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andrewuk
Thu 07 November 2013, 04:23
Hi its time to order the contactor ,ill be running a 2.2kw spindle but i am a little confused about the right contactor amperage, do i follow AC1 or AC3 specs i think it should be AC3 Thanks

danilom
Thu 07 November 2013, 15:15
AC-1 - This category applies to all AC loads where the power factor is more than 0.95. These are primarily non-inductive or slightly inductive loads, such as heating. Breaking the arc remains easy with minimal arcing and contact wear.

AC-3 - This category applies to squirrel cage motors with breaking during normal running of the motor.
On closing, the contactor makes the inrush current, which is about 5 to 7 times the rated full load current of the motor.
On opening, the contactor breaks the rated full load current of the motor.



So look at AC3 10-15Amps as the spindle should not pull more than 8 if its a single phase vfd.

KenC
Fri 08 November 2013, 08:31
The biggest strength of a VFD is low inrush current. It will only draw 1x max motor current thanks to the VFD ramping up the motor with frequency instead of current. hence AC1 good enuf, but no harm using AC3. The cost difference is negligible consider the total project cost.