Control Panels & Digital Common

[Otto Von Bismark]

So I ran into something today that surprised and confused me. While troubleshooting a DC circuit I normally put one lead on a ground and probe areas to follow a 24V signal around. Red flags started waving as I was only able to find 10.5V anywhere I searched.

I followed it all the way back to the DC power supply. 10.5V from the positive to ground. However, 24V from positive to negative. I then checked, and the DC common is indeed NOT connected to ground.

I checked another panel that performs the identical task with an identical circuit. It is also the same, no path to ground. Check a few other panels made by the same company that does different tasks, and they are all connected to ground.

Is there any right or wrong about this??

 

[the_msp]

http://www.plctalk.net/qanda/showthread.php?t=23355&highlight=0v+earth

 

[Otto Von Bismark]

http://www.plctalk.net/qanda/showthread.php?t=23355&highlight=0v+earth

Wow, interesting. A lot more contentious that I would have thought. Thank you for directing me. I appreciate it.

 

[BobB]

I do not ground 24VAC or 24VDC negatives.

 

[GaryS]

If the power supply is not connected (bonded) to the ground
Then any voltage reading you would get in reference to ground is boges
UL dose state that all power sources must be bonded to earth for safety and to prevent errant voltage reasons
You also run the risk of short to earth could start a motor
A reminder proper grounding is so important

 

[parky]

Always ground them most PSU Mfr's show that in their literature, Once saw an electrician get quite a shock off a 24v -ve, he assumed such a low voltage would not be a problem, however, because of some water in the panel compared to earth it read 160 odd volts, turns out even the 24v was over 150 compared to ground.

 

[agdacanay77]

Another thread below:
https://control.com/forums/threads/should-0v-be-connected-to-ground.10661/

Kind Regards,