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 11 (Black plate) Chapter 1: Building and Service Entrance Grounding VS HA VS HB VF VN 11 The third component of the grounding electrode system is concrete-encased electrodes. These are usually referred to as “rebar,” which is short for reinforcing bar (Fig. 1-28 and 1-29). Rebar is used to add strength to poured concrete installations and by its nature tends to be an excellent grounding electrode.
Grounding Book 4/14/99 12 10/5/99 6:01 PM Page 12 (Black plate) Practical Guide to Electrical Grounding electrode conductor is connected to buried electrodes the clamp or fitting must be listed for direct soil burial. CADWELD offers the best solution for contractors trying to meet the NEC requirements for connecting to rebar. CADWELD offers a full line of connections in various configurations for welding of grounding conductors to reinforcing bars (Figure 1-31).
Grounding Book 4/14/99 10/5/99 6:01 PM Page 13 (Black plate) Chapter 1: Building and Service Entrance Grounding 4" 30" Trench 1" GEM 1 4 Soil 4" 1" GEM 2 5 Soil Backfill Ground Conductor GEM 3 6 GEM Trench Installation 3" or Larger 6" Augered Hole GEM packed around Ground Rod 6" shorter than Ground Rod 1 3 6" Ground Rod Soil Backfill 12" 2 GEM Ground Rod Installation Fig.
Grounding Book 4/14/99 14 10/5/99 6:01 PM Page 14 (Black plate) Practical Guide to Electrical Grounding Section 250-83 contains requirements for other (frequently referred to as “made”) electrodes. These electrodes can be used to supplement the grounding electrode system or are to be used when none of the grounding electrodes covered previously are available.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 15 (Black plate) Chapter 1: Building and Service Entrance Grounding Also fitting into this category are chemical type ground electrodes consisting of a copper tube filled with salts. Moisture entering the tube slowly dissolves the salts, which then leach into the surrounding earth thru holes in the tube. (Fig. 1-38) This lowers the earth resistivity in the area around the electrode, which reduces the electrode resistance.
Grounding Book 4/14/99 6:01 PM Page 16 (Black plate) Practical Guide to Electrical Grounding each end of the enclosure or raceway to the grounding conductor. IEEE paper No. 54 and other studies have shown that, in cases where such bonding is omitted, the impedance of the conductor is approximately doubled. Bonding in these cases is essentially to ensure proper operation of the grounding electrode system.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 17 (Black plate) Chapter 1: Building and Service Entrance Grounding CONCRETE ENCASED ELECTRODES, “UFER GROUNDING” 3-1 /2" /2" 3-1 3-1/2" Weld Collar Broken Cable Stub CADWELD Spliced Cable 1" Min.
Grounding Book 4/14/99 18 10/5/99 6:01 PM Page 18 (Black plate) Practical Guide to Electrical Grounding The damage to the concrete can be explained due to its non-homogeneous character and moisture content. During a fault, one path from the rebar to the outside soil through the concrete will have a lower resistance than any other. The fault current following this path will cause heating and vaporization of the water (moisture).
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Grounding Book 4/14/99 10/5/99 6:01 PM Page 21 (Black plate) Chapter 2: Building Lightning Protection 21 Chapter 2 Building Lightning Protection A Critical Extension Of Grounding
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Grounding Book 4/14/99 10/5/99 6:01 PM Page 23 (Black plate) Chapter 2: Building Lightning Protection LIGHTNING - AN OVERVIEW about 100 amperes extends down from the cloud, jumping in a series of zigzag steps, about 100 to 150 feet (30 to 45 m) each, toward the earth. As the leader or leaders (there may be more than one) near the earth, a streamer of opposite polarity rises from the earth or from some object on the earth.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 24 (Black plate) Practical Guide to Electrical Grounding 24 New detection devices have been installed around the U.S. which count the total number of lightning strokes reaching the earth. This data results in precise occurrence of the total strokes for a particular period of time for any particular area rather than thunderstorm days per year.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 25 (Black plate) Chapter 2: Building Lightning Protection 25 There is general agreement that the best theoretical lightning system is a solid faraday cage around whatever it is that is being protected. An airplane is an example of this. But even in the case of the airplane, there are incidents reported of damage from direct lightning strokes.
Grounding Book 4/14/99 26 10/5/99 6:01 PM Page 26 (Black plate) Practical Guide to Electrical Grounding inception over 200 years ago, the nature and scope of lighting protection has changed considerably. Lightning protection then was principally a defense against fire. Wooden buildings, when struck by lightning, would often burn. Barns and churches were the main facilities seeking this protection due to their height. Today, fire is still a concern, but not always the main concern.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 27 (Black plate) 27 Chapter 2: Building Lightning Protection Calculation of the Protective Coverage offered by an air terminal Collection Volume Design Method A more efficient air terminal demands a new design philosophy and discipline. ERICO has developed an alternative design method matched to the performance of the System 3000™ lightning protection system. This method is based on the work of Dr. A. J. Eriksson, the noted lightning researcher.
Grounding Book 4/14/99 28 10/5/99 6:01 PM Page 28 (Black plate) Practical Guide to Electrical Grounding alternative structure or feature on the ground). This leads to the development of a limiting parabola. The enclosed volume is known as the Collection Volume. A downward progressing leader entering this volume is assured of interception. Figure 4 shows how the velocity parabola limits the size of the Collection Volume.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 29 (Black plate) Chapter 2: Building Lightning Protection The following are basic components for a lightning protection system. Sketches at the end of this section depict the many requirements discussed. Air terminals, often called lightning rods, lightning points or strike termination devices are blunt or pointed, solid or tubular rods of copper, bronze, stainless steel or aluminum. On large (over 500 sq. inch [0.323 sq.
Grounding Book 4/14/99 30 10/5/99 6:01 PM Page 30 (Black plate) Practical Guide to Electrical Grounding air without support for more than 3 feet (0.9 m) (Fig. 2-8) and they must be fastened at a maximum of every 3 feet (0.9 m) using non-ferrous fasteners. (Fig. 2-9) Conductor material must comply with the lightning codes and be compatible with the surfaces which it contacts. Aluminum conductors cannot be used within 18 inches (460 mm) of finished grade.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 31 (Black plate) Chapter 2: Building Lightning Protection 31 24" Minimum 10' Or More 24 Feet Minimum Shallow Sandy Soil Fig. 2-13 Moist Clay Soil Fig. 2-11 12" x 12" (1 Square Foot) 12 Inch to 24 Inch Minimum 12 Feet Minimum Shallow Topsoil Fig. 2-12 necting or bonding of the two systems helps to ensure that there is little possibility of a difference of potential between the two systems or the two systems’ components.
Grounding Book 4/14/99 32 10/5/99 6:01 PM Page 32 (Black plate) Practical Guide to Electrical Grounding 10' Min. 10' Min. 10' Min. Sandy Or Gravelly Soil 10' Min. Alternate Layouts Fig. 2-15 electrodes as required by the NEC (250-81 and 250-86) and the several lightning codes such as NFPA 780.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 33 (Black plate) Chapter 2: Building Lightning Protection 33 NFPA 780, STANDARD FOR THE PROTECTION OF LIGHTNING SYSTEMS - AN OVERVIEW 5. In addition to the general requirements covered above, the following requirements apply to those lightning installations which must be installed in conformance with NFPA 780. Keep in mind that these requirements represent a small portion of NFPA 780.
Grounding Book 4/14/99 34 10/5/99 6:01 PM Page 34 (Black plate) Practical Guide to Electrical Grounding 10. Section 3-19.4: Where the building structural steel is used as the main conductor of the lightning protection system, a ground rod or other ground terminal shall be connected to approximately every other perimeter steel column. Such connection shall be made at the base of the column and at intervals not to exceed an average of about 60 feet.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 35 (Black plate) 35 24" Min. Chapter 2: Building Lightning Protection Bond Roof Flashing To Lightning Protection System. Roof Horizontal Beam Typical Installation Jumper Bond Between Horizontal Beam And Column. Exterior Wall Column Air Terminal At Mechanical Equipment Bonding Jumper Typical Installation Weld Bond At Column Base. First Floor 3'-0" Note: Provide A Jumper At All Bolted Horizontal Beam At All Exterior Wall Columns.
Grounding Book 4/14/99 36 10/5/99 6:01 PM Page 36 (Black plate) Practical Guide to Electrical Grounding LIGHTNING SAFETY ANALYSIS It is recommended that a lightning safety analysis be made of facilities and areas subject to lightning. Following are parameters to consider and recommendations: 1. Make a physical inspection. Identify hazards and threats which will contribute to lightning danger at the site. 2. Make a study of lightning strike probability.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 37 (Black plate) 37 Chapter 2: Building Lightning Protection Pocket Or "V" Incorrect Incorrect Correct Correct Fig. 2-26 The main conductor must never be coursed upward. Fig. 2-24 Conductors must never be coursed upward. A If over 40 feet, add down lead at "A" Pocket, Incorrect Downlead, Correct Fig. 2-25 The conductor must never be coursed upward. Fig.
Grounding Book 4/14/99 38 10/5/99 6:01 PM Page 38 (Black plate) Practical Guide to Electrical Grounding If Over 40 Feet, Add A Down Lead At "A" #2/0 Finished Roof CADWELD Connection A Fig. 2-28 If a projection extends over 40 feet, a downlead at (A) must be provided on the projection. CADWELD Connection Bare Copper Conductor 3/4" Schedule 80 Non-Metallic Conduit Concrete Slab Fig. 2-31 Using the structural steel as the down conductor.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 39 (Black plate) Chapter 2: Building Lightning Protection 39 Seal End Of Conduit 12" x 12" (1 Square Foot) Lightning Conductor Final Thru-Roof Flashing By Roofing Contractor 8" Max. Fig. 2-35 Electrodes made from copper or steel plates are often used in soil less than 12” thick. Cable Behind Parapet 1" PVC Conduit Cable And Conduit Down To Ground Cable On Top Of Parapet Fig. 2-33 Detail of conductor through the roof.
Grounding Book 4/14/99 40 10/5/99 6:01 PM Page 40 (Black plate) Practical Guide to Electrical Grounding ax tM ee F 50 x et e 0F Ma 5 Ov er 50 Fe et Fig. 2-38 On large flat roofs or gently sloping roofs, air terminals are placed in the center area at intervals not exceeding 50 feet. Place Air Terminal Anywhere Within Hatched Area Fig. 2-40 Conductor may be welded to air terminal or attached with an approved clamp. 2 Protected 1 24 "M ax ax "M 24 Air Terminal Required 2 Fig.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 41 (Black plate) 41 Chapter 2: Building Lightning Protection Fig. 2-42 Concealed systems are common on residential installations. Fig. 2-45 Structural steel may be used as the conductor if properly bonded. Ridge Higher Than Outer Ridge 24 Inch Maximum A Finished Roof A A #2/0 CADWELD Connection Ridge Equal To Or Lower Than Outer Ridge Fig. 2-43 Detail of air terminal with the steel structure used as the down conductor.
Grounding Book 4/14/99 6:01 PM Page 42 (Black plate) Practical Guide to Electrical Grounding 24" Min. 42 10/5/99 Fig. 2-47 More extensive systems are required on larger buildings and with different soil conditions. Fig. 2-50 All rooftop equipment must have air terminals unless they have skins more than 3/16 inch thick. If they have skins more than 3/16 inch, they must be properly bonded and will be considered as air terminals. Lightning Mast (Pipe) CADWELD Type VB Weld Copper Downlead Fig.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 43 (Black plate) Chapter 2: Building Lightning Protection When Used As Midroof Air Terminal. 50' Maximum Spacing Bare Copper Point 20' Max. Spacing Flat Copper Cable Holder. Secure With Adhesive 43 CADWELD TypeGS (Prefab) or GC CADWELD Type PC Cast Bronze Adhesive Point Base. Secure With Adhesive. CADWELD Type GY Connection NOTE: Actual point base to be determined by field conditions Main Copper Conductor Main Copper Conductor Alternate Method Fig.
Grounding Book 4/14/99 44 10/5/99 6:01 PM Page 44 (Black plate) Practical Guide to Electrical Grounding Flat Gable Mansard Hip Roof Types And General Air Terminal Placement Fig. 2-56 Air terminal placement shown on various types of roofs. 4 1 1 8 Over 40 Feet 40' Or Less Flat Or Gently Sloping Roof Fig. 2-57 Flat or gently sloping roofs are defined as shown.
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Grounding Book 4/14/99 10/5/99 6:01 PM Page 47 (Black plate) Chapter 3: Building Interior Bonding and Grounding 47 Chapter 3 Building Interior Bonding And Grounding The Bonding And Grounding Of Building Steel, Electrical Panels And Other Power Systems Equipment.
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Grounding Book 4/14/99 10/5/99 6:01 PM Page 49 (Black plate) Chapter 3: Building Interior Bonding & Grounding INTRODUCTION In addition to electrical service grounding and supplemental building grounding, designers and installers of electrical systems face critical grounding and bonding decisions throughout the entire building. The purpose of this chapter is to focus on the equipment grounding and bonding requirements set forth in the National Electrical Code (NEC).
Grounding Book 4/14/99 50 10/5/99 6:01 PM Page 50 (Black plate) Practical Guide to Electrical Grounding devices. This would include fittings such as bonding-type locknuts and grounding bushings. These fittings are designed to make good contact with the metal enclosure and help to ensure good electrical continuity. Bonding Other Enclosures. In addition to the service equipment enclosures, other noncurrent-carrying enclosures are also required to be bonded by the NEC.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 51 (Black plate) Chapter 3: Building Interior Bonding & Grounding comprise the grounding electrode system. While these guidelines may appear to be somewhat vague, a good rule of thumb to follow is: If the interior metal piping system contains any electrical devices, such as, solenoids or mechanized valves, the piping “may become energized” and it should be bonded. The last part of Section 250-80 contains a new requirement in the 1996 NEC.
Grounding Book 4/14/99 52 10/5/99 6:01 PM Page 52 (Black plate) Practical Guide to Electrical Grounding Steel Beam 4/0 CADWELD Connection Type QW To Flange Of Beam (Or Type VN on Large Beam) TAC2Q2Q Connection Steel Column LJ Type Mold, Field Modified Bottom Chord Of Bar Joist CADWELD Connection Type VV Fig. 3-4 To Ground Building Steel Ground Fig.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 53 (Black plate) Chapter 3: Building Interior Bonding & Grounding extend to each floor (Fig. 3-7). For accessible ground points at each floor, ground bars provide the ideal solution. They can be bolted to either the wall or the floor or a long bus attached to the wall with insulators and mounting brackets. (Fig. 3-8). On exposed steel buildings, the ground bars can be welded directly to the steel column (Fig. 3-9 and Fig. 3-10).
Grounding Book 4/14/99 54 10/5/99 6:01 PM Page 54 (Black plate) Practical Guide to Electrical Grounding Masonary Anchors For Mounting Bolts ERICO Insulator and Mounting Bracket (Includes Insulator Mounting Bolts And Assembly Washers) Copper Bus Along Wall CADWELD Type LJ Connection Cable To Bus Insulated Or Bare Copper Insulated Or Bare Copper Conductor To Below Floor Ground Grid Conductor To Ground Grid Via 1" Dia. PVC Sleeve In Floor Slab Min.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 55 (Black plate) Chapter 3: Building Interior Bonding & Grounding 55 Column Structural Rebar Right Hand Weld Left Hand Weld CADWELD Connection Prefab Type RR 1/2-13 x 5/8" Silicon Bronze Bolt W/Washer 2 Required Copper Conductor, Size To Suit (4/0 Max.
Grounding Book 4/14/99 56 10/5/99 6:01 PM Page 56 (Black plate) Practical Guide to Electrical Grounding Blank Device Plate-Engrave "Floor Ground" 2" AS Req. 18" 18" Copper Sheet With Strip Pigtail CADWELD Connection TWR 107A3, #32 CADWELD Connection #6 Solid Copper To Copper Strip HAC1H003, #25 26 Gage x 2" Wide Copper Strip Conductive Flooring Top Of Slab 18" SQ.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 57 (Black plate) Chapter 3: Building Interior Bonding & Grounding EQUIPMENT BONDING 1/8 x 3 x 3 Steel, Arc Weld To Cable Rack Channel CADWELD VB CADWELD VN Alternate Specify Right Hand Or Left Hand Cable Rack Grounding Fig. 3-18 Upper Rack 57 CADWELD Connection VTC2V Mold #150 Weld Metal CADWELD Mold Equipment within the facility must be carefully considered as to its need to be bonded to the facility ground system.
Grounding Book 4/14/99 58 10/5/99 6:01 PM Page 58 (Black plate) Practical Guide to Electrical Grounding Fig. 3-25 Fig. 3-22 CADWELD Type GL Silicon Bronze Stud, With 2 S.B. Nuts And Washers. GROUNDING Copper CADWELD Type HX Fig. 3-23 General Provisions - Equipment Fastened in Place. As noted above, the primary reason equipment and enclosures are grounded is to provide a low impedance path for ground-fault current.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 59 (Black plate) Chapter 3: Building Interior Bonding & Grounding 59 500 - 517 of the NEC and installers and designers of electrical systems should review these articles prior to designing or installing electrical systems in these types of locations. 500 - 517 of the NEC and installers and designers of electrical systems should review these articles prior to designing or installing electrical systems in these types of locations.
Grounding Book 4/14/99 60 10/5/99 6:01 PM Page 60 (Black plate) Practical Guide to Electrical Grounding employ a system of double insulation which is distinctively marked on the tool or appliance. Receptacle Grounding. Since the early 1970s Section 210-7 of the NEC has required that all receptacles installed on 15- and 20- ampere branch circuit be of the grounding type.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 61 (Black plate) Chapter 3: Building Interior Bonding & Grounding isolated ground (IG) receptacles. These IG receptacles are frequently used for electronic/data processing equipment applications. The use of a separate, “isolated” grounding Fig. 3-29 Insulators and mounting brackets are available for mounting your own bar. 61 conductor ensures that the cord-and-plug connected equipment receives a “clean” source of power, free from EMF or RF interference.
Grounding Book 4/14/99 62 10/5/99 6:01 PM Page 62 (Black plate) Practical Guide to Electrical Grounding CADWELD Connection Ground Bar To Ground Rod Type CR Ground Wire From Transformer CADWELD Terminal TYPE GL With NEMA Lug Grade 1/4"x4"x36" Ground Bus Copper Bonded Ground Rods Transformer Ground Bus Detail Fig.
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Grounding Book 4/14/99 10/5/99 6:01 PM Page 65 (Black plate) Chapter 4: Transients & Other High Frequency “Grounding” & Bonding 65 Chapter 4 Transients And Other High Frequency Bonding And “Grounding” The Bonding And Grounding Of Electronic Systems
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Grounding Book 4/14/99 10/5/99 6:01 PM Page 67 (Black plate) Chapter 4: Transients & Other High Frequency “Grounding” & Bonding INTRODUCTION TO ELECTRONIC SYSTEM “GROUNDING” Grounding electronic equipment for personal safety and clearing of faults is no different than that of any other equipment.
Grounding Book 4/14/99 68 10/5/99 6:01 PM Page 68 (Black plate) Practical Guide to Electrical Grounding SOME IMPORTANT POINTS ABOUT GROUNDING (1) Typically the safety grounding of equipment is exactly the same for electronic equipment as it is for any other kind of apparatus, whether it is a refrigerator or a printing press. The “green wire” and conduit/raceway system’s grounding which is well documented in the NEC and other codes, defines these requirements completely.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 69 (Black plate) Chapter 4: Transients & Other High Frequency “Grounding” & Bonding much as 200% of the ampacity used for the related line conductors. This is regularly done in order that a fire be avoided due to current overload from third harmonic and other odd multiple harmonics called “triplens”. Other steps may be required to prevent harmonics from interfering with proper system operation.
Grounding Book 4/14/99 70 10/5/99 6:01 PM Page 70 (Black plate) Practical Guide to Electrical Grounding to ensure good longitudinal coupling. In addition to being well grounded/bonded to the equipment at the ends of the run, the conduit or raceway should also be bonded to any nearby structural steel along the run.
Grounding Book 4/14/99 10/5/99 6:01 PM Page 71 (Black plate) Chapter 4: Transients & Other High Frequency “Grounding” & Bonding an isolation transformer is installed adjacent to the served loads and is positioned between the output of a transfer switch and the input of the served electronic loads.
Grounding Book 4/14/99 72 10/5/99 6:02 PM Page 72 (Black plate) Practical Guide to Electrical Grounding GROUND CURRENT INTERFERENCE WITH CATHODE RAY TUBE (CRT) BASED EQUIPMENT Low frequency magnetic fields such as those associated with the power system’s fundamental of 60 Hz and harmonics from it, will sometimes be seen to interfere with the normal deflection of the electron beam being used to paint the image on the CRT’s screen.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 73 (Black plate) Chapter 4: Transients & Other High Frequency “Grounding” & Bonding 73 Ground Loop (unwanted)— Any conductive path involving “ground” via a grounding or grounded conductor or the earth itself, through which any part or all of the desired signal process current is passed, so that it may be algebraically added to any unwanted current such as “noise” that may also be flowing in the shared ground path.
Grounding Book 4/14/99 74 10/5/99 6:02 PM Page 74 (Black plate) Practical Guide to Electrical Grounding (1). Where possible, cluster the interconnected electronic equipment into an area that is served by a single signal reference grid (SRG). If the interconnected equipment is located in separate, but adjacent rooms, then a common signal reference grid should serve all the rooms. (2) Effectively bond each frame/enclosure of the interconnected equipment to the SRG.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 75 (Black plate) Chapter 4: Transients & Other High Frequency “Grounding” & Bonding 75 otherwise the reinforcing steel is simply periodically welded to the SRG at those points where the two structures have nearby or intersecting elements.
Grounding Book 4/14/99 76 10/5/99 6:02 PM Page 76 (Black plate) Practical Guide to Electrical Grounding TELECOMMUNICATIONS SYSTEMS GROUNDING The publisher of the above standards is: Grounding of telecommunications systems, such as voice and data grade telephone circuits, has become a well defined area of grounding. The rules are explicit. If not followed, the systems will be more sensitive to noise disturbances.
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Grounding Book 4/14/99 10/5/99 6:02 PM Page 79 (Black plate) Chapter 5: Selection of Components Used In Grounding 79 Chapter 5 Selection Of Components Used In Grounding Grounding Conductors Connectors Grounding Electrodes
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Grounding Book 4/14/99 10/5/99 6:02 PM Page 81 (Black plate) Chapter 5: Selection of Components Used In Grounding SELECTION OF GROUNDING SYSTEM COMPONENTS The overall effectiveness of any grounding system will be determined by the individual components that are used to construct the system and the manner in which the components are connected. The purpose of this chapter will be to review the selection of these components and the methods by which they should be interconnected.
Grounding Book 4/14/99 82 10/5/99 6:02 PM Page 82 (Black plate) Practical Guide to Electrical Grounding aluminum. Copper-clad aluminum is constructed of a minimum of 10% copper which is metallurgically bonded to the aluminum core. The GEC is permitted to be a solid or stranded conductor and it can be an insulated, covered or bare conductor. Solid conductors provide less surface area to corrode and subsequently are used when installed in corrosive locations.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 83 (Black plate) Chapter 5: Selection of Components Used In Grounding 83 upper end of the rod or pipe must be flush or below grade unless the top end and the connector are protected from damage. Pipe electrodes shall be 3/4 inch trade size or larger and shall have their outer surface galvanized or another metal coating for corrosion protection. Rod electrodes shall be 5/8 inch diameter if of iron or steel.
Grounding Book 4/14/99 84 10/5/99 6:02 PM Page 84 (Black plate) Practical Guide to Electrical Grounding Often, one ground rod will not provide the ground resistance required for the particular installation. The NEC requires the ground resistance with one rod, pipe or plate electrode to be 25 ohms or less. If it is over 25 ohms, a second electrode is required, connected to the first electrode and separated by 6 feet or more.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 85 (Black plate) Chapter 5: Selection of Components Used In Grounding Although the welded type are more expensive, they assure that the couplings will not become a high resistance member in the current path over the life of the system. One loose coupling will render all of the lower rod sections useless. Also available is a connection which is a combination of a screw coupling and a welded coupling.
Grounding Book 4/14/99 86 10/5/99 6:02 PM Page 86 (Black plate) Practical Guide to Electrical Grounding Description CADWELD R Screw Coupler Split Bolt Service Posts Pipe Clamp Compression Devices Ground Rod Clamps Brazed Connection CADWELD Connection Relative Cost Installation Time LOW LOW Codes Tests MEDIUM MEDIUM MEDIUM MEDIUM MEDIUM TO HIGH TO HIGH VERY MEDIUM LOW LOW HIGH UL UL UL UL MEDIUM MEDIUM TO HIGH TO HIGH IEEE Std 80, IEEE Std 837 and UL UL R + CADWELD = Connectors Table 5-
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Grounding Book 4/14/99 10/5/99 6:02 PM Page 89 (Black plate) Chapter 6: Special Grounding Situations 89 Chapter 6 Special Grounding Situations Areas Not Covered Elsewhere Airports Corrosion And Cathodic Protection Radio Antenna Grounding Static Grounding Wire Mesh Fences And Gates
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Grounding Book 4/14/99 10/5/99 6:02 PM Page 91 (Black plate) Chapter 6: Special Grounding Situations AIRPORTS Airports require special attention to grounding. They not only handle fuel in close proximity to masses of people, but the airport is usually on high ground and therefore subject to lightning strikes. Static grounding is required whenever an airplane is refueled.
Grounding Book 4/14/99 92 10/5/99 6:02 PM Page 92 (Black plate) Practical Guide to Electrical Grounding Electomotive Series Material Magnesium Aluminum Zinc Cast Iron/Steel Brasses Tin Lead Hydrogen Copper Silver Graphite (Carbon) Platinum Gold Fig. 6-2 Anchor rods are also used for static grounding and tie downs. Voltage -2.34 -1.67 -0.76 -0.44 -0.28 -0.14 -0.13 0.00 +0.34 +0.86 +0.86 +0.90 +1.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 93 (Black plate) Chapter 6: Special Grounding Situations 93 + Power Supply dc - Pipe Line Stray DC Current Fig. 6-6 and/or are damaged when the pipe is installed. The breaks in the coating (called holidays) are protected by the cathodic protection system. Since the amount of steel exposed at the holidays is very small compared to a bare pipeline, the amount of current required to protect the pipeline is reduced in a direct ratio.
Grounding Book 4/14/99 94 10/5/99 6:02 PM Page 94 (Black plate) Practical Guide to Electrical Grounding made below the liquid level. Pure fuel will not burn or explode. It will burn or explode only when mixed with oxygen (air) within certain ratios. Codes & Standards. Section 80 of the 1994 Canadian Electrical Code contains installation requirements for impressed current cathodic protection systems.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 95 (Black plate) Chapter 6: Special Grounding Situations 95 Tube Splice Tube Tee Fig. 6-7 Tube To Ground Rod Cable Tap To Tube Fig. 6-9 CADWELD Connections on copper tubing used for high frequency grounding, with copper tube flattened. Fig. 6-8 Copper Strip CADWELD Connection CADWELD Connection Fig.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 96 (Black plate) Practical Guide to Electrical Grounding 96 Strip To Be Welded Guy Anchor Sandwich Pieces, Top And Bottom, Same Size As Strip Being Welded CADWELD Connection Finished Grade CADWELD Connection ERITECH Ground Rod CADWELD Connection #2 AWG, Tinned CU Fig.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 97 (Black plate) Chapter 6: Special Grounding Situations Some specific areas where static electricity is generated include: Piping Systems - In piping systems, the generation rate and the subsequent accumulation of static charges are a function of the materials, the flow rate, flow velocity, pipe diameter and pipe length.
Grounding Book 4/14/99 98 10/5/99 6:02 PM Page 98 (Black plate) Practical Guide to Electrical Grounding level in the mixer and/or providing a liquid conductive medium to dissipate the charge will help. If this is not possible, the vessel should be inerted. It should be noted that the static accumulation in liquids should be controlled by raising the ambient humidity.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 99 (Black plate) Chapter 6: Special Grounding Situations through most paint, rust and surface contaminates. Single point clamps are superior to battery type and “alligator” type clamps for making direct contact. Caution must be exercised in the installation of static grounding systems so that no part of the electrical currentcarrying system is used as a ground.
Grounding Book 4/14/99 100 10/5/99 6:02 PM Page 100 (Black plate) Practical Guide to Electrical Grounding Conductor Sizing Proper sizing of conductors is determined by many factors such as industry standards, insurance requirements, local codes, etc. These standards supersede any recommendations in this book. The following is based on many years of experience and NFPA 77 “Static Electricity,” 1994. There is no single answer to conductor sizing, although the following guidelines can be provided: 1.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 101 (Black plate) Chapter 6: Special Grounding Situations 101 The Ground To Overhead Door Support Grounding Reel Exothermic Weld To Overhead Door #6 Bare Copper Ground Door Track (Typical For 2) Exothermically Weld To Overhead Door Track Track Type Overhead Door Bonding Jumper, Exothermically Welded To Each Door Section Weld To Existing Building Ground System Existing Bare Copper Building Ground Overhead Track Type Door Grounding Fig.
Grounding Book 4/14/99 102 10/5/99 6:02 PM Page 102 (Black plate) Practical Guide to Electrical Grounding Fig. 6-21 Stand-off Bracket 2700 Insulator CADWELD Splice 4" 1/4 x 3 Copper Bus 36" Connection To Ground Detail "A" See Detail "A" Clamp 3/16 Insulated Flex Cable Length "L" See Detail "B" 1/8 x 1", 2 Hole Copper Lug P/N B536A "L" "L" = Length In Feet Detail "B" Fig.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 103 (Black plate) Chapter 6: Special Grounding Situations 103 Following are application sketches showing a few of the static grounding schemes. Figures 6-23 through 6-37 Bus to facility ground and pipe grounding. Fig. 6-26 Attachments to ground bus. Fig. 6-23 FM Temporary bonding jumper to pail. Fig. 6-27 Jumper to ground bus. Fig. 6-24 Drum or pail bonding to ground bus. Fig. 6-25 Drum pump bond. Fig.
Grounding Book 4/14/99 104 10/5/99 6:02 PM Page 104 (Black plate) Practical Guide to Electrical Grounding Drum and pail bonding. Fig. 6-31 Drum and pail bonding. Fig. 6-29 Mixer bonding. Fig. 6-32 Pipe and drum. Fig.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 105 (Black plate) Chapter 6: Special Grounding Situations 105 B2614A Spring Clamp With A822SB111C20 Coiled Cable Pipe Swivel Joint B2616Axx Pipe Clamps With A806A3F5 Cable CADWELD Type VV Weld B2600E2C Rail Siding Typical Parts Needed For Static Grounding CADWELD Type ST Weld CADWELD Type GT Weld Tank car bonding at siding. Fig.
Grounding Book 4/14/99 106 10/5/99 6:02 PM Page 106 (Black plate) Practical Guide to Electrical Grounding WIRE MESH Pipe Swivel Joint Bonding Fig. 6-35 ERICO prefabricated wire mesh is a convenient, efficient and economical means of improving grounding systems at large facilities of high voltage installations and wherever large area communications grounds are required.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 107 (Black plate) Chapter 6: Special Grounding Situations 107 Fig. 6-41 To Equipment Ground Fig. 6-39 CADWELD ERICO Ground Bar CADWELD Lugs CADWELD CADWELD Ground Plate Assembly ERICO Mesh For applications of mesh used as signal reference grid (SRG) embedded in the concrete floor, a CADWELD Cast Ground Plate is mounted flush with the finished floor and connected to the mesh. Future equipment is then connected to the ground plate. Fig. 6-40 Fig.
Grounding Book 4/14/99 108 10/5/99 6:02 PM Page 108 (Black plate) Practical Guide to Electrical Grounding 1. Electrically connect the fence grounding system to the facility ground system (Fig. 6-46). This method must be used when the fence is within or close to the facility ground grid. 2. Use a separate grounding system for the fence, isolated from the facility ground system (Fig. 6-47). 1/2 M + 2" Fence M M M Grid Fig. 6-44 Grid most commonly used is No.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 109 (Black plate) Chapter 6: Special Grounding Situations Perimeter Conductor 109 Splitbolt (Typ.) Fence Grid Grid Fig. 6-48 With the perimeter conductor one meter outside the fence, a worker standing inside the fence will have an increase in touch potential, but only by about 10%. If the fence is not connected to the main grid (Fig. 6-47), the following must be considered: 1. Could an energized line fall on the fence? 2.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 110 (Black plate) Practical Guide to Electrical Grounding 110 Note: It is not necessary to connect to the fence fabric or top rail (Except in Canada) if the posts are of a conducting material. (Ref: NESC 92E5&6) Steel Line Or Corner Post CADWELD Fence Post Clamp CADWELD Type VS Or VB Ground Wire (3 Feet Outside Of Fence Typical) Alternate For Aluminum Or Thin Wall Steel Posts. CADWELD Type TA Fig.
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Grounding Book 4/14/99 10/5/99 6:02 PM Page 113 (Black plate) Chapter 7: Application Of Surge Protection Devices 113 Chapter 7 Application Of Surge Protection Devices
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Grounding Book 4/14/99 10/5/99 6:02 PM Page 115 (Black plate) Chapter 7: Application Of Surge Protection Devices SURGE PROTECTION Good grounding without good surge protection may not be totally effective in protecting equipment and data. Surge protection devices (SPDs) are usually needed. These devices are proven and inexpensive - the best life insurance your money can buy. But SPDs must be selected and installed properly, otherwise they are not very effective.
Grounding Book 4/14/99 116 10/5/99 6:02 PM Page 116 (Black plate) Practical Guide to Electrical Grounding present. (Fig. 7-1) Power line faults, power line equipment problems and lightning are the greatest threat at this location. In many cases the local electric power company provides surge protection on the high voltage side of the supply transformer. The transformer itself is usually provided by the local electric company.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 117 (Black plate) Chapter 7: Application Of Surge Protection Devices Location Zone (1)Exposure A1 A2 A3 B1 B2 B3 C1 C2 C3 System <> Volts - kV peak (2) Low Medium High Low Medium High Low Medium High Current - kA peak, 1.2/50 µs 2 4 6 2 4 6 6 10 20 and 8/20 µs Amps 0.5 µs-100kHz Ring Wave 70 130 200 170 330 500 117 1.2/50 µs Volts -kA pk (4) 1 2 3 3 5 10 Location Category And Exposure Levels As Defined By IEEE STD C62.
Grounding Book 4/14/99 118 10/5/99 6:02 PM Page 118 (Black plate) Practical Guide to Electrical Grounding Service Entrance Meter Service Entrance Outbuilding Meter Underground Service Service Entrance Outbuilding Meter Xformer Underground Service A ¥ Equipment or outlets and long branch circuits ¥ All outlets at more than 10m (30 feet) from Category B ¥ All outlets at more than 20m (60 feet) from Category C B ¥ ¥ ¥ ¥ Feeders and short branch circuits Distribution panel devices Bus and fe
Grounding Book 4/14/99 10/5/99 6:02 PM Page 119 (Black plate) Definitions DEFINITIONS Air Terminal: That component of a lightning protection system that is intended to intercept lightning flashes, (commonly known as lightning rod). NFPA 780 [3] Bonding: The permanent joining of metallic parts to form an electrically conductive path that will ensure electrical continuity and the capacity to conduct safely any current likely to be imposed.
Grounding Book 4/14/99 120 10/5/99 6:02 PM Page 120 (Black plate) Practical Guide to Electrical Grounding Lightning Protection System: A complete system of air terminals, conductors, ground terminals, interconnecting conductors, surge protection devices, and other connectors or fittings required to complete the system.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 121 (Black plate) References and Bibliography REFERENCES 121 BIBLIOGRAPHY [1] ANSI/NFPA 70-1996, National Electrical Code (NEC). ANSI/IEEE Std 80, IEEE Guide for Safety in AC Substation Grounding. [2] ITU K27-1991, Bonding Configurations and Earthing Inside a Telecommunication Building. (Formerly CCITT.) ANSI/IEEE Std 81, IEEE Guide for Measuring Earth Resistivity, Ground Impedance and Earth Surface Potentials of a Grounding System.
Grounding Book 4/14/99 10/5/99 6:02 PM Page 122 (Black plate) INDEX 122 Page A AC System, electrode system grounding Active Attraction Systems, lightning Active Prevention Systems, lightning Air Terminal, lightning protection protective coverage calculation Airports, grounding situations Ambient Electric Field, lightning Anchor Rods, airport grounding 16 24 24 24, 29 27 91 25 91 B Bibliography 123 Bonded, lightning protection 29 Bonding, electrical systems 15 - 16 service equipment 49 - 50 static e
Grounding Book 4/14/99 10/5/99 6:02 PM Page 123 (Black plate) INDEX Page L (Cont.
Grounding Book 4/14/99 124 10/5/99 6:02 PM Page 124 (Black plate) Notes
