Grounded vs. Ungrounded Lines in an Operating Room

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When visualizing the word “Line” as it relates to operating rooms, picture all of the components in an ungrounded system. The ungrounded system is more than the outlets and wires behind the wall and everything that plugs into the outlets becomes part of the ungrounded electrical system. The goal of an ungrounded system is to isolate and insulate every electrical device from the ground system.

When visualizing the word “Line” as it relates to operating rooms, picture all of the components in an ungrounded system.  The ungrounded system is more than the outlets and wires behind the wall and everything that plugs into the outlets becomes part of the ungrounded electrical system.  The goal of an ungrounded system is to isolate and insulate every electrical device from the ground system. 

Below is a partial list of components often found connected to “Ungrounded Systems” in operating rooms:

  • Isolation transformer secondary winding.  (Note that the transformer’s primary winding is attached to a different isolated electrical system).
  • Circuit Breakers (CB) in the Isolation Power Panel (IPP).
  • The Line Isolation Monitor (LIM) is also connected to the ungrounded electrical system.
  • Most receptacles (electrical outlets) distributed throughout the operating room.
  • The surgical lights within six feet of the patient should be part of the ungrounded system.
  • Power cords have insulated copper conductors.  The purpose of the cord’s insulation is to keep the copper from touching “Ground.”
  • When plugged into a receptacle, the instruments used by the medical team become part of the ungrounded electrical system.
  • Suction pumps, ventilators, Bobies - Bipolar electrocautery tools, heart and oxygen monitors.

 

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There are many more components that make up the isolated ungrounded electrical system.  In an ideal scenario, all the above components, including the power cords, will remain insulated from ground.  Unfortunately, things go wrong, insulation wears off, wire connections come loose, and components on circuit boards fail which results in ground-faults.

In order to have a healthy appreciation of the electrical hazards in an operating room, we must assume and understand that the patient laying on the OR table is connected to the ground and therefore a part of the electrical ground system in the operating room.  This is also true for the nurses and doctors.  What are the implications of this assumption?  Simply put, electrical currents can flow through the people in the operating room (electrocution) when insulation failure occurs.  The severity and probability of electrocution depends on the type of electrical protection designed into the operating room.  “Ungrounded Systems” require insulation faults at two different points and a large enough voltage difference between those two points before current will flow through ground.  As we will discuss later, “Grounded Systems” only require one fault to result in electrical current flow through ground.

 

The room “Ground” system often incorporates the following:

  • Anesthesiology cart and or Anesthesia Boom.
  • The floor may be conductive and therefore grounded.
  • The patient’s bed / table should be connected to “Ground.”
  • The patient is connected to the “Ground” system via standing fluids.
  • Doctors are connected to the “Ground” system via standing fluids.
  • Nurses are connected to the “Ground” system via standing fluids.
  • Light fixture housings should be grounded. (Note that the light bulbs themselves are isolated, but the housings are grounded)
  • Medical device chassis and frames should be connected to ground as well.

 Nearly anything a person can touch in an operating room should be connected to ground.

An “Ungrounded System” is accomplished by using an isolation transformer.  Electrical systems in operating rooms, under normal conditions, are often “Ungrounded,” meaning that they are not intentionally attached to ground.  It is important to keep in mind that “Ground” still exists throughout the operating room.  Ground always exists, but in an ungrounded system, the output of an isolation transformer is not intentionally attached to Ground.

Why do engineers prefer an ungrounded electrical system vs. a grounded electrical system in an operating room or ICU?  Simply put, electrical current cannot flow back to the power source via “Ground” in an ungrounded system.  Just like the cars racing around the track in Daytona, current flows in loops.  If you open the loop, electrical current can’t flow.

Nobody wants unintended electrical current flowing through a patient or the care providers in an operating room.

There’s another huge benefit to a well monitored “Ungrounded System.”  There’s no need to trip (remove power) when the first fault (failure) occurs in an ungrounded system.  This benefit is often referred to as continuity of power.

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Stock photo of a hospital