Should I be afraid of ground loops?

Discussion in 'General Electronics Chat' started by xiv014, Nov 9, 2010.

  1. xiv014

    Thread Starter New Member

    Nov 9, 2010
    I am working on a circuit that has multiple "ground" inputs such as RS232, USB, PCI-bus, a wall wart AC-DC converter, etc. I have measured up to 200 mV of difference between the various grounds.

    What is the proper way to isolate these grounds from each other?
  2. gootee

    Senior Member

    Apr 24, 2007
    If there are voltage differences between them, maybe they are already isolated from each other. Do you want to isolate them or are you worried about connecting them together?

    "Ground" is often relative; just an artificial reference point. Often it's relative to the "ground" voltage reference point in a power supply. It is often unrelated to "earth ground". Apparently some of the "grounds" you have might be isolated or partially isolated from earth ground. Have you tried disconnecting everything from power and measuring the resistances between the various grounds, and between the various grounds and earth ground?

    The question should be: What problem(s) are they causing, or might they cause?
  3. themindflayer


    Oct 29, 2010
    proper way is to keep them isolated ... if that is not an option make sure that the current from the RS232 signals return to their OWN ground ... this can be done by having a good layout (advanced / expert routing skills and understanding of the circuit req)

    with the above rule in mind you do connect the grounds .... traces of all the grounds are brought together and joined at a single point .....
  4. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    Drains, shields, bonds, are a certain thing, power common is another. Mixing them up can lead to problems. Be mindful of what 'ground' means to you and how it is applied.
  5. xiv014

    Thread Starter New Member

    Nov 9, 2010

    Thanks for the responses everyone!

    What is the best way to isolate the different grounds from each other?
  6. beenthere

    Retired Moderator

    Apr 20, 2004
    You might be trying to cure a non-existent problem. You can always put the circuit and cabling together experimentally and see if a problem exists.

    It's always best to use a star ground technique, where the individual grounds come together in one and only one location. Several worthwhile articles about star grounding and ground loops may be found on the internet -
  7. t06afre

    AAC Fanatic!

    May 11, 2009
    If it ain't broken, don't fix it ;) Often very simple things can help out on grounding problems. And it also wise to have a grounding strategy in new design. But if you have no problems. It is often no reason for worry.
  8. themindflayer


    Oct 29, 2010
    the term isolation is used for systems which need to be electrically isolated .... there is no path of current from one system to another .....

    when you wrote 'isolate the grounds' .... what we read was 'preventing ground loops' ...

    what gootee and getdeviceinfo meant was that the term ground is ambiguous which is why we use 'return' ... the return for RS232 should NOT be the return for the USB if it IS then it means that the 'ground' of RS232 is at a lower potential than that of USB and the current from USB signals travels to the RS232 'ground' and then THROUGH the RS232 section finds a path back to USB .... USB is hi-speed with hi speed comes noise with noise comes ... well you know highly erratic data ....

    so how is that you 'isolate' grounds ....? you dont isolate .... you take care of the problem with routing etc ....

    beenthere has suggested the most practical approach .... run the system and if you are having problems address them .... else dont try to fix a thing if it aint broken!!! t06afre!

    maybe if you presented what is it that you actually want to do we could help you out (whether you really need to worry or not)

    hope this helps