Ground Loop

[AKesh]

Hello everyone, I have a quick question regarding Din rails, chassis ground and ground loops. Here is where I am getting confused. I connect my back panel to earth ground which, connects my control panel chassis to earth ground. I screw din rails on my back panel. Question #1: logically, my din rails are now connected to earth ground through the screws connecting to din rails to the back panel. Am I wrong here? As I have seen in many control panels, I connect a ground terminal block to my din rail and connect it to earth ground (the terminal block couples with the din rail through metal clamps). I now use that ground terminal block as a single point source to ground all my other components in the control panel (I connect my ground terminal block to earth ground using a wire).. *** the ten thousand dollar question is Didnt I just create a ground loop between my ground terminal block mounted on the din rail and my back panel chassis ground. For one reason or another the two different location might be at slightly different potentials causing current to flow. Where is my logic off here???? Thank you

[Mendon Systems]

If the bonding was done correctly there shouldn't be any difference but ..... If you have high ground currents going to those blocks it is possible that you might see some difference. The question becomes .... why do you have current flowing through the grounds? IF you do there is something wrong with the system design.

[AKesh]

Thank you I dont have current flowing through the ground. I was under the assumption that your grounding should be centralized from one point source. If i connect the chassis and ground terminal to earth ground I have created multiple paths. Hence a ground loop COULD occur if let say, I have a noise region in my panel. Couldnt noise cause a ground loop? Thanks

[Mendon Systems]

Well .... I suppose it could but there would have to be sufficient noise to generate current flow. Possibly something like a radio antenna? The most common source of ground loops is grounding a shield at both ends of the wire. If there is a difference in ground potential the shield becomes a current conductor. I ran into one case where this happened becaue two separate buildings were running from different sub-stations which were not in phase. The ground potential between them was about 20 volts.

[AKesh]

Thank your for the info!

[DanW]

>Didnt I just create a ground loop between my ground terminal block mounted on the din rail and my back panel chassis ground. Yes, but how much potential can develop across a resistance of 0.000001 ohms, the resistance between the two points? It's a short circuit.

[AKesh]

Thank you sir!

[dogleg43]

To help things out make sure you grind the paint off of the backpanel where the ground bar is mounted. Also, ground the doors and the enclosure itself. Sometimes when checking continuity with a meter between ground and the backpanel I have'n't had a good connection.

[spitzy]

I suppose if you are using 24VDC and connecting the 0VDC to ground then you do not have to use a ground terminal. A standard terminal could be used and then in theory there is still only one point to ground. However you would still have the same consideration for the incoming voltage to the power supply that the 24VDC is derived from.