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Pf Correction


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#1 o brudo

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Posted 27 December 2007 - 11:49 PM

Hello : My question is regarding the statement in PF correction link under the subtitle - Static correction - " It is better practice to use two contactors, one for the motor and one for the capacitor. Where one contactor is employed, it should be up sized for the capacitive load ."
What does " up sized " mean ? Does it mean larger current rating? the schematic shows the capacitor on the load side of the contactor , just as the motor is on the load side of the same contactor ; so, if anything, the current seen by the contactor will be less with the capacitor than without ???

#2 marke

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Posted 29 December 2007 - 12:22 AM

Hello o brudo

Welcome to the forum.

When the contactor closes, it will have to carry the inrush to the motor plus the inrush current to the capacitors. The contactor will see a reduced steady state current when the motor is running, but the closing transient could be sufficient to damage the contacts, hence the rating should be increased.

Best regards,




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