help me better understand grounding in a control panel with AC/DC

diat150

Lifetime Supporting Member
Join Date
Mar 2006
Location
Louisiana
Posts
1,473
Proper grounding is one of the things I want to get better knowledge of. In a PLC Cabinet that has a mixture of AC and DC IO, how do you usually handle the grounding? Should all components go back to a common ground bar? Should the shields on the DC Analog cabling be brought to an isolated ground bar that is separate from the AC Ground?

Also, can anyone recommend any documentation or classes that I can take to get a better understanding of grounding?
 
Standard practice is usually to only have ONE ground system for everything in the panel. This can be a ground bar that bolts to the backplane, making the backplane an effective ground, and additional ground bars or terminal block grounds can be added. Of course the incoming feeder ground must be tied into that system somewhere.

Terminate analog shields at that same ground. As far as whether to ground the 24VDC common or not, you will get a LOT of differing opinions on that. I prefer not to ground the DC.
 
how about control transformer grounding? from what ive read the X2 side of the transformer should be grounded. so the X2 terminal on the transformer would have a white wire for the secondary voltage neutral for the panels needs and also a green wire for grounding purposes. but ive seen some instances where the ground wire is brought all the way back to the main ground buss in the panel, and other instances where the ground wire is brought right to one of the bolts that mounts the transformer to the backpanel. of course the paint in this instance would be ground off the backpanel as well as off whatever leg on the transformer that you would use the bolt to attach the ground wire to. which is right? which is better?
 
I do not ground the DC from a switchmode - you lose your isolation. I use double wound (safety) transformers - grounding the secondary also kills the isolation. It also floats in my panels. I would ground the secondary on a tap type transformer but never use them anyway.
 
we use floating DC systems as well. While ensuring there are no grounds on all the devices and instruments is a chore and sometimes requires installing an isolating supply to feed all the devices which internally have grounds, it is worth having the isolation from ground for the instruments and it helps avoid outages as the process can operate with a ground fault without any loss of power to other devices on the same feed
 
I always ground my systems - here's why - the regulations in Europe which are developed by larger brains than mine say I should.

There are lots of discussions here about the subject, have a search. But so long as the regs say I should, and so long as I can't come up with a reason that would sway a Jury, I will keep grounding the 0V from the power supplies.
 
We ALWAYS ground the x2 of a transformer to the panel.
the utility company failed to properly ground the plant side of the transformer and had a 75 volt floating ground. we had to modify some equipment and everytime we powered any hand tool, we got zapped.
Since we started doing that, on issues any where.

james
 

Similar Topics

A thread to suggest improvements to Red Lions G3 Touch Screens. Im starting this thread as a carry over from...
Replies
500
Views
262,196
Hi!! I'm looking for Temperature rise calculation software from Rockwell, I just download "Product selection toolbox 2022" but this software is...
Replies
1
Views
86
Please see attached file. I need this program in Function Block form but I am totally lost on this. Any help would be appreciated. Thanks!
Replies
8
Views
255
Took a new job and the controls schemes are fairly old and I'm used to Allen Bradley and Siemens. I'm looking to replace a pair of Superior...
Replies
1
Views
85
Hello, I have a question about fuses and how to calculate their required size. I understand that determining the appropriate fuse size isn't...
Replies
0
Views
111
Back
Top Bottom