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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

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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  • 4 weeks later...

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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  • 3 years later...

Bumping an old thread for comments from all on something new.

Recently I had to replace an old IDEC DIN rail supply and due to both urgency and enclosure depth limitations I had limited purchasing options.  Ended up the best was a Mean Well but it did not have an earth. It was an HDR-30-24 and it looks like the entire range of this series is the same configuration, being double insulated.  I haven't actually purchased a DIN rail supply like this for a few years, so maybe earths got dropped a while back. 

Being double insulated makes me intrigued about best practice regarding commoning of the negative, and also earthing practices etc, as it is in some ways now a fully isolated, floating supply.  

Love to hear all the viewpoints on this "new" variation.   I can't find any information on the MW site regarding best practice, but feel sure that running it not connected to earth is going to upset a host of reading types that rely on miniscule amounts of electricity.  In this particular case it doesn't matter, but I see the potential for it to be an issue.

cheers, Aus

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Hi  Ausman, in this case i found many different  solution on real machines.

As for me no earth contact on power supply is MW idea for cost saving.  Now i see both variant of MW PS - old MDR with EARTH  and new without.

Old wariant is approx 10-15% bigger price.

But I think the grounding (or not present gronding) of the primary side doesn't matter if the power supply has a grounded minus of the secondary part.

 

Maybe you can find useful this link.

https://www.klocknermoeller.com/klockner.moeller/Wiring_Manual_English.pdf

start from p.1-17.

 

In this document is presented OV connection to the ground with waveforms:

https://literature.rockwellautomation.com/idc/groups/literature/documents/rm/gmc-rm001_-en-p.pdf

p.110.

 

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That AB document is one hell of a treasure trove of information.  There's stuff in there I knew, stuff I didn't know, and stuff I was wrong about.  I'm especially impressed that they included the waveforms.

Thanks for posting the link!

Joe T.

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