Grounding 0V of 24VDC System. Micrologix 1100

69FIREBIRD

Member
Join Date
Oct 2004
Location
New Zealand
Posts
102
Hello, hoping to get some feedback on this overnight.

I have a couple of Omron FQ2 cameras connected to a 1763-BBB Micrologix & 1762-OB8 transistor output module that have been added as an independent system to an injection molding machine. We have had IO fail on the camera and trying to determine where a possible cause may be.

We had not directly grounded/earthed the 0V/-. But during some testing we found that the 0V is tied to earth. We traced this to an internal link on the 1763-BBB Micrologix between its earth terminal and the 0V/-. Unless we don't earth the controller I think we should be looking to formally ground the 0V at the common 0V terminal block. Other devices associated with the system have ether no connection between their 0V terminal and earth or some lowish resistance or assume capacitor connection to earth (resistance changes when metered).

My question is why would we not want to earth the 0V. It would seem unlikely at this stage that we can fully isolate it anyway.

Thanks in advance.
 
Lots of commentary:

URLs to discussions of grounding the power supply

Control.com: PLC auxiliary power supply - floating or grounded
http://www.control.com/thread/1236976011

PLCs.net: 24 Volt Inputs and Grounds (2004)
http://www.plctalk.net/qanda/showthread.php?t=13249

PLCs.net 24v power supply (2012)
http://199.193.246.108/qanda/showthread.php?t=73352

PLCs.net: Grounding question 24v power supply
http://www.plctalk.net/qanda/showthread.php?t=30839


Mr.PLC: Ground the 24VDC Power Supply Common?
http://forums.mrplc.com/index.php?showtopic=15175
 
I trust that you have found the little metal plate on the backside of the ML1100 connecting it to the din rail?

You have to take that off as well as disconnect the ground terminal if you wish not to have the controller grounded.

This has caused me problems in the past as the short between 0V and ground will sometimes show as a fault on some fault current devices on ships.
 

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