Conductor Conduct or Stringing Safe Practice Guide
ihsa.ca
Infrastructure Health & Safety Association
Safe Practic e Guide
Conductor Stringing Foreword
This Guide designates the practices that should be followed by the member firms of the Infrastructure Health & Safety Association (IHSA) when involved in conductor stringing operations. This Guide is not designed as a training manual, but contains information, best practices and general recommendations deemed appropriate to perform a job in a responsible and safe manner. The contents of this Safe Practice Guide, including all advice, recommendations and procedures, are provided as a service by the Infrastructure Health & Safety Association. No representation of any kind is made to any persons whatsoever with regard to the accuracy, completeness or sufficiency of the information contained herein. Any and all use of or reliance on this Safe Practice Guide and the information contained herein is solely and entirely at the user's risk. The user also acknowledges that the safe practices described herein may not satisfy all requirements of Ontario law. The Infrastructure Health & Safety Association wishes to express its appreciation to those who assisted in the preparation of this Guide.
All rights reserved. This publication may not be reproduced, in whole or in part, without the express written permission of the copyright owner.
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12/05
TABLE OF CONTENTS
Introduction Purpose
4 4
SECTION I GENERAL
100 101 102 103 104 105 106 107
Safe Execution of Work Competent Personnel Job Planning – Tailboard Talks Communication and Teamwork Suitable Equipment – Work Methods Utility Work Protection Code Work Area Protection Protective Cover-up Devices
6 6 6 7 7 7 8 8
SECTION II STRINGING PROCEDURES
200 201 202
Personal Protection Initial Preparation Preparation for Work
10 10 11
2
SECTION III TEMPORARY GROUNDING AND BARRICADING OF EQUIPMENT
300 301 302 303 304
General Precautions 14 Procedures for Setting Up Ground Gradient Mats 15 Procedure for Setting Up Stringing Equipment 17 Procedure for Setting Up Barriers 17 Procedure for Grounding/Bonding During Stringing Operations 18
SECTION IV CONVENTIONAL STRINGING METHODS
400 401 402 403 404
General Tension Brake Devices Pulling Devices Miscellaneous Equipment Removing Old Conductor
28 28 30 31 34
SECTION V TENSION STRINGING METHODS
500 501 502
General Miscellaneous Equipment Pulling Ropes
3
38 38 39
INTRODUCTION
Conductor stringing operations date back to the beginning of the electric power era. However, the original stringing methods used in the past no longer provide the safe work zone required by current regulatory agencies and management philosophies. The ever-increasing presence of obstacles such as telecommunications plant, other power lines, roads, highways and railroad right of ways have made it necessary to use different methods of conductor stringing in order to avoid unnecessary risk or interference from these obstacles. More modern types of conductor stringing equipment have been developed, and many complex stringing jobs have been completed safely using this equipment.
PURPOSE
This Safe Practice Guide has been compiled to familiarize utility and telecommunications personnel, and their contractors, with various conductor stringing methods, safe work practices, and the equipment necessary to undertake a stringing operation in a safe manner.
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SECTION I GENERAL 100
SAFE EXECUTION OF WORK
101
COMPETENT PERSONNEL
102
JOB PLANNING – TAILBOARD TALKS
103
COMMUNICATION AND TEAMWORK
104
APPROPRIATE EQUIPMENT – WORK METHODS
105
UTILITY WORK PROTECTION CODE
106
WORK AREA PROTECTION
107
PROTECTIVE COVER-UP DEVICES
5
SECTION I GENERAL
100 SAFE EXECUTION OF WORK The safe execution of a conductor stringing operation requires:
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competent personnel proper, detailed job planning approved work methods effective communication and teamwork well maintained, appropriate equipment
101 COMPETENT PERSONNEL Only competent personnel, or personnel in training under the direct supervision of a competent person should engage in conductor stringing operations.
102 JOB PLANNING – TAILBOARD TALKS As in all other phases of utility and telecommunications work, job planning is of the utmost importance so that the work may be performed safely and efficiently. A documented tailboard talk should be held with all involved in the project prior to the commencement of work. This includes workers at both the pulling and tensioning ends. The details of the tailboard talk should include all known hazards, and the barriers that will be used to protect workers and the public. All workers must understand the procedures and their respective duties and responsibilities before work commences. Should it become necessary to change the original job plan, all workers should be brought together and the new plan explained thoroughly to them.
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103 COMMUNICATION AND TEAMWORK Effective communication is essential while the work is being performed. Operators at the “pull in” and “pay out” ends should be in constant communication with one another during the stringing operation. In addition, a competent person should follow the progress of the “running board” or rope/conductor connection. This person should be in constant communication with the puller/tensioner operators. Teamwork is essential to ensure the safe and efficient execution of the job. 104 APPROPRIATE EQUIPMENT – WORK METHODS
Various types of conductor stringing equipment are currently being used. However, it is imperative that only appropriate equipment in good repair be used for the stringing method to be followed on each particular job. This would apply to pulling lines, travellers, pulling devices, tensioning, grounding methods and braking devices, etc. Local conditions will determine the appropriate stringing method to be used. Before deciding on a particular conductor stringing method, consider factors such as the length of pull, the location of other circuits, road crossings, etc.
105 UTILITY WORK PROTECTION CODE During any stringing operation that is to be carried out in proximity to existing energized apparatus, the possibility exists that a conductor being pulled in could inadvertently contact the energized apparatus. Therefore, it is of the utmost importance that the person in charge of the work obtain suitable hold-off protection on all of the energized circuits or apparatus which could cause a hazard to the stringing operation.
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Any existing isolated lines in proximity to the stringing operation should be suitably tagged and grounded in accordance with the Utility Work Protection Code, or equivalent.
106 WORK AREA PROTECTION Stringing operations may be carried out along busy thoroughfares and, because personnel and equipment may be situated in various locations along the route, proper work area protection is a prerequisite for the safe execution of the job.
Work area protection should be established in accordance with the current Ministry of Transportation, Ontario (MTO), the Ontario Highway Traffic Act and local bylaws.
107 PROTECTIVE COVER-UP DEVICES Whenever conductors are being installed or removed near energized conductors or apparatus, an electrical hazard is possible. The preferred course of action is to eliminate the hazard by re-routing the feed to provide for circuit isolation. In cases where isolation is not feasible, relocation of the conductors and appropriate cover-up would be the next choice. In some instances, appropriate cover-up is the only alternative. Always use cover-up of the appropriate voltage rating. Special attention should be given to locations where the conductor being pulled crosses any energized apparatus. NOTE: To prevent rope burns to pro tective cover-up devices, ensure that the str inging rope and/or conducto r being pulled in does not drag across the cover-up durin g the stringing operation.
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SECTION II STRINGING PROCEDURES 200
PERSONAL PROTECTION
201
INITIAL PREPARATION
202
PREPARATION FOR WORK
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SECTION II STRINGING PROCEDURES 200 PERSONAL PROTECTION During all stringing operations in proximity to energized apparatus, all personnel should follow the “ground to ground” rubber glove rule as set out in the Electrical Utility Safety Rules (EUSR). Also, personnel working in areas not protected by equipotential grounding and bonding should wear rubber gloves. 201 INITIAL PREPARATION – JOB PLANNING 1. Ensure that work orders, detailed drawings, job instruction, etc. are prepared in advance.
2. Ensure that any necessary applications for work protection are arranged for in advance. 3. Decide on the safest and most practical way to do the job. 4. Check each pole and span to determine what work can be performed prior to stringing. 5. Decide on the most suitable locations for setting up the stringing equipment. 6. Ensure sufficient equipment, material and personnel will be available for the job. 7. Additional personnel may be required at various locations to protect the public from possible safety hazards arising during the stringing procedures. 8. Extra traffic control devices may have to be obtained from other crews or rental centres. 9. Obtain permits when stringing conductor over major thoroughfares, railroads, etc. Police or the railroad company may be required to assist. Make arrangements well in advance of the project.
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202 PREPARATION FOR WORK 1. One person should be in charge to supervise and co-ordinate the overall operation.
2. Conduct a tailboard talk prior to the commencement of the job. If a change in procedure is necessary during the stringing operation, everyone should be informed of the change by means of additional tailboard talks. 3. Items to be recorded and discussed during the tailboard talk include: (a) hazards of all types (b) work location for each crew member (c) methods of communication (two-way radio hand signals, etc.) NOTE: The person in charge of the overall job should b e the only person to order the commencement of pulling. Anyone noting a probl em must immediately communicate the need to cease pulling.
Figure #1: Tailb oard Talk decal
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(d) traffic control (e) hazardous locations (road intersections or line intersections, etc.) (f) personal protective equipment (g) work protection in effect (hold-off, work permits, etc.) (h) emergency plan
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SECTION III TEMPORARY GROUNDING AND BARRICADING OF EQUIPMENT
300
GENERAL PRECAUTIONS
301
PROCEDURES FOR SETTING UP GROUND GRADIENT MATS
302
PROCEDURE FOR SETTING UP STRINGING EQUIPMENT
303
PROCEDURE FOR SETTING UP FENCE BARRIERS
304
PROCEDURE FOR GROUNDING THE CONDUCTOR
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SECTION III TEMPORARY GROUNDING AND BARRICADING OF EQUIPMENT 300 GENERAL PRECAUTIONS Follow proper grounding procedures when stringing conductor in proximity to other energized circuits. Whenever stringing conductors, use grounds to ensure there is no possibility of inducing a charge onto the conductors. Make consideration for induction from high voltage circuits, even at distances of 150 m (500 ft.) and more.
Properly grounding equipment and conductors is essential. Therefore, appropriate sized ground leads, clamps, connections and reference to the system protective devices (i.e. fuses, reclosers, breakers and available fault current for the system) must be taken into consideration. Proper temporary grounding helps ensure the operation of isolating devices and minimizes fault duration, which is the objective of grounding. However, the rapid rupturing of fuses or tripping of reclosers may not entirely eliminate the possibility of dangerous potential rises. Therefore, good electrical connections must be made from the system protection to the conductor at every opportunity throughout the project. The best return route to the system protection is via the system neutral. In some situations, it may be through ground probes, or a combination of both. All workers (except those necessary to operate the machinery) should stand clear of conductive equipment during the stringing process. Those workers operating machinery must be in an equipotential zone, where the possibility of step or touch potential differences has been eliminated.
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Equipotential zones are created by bonding and/or grounding all metallic apparatus together (i.e. conductors, ground gradient control mats, reel stands, pullers and tensioners).
301
PROCEDURES FOR SETTING UP GROUND GRADIENT MATS The purpose of the ground-gradient mat is to provide an equipotential zone of adequate size upon which all of the conductor stringing machinery can be be situated and all work activities, such as reel changing and splicing, can be performed where no potential differences could occur. If contact with another circuit occurs, there is still the possibility of a potential rise of tremendous magnitude before the system protection activates – no matter how well this equipment is connected. The key to a safe work zone is to minimize the possibility of this happening. Should an incident occur that causes a potential rise, no one working in a properly constructed equipotential zone will sustain current flow through their bodies. Where there is no current flow, there can be no electrical injury. NOTE: The mat should be large enough to carry out all work without stepping off the mat.
At the tension (pay out) end, work includes operating the machine, changing reels and splicing conductors. A space of 2.4 to 3 m (8 to 10 ft.) is necessary to splice conductors behind a tension machine, without stepping off the mat. 1. A common ground-gradient control mat is a grid of metal galvanized steel, or high-flex copper braid, strategically positioned on fabric. The design of the mesh should be arranged so that workers will always be bridging the grid with their feet, whether
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they are standing or walking on the mat. To accomplish this, the steel mat typically consists of a minimum No. 10 gauge (0.1350) galvanized steel wire, constructed in a 5 cm (2 in.) square mesh, 1.5 m by 6 m (5 ft. by 20 ft.), or as required (ie. circumstances dictate the length and width of the mat). In fact, most stringing operations require two or three such mats bonded together. Ground gradient mats should be laid into position whenever there are adjacent circuits and/or the possibility of induction. All conductor stringing equipment and related activities should be carried out on the mats. 2. IHSA recommends that a 1/0 high flex copper cable be positioned around the perimeter of each mat. The cable shall be affixed to the mesh of the mat at intervals not exceeding 0.90 m (3 ft.) to ensure continuity at all times. A flex copper lead of at least the same dimension or greater, should be connected to a common point on the tensioning machine. NOTE 1: If the pulling m achine will have direct contact with a conductor (when pulli ng out existing conduc tors, and the pulling line is metallic, or when the new conductor h as to be brought t o the puller) the puller shall also be placed ont o a ground gradient mat. NOTE 2: Ground rods m ust be used when only delta connected circuits are invol ved. At each of the four cor ners of the layout, ground rods are driven and connected to t he wire lead around the perimeter o f the mat. Where practi cal, dri ve as many ground rods as necessary to obt ain a megger r eading of 25 ohms or less.
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302
PROCEDURE FOR SETTING UP STRINGING EQUIPMENT After the ground gradient mats have been properly installed to the dimensions required for the work area, move the tension device, reel trailers and all related equipment into place onto the mat. Any metallic equipment on the mat must be bonded together by suitable connectors to the lead running around the perimeter of the mat, using 1/0 copper leads to the grounding lugs on the equipment. NOTE 1: The firs t and last travellers of the string ing project should be grounded. NOTE 2: Whenever another circ uit t raverses the conduc tor being stru ng, the travellers on either si de must be grounded. NOTE 3: If the pulli ng rope is metallic , wet, contaminated with dir t or aluminum, or the conductor is to be pulled to the pulling machine, it must be placed on a ground gr adient mat in the same manner as the tension machine.
Pullers and tensioners shall be anchored, regardless of the tension anticipated during the conductor stringing project. Weight change from the conductor at the pay out end, or a sudden stop, could cause these machines to shift. When the stringing equipment is sitting on a ground gradient mat, it is critical that conductive wire rope or chains do not extend beyond the ground gradient mat. The use of web slings and insulators will isolate the machines from the anchor. 303
PROCEDURES FOR SETTING UP BARRIERS
1. Nonconductive barriers should be installed around the perimeter of the ground mat, to prevent personnel from straying on and off the mat except at a controlled location. This controlled location is a 0.9
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m (3 ft.) opening for entry/exit. The barrier system will also remind personnel that they should not hand tools into and out of the zone when stringing is in progress. 2. Approximately 0.9 to 1.2 m (3 to 4 ft.) outside this barrier, another barrier (rope, tape, barricades, etc.) should be installed around the enclosure – “Danger Live Apparatus” signs should be hung on this barrier. 3. At the entry/exit point, a piece of plywood 0.9 m by 1.8 m by 1.3 cm (3 ft. by 6 ft. by ½ in.), covered by a nonconductive rubber or plastic mat, should be placed so that one end is on the ground mat and the other is clear of the barrier around the enclosure. This is to protect personnel from step potentials when entering or leaving the enclosure. No personnel may enter or leave the enclosure when stringing is in progress. (See Figure #2) 304
PROCEDURES FOR GROUNDING/BONDING DURING STRINGING OPERATIONS Considerable emphasis is placed on isolation techniques and grounding procedures when using large hydraulically-driven tension machines. However, there is a tendency not to take the same precautions when involved with routine stringing operations using small tension brakes or reel brakes, in conjunction with reel trailers – even though the stringing may be done in the area of energized equipment. The same precautions should apply to routine stringing operations near energized equipment as apply to major stringing jobs using large hydraulically-driven tension machines.
The grounding/bonding of tensioning machines, pulling machines, ground gradient mats, conductors, and travellers is to create an equipotential work zone.
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Plywood covered with rubber mats, used to provide entranceway in and out of enclosure
First physical barrier
Second physical barrier Ground mat wire fabric Equipment requiring ground mat protection
Work area inside second physical barrier 1/0 stranded copper bonding lead, threaded around perimeter of mat and connected to system neutral
Setting up groun d gradient mat area for st ringi ng Figure #2
This is a very important component in providing a safe work zone for crew members and the general public. Every effort taken during preparation to eliminate a potential difference throughout the project will help prevent injury should something go wrong. Sometimes, through equipment failure, loss of control, missed communication, oversights or misjudgements, the conductor being strung contacts something that is energized. Equipment may be damaged, power interrupted, and the project delayed. However, if this unplanned event causes no personal injuries, the grounding/bonding has worked as designed.
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All grounding/bonding connections must be regarded the same as making electrical connections. The lower the resistance and the more direct path to the system protection (fuses, reclosers, etc.), the more rapid the interruption. Therefore, the preferred connections would always be to the system neutral, when available. In locations where a system neutral is not available, a series of ground probes with 25 ohms or less resistance is the next best choice. In rural areas, a combination of ground probes and the non multi-grounded system neutral is necessary. A ground gradient mat shall be used for the placement of the tension machine. NOTE: The mat should be large enough to carry out all work without stepping off the mat. At the tension (pay out) end, work includes operating the machine, changing reels and splicing conductors. A space of 2.4 to 3 m (8 to 10 ft.) is necessary to splice conductors behind a tension machine, without stepping off the mat. In most instances, two or three separate mats will need to be positioned to adequately encompass the equipment placed upon it. Each mat used must be bonded to a common bus to ensure an equipotential work zone is created. Bonding cable of 1/0 bare, braided or stranded copper is threaded around the perimeter of the mat, then the mat and lead (bonding cable) are connected together with an appropriate connector, approximately every 0.9 m (3 ft.). At an appropriate location, an extra flex lead, equipped with an approved type grounding clamp should be connected from the bonding lead to the system neutral.
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This lead should be a minimum of 1/0 extra flex copper, and should be treated as a possible energized conductor. NOTE: Ground rods are required when working with delta connected circuits. At each corner of the mat, ground rod s woul d be driven and connected to th e bonding c able. Where practical, sufficient grou nd rods should be driven to obt ain a megger reading of 25 ohms or l ess. Grounding/Bonding During Stringing Operations To achieve the goal of establishing a safe work environment, the following setup would be considered as necessary. (See Figure #3) Connect to system Connect to System Neutral neutral whenever Whenever Available
Neutral
Neutral Travelling ground Conductor Conductor
Travelling Ground
1
4
available
Connect tail of Connect Tailto of conductor Conductor to reel stand Reel Stand 2
Connect to driven Connect torod ground Driven Ground when no Rods when no Neutral is is neutral available available
High 1/01/0 extra Flex Copper flex copper 3
Eachsection section of Each of Grounding Mat grounding mat connects to Common Grounding connects toPoint common grounding point
Figure #3 At the Reel This is the first of a series of grounds to be applied. Even though there are several types of tension machines in use, a standard method is used to ground
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the conductor on the tension stringing reels. On the large hydraulic tension machines, a bonding lead is connected from the tail of the conductor (projecting through the reel) to the ground lug provided on the drive arm of the tensioner. Internally, on the drive shaft, a collector ring provides an electrical path, through a set of brushes and extra flex copper, to an external ground lug on the tensioner. NOTE: This is the only opportunity to ground covered conductor dur ing the stringi ng procedure. Ahead of the Reel (Travelling Ground) This is the second opportunity to ground the conductor. It maintains a high integrity connection to system protection throughout the entire run. To help ensure this: a) the full capacity leads and clamps should be thoroughly inspected and adequately tightened; b) the entire circumference of the wire is involved; c) the mechanism is spring loaded to accommodate all irregularities in the conductor.
This ground will ensure continuity with the equipotential zone around the tensioner. It will also ensure the conductor is grounded as it passes up through any underbuilt circuits. It is also move-able and remains on the conductor tail as the conductor is cut and lowered down through any underbuilt circuits. The travelling ground is connected to the tension machine using a 1/0 extra flex copper lead attached to a common grounding point. (See Figure #4) The ground gradient mat(s) are also connected to the common grounding point. Another 1/0 lead is connected to either the system neutral or to ground probes, as discussed earlier.
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First and Last Traveller This is the third and last point in the run to ground the conductor. The conductor's angle of deflection at these travellers allows for greater surface contact between the conductor and grounded travellers.
Pressure and increased contact area between these travellers and the conductor is desirable to provide a good path to ground. These may be the only travellers in the run that are able to be grounded.
Figure #4
When the conductor is cut after dead-ending, the grounded traveller continues to provide some contact with ground. NOTE: Travellers with prot ective coatings on the sheaves are not design ed to be grounded. General Rule: Fifth Traveller Grounding This grounding will provide additional paths to ground throughout the run.
In circumstances where induction could be present, these multiple grounds will help ensure continual draining of induced voltage. Should an inadvertent contact occur, these grounds will help isolate the offending circuit more rapidly. This is also the rationale for grounding both sides of traversing energized circuits.
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All workers must understand when grounding any apparatus they are making electrical connections. The same care is to be taken as if the device was being connected to an energized medium to carry current. The fault current during a short circuit could rise to tens of thousands of amps. Any underrated, loose, or corroded connections will fail, some with catastrophic results. The more paths to ground the better. The better the connections, the more rapid the protection system will operate; thereby providing a safer work environment. (See Figure #5) Last Traveller Traveller Last Traveller Grounded Traveller Grounded Puller grounded Puller
Traveller Grounded (everyTraveller fifth Grounded structure) (Every 5th Structure)
First Traveller Traveller 1st Traveller Traveller Grounded Grounded Equipotential Work Zone Equipotential Work Zone Conductor Conductor Grounded Grounded
Grounded
25 25 ohms OHM’s
25 OHM’s
25 ohms Pulling End Tension End Tension End
Pulling End
Figure #5
When full puller/tensioner machines are not used, other types of tension devices are used, as shown in Figure #6. Regardless of the type of tensioning or pulling device used, the grounding procedure should be adequate to protect the workers and the general public. Equipotential work zones are always the objective when grounding systems are being installed.
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Vertical pivoting action
Horizontal pivoting action
Figure #6
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SECTION IV CONVENTIONAL STRINGING METHODS
400
GENERAL
401
TENSION BRAKE DEVICES
402
PULLING DEVICES
403
MISCELLANEOUS EQUIPMENT
404
REMOVING OLD CONDUCTORS
27
SECTION IV CONVENTIONAL STRINGING METHODS
400 GENERAL Conventional stringing methods would apply in cases where constant, positive control of the conductor is not required. In some instances (to clear driveways, trees, etc.), a certain amount of conductor tension is necessary. Most tension brake devices are suitable for this application. However, in situations where absolute control of the conductor is necessary, E&USA recommends the use of full puller/tensioner conductor stringing machines. 401 TENSION BRAKE DEVICES 1. Several types of mechanical and hydraulic tension brakes are available that will provide a certain degree of control over the conductor during a stringing operation. However, they do not have the capability of reversing the direction of the pull.
2. Reel brakes in various forms are used extensively for conventional stringing operations. Tension is maintained by an adjustable spring and brake band, and the unit can be mounted on all types of conductor reels. (See Figures #7 and #8) 3. A type of tension brake device that will mount on a truck or reel trailer is
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Figure #7
Figure #8
available. This unit will handle conductor sizes up to 556 circular mils. The braking action is applied by placing the conductor between a series of “bogey” wheels and then adjusting a crank to force the wheels against the conductor. This unit is designed to swivel both horizontally and vertically to accommodate the pulling angle. (See Figure #9)
Vertical pivoting action
Horizontal pivoting action
Figure #9
4. Another type of braking system being used is the hydraulic disc brake. (See Figure #10) The use of this precision braking device is still categorized as conventional stringing because it cannot be reversed. This type of system can experience heat buildup, therefore, installing a conductor grip as an additional measure of safety is recommended if it is left unattended. A pressure decline during cooling could allow unexpected pay out.
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Figure #10 402 PULLING DEVICES 1. When an appreciable degree of conductor tension is required during a stringing operation, the conductors can be pulled effectively using a capstan head in conjunction with a truck-mounted deck winch. The capstan head is not to be confused with the collapsible takeup reel, which is not designed to safely withstand any significant degree of tension. Its use should be restricted to “slack stringing” operations or for installing pulling ropes. Collapsible takeup reels should not have a buildup of rope on them. They should only have enough turns placed on them to effect the desired tension. (Between three and six turns should be sufficient.) Rope allowed to accumulate under tension will cause the reel to implode.
2. Boom tip winches should not be used to pull conductor, since most are not designed for the continuous operation typical of an extensive
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conductor stringing job. Such continuous operation could cause winch components to overheat, which could result in total loss of control of the conductor. 403 MISCELLANEOUS EQUIPMENT 1. In order to carry out a conductor stringing operation in a safe and efficient manner, various additional pieces of equipment are necessary. This would include appropriate travellers, conductor pulling rope, pulling grips, swivels, connectors, a banding tool and bands, running board, etc.
2. Travellers should be of the proper type and size for each application and conductor size, and inspected prior to use. Normally, the type of travellers shown in Figure #11 are used throughout the run. However, severe corners and the first and last structures require larger travellers, as shown in Figure #12. Along the run, the sheave size should range from 10 to 17 cm (4 to 7 in.) with a load rating
Grounding Traveller
Figure #11
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capacity of 1134 kg. (2,500 lbs.). Where severe angle changes occur, use a larger traveller. Sheave size should range from 25 to 50 cm (10 to 20 in.) with a load rating capacity of 1814 kg. (4,000 lbs.). Three sheave travellers are available for simultaneous multi-conductor pulls Figure #12 using a running board. If the conductors are being strung individually, use single sheave travellers. All travellers should be equipped with a device which prevents the conductor from jumping out of the traveller. 3. Use an adequately sized synthetic pulling rope for conductor stringing operations. The length of pull, size and type of conductor being strung, and the degree of tension involved will determine the minimum size of rope. 4. Use appropriate sized conductor pulling grips to join the conductor to the pulling rope. Use a free running swivel between the pulling rope and the conductor pulling grip to prevent rotation of the rope. Using a swivel to join the pulling grip on the pulling rope with the pulling grip on the conductor, will prevent build up of excessive torque. When pulling conductor, the torque builds up rapidly as a result of the pull on the synthetic rope by the pulling equipment. Using a straight pulling rope connector would not allow this torque to dissipate. Two recommended methods of attaching the conductor to the pulling rope are:
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to connect the swivel to a manufacturer ap proved eye splice on the end of the rope, or to install a manufacturer approvedpulling grip onto the pulling rope and apply locking as per manufacturers specifications bands (See Figure #13)
Some types of pulling grips are equipped with a permanent swivel on one end, however, a high quality ball bearing swivel should also be used. (See Figure #18) When using a running board for multiconductor stringing operations, swivels are necessary at all running board connections to help prevent running board rotation and conductor entanglement. 5. Secure the tail end of all pulling grips to the conductor (using a locking band) to prevent them from accidentally slipping off. Locking bands must be installed on the open end of all pulling grips, 2.5 cm (1 in.) from the end (see Figure #13). This is to prevent the edges of the grip from catching on the travellers and pulling the grip off. It is recommended that the front (pulling end) of the grip be
Figure #13
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taped so the conductor will not come through the aluminum shoulders on the grip. (a) Conductor pulling grips should be banded as shown in Figure #14. Double Bands
End of Conductor
Figure #14
(b) Conductor pulling grips that will run backward or be reversed should also be taped, to prevent any possibility of snagging, which could cause sudden release. (See Figure #15)
Figure #15
(c) Conductor pulling grips that are worn or frayed at the wire ends should have another band applied before the taping process is done. (See Figure #16)
Figure #16 404 REMOVING OLD CONDUCTORS Existing conductors will need to be replaced. Since the existing conductor is already in position, it could be used to pull in the conductor pulling rope or the new conductor.
Several factors should be considered before proceeding with this approach, including:
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size and type of existing conductor age and condition of existing conductor age and condition of the existing structures including guys location of other energized circuits degree of tension required while pulling size of new conductor to be installed
The old conductor should be visually inspected and analyzed for defects prior to untying or unclamping. Defects can be caused by age, lightning, accidental contacts from trees, hoisting booms, etc. If the conductor is of adequate strength and in good condition, it may be used to pull in the pulling rope or the new conductor. Grounding should be the same as it would be for stringing new conductor, with one exception: the pulling and pay out ends will have to be set up exactly as discussed in Section 304 of this guide. Automatic type sleeves should be removed before proceeding. Non-compression (automatic) sleeves are reliant upon multiple “fingers” gripping the outside sur-face of the conductor strands. The tension is constant and the loading is linear (in-line). As the tension increases, the fingers grip more firmly into the outside strands as they are forced into the tapered barrel of the sleeve. Axial loading and fluctuations in loading will cause failure (e.g. sudden release of tension could cause the fingers to lose their grip), and axial loading will cause the hollow barrel of the centre to collapse. Preparing the old cond uctor f or removal 1. Automatic sleeves should be replaced with either compression sleeves or conductor pulling grips. Defects found during the visual inspection and
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dead-ends should be removed, and the conductor connected end-to-end. 2. Installing conductor pulling grips back-to-back will act as a temporary solution. However, doing so requires that the grip leads be attached together. This can be done in several ways: (a) An alloy steel connector of the appropriate strength can be Figure #17 used if it is wire on either side. (See Figure #17) (b) An alloy steel swivel of the appropriate strength can be used if it is a wire-to-wire situation and should be used if rope is on one side and wire on the other. (See Figure #18)
Figure #18
(c) An approved alloy connecting link may be used where a swivel is not required. (See Figure #19) NEVER run sw ivels or connecting links onto bullwheels or conductor reels. They are not designed for side loading, which wo uld happen when wrapped around a bullw heel or reel. Figure #19 NEVER use a non-r ated threaded link for conduc tor strin ging.
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SECTION V TENSION STRINGING METHODS 500
GENERAL
501
MISCELLANEOUS EQUIPMENT
502
PULLING ROPES
37
SECTION V TENSION STRINGING METHODS
500 GENERAL Although there has been a reasonable degree of success tension stringing with conventional braking devices, these devices should not be used during operations where the absence of constant, positive control of the conductor could create a safety hazard. 501 MISCELLANEOUS EQUIPMENT Hydraulically-driven puller/tension machines, like the one shown in Figure #20, are the accepted standard for true tension stringing operations. At least two
Figure #20
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machines are necessary for single conductor stringing – one as a pulling device and the other as a tensioner. Both machines are essentially the same. However, the pulling device would be adjusted to produce slightly more tension than the tensioning device. Consequently, should the pulling line or conductor snag, the entire operation will cease without introducing a significant increase in line tension. One definite advantage of this type of machine is its ability to operate in either direction under desired tension or speed. Therefore, a snagged conductor or pulling line can be more easily cleared than with conventional types of equipment. Also, both machines will react immediately to remove unexpected slack. All travellers, swivels, connectors, running boards, and pulling grips that are normally used during conventional stringing operations may also be used in conjunction with tension stringing techniques, provided it is of adequate size and strength for the job at hand. 502
PULLING ROPES
1. During tension stringing operations, experience has shown that the main pulling rope (bull rope) can be installed more easily if a smaller diameter synthetic rope (pea line) is first installed through the travellers, and used to pull in the pulling rope. The suggested size for this pea line would be a minimum of 10 mm (3/8 in.) in diameter. 2. The main pulling rope should be a synthetic rope of the appropriate size. Many stringing operations use a 19 mm (3/4 in.) diameter two-in-one braided rope. Several speciality ropes are being manufactured for conductor stringing. Double braid polyester sheath, polyester core and hollow braided polyvinyl coated polyester ropes are preferred.
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These ropes should have a minimum breaking strength of approximately 7,439 kg (16,400 lbs.), which will be adequate to safely handle most tension stringing operations on distribution plant. NOTE: Visually inspect the pulling rope before using it and remove from service any rope foun d to be damaged. Some types of rop e can be field splic ed; others require sophisti cated splici ng procedures. These ropes may be joined us ing backto-back conduc tor pull ing grips banded for secur ity. Refer to the rop e manufacturer specifications for approved methods.
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Available Safe Practice Guides • Bare Hand Live Line Techniques
• Ladder Safety
• Conductor Stringing
• Live Line Tool Techniques
• Entry and Work in a Confined Space
• Low Voltage Applications
• Excavating with Hydrovacs in the Vicinity of Underground Electrical Plant • High Voltage Rubber Techniques up to 36 kV • Hydraulics
• Line Clearing Operations
• Pole Handling • Ropes, Rigging and Slinging Hardware • Temporary Grounding and Bonding Techniques • Underground Electrical Systems
T 905-625-0100•T 1-800-263-5024•F 905-625-8998
[email protected]•ihsa.ca
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