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Power Supply Wiring

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Should I be grounding the power supply 0V. The wiring guidelines for the modules suggest that it should be earthed. I have seen many arguments for and against

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Should I be grounding the power supply 0V. The wiring guidelines for the modules suggest that it should be earthed. I have seen many arguments for and against

I never do it (since 2001 and a lot of Unitronics PLC installed that way in that time) and still not having a problem. But that´s just my personal experience. This is your first project?

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No, not my first project. I have not been grounding the 0V either but noticed the other day when testing my program with a 4-20 calibrator that my inputs were sweeping up and down, about 1/2 mA total. My calibrator output is rock solid since I checked it with a separate meter. When I grounded the 0V on the power supply the sweeping stopped and the input was rock solid. I guess its dependent on the bonding in the building the PLC is installed in and I should handle it on a case by case basis?

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No, not my first project. I have not been grounding the 0V either but noticed the other day when testing my program with a 4-20 calibrator that my inputs were sweeping up and down, about 1/2 mA total. My calibrator output is rock solid since I checked it with a separate meter. When I grounded the 0V on the power supply the sweeping stopped and the input was rock solid. I guess its dependent on the bonding in the building the PLC is installed in and I should handle it on a case by case basis

You need to have a good earth on the system. That´s all I check, if the earth is not a good one, then problems with analog signals are normal.

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I usually connect 0V to ground because it makes troubleshooting easier - clip the negative of your meter to a DIN rail and you can poke around with the positive lead.  

+1 on what HigHTech says - make sure you have a really good earth ground or you'll have problems with your analog signals if you ground the DC power supply.

Joe T.

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