Document kDJK4127J9n3aGjbE6qEKdY5n

*/c components; conductors Advances ol a generation ago. such as rubber compounding, took like minor changed when stacked up against develop ments In Insulation and coverings made in the last 10 years. Synthetic Rubber*. During World War 11. natural rubber dropped out. and synthetics substituted. In but a lew years, both cable makers and power engineers lound many (actors favoring the new synthetic*. So many, in loci, that natural rubber is now disappearing as a wire and cable insulation. Heat is the groat acceptod enemy ol Insulations. But the "cold'' rubber in tc*djy`* type R does a good job ol resisting heat compared to type fl ol some years back. Going iurther sllll is type RH-RW, although a little more costly, U'e being used enough lo materially olleci sales ai type R. Ocone-resisiont buiyl-base compound is another eicellont performer. It's today's dependable compound ior voltages to IS kv, and oilen higher, offering stability, slow aging, low pi, other desirable physical and electrical characteristics. Neoprene Jacketing lor rubber-insulated coblot l making big strides. Relatively inexpensive. It's dependable under many tough conditions in moist or dry conduit, in earth, or in aerial runs. Silicone rubber is another nowcomer. Its re sistance to heal, many oils, solvents and other chemicals makes it suitable lot some process-plant applications. Thermoplastics. You can do a wiring Job in your plant today using only material* that barely existed in 1940-- typical art the thermoplastics. Polyvinyl chloride and polyethyleno. Polyvinyl chloride -- pvc lor short - Ills a wide range ol ap plications. It resists oils, acids, alkalis, greases, .gasoline, moisiure. abrasion. With normal treatment and protection it oilers long Hie. We've mentioned bul a lew oi tho thermo^ platlic*. The list has grown long In recent years: Rulan, Nylon, Cordolile. Saran. Tend# II. Slyraloy. TeDon. 'wV has been lh# koekben* ol industrial wiring ,Wr,iC7|or generations. In the day* ol lower lobor costs, threading. cutting and bending wasn't a* critical. It-.w0* no substitute that oifered ail the advantages lop mechanical protection, good electrical conduc- Cooduit, During the 1930's, thlnwall conduil began its tssth In industrial plants. It ellered light weight, cutting and. ol grealor value, no threading. Compres- ^v^^ypUngs and terminal fittings, slipped over the new - Suit, permitted installation with only hand tools. Bending "I^Shu# an easlor job with tools designed lo handlo the NbM IPOWEB. May 1951 pp 126. 129). .'5*ff^od Ducts. Thinwoll was Jus! the beginning ol a con- **"* uWwmtfd effort to lind low-cost easily installed rocoways. I' an(| duets.have and will continue to be used, especial- fehste won* vrlres or cables are to bo carried in the same' * jjrmtil or*0- Typical would be control wiring and tow-volt- ' '^dge^secondory leedor*. Trays ore available prefabricated. ^:;':^giplste with littings to dodgo around obstructions. Their big .,^eturs i* ability to carry many vrites and cables in the one .>s'''`ae9Vay. And when future additions coll lot more, it's a metier to toy the needed additions in place, tl amplo jj-.^ipqce a provided In original design. Today's Hays are Logically, thermoplastics replace rubber ior seme appitco- mado ol expanded metal for lightness. I. f vfh# Mil-contained wiring system* (fnfertocked-armor and lions, bul nol all. Toughness oi thermoplastic* permits use - .* ?* -(fierat-miulated capper-sheathed) lit into this move to do- without proiecilve braid. This factor atone means smotlsr V1 v v ,#(op |ew-cosl enclosed wiring sysloms. over-all diamoter, loss space needed In conduit. In modem!- v') >' .v,\ Whsrs trays and rocks aro used in place el conduit, gen- tallon programs where existing conduits are reused) more ' >i \:*ral practice today dictates keeping primary, secondary and coppor can be pulled In. an important consideration whsn V' central cables segregated. A typical arrangement is sketched, rewiring commercial and institutional buildings. -A'-JI*-'.-Trlffhl. Note the ladder-like rack sorvlng as support ior the hiph-vollage primary feeders ot the ihterlocked-armor type. Is rigid conduit out as a raceway in industrial plants? Far from it. Where fop mechanical protection Is needed, there is no substitute lor heavy-wall rigid conduit. But where number of cables required caffs for running a large number of con duits. and where degree ol protection offered by conduit isn't needed, trays and'ducts are a llkoly answer. -- - aV. After mastering basic differences between aluminum and copper . '. engineers find more uses for light, corrosion-resistant metal Aluminum is working its way Into plants as an electrical conductor. It is growing in importance as cost ol aluminum con tinues to drop. In time It will (ind its proper spat; but copper is. and will re main, ihe No. I conductor. There's nothing roally new about all this. Back in 1098, the lighl melal was installed as a bus conductor in the 600-v 60.000-amp bus at Nlagoia Work*. Aluminum tubular conductors lor out door switching stations followed. Hore it offered resistance to weathering and longer permissible span lengths, It also found application in the chemical in dustry where capper corrosion was a problem. Aluminum has teen service in plallng rooms where sulphuric-add, cyanide and cadmium-oxide lumes are present. Where It Fils, Aluminum has natural advantages tilting It lor several spots in the industrial system. For overhead in stallations, light weight per amp is a major (actor. The (act that larger diame ter is needed than ior copper proves el little Importance overhaod since no con duit is used. Another natural Is buswork in primary substation* But (o (ind suit able applications in your plant calls lor an engineering study weighing all (acts. There's lest advantage in going to aluminum for smaller conductors. By small we mean about No. 6 or less. In (his rango. weight advantage is Huio and greater number of connection* may quickly cancel out ony other advan tages. Connecting aluminum has been a problem. Al presant mast Held troubles crop up because electricians and even same design engineers, fall to get moro than a nodding acquaintace with the "how-lo" side of aluminum as a con ductor in wiring systems. Aluminum!* Different When aluminum building wire bowed In shortly alter the last war, its hard-drawn finish gave it an undeslrablo "springy" quality. Bul an intermediate temper was adopted that gave belter handling qualities. This change in tempering also improved "nickabillly"-- breaking oil if accidental ly nicked by ihe knile when insulation is skinned. But thsro still ars basic dillo/oncos between aluminum and capper. Six# is one. Capper is a better conductor; aluminum Is about 6j% as conductive for any given wire diameter. This fac tor alono goneially dictates larger con duits for aluminum. And there's where an aluminum installation can go off base. You can't decide, alter conduit runs ore laid oul, and perhaps installed, that aluminum would be a good bet in sens part of ihe system. Aluminum musl bs designod as a systam: it needs lie own connectors, forger boxes and conduit. Aluminum Oxide. When aluminum is ex posed lo air, an oxide forms. A poor conductor, it can be scraped oil but re forms immediately, Today's procedure coats cable with one of sevoral avail able compounds; oxide is then removed, usually with a wiro brush. Cable end, compound and all, is put into connector. With compression-type connectors, pres sure rubs oxide Ulm oil cable strands. Since all air Is squeesed out ot Joint, in- 7-iulating oxide film doesn't gel a chance `p n'lorm, Rosuh: A goad electrical con-`oeclion between strands in cable and ' between cable surface and connector. birtrelytlc Action, This is another factor soiltlbetory oluminum-to-oJumlnum Joint. On a large Job. calling for many joints, consider use of argon-are welding and aluminum terminals. No flux is needed. Resultant weld is clean, completely con - to consider when Joining aluminum and ' copper whore moisture Is present. A : ninioture electric eell can bo set up and one oi the metals, aluminum, will be eaten away. Solution appears to be ductive. Ireo al inclusions. Belled or compression littings often give a faster and moro reliable joint. Bolted littings cut down installation lime and require few tools. If made ol use of Un-pfated aluminum lugs. Place copper or copper alloy, they are coaled aluminum above copper so copper salts to protect against electrolysis. formed will (low away from Joint. Aluminum has a higher creep rale thon topper. That's why connectors (or . aluminum bavo more surlaco -- to re duce pressuro on conductors in Joint yet Compression Fittings. These have been used lor over 40 yearn, primarily on overhead aluminum transmission lines. Now similar lining* ore available lor use on insulated wire and cable. Spe keep them Irom working loose. Thermal expansion differences ' be* cial tools that exort heavy pressure are used lor application. Pressure com tosen copper and aluminum must also be taken into account. Aluminum's coflicienl of expansion is about 39% Greater than copper's. Thus, usual run el copper connectors are nol suitable. For a good joint, connector must be dedgnod to handlo the differences in rat* presses body ol fitting around the cable, torming a deep indent. Cross-sections oi compression joints show that cable strands In tho titling have been packed into practically a solid mass. Wiping ac tion ol motal during compression breaks the oxide Him. yielding low electrical *1 expansion oi the two metals. resistance. Whether boiled Or compres Making Joints. In addition lo the tacts sion fittings aro employed, however, outlined above, remember that joints good practice call* for a suftobfe com An also bo made with standard heal pound lo maintain a good joint. methods. Aluminum eoldor, used with All things considered, aluminum as a *uitable (lux and torch, will turn out a conductor In the industrial plant Is here and will remain. Manufacturer* anxious lo exploit aluminum's advantages have largely overcame the space and con nector problems in thoir equipment. Plant electricians Hk aluminum be cause ol It* fighter weight. But you'll have to keep dose tabs on them until they become familiar with using it, and thoy'll have io pay attention to details of good practice. When you buy equipment, tell the manufacturer whether you plan to use aluminum with it. Otherwise it may be delivered to you with copper connectors, probably unsuited lor aluminum. too TObAY'J mCTS'CM PtAChCf OOoiCI 1991 TOOAV'S rtECTSfCAt MACriCf