Instrument Power 0VDC Referenced to Ground?

[jantoffman]

I'm looking for what is considered best practice as far as referencing the negative (common) side of a 24VDC instrument power system to ground.
This is the instrument power (not signal) for 4-wire transmitters (not loop powered transmitters).
Are there any pros / cons to doing it?
My thought was that it would be safer as voltages in the field would be sure not to float above 24V, but my staff tell me that they are worried of shorting out instruments if the + is accidentally grounded during maintenance.

Any IEEE or other references on this?

Thanks in advanced,
Jan T.

 

[Henneshoe]

We tend to tie the common side to ground through a parallel resistor and capacitor. R = 1Mohm, C = .01 uF.

 

[jantoffman]

Thanks Henneshoe. Any reason you do it this way?
Any Pros / Cons for floating the 24VDC vs grounding it?

 

[Skogsgurra]

Floating it may cause electrostatic build-up with subsequent (sometimes interfering) discharges to ground. So, a "leak" to ground is good to have. The capacitor is good to short high-frequency interference to ground. Often, the 0.1 uF capacitor gets a ceramic HF capacitor in parallel.

Sometimes, it is good to "ground everything everywhere". But that does not seem to be the first choice in instrumentation. More so in automation and drive applications.

Gunnar Englund

http://www.gke.org

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