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Old June 16th, 2017, 06:16 AM   #13
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Location: ENE of Nowhere Oklahoma
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I will only tie the 24VDC common to ground if required by some oddball piece of hardware in the system that has it done that way internally. I can think of one recent device like this that would lose its marbles if I didn't ground my DC negative side.

The only advantage I can think of aside from the above is that if you are troubleshooting a field device where the DC common is not present and you want to see if the right 24+ voltage is present, you can touch one meter lead to a good ground.

The disadvantages have already been described: 1) higher susceptibility to ground fault noise. 2) potential for false (sinking) inputs if a conductor shorts to ground.

There would not be a shock hazard with 24vdc. I'm with BobB on this but will make exceptions.
It's not all the variables I am most concerned with, it's the undiscovered constants.
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