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FACILITIES INSTRUCTIONS, STANDARDS, AND TECHNIQUES

Volume 3-3

ELECTRICAL CONNECTIONS FOR POWER CIRCUITS

Internet Version of This manual Created August 2000

FACILITIES ENGINEERING BRANCH DENVER OFFICE DENVER, COLORADO

The Appearance of the Internet Version of This Manual May Differ From the Original, but the Contents Do Not

UNITED STATES DEPARTMENT OF THE INTERIOR BUREAU OF RECLAMATION

NOVEMBER 1991 CONTENTS

Section Page 1. Purpose ...... 1 2. Scope ...... 1 3. Characteristics of Conductors ...... 1 3.1. Properties of conductor ...... 1 3.2. Oxidation of conductors ...... 3 3.3. of conductors ...... 3 3.4. Expansion of conductors ...... 4 3.5. of conductors ...... 4 3.6. of conductors ...... 4 3.7. Anodizing of aluminum ...... 5 4. Preparation of Conductors ...... 5 4.1. Cleaning conductors ...... 5 4.2. Joint compounds ...... 5 5. Connections ...... 6 5.1. General ...... 6 5.2. Fusion connections ...... 6 5.3. Pressure connections ...... 7 5.4. Selection of connectors ...... 7 6. Procedure for Making Connections ...... 9 6.1. Aluminum-to-aluminum bus ...... 9 6.2. Aluminum-to- or -bronze (tinned or untinned) bus ...... 9 6.3. Copper-to-copper or bronze-to-bronze connections ...... 9 6.4. Aluminum cable to connector joints ...... 10 6.5. Cable joints ...... 10 6.6. Torque moments and procedures for bolted connections ...... 11 7. Temperature Considerations ...... 12 7.1. Current and temperature limitations ...... 12 7.2. Temperature of connections ...... 12 7.3. Measurement of connection temperature ...... 13 7.4. Thermographic (infrared) surveys ...... 13 Bibliography ...... 17

i (FIST 3-3 11/91) CONTENTS (Cont.)

TABLES Page

1. Properties of conductors ...... 2 2. Electrolytic series ...... 4 3. Recommended electrical connectors ...... 8 4. Recommended tightening torque on aluminum and silicon bronze bolts ..... 11 5. Temperature sensitive paints, crayons, and other materials ...... 14 6. Some infrared testing services ...... 17

FIGURES Page

1. Electrolytic diagram ...... 8 2. Clamp tightening sequences ...... 11

(FIST 3-3 11/91) ii 1. Purpose which is both impermeable and protective in nature, forms quickly on exposed Operating experience with high- power aluminum. Once stabilized, the oxide systems has shown that defective electrical prevents further oxidation. For highly connections are involved in many circuit or corrosive environments, a proper equipment failures. This chapter is designed to selection of or anodization may be be used as a guide in the assembly and used. preventive maintenance of efficient electrical connections for power circuits. An efficient Arcing effects: Aluminum resists pitting connection being defined as one which from arcs better than any other . exhibits minimum resistance, both at initial assembly and in the long run. Galvanic action: Aluminum is one of the most anodic metals. When placed with 2. Scope copper or steel in an (e.g., water) the potential difference between Data and experience gained through years of the conductors varies proportionally with testing and actual usage on power circuits by the distance between them in the both manufacturers and field organizations are electrolyte series (see table 2, section included. The actual test and procedures are 3.3.1). This difference causes a flow of beyond the scope of this chapter, however, pitting the aluminum but leaving their results are incorporated in the the cathodic material unharmed. recommendations. Properties of conductor metals and recommended methods of making Insulation compatibility: Aluminum ex­ connections are discussed to illustrate the hibits none of the sulfur combining need for the proper selection of connectors; properties of copper nor does it produce the proper preparation of conductors; and the soaps by combining with oil. Usual proper application of fusion, compression, and insulating materials do not adhere to the bolted connectors. aluminum.

3. Characteristics of Conductors Advantages: For equal ampere ratings, an aluminum conductor must have 1.66 3.1. PROPERTIES OF CONDUCTOR times the cross-sectional area of a copper METALS.- conductor. At this gauge, aluminum has 75 percent the tensile strength and 55 3.1.1 Aluminum.- Aluminum, the most percent of the weight of copper. The abundant of all metals, is never found in larger size, in spite of its higher its pure state because of its affinity for resistance, keeps the conductor cooler other elements. This affinity enables a and also helps keep the corona loss wide range of alloying characteristics; down. However, its required larger size however, it also increases refinement restricts its use in applications (i.e., costs and lowers the conductivity. enclosed switchgear, etc.) where there are space limitations to be considered. : Easily worked by rolling, drawing, spinning, extruding, or forging. 3.1.2. Copper.- Copper, a reddish material, is plentiful in nature and easy to process. Corrosion resistance: Very good except in Because of the abundance, ease of a saline atmosphere. A tough, very hard, manufacture, and, therefore, low cost, invisible, and high resistance oxide,

1 (FIST 3-3 11/91) copper was once the most widely used When the copper is heated (e.g., by bad . Currently copper has connection), more oxides are formed. increased in cost considerably and its These high-resistance oxides will availability is limited causing aluminum to be continue to increase the heat until the used more readily as an electrical conductor. conductor breaks. At temperatures above 88 EC (180 EF), copper oxidizes in dry air. Ductile: Can be cast, forged, rolled, Copper is oxidized in an ammonium drawn, and machined. Hardens when environment and is also affected by sulfur worked, however, annealing will restore dioxide. soft state. Alloying: Manganese, nickel, zinc, , and Corrosion resistance: Copper oxide forms aluminum harden copper and diminish its immediately upon exposure to the ductility. Manganese, phosphorous, and atmosphere. Once stabilized, this oxide tin increase the tensile strength. prevents further oxidation of the copper.

Table 1. - Properties of conductors

Properties Pure aluminum Pure Copper Low-alloy steel

Electrical conductivity 62 percent 100 percent 12 percent (by volume at 20 EC). Electrical conductivity 214 percent 100 percent – (by mass at 20 EC). Thermal conductivity 218 391 59.8 [W/(m.K)]. Corrosion resistance. Good2 (depending on Very good. Poor. atmosphere and alloy). Tensile strength. 89 600 MPa 172 400 MPa 517 000 to 620 500 MPa (13 000 lb/in2) (25 000 lb/in2) (75 000 TO 90 000 lb/in2) Elastic limit1 34 500 Mpa 55 200 Mpa 60 to 80 percent of maxi­ (5000 lb/in2) (8000 lb/in2) mum tensile strength. Density (g/cm3). 2.70 8.96 7.83 Linear density (kg/mm2)/m. 2.70 x 10-3 8.96 x 10-3 7.83 x 10-3 23.6 x 10-6/OC 16.5 x 10-6/OC 11.0 x 10-6/OC coefficient. Resistivity, MO, M 0.28 0.17 0.7 to 1.2. Melting point. 667 OC 1084 OC 1484 OC (1233 OF) (1983 OF) (2793 OF)

1Cold flow, deformation as a result of exceeding the elastic limit by either compression or elongation may occur if this is exceeded.

2Aluminum has excellent resistance to atmospheric corrosion; however, galvanic erosion is included in its resistance.

(FIST 3-3 11/91) 2 Brass: Low-conductivity, high 3.2.1. Copper oxide.- Copper oxide is strength alloy. generally broken down by reasonably low values of contact pressure. Unless Bronze: Good conductor and atmo­ the copper is very badly oxidized, good sphere corrosion resistance. contact can be obtained with minimum cleaning. Copper chromium: Eighty percent conductivity of pure copper; 496,000- 3.2.2. oxide.- Silver oxide is to 552,000-MPa (72,000- to 80,000- easily broken down by contact pressure 1b/in2) tensile strength. and forms less readily at elevated temperature. Thus it is good practice to Copper beryllium: Forty-eight percent silverplate copper contact surfaces that conductivity; (593,000-MPa (86,000- must be operated at elevated lb/in2) tensile strength. temperatures.

Advantages: Because of copper's 3.2.3. Aluminum oxide.- Aluminum small size per current-carrying capac­ oxide is a hard, high-resistance film ity, second to silver, copper is widely that forms immediately on the surface used in armor cable. Its higher tensile of aluminum exposed to air. This tough strength (see table 1) also makes it film gives aluminum its good corrosion favorable to aluminum since it is less resistance. After a few hours, the oxide prone to metal deformation. film formed is too thick to permit a low- resistance contact with cleaning. The 3.1.3. Steel.- For current conductors, the film is so transparent that the bright steel used is of the low-alloy variety. It is a and clean appearance of an aluminum low thermal and electric conductor (see conductor is no assurance of a good table 1). It is used primarily as a strength­ contact. After cleaning the oxide film ening agent for conductors. Some of its from aluminum, a compound must applications are: ACSR (aluminum cable immediately be applied to prevent the steel reinforced), CCSR (copper cable oxide from reforming (see section 4.2). steel reinforced, copper weld, and alumaweld. 3.3. Corrosion of Conductors.- Corrosion is the electrolytic action of Its main advantage is its strength. moisture and other elements of the atmosphere in conjunction with the metals 3.1.4. Table 1 is a summary of the physi­ of the connection. Corrosion is a minor cal, metallurgical, and electrical properties factor in copper or copper alloy of metals commonly used as electrical connections; however, it is a vital factor if conductors. aluminum is involved unless moisture can be kept away from the connection. 3.2. OXIDATION OF CONDUCTORS.-High- resistance oxides form very quickly on 3.3.1. Galvanic action.- Whenever aluminum and copper conductors expose to dissimilar metals are in the presence of air. Once the oxides are stabilized, they pre­ an electrolyte, an electrical potential is vent further oxidation of the parent metal; developed. One metal becomes the however, due to this high electrical resistance, cathode and receives a positive these oxides must be broken or removed charge. The other becomes the before making up connections. Oxidation- and receives a negative charge. When inhibiting joint compounds are used to prevent these metals are in contact, an electric reoxidation of the metals in the connections.

3 (FIST 3-3 11/91) current will flow and this electrolytic 3.3.2. Crevice corrosion.- Electrolytic action causes an attack on the anodic attach can also occur between like metals (negatively charged) metal leaving the due to a phenomenon known as cathodic (positively charge) metal concentration cell or crevice corrosion. unharmed. The extent of the attack is Since oxygen is necessary for corrosive proportional to the strength of the elec­ action, a variation in the concentration of trolytic current, which in turn is propor­ oxygen where a metal is exposed to an tional to the developed. electrolyte will generate an electrical po­ tential and cause a corrosive attack in the The magnitude of the electrical potential oxygen starved area. Thus, since an elec­ generated between two dissimilar metals trolyte in a deep crevice is freely exposed can be seen by the positions of these to the air at the outside, the concentration metals in the electrolytic series shown in of oxygen will be greatest at the mouth of table 2. When two metals are in contact the crevice. Then corrosion can be ex­ in an electrolyte, the higher up in the pected to occur in the crevice remote series is the anode or corroded metal from the surface. Crevice corrosion can while the one lower down is the cathode be prevented if the crevice is filled with a or protected metal. The farther apart the waterproof compound to exclude metals are in the series, the greater the moisture. Thus, within the contact groove electrolytic potential and the greater the of an aluminum connector containing an attack upon the anodic metal. aluminum conductor, there will be numerous crevices in which corrosion will Table 2.- Electrolytic series take place unless a good connector compound is applied during installation. Corroded end (anodic) Copper, being a more noble metal, appears to be much less subject to Magnesium. crevice corrosion; however, a waterproof Aluminum. connector compound application is still Duralumin. justified to inhibit oxidation. Zinc. . 3.4. EXPANSION OF CONDUCTORS. ­ Iron. Aluminum, copper, and steel have vastly dif­ Chromium iron (active). ferent coefficients of expansion and allowances Chromium-nickel-iron (active). for expansion must be considered when Soft solder. designing bus runs as well as connectors. Tin. Lead. 3.5. ANNEALING OF CONDUCTORS.- An- Nickel. nealing is the process of heating and slow Brasses. cooling of metals. For conductors, this is an Bronzes. undesirable process because annealing de­ Monel. creases the tensile strength of the metal. Copper. Annealing is a cumulative process and is very Chromium iron (passive). dependent on the type of parent metal, alloys Silver solder. if present, and the amount of previous cold Silver. reduction. . Platinum. 3.6. PLATING OF CONDUCTORS.- Silver oxide is easily broken down by contact pres- Protected end (cathodic)

(FIST 3-3 11/91) 4 sure and forms less readily at elevated tem­ connection thus reducing the chances of peratures. Therefore, silver plating is recom­ corrosion. Several widely used compounds mended for copper contact surfaces which and their specific applications are discussed must be operated at elevated temperatures. below. Tin and nickel platings are sometimes used on copper and aluminum connectors to prevent 4.2.1. Petrolatum.- Petrolatum (trade the formation of oxides. However, when wet, name Vaseline) is perhaps the first- used these plated metals can cause galvanic joint compound. It aids in preventing ox- corrosion. idation and aids in excluding moisture from connections. It is still useful in mak- 3.7. ANODIZING OF ALUMINUM.- Anodizing ing copper and plated copper connec­ is an electrolytic process which increases the tions. corrosion and abrasion resistance of aluminum (primarily bolts). The aluminum is made anodic 4.2.2. NO-OX-ID.- This grade "A special" with respect to a dilute acid which causes an is a petroleum base compound with additional porous oxide layer to form on the higher melting point, higher oxidation re- aluminum. This layer can be dyed and/or sistance, and better weathering charac­ coated. teristics than petrolatum. It is widely used for copper-to-copper or bronze-to-bronze 4. Preparation of Conductors bus connections.

4.1. CLEANING CONDUCTORS.- Surface 4.2.3. Alcoa No. 2 EJC.- Alcoa No. 2 contamination, specially surface oxide, EJC, electrical joint compound, is a pat- must be expected on all conductors. These ented compound of an active chemical in surface oxide films are insulators and must a grease-type sealer. It penetrates oxide be broken down to achieve the metal-to- film by chemical action and is recom­ metal contact required for efficient electrical mended for aluminum- to-aluminum con- connections. Aluminum oxide, in particular, nections, particularly bolted aluminum forms very rapidly; therefore, aluminum cable connectors on weathered aluminum conductors must be thoroughly cleaned by cable. Alcoa No. 2 EJC is corrosive to use of an emery cloth or a rag immediately steel and tinned copper fitting and it prior to making the connection. In addition should not be used on flat-pad bus con- to cleaning, the surface should be covered nections in substations. with a good joint compound to exclude moisture, thus preventing the oxide from 4.2.4. Alcoa filler compound.- Alcoa reforming. Somewhat better results may be filler compound has a fine grit of alumina obtained by abrading the aluminum (not suspended in it and is used for transmis­ copper) surface through the joint sion line compression dead- end, splice, compound. When joining or terminating and terminal joints on aluminum or ACSR insulated conductors, the insulation should conductors. be removed from the contact area by "pencilling" rather than by "ringing" with a 4.2.5. Pentox "A" (Burndy) and Alnox sharp tool. This will limit conductor damage (Alcoa).- These are electrical joint com­ and facilitate application of insulating tape pounds used for aluminum-to-aluminum and/or compound. and aluminum-to-copper connections, particularly of the bolted flat-pad type. 4.2. JOINT COMPOUNDS.- Joint com- Pentox "A" consists of a suspension of pounds are used when making electrical zinc granules in a paste carrier which is connections to (1) prevent formation of ox- workable over a wide temperature. The ides on the cleaned metal surfaces and (2) zinc granules tend to embed into the to prevent moisture from entering tile

5 (FIST 3-3 11/91) contact surface, penetrating the oxide coating temperature solder such as silversolder. Its and providing additional current paths between high temperature requirement of 650 to contact surfaces. The paste inhibits corrosion 700EC (1,200 to 1,300 EF) may damage from reforming by keeping moisture and air insulation and anneal the conductor. from entering the voids between joining surfaces. Alnox is similar in composition and 5.2.3. .- One of the best electrical recommended application to Pentrox "A." Alcan connections is that made by a perfect weld. universal jointing compound, containing Welding fuses the parent metals of the two titanium dioxide, may also be used in these conductors being joined and theoretically applications. produces a perfect joint. Because of the special skill required, welding has not been 5. Connections widely used as a field method of making connections. However, the widespread use 5.1. GENERAL- Electrical connections be­ of aluminum pipe bus has brought about a tween conductors are made by fusion or limited application for welding since pressure. Fusion involves joining by melting or aluminum is difficult to of the two parent metals or a third metal as control. in soldering and brazing. Pressure connec­ tions are made by physical contact between a. The process used in welding alumi- coincident peaks in the parent metals. With num is the inert gas shielded electric suitable pressure, as from a connector, the arc method using helium or argon to peaks are deformed creating a greater con­ shield the arc to prevent oxidation of tact and conducting area. Because of un­ the aluminum. In a welded joint, it is the equal expansions of different conductors welding bead that carries the current and/or connectors, voids may be reformed between conductors. Therefore, this between conductor and connector. If the bead must be made with great care and connection is not airtight, the voids provide skill, and must have a cross-sectional a place for oxides to form. are equal to that of the conductors being joined. 5.2. FUSION CONNECTIONS.- b. The Thermit welding process, such 5.2.1. Soldering.- Soldering is one of as the Burndy "Thermoweld," long used the oldest means of joining electrical in steel construction, has been adapted connections. A well-made soldered joint for joining copper conductors. The is a good joint but the quality is directly process uses finely divided metallic dependent on skill and inspection is aluminum as the reducing agent with nearly impossible. Soldering increases copper oxide to cause molten copper to the probability of corrosion by the flow into a mold containing the con­ introduction of different metals and flux. ductors. The Thermit process is often Also, soldering may weaken the used in connecting the conductors of conductor by annealing and the heat the grounding grid in switchyards. may damage adjacent cable insulation. The low melting point of solder may c. Other forms of welding such as cold permit a joint failure under overload welding, flash welding, spot welding, conditions. friction welding, -beam welding, laser welding, and percussion welding 5.2.2. Brazing.- Brazing makes an excel­ are used essentially in the lent connection with properly done. It is manufacturing process rather than in essentially a soldering process with a high-

(FIST 3-3 11/91) 6 the field to make electrical connec­ as shown in table 3, will reduce the effects of tions. corrosion.

5.3. PRESSURE CONNECTIONS.- Because 5.4.1. Aluminum-to-aluminum con- of their reliability, convenience, and economy, nections.- For joining aluminum-to- pressure connectors have become widely aluminum conductors, there is little accepted as the most suitable method of disagreement that an aluminum- making electrical connections in the field. bodied conductor is the proper choice, Pressure connectors apply and maintain since this obviously eliminates the pressure between the contact surfaces by galvanic corrosion of dissimilar means of a clamp-type or compression-type metals. However, even for this case, fitting. care must be taken to prevent crevice corrosion and to select an alloy of 5.3.1. Clamp-type connectors.- aluminum for the connector body that Clamp-type connectors apply and is free from cracking due to stress maintain pressure by means of corrosion. clamping bolts, wedges, springs, or a combination of these. 5.4.2. Aluminum-to-copper connec- tions.- Similarly, for joining aluminum 5.3.2. Compression-type to copper conductors, an aluminum connectors.- Compression bodied connector is the best choice connectors apply and maintain since it prevents galvanic corrosion of pressure by compressing the the aluminum conductor, the most connector about the conductor by vulnerable element to attack in the means of suitable tools. connection.

5.3.3. Powder-actuated 5.4,3. Massive anode principle.- By connectors.- A line of connectors making the aluminum connector utilizing a powder charge to facilitate massive in comparison to the copper installation is produced by AMP conductor, where the copper Special Industries. These connectors conductor emerges from the fall into two basic groups: connector, the electrolytic current density over the exposed face of the a. Wedge-type connectors (for aluminum connector is greatly taps, jumpers, etc.) installed by a reduced. This is schematically special tool which utilizes a represented in figure 1. Since the rate powder cartridge to supply the of corrosion is directly related to the wedging force, and current density on the surface of the anodic material, the relatively large b. Internally fired connectors face of the aluminum connector will (terminal lugs, dead ends, and suffer only minor attack. line splices) which utilize internal wedges actuated by powder In addition, because the aluminum charges fired by impact or an connector body is massive in the external electrical circuit. region where the corrosion occurs, the small loss of metal caused by 5.4. SELECTION OF corrosion is insignificant even after CONNECTORS. - Manufacturers and long periods of service. Furthermore, utility companies have done a great the connector design should be such deal of corrosion testing of connectors that clamping bolts (if used) and areas and a considerable area of agreement of high stress which provide structural has been reached in spite of minor strength are not in the regions subject differences in recommended prac­ to galvanic attack. tices. Proper selection of connectors

7 (FIST 3-3 11/91) Table 3. - Recommended electrical connectors

Connection Connector Bolt material bodv and washer

Aluminum to aluminum. Aluminum. Aluminum with Iockwasher. Aluminum to tinned Aluminum. Aluminum with Iockwasher. aluminum Aluminum to tinned Aluminum. Aluminum with Iockwasher. copper. Copper to tinned Bronze. Bronze or steel with aluminum. Iockwasher. Copper to tinned Copper or Bronze with bronze copper, bronze. Iockwasher. Copper to copper or Copper or Bronze with bronze bronze to bronze, bronze. Iockwasher. Tinned copper to Aluminum or Aluminum, bronze, or tinned aluminum, bronze. steel with Belleville washer.

NOTE: (a) Nuts, flat washers, and Iockwashers (if used) must be of the same material as the bolt. (b) Bronze is silicone bronze. Steel bolts may be zinc or cadmium plated or stainless steel. (c) When steel bolts are used for bolting flat aluminum bus bar or aluminum to copper, the use of Belleville washers in place of flat washers to compensate for the differences in ex­ pansion of steel, aluminum, and copper is recommended.

Figure 1. - Electrolytic current density diagram.

(FIST 3-3 11/91) 8 5.4.4. Position of conductor.- A prop­ 6.2. ALUMINUM-TO-COPPER OR - erly designed aluminum connector for BRONZE (Tinned or Untinned) BUS.- joining aluminum to copper must provide adequate separation between the con­ 6.2.1. Whenever possible, place the alu­ ductors to prevent electrolytic attack on minum member above the tinned copper the aluminum conductor. Even then, it is member to prevent copper salts from good practice to install the aluminum con­ washing into the joint which may result in ductor above the if pos­ galvanic corrosion. sible. This will prevent pitting of the aluminum conductor due to copper salts a. Clean aluminum as described in being washed over the aluminum. section 6.1.1.

6. Procedure for Making Connections b. Clean the tinned copper or bronze surface by a few light rubs with fine 6.1. ALUMINUM-TO-ALUMINUM BUS.- steel wool.

6.1.1. Clean contact surfaces immediately c. Clean untinned copper or bronze prior to making connections. Use a rag or surface to bright metal with emery emery cloth to remove direct, black cloth. Remove ridges or nicks by filling. deposits, and any old joint compound. Wipe off copper particles before coating. Do not abrade or brush 6.1.2. Completely coat the contact sur­ either tinned or untinned copper or faces with a liberal amount of Pentrox "A" bronze surfaces, as this may result in or Alnox joint compound. galvanic corrosion.

6.1.3. Abrade the contact surfaces through 6.2.3. Coat the contact surfaces with the joint compound with a wire brush. Pentrox "A" or Alnox joint compound as Aluminum oxide forms immediately upon described in section 6.1.2. exposure; therefore, do not remove joint compound during brushing. 6.2.4. Abrade the aluminum contact sur­ face through the joint compound as de­ 6.1.4. Add more joint compound to contact scribed in section 6.1.3. surfaces and prepare to make the connection. 6.2.5. Add more joint compound to con­ tact surfaces. 6.1.5. Bolted bus connection: 6.2.6. Bolt the bus connection as de­ a. Lubricate bolts with a nongrit joint scribed in section 6.1.5. compound (NO-OX-ID or Alcoa No. 2 EJC). 6.3. COPPER-TO-COPPER OR BRONZE- TO-BRONZE CONNECTIONS (Tinned or b. Torque all bolts in accordance with Untinned).- manufacturer's instructions or, in the absence of these, in accordance with 6.3.1. Clean the contact surfaces im­ table 4 in section 6.5. mediately prior to making tile connection

c. Remove excess joint compound but leave a bead around joint to prevent entrance of moisture and dirt.

9 (FIST 3-3 11/91) to remove dirt deposits and any old joint Cables under No. 8 AWG are usually not compound. coated.

a. Prepare tinned contact surfaces by 6.4.4. Immediately prior to installing the rubbing with fine steel wool. connector, wire brush the cable and con­ nector contact surfaces through the joint b. Prepare untinned contact surfaces by compound. Do not abrade plated con­ cleaning to bright metal with emery nectors as the plating will be damaged. cloth. Remove nicks and ridges by fill­ ing. Wipe off all copper particles. 6.4.5. Add more joint compound to con­ ductor. 6.3.2. Coat the contact surfaces with a "nongrit" joint compound such as NO-OX-ID 6.4.6. Push prepared conductor all the way "A-Special." Use of Pentrox "A" or Alnox into the connector. Make sure all insulation which contain the embedded zinc particles is tripped from the contact area. 'Fasten will cause a poorer connection due to the connector to the cable: lower conductivity of zinc. a. For bolted mechanical connectors, 6.3.3. Do not abrade the copper contact tighten and torque bolts in accordance surfaces through the joint compound, as with section 6.6. and table 4. this will roughen the contact surface and damage plated surfaces. Smooth surfaces b. For compression connections, select have much higher incidences of mi­ the proper die and work tile tool croscopic point-to-point contacts, and thus completely to obtain the proper pres­ exhibit much lower contact resistances. sure. Refer to connector manufacturer's instructions on the proper selection of 6.3.4. Bolt the bus connection as described dies and tools. in section 6.1.5. 6.4.7. Prepare the joint between the cable 6.4. ALUMINUM CABLE TO CONNECTOR connector and the bus as previously de­ JOINTS.- scribed for various types of bus connec­ tions. 6.4.1. Use UL-approved aluminum-bodied connectors for aluminum cable, as these 6.5. CABLE JOINTS.- The basic requirements will expand and contract at the same rate of any cable joint and/or connection are that it as the cable; i.e., thereby main-raining must assume the mechanical and electrical contact pressure. strength of the cable(s) with which it is used. The workmanship and materials used should 6.4.2. "Pencil" the insulation from alumi­ be of the highest quality, so that good num conductor. Never "ring" the insulation. electrical/mechanical contact and insulation (if Avoid nicks and cuts in the conductor. required) will be ensured. The insulation materials must be equivalent in insulation 6.4.3. Coat the conductor and connector properties to that of the insulated cable itself. with electrical joint compound (Pentrox "A" or Alnox). Alcoa No. 2 EJC may be used on 6.5.1. Prepare the contact surface(s) ac­ unplated aluminum connectors. cording to the appropriate preceding sec- tion(s), i.e., 4.1., 6.1., 6.2., 6.3., and 6.4.

(FIST 3-3 11/91) 10 6.5.2. The specific procedure(s) and ma­ reputable electrician's handbook for general terials to be used in the installation of the instructions, large variety of connectors and insulation materials currently available are beyond the 6.6. TORQUE MOMENTS AND PROCE­ scope of this bulletin. Therefore, refer to the DURES FOR BOLTED CONNECTIONS.- connector/cable manufacturers' instructions for the proper procedure(s) and materials to 6.6.1. Torque moments.- All bolts in bolted be employed. In the absence of these connectors should be tightened with a torque specific instructions, refer to a wrench to the torque value recommended by the connector manufacturer. In the absence

Table 4. - Recommended tightening torque on aluminum and silicon bronze bolts [Torque moments in newton meters (foot pounds) for lubricated bolts]

Bolt size/ Silicon Aluminum thread bronze

1/4 inch - 20. 8.1 (6) 5/16 inch -18. 13.6 (10) 10.8 (8) 3/8 inch- 16. 23.0 (17) 14.9 (11) 1/2 inch -13. 47.5 (35) 31.2 (23) 5/8 inch -11. 67.8 (50) 54.2 (40) 3/4 inch- 10. 88.1 (65) 74.6 (55)

NOTE: If steel bolts are used, the torque moment will depend on the compression of the Belleville washer (which should always be used with steel bolts). Care must be taken to avoid overcompression (flattening) of the Belleville washer.

Figure 2. - Clamp tightening sequences.

11 (FIST 3-3 11/91) of manufacturer's specific torque values, the with a hottest spot total temperature torque values in table 4 should be used. limit of 70 EC (158 EF).

6.6.2. Torquing procedures.- The following The standard allows a hot spot temper-attire procedure is recommended for installing all rise of 65 EC (117 EF) for metal-en-closed bolted connectors. applications where silver contact surfaces are used on connections and a hot-spot a. Lubricate bolt threads with a suit- temperature rise of 45 EC (81 EF) for silver- able nongrit joint compound. surfaces terminals of outgoing circuits. Aluminum used for bus work ordinarily has a b. Fit the connector to the conductivity of 63 percent, as compared to conductor and tighten all nuts copper at 99 percent. For a given current "finger tight." rating and for equal limiting temperatures, the area of an aluminum bus will be about 133 c. With a torque wrench, tighten the percent of the area of a copper bus. nuts alternately to one-half of the rec­ ommended torque (manufacturer's 7.1.2. Allowable current density in a recommendation or values from table bus.- Allowable current density in a bus is 4). Figure 2 illustrates a tightening the amount of current that the bus can carry sequence: per square inch or cross-sectional area without exceeding the permissible d. Go back to nut No. 1 and tighten temperature rise. For both ac and dc buses, all bolts in sequence to the full densities may var~v from values of 9.3. X recommended torque. This will 105 and 1.09 X 10~A/m2 (600 and 700 A/in2) ensure full clamping force and in heavy current-carrying copper buses to contact area. 1.86 X 106 and 2.17 X 106 A/m2 (1,200 and 1,400 A/in2) in light buses under favorable Temperature Considerations conditions. For aluminum, densities of 75 percent of the above values are usually 7.1. CURRENT AND TEMPERATURE permitted. LIMITATIONS.- The amount of heat generated in a conductor is proportional to 7.1.3. Current-carrying capacity of its resistance and to the square of the conductors.- No method has been gen­ current it carries, while the temperature rise erally accepted by the industry for the depends on the rate at which the heat is calculation of the current- carrying capacity dissipated through convection, radiation, of conductors for overhead power and conduction. transmission lines. However, Reclamation designs its ACSR capacity 7.1.1. Current-carrying capacity of a in accordance with tables, charts, and bus.- The current-carrying capacity of a procedures in the "Aluminum Electrical bus is limited by the temperature rise Conductor Handbook," 1971 edition or produced by the current and other specific instructions from the conductor factors. Buses for generating stations manufacturer. and substations are generally rated on the basis of the temperature rise which 7.2. TEMPERATURE OF CONNECTIONS.- can be permitted without danger of The principal function of an electrical overheating equip-merit terminals, bus connection is to satisfactorily carry the connections, and joints. ANSI C37.20C- over its entire service life. The 1974 (IEEE standard 27-1974) permits a electrical load can be expected to have daily hottest spot temperature rise for plain fluctuations from no load to full load and copper buses of 30 EC (54 EF) above an frequently to very heavy overloads, thus ambient temperature of 40 EC (104 EF),

(FIST 3-3 11/91) 12 causing wide fluctuations of operating tem­ 7.3.3. Infrared thermometers.- Infrared perature. In addition, the ambient temperature thermometers provide instant tempera­ can be expected to fluctuate between daily ture measurement of energized equip­ extremes and between seasonal extremes. ment without contact. Such devices are The effect of this heat cycling on a poorly extremely useful in monitoring suspected designed or improperly installed connection is hotspots in switchyard bus and equip­ frequently progressive deterioration and ment terminal connections and in trans­ ultimate failure of the connection or associated mission line conductor splices, jumpers, equipment. Therefore, temperature rise and support points. In use, the infrared provides an important and quite convenient device is signed on the connection in method of monitoring the condition of question and the temperature read on the electrical connections. self- contained meter in degree Celsius above ambient with an accuracy of 2 EC 7.3. MEASUREMENT OF CONNECTION (4 EF) or better. TEMPERATURE.- To evaluate the condition of an electrical connection by temperature, the Several manufacturers market a product conductor must be energized and carrying as line of infrared thermometers with near rated load as possible. Temperature several models for specific applications measurement under these conditions, such as: therefore, requires the use of special equip­ ment, materials, and procedures, a few of a. "Raytek Raynger," marketed by which are described in the following para­ Raytek Division, Optical Coating graphs. Laboratory, Inc., Mountain View, California. 7.3.1. Thermometers, , and resistance temperature detectors.- b. "Heat Spy," marketed by Wahl In- Thermometers, thermocouples, and re­ struments, Inc., Culver City, sistance temperature detectors, designed California. for use with hot sticks, are commercially available. These devices are useful for c. "Mikron" models 5, 10, 22, and 56, determining the temperature of accessi­ marketed by Mikron Instrument ble energized connections which visual Company, Inc., Ridgewood, New inspection indicates may be overheating. Jersey.

7.3.2. Temperature sensitive paints, d. "Digital Infrared Thermometer," crayons, and adhesive labels.- These marketed by M-C Products, Division are available for use on conductors and of Material Control, Inc., Scottsdale, connectors, which are not readily acces­ Arizona. sible when energized and/or at maximum temperature. These materials are partic­ 7.4. THERMOGRAPHIC (INFRARED) ularly useful in determining the maximum SURVEYS.- Sophisticated infrared equipment temperatures of insulated connections in vans or helicopters is now widely used such as in generator of motor windings, throughout the electric power industry for rapid cable splices, etc. These materials are scanning of substation and switchyard bus and known as fusible or phase-change indica­ equipment as well as transmission lines. tors and indicate predetermined tempera­ Available equipment can survey an average- ture by melting or an irreversible change sized switchyard in about 30 minutes. in color. Table 5 contains a partial list of Experience in the industry has proven the supplier of phase-change temperature in­ technical worth and economic justification of dicators. infrared testing as a preventive maintenance tool.

13 (FIST 3-3 11/91) Table 5. - Temperature sensitive paints, crayons, and other materials

Model Range Principle. comments W. H. Brady Co.

Thermomarker. 38 to 260 EC. Press-sensitive, nonreversible temperature (100 to 500 EF). indicators.

CAMWIL, Inc.

Thermtab. 38 to 232 EC. Press-sensitive labels have accuracy (100 to 450 EF). temperature

Klinger Scientific Apparatus Corp.

KH2004 Thermochrome 65 to 600 EC. Set of 12 crayons, color changes at (149 to 1112 EF). temperature.

MARKAL Co.

Thermomelt sticks. 38 to 1204 EC. 5E/10E intervals to 650 EF; 20E intervals (100 to 2200 EF). to 2200 EF. Thermomelt liquid. Same. Same. Thermomelt pellets. Same. Same. Thermomelt thinner Paintstiks ball For identifying and marking measure­ point marker. ment data.

Marlin Manufacturing Co.

Tempilstiks. 38 to 1371 EC. Indicating crayons, calibrated melting (100 to 2500 EF). points. Tempilaq. 38 to 1371 EC. Lacquer of calibrated melting points (100 to 2500 EF). suspended in volatile vehicle. Tempil pellets. 38 to 1760 EC. Indicating tablets of calibrated melting (100 to 3200 EF). points. Tempilabels. 38 to 260 EC. Self-adhesive temperature monitors. (100 to 500 EF).

Omega Engineering, Inc.

Tempilaq aerosol. 38 to 1371 EC. Temperature sensitive spray lacquer; (100 to 2500 EF). accuracy ± 1.0 percent. Tempilstiks. 38 to 1371 EC. Temperature indicating crayons, smooth (100 to 2500 EF). or rough surfaces; accuracy ± 1.0 percent. Tabs. 38 to 260 EC. Self-adhesive temperature monitors; (100 to 500 EF). accuracy ± 1.0 percent. Temp pellets. 38 to 1788 EC. Pellets; 20/tube; special series for reduc­ (100 to 3250 EF). ing atmosphere; accuracy +- 1.0 percent. Tempilaq lacquer. 38 to 1371 EC. For fabrics, rubber, plastics, smooth sur­ (100 to 2500 EF). faces, etc.; accuracy ± 1.0 percent.

(FIST 3-3 11/91) 14 Table 5. - Temperature sensitive paints, crayons, and other materials

Model Range Principle. comments

Paper Thermometer Co.

Sensitive paper Thermopaper, thermolablel, thermotube­ single and multiple temperatures, ad­ hesive backing, clear plastic window.

Tempil Division, Big Three Industries, Inc.

Tempilsticks. 38 to 1371 EC. Temperature indicating crayons in (100 to 2500 EF). aluminum holder. Tempilaq. 38 to 1371 EC. Temperature indicating liquids. Brush (100 to 2500 EF). or aerosol spray application. Tempil pellets. 38 to 1760 EC. Temperature indicating pellets. Special (100 to 3200 EF). series for reducing atmosphere. Tempilabels. 38 to 260 EC. Self-adhesive temperature monitor tabs. (100 to 500 EF).

William Wahl Corp.

Temp-Plate. 38 to 593 EC. Turns black at critical temperature; (100 to 1100 EF). eight-position recorder (101-8) has ± 1.0 percent accuracy from 43 to 260 EC) (110 to 500 EF).

7.4.1. Thermal imaging devices.-Ther- a. "Thermovision" model 750, marketed by mal imaging devices are useful in permit­ AGA Corporation, Piaya ting a rapid scan of switchyard buses and Del Rey, California. equipment terminals to detect temperature differences. Infrared signals from b. "Probeye," marketed by photovoltaic detectors are electronically Industrial Products Division, Hughes amplified and transmitted to a small tele­ Aircraft vision viewing screen producing an image Company, Carlsbad, California. corresponding to the thermal patterns within the viewed scene. Temperature dif­ 7.4.2. Thermal imaging units. ­ ferences are shown in varying shades of Thermal imaging television units are gray or in different colors. An accessory sophisticated, infrared-sensitive television instant camera may be used to provide a cameras, which display the thermal image on a permanent record of temperature differ­ television monitor or feed into an accessory video ences. Thermal imaging devices that have recorder for future playback. These units may be been used by Bureau personnel include: hand-held or mounted in vehicles or helicopters for rapid thermal scanning of transmission

15 (FIST 3-3 11/91) lines and switchyards. Several of these buses under loaded conditions. Each units are described below: hotspot detected by an infrared survey should be physically inspected and evaluated. a. "XS-410," marketed by the XEDAR Judging the severity of a faulty Corporation, Boulder, Colorado, is a connection by temperature readings alone pyroelectric vidicon camera which can be misleading. A reading of 50 EC produces a thermal image, which is (90 EF) above ambient in one case can be viewed on a 76-mm (3-in) integral as serious as one 180 EC (325 EF) above television display, or may be fed into ambient, especially if the load is low in the a video recorder. first case. A followup inspection of suspect and/or repaired connections should be b. "lnfravision," marketed by FLIR performed with a hand-held infrared Systems, Inc., Lake Oswego, thermometer, temperature-sensitive tape, or Oregon, utilizes an MCT (mercury other suitable means. cadmium telluride) detector, which is cooled by compressed argon gas. 7.4.4. Contracting for infrared inspection This unit has several remote- services.- Contracting for infrared inspection controlled mounting options, which services is presently regarded as more facilitate its use in vehicles or feasible for Reclamation's power systems helicopters. The thermal image is than the purchase and operation of the displayed on a separate television required sophisticated equipment. The monitor or may be fed into a video Bonneville Power Administration, Public recorder. Service Company of Colorado, and other utilities interconnected with Federal power c. "VideoTherm 84," marketed by systems which operate thermovision LENTECH International Corporation, equipment, have provided infrared surveys for San Diego, California, is a Federal stations in their service areas at a pyroelectric vidicon camera, similar nominal cost. to the "XS- 410" above. It has a number of options which make it a Table 6 lists a number of commercial firms quite versatile unit. which provide infrared testing services to power utilities. Transportation to and from the 7.4,3. Scheduling of infrared surveys.- stations to be tested accounts for a Scheduling of infrared surveys to detect considerable portion of the survey cost. hotspots in electrical connections and Therefore, it is usually advantageous to equipment is an important facet of an ef­ schedule testing at a number of stations in a fective infrared testing program. Under given area in cooperation with another utility such a program, each major station should in that area, to reduce overall transportation be tested every 2 or 3 years, and less costs. Also, contracting for infrared testing on important stations every 3 to 4 years. a regionwide (or several regions) basis offers Such surveys should be conducted during some economies over such testing on a periods of high system loads, which project or single-station basis. Contracts for circuits in a given station are sufficiently infrared testing services should be handled in loaded to reveal existing or potential strict accordance with Federal procurement hotspots. Subsequent surveys should be regulations. scheduled to test transfer of auxiliary

(FIST 3-3 11/91) 16 Table 6. - Some infrared testing services

Bisbee Infrared Services, Inc. Diversified Inspections, Inc. P O Box 51 2255 West Northern Avenue Jackson MI 49204 Suite B-111 (517) 787-4620 Phoenix AZ 85021 (602) 995-5800 Diversified Inspections of California, Inc. Heliwest, Ltd. 12007 Palo Alto Suite 600 Etiwanda CA 91739 300 Union Boulevard (714) 989-1551 Lakewood CO 80228 (303) 989-9310 Independent Testing Laboratories, Inc. Infrared Surveys, Inc. P O Box 657 Suite 609 No. 1 Rand Street 9001 Airport Boulevard Searcy AR 72143 Houston TX 77061 (501) 268-7191 (713) 944-0061

ThermoTest Inc. 3940 Geary Boulevard San Francisco CA 94118 (415) 387-2964

BIBLIOGRAPHY

Standard Handbook for Electrical Engineers, Burndy Basic Connection Principles, 2nd edi- Fink and Carroll, 10th edition. tion, September 1965.

Aluminum Electrical Conductor Handbook, 1st "Making Bus Connections," Bonneville Power edition, September 1971. Administration Substation Maintenance In­ formation, April 22, 1974. Alcoa Aluminum Bus Conductor Handbook, Copyright 1957. Transmission Lines and Substations Branch Memorandum, June 25, 1974. Lineman's and Cableman's Handbook, Kurtz, 4th edition. Live Line Barehand Manual, Colorado River Storage Project, 1974. ANSI Standard C37.20C-1974, "Standard for Switchgear Assemblies Including Metal-En- Standard Handbook for Electrical Engineers, A. closed Bus." E. Knowlton, 9th edition.

Croft's American Electricians Handbook, Carr, 8th edition.

17 (FIST 3-3 11/91)