I have a customer that is going to install a 150 hp vfd drive this drive is going to control two 75 hp motors. They are going to install overloads off this drive to each 75 hp motor I know that the code book said has them down for 96 amps at 480 volt three phase the name plate rating has the motor at 85 amps at 480 volt three phase. Can I calculate the circuit that is coming from the overloads to the motors at 85 amps are do I have to calculate is as 96 amps x 125 percent and if it is on a vfd do you still calculate 125 percent of the load
430 Motors
- Thread starter acid75070
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petersonra
Senior Member
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- Northern illinois
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- engineer
i am not sure just what you are asking but the motor circuits have to have 125% of the ampacity from the chart in the book, not what is on the nameplate.
the ampacity of the circuit feeding the drive has to be 125% of the rated input current of the drive.
the ampacity of the circuit feeding the drive has to be 125% of the rated input current of the drive.
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Deleted: wrong thread.
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- San Francisco Bay Area, CA, USA
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No. The rules do not change.
Yes, because the rules do not change.
Yes, because the rules do not change.
See the trend here?
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- San Francisco Bay Area, CA, USA
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- Electrical Engineer
By the way, you still set the OVERLOAD relay based on the 85A, and per the instructions from the OL relay mfr.
Also to that point, don't use Service Factor in that process on a motor connected to a VFD, or put another way, all motors fed by a VFD should be considered 1.0SF. That is not (nor ever was) part of the NEC, that comes from the motor manufacturers.
Also to that point, don't use Service Factor in that process on a motor connected to a VFD, or put another way, all motors fed by a VFD should be considered 1.0SF. That is not (nor ever was) part of the NEC, that comes from the motor manufacturers.
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