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Ben

20HP @ 575VAC Motor Starter

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Hi, I have an application where in addition to usual control stuff, I have to start/stop two 20HP pumps (only one at a time). At first I started with single contactor with o/l relay but now I'm thinking it would draw too much startup current. So question is should I use star-delta starter or a soft starter? I have PLC and PC in the same control panel. Any suggestions with circuit diagrams and/or catalog numbers (Allen-Bradley preferred) would be highly appreciated.

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A "Wye-Start Delta-Run" would be the most cost efficient choice, however, it applies ONLY to 6-lead (Wye-Delta) built AC Motors (European style). This method's implementation requires three starters and a timing relay. At Start-Up the motor windings are connected in SERIES via Line Contactor L and Wye Contactor S (thus reducing the voltage applied to/current drawn by motor's windings); when the timing relay times out, contactor S drops and the load will be switched onto Contactor R which applies full line voltage to the AC motor windings, this time connected in PARALLEL, substantially reducing the 700-800% FLA current which passes through a full voltage starter when commanded ON. Again, the motor will have to allow this configuration and all 6 leads will have to be present within the starter enclosure. http://www.usmotors.com/products/ProFacts/1-120-6.htm or, in more detail: http://www.abb-control.com/pdf/catalog/lv023/3.83.pdf A soft starter is a solid state motor starter that is used to start or stop a motor by notching the voltage waveform, thereby, reducing the voltage to each phase of a motor and gradually increasing the voltage until the motor gets up to full voltage/speed all at a fixed frequency. A-B Bulletin 150 — SMC™ Smart Motor Controller family has become pretty reliable lately. http://www.ab.com/en/epub/catalogs/12768/229240/229262/3073021/1179231/index.html We've been also using with good results the ABB PSS series softstarters . http://www05.abb.com/global/scot/scot209.nsf/veritydisplay/c203bef4f35d06508525763200560ffd/$file/1sxu132199c0201.pdf Edited by dmargineau

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Thanks for all the links dmargineu, I am leaning towards soft starter for smoother controls.

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