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Old October 21st, 2007, 04:28 PM   #10

PeterW is offline
Join Date: Jun 2006
Location: Edmonton
Posts: 2,522
Originally Posted by CJones
Well, I'm no expert

But where else would you put the contactor, you mentioned never after the inverter, that leaves in front of the inverter which seems worse by far.

Even if you didn't use a contactor but had overloads shouldn't they go after the inverter?

Many times we will use a 20hp inverter and have 4 motors on a line with the one inverter powering all 4 motors. contactors after the inverter seems like the only way to go.

The only contactor required for an inverter, would be the power on contactor, which could be the safety contactor, which would be BEFORE the inverter.

Doug is quite correct, you should not put a contactor between the inverter and the motor. You use the control signals to RUN/STOP the motor, not the contactor.

Overloads also go before the inverter as you are protecting the inverter, the inverter protects the motor.

Where the inverter supplies multiple motors, each motor should have its own protection after the inverter (in addition to the inverter protection), but if one trips the inverter should be stopped.

We had a HMI selection where we selected if a drive was enabled or not, therefore if one had a fault and tripped the feedback would be different to selection and the inverter commanded to stop. If the motor had a fault, then the HMI would be used to de-select that drive to enable restart without it. The breaker would be locked out. If someone turned on a breaker that was de-selected then again the inverter stopped.
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