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Isolated Ground

  1. Sep 11, 2010 #1
    I've seen many 'isolated ground' outlet, in schools and hospital. Tried to google it but didn't find much information about those. They're and orange case, and usually are just beside the normal mains. What is special about those? Are they safer?
    Thanks, Sakha.
  2. jcsd
  3. Sep 12, 2010 #2
    No, they are meant for critical equipment and are tied into the hospital's generator backup in case of power failure. You don't use them for the TV but you do for the IV pump etc.
  4. Sep 12, 2010 #3


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    Isolated or non-isolated receptacles that have patient equipment attached are designed for less leakage current (mircoamp range) and are said to be hospital grade. You can recognize them from their green dot.
  5. Sep 12, 2010 #4
    I've been told that they also have independent ground wires leading back to a single point in order to avoid ground loops between various pieces of sensitive equipment. I don't know if that was just something someone made up when I asked or not though...
  6. Sep 13, 2010 #5


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    It can mean different things. However, in many hospitals (and in e.g. some research labs, including a lab where I used to work) they have a separate earth (safety ground) for sensitive equipment. Then the ground wires are NOT connected to the "usual" mains earth but are connected to a separate ground point somewhere in basement the building (this "point" can e.g be a copper mesh buried in the ground, or as simply a large chunk of metal).

    It can also mean that the outlet is connected to the mains via an isolation transformer which separates the ground from the ground of the mains, i.e. the outlet is floating. This is not very common but it is used in some hospitals for sensitive equipment (e.g a spark gap is used to make sure that the potential of the two grounds do not differ too much).
    Last edited: Sep 13, 2010
  7. Sep 16, 2010 #6
    Post 4 is likely correct. US GFCI's for general people protection trip about 5 ma. Sounds like this hospital grade are MUCH more sensitive.


    Interestingly, grounding in wet marine environments also requires separate ground wires for ac (household type generator) and dc ( battery) which are in general connected only at a single point. Here the main prupose is to avoid loops which can pick up galvanic protection currents (from bonding circuits protecting against galvanic corrosion) and also carry potentially dangerous ground fault (equipment failure) conditions.

    In the hospital environment, I suspect they want to keep traditional ground circuits designed for equipment/people shock reasons separate from more sensitive grounds for certain equipment.
    Last edited: Sep 16, 2010
  8. Sep 18, 2010 #7
    I concur, but with the added factor of lab-tested reliability. They're significantly more reliable than housing-grade GFIs, one of the many reasons why a day's stay at home costs you $35, while a day's stay in the hospital will cost you $1,500.

    As an absolutely minimum.
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