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2 centralized control A modern control center consists of starters and associated equipment for motor control, together disconnect switche-s--.-------- -..-mm creators or ^ with interwiring and buswork. all housed in a steel cabinet ready for Held installation. Then all that's Anything from across-lhe-lino starters loauiomnti needed is to run a feed to the control center and transformer-type starting equipment can be Kur feeds from it to individual motors -- plus any remotecontrol-station wiring required. into control centers, as can lighting panels. An all-aluminum control center is now available This central system contrasts with locating indi 65% lighter than its steel-and-copper counterpart It vidual control units at each machine, or grouping pegged lor food plants where cleanliness is motor-control equipment in a central spot by hand mount, chemical plants with corrosion problems. assembly of individual components. Initial equipment coat of today's control center Advantages. Centralized control offers: simplicity in generally runs higher than that ol an equivafon planning and installation, compactness and neat ap pearance, high degree of solely, centralized opera tion and maintenance, flexibility. number of separate starters. But total installed cot is apt to run less lor the control center. Location. Control centers may be put on the floor c In lixcd-connection type, line connection^ of indi In space between roof and lower structural memben vidual units bolt to busbars. In plugin type, con Many engineers like control centers in separate!; nections are made by clips which slide over vertical busbars, simplifying removal o! individual units. ventilated rooms away from work areas. This oltsi avoids need (or special enclosures to resist hazard ous or corrosive atmospheres. Consider these factors to determine if centralized control is the.. Centralized motor-control units aro far from a universal oniw*r. You must determine whether they are best suited for your particular Installation, or whether some larm of local or group control is Iho boat engineering bet. How Pomemsalf One point to consider is the degree ol "penaonence*' of your production equipment. Can the ma chines bo expected to sloy In their present positions lot some year* to come? (f they con, and If they're closely grouped, tho odds favor a centralited-conlrol setup. But In many Industries It's reasonable to expect shills in machine location (ram tim to time. In' the automotive indus try, for example, machine locations shift os models change. Here, bus duct with Individual motor starlors at each machine is usual practice, lo stmpHty moving machines. Individual motor darters til well where machines are iar apart and also where control is aulte complex, with multispeed equipment and much control wiring. In adopting any system of centralised control, keep your eye on available short-circuit currents. A central Cents] should not be connected to a system where available shed-' circuit current is greater than rating of the center. Available short-circuit current tc that which would flow through astro- impedance fault at the line terminal of the motor-control center. Allowable short-circuit current rating assigned lo a meter control center fs 25.000 amp rme asymmetrical.. Manufacturers brace the buswork to withstand this passible short-circuit current, But. in addition, short-circuit rating el a control center depends on tho type of protective means used within each individual combination starter and whether or net the control center as a whole has an Incoming-line circuit breaker. When Is Line Breaker Needed? Whore Incoming short-drcull current is within 15,000 amp, no incoming-line droit breaker is needed. And the combination starter* can be aelded-cass TOOArS CIKCTMCM HACT1C8 WWfl pother scheme, units ore spotted on the ma* hooked up lo cm outside sourco ol clean t**^SUfe in control unit Is kept slightly above o( Ihe surroundings, Thle Ib particularly advan- ^ous in dusty areas. Types. There are Ihree standard NEMA (ypes, ^ ^ by far the simplest, having no terminal and no wiring. Standard combination starters ^eult breakers aro factory-assembled in the factum, connected to vertical buses. Motor and wires conned direct to starter terminals, fype B has individual terminal blocks In each jgrtet. This makes It easy to install or remove jjortor, simplifies field wiring. Type C is completely l0C4ory wired, Including Typo B individual motor y^cks. It also includes wiring to master terminal blocks either at top or bottom ol the structure. This construction may include any sequence wiring or fririntg rfeqlu-ir-e-d-between starters ^ best betfor you. Then follow these steps to plan an installation air breaker typ. having a short-circuit rating of 15,000 amp. &ii If up to 25,000 amp are available on ehort circuit, then an lucoolng-line air breaker with 2S,000-arop Interrupting capac ity t required if moldod-cose air breakara are lo be ueed In molor-eonirol units necessitated can be made more easily on Type B them on ihe completely prewired Type C. List Accessories. At this stage It's also a good idea to list accessories and modifications (hot depart from standard equipment shown In catalogs of Ihe controi^onter supplier. tbs combination starters. One reason you can use (hie setup Is (hat the Internal Im pedance within the combination etartere can be counted on to limit the short-circuit current within 15,000 amp, even tough 25.000 amp are available on Incoming tide ol control Although "specials" are often Ihe logical answer to overcome local problems, strive (or adoption ol standard equipment throughout. Costwtee It's always to your benefit to use stand ard designs. And It simplifies maintenance and repair later. Then pin down location. Try to spot control centers in least- center. Principal Impedanco In this setup comae from overload beatarm. That's why it's mighty important to select moldedcae oir-breoker trip to coordinate with overload heaters. Circuit breaker must start to trip before overload heaters be auts so hot they are in danger el (using. 0 you decide that cenlralited control equipment is beet far your needs, the Ural atop la to calculate whether standard valuable areas -- where machines can't be fitted, in root structure, or In a eeparate control room. This lost Is often best In Industrie* such as textile and steel where ambient condi tions may require, special enclosures te resist hazardous or corrosive atmosphere. Keep in mind that control centers can be lined up in a straight row, put back to back, or arranged in L-ehaped or U-shapod layouts. control centers available Irom one ol the many makers will asst your short-circuit requirements, Keep In mind the llmltaUrn ol 25,000 amp and tind out U a liguis boyond that Is 0vr Wi r i 'iv/li oraltable at the point where you plan to tle-ln to the food. This Is especially important U the control center is banked alongside a secondary unit substation, where short-drcull aiireni can be of a high order el magnitude. This may call lor relocation of tho control center, use ol ft i*i w Juoka fOJp hlgh-rupiurlng-capodly luses on incoming side of the center, a, possibly, ihe use ol reoctore. it Usd step la to |ot down hp load and arrangomont desired. This is Indicated in sketch at rtght. At Ihe same time, decide on some oi the basic design considerations of the control center. For example, are you going to use bolted or etub-lype Afsrskrt disconnect*? Also pin down your choice on molded-case air breakers v* fuses. Third logical step in planning a motor-control center is to $ dstermine NEMA type. As outlined, these types dUler in ii - degree oi completeness of tho unit as furnished by Ihe maker. ivj> This Is something only you can determine, keeping In mind (he installation cost involved if you choose Type A or B. Many power engineers (eel that Type B can be fulfilled by Ughtly lower equipment cost compared lo Typo C. And in "any cases, slight changes occur between time control equip, ent te specified and time of delivery. The Interchange of |WrV, i*1", .it'*;1 0' mL .B-IV l!|. OOOIll 1951 TODAY'S CICCTItCAl PKACTta