What is the Difference Between Grounded vs. Ungrounded Lines in an Operating Room?

Stock photo of a hospital exterior
How to protect patients and hospital staff from electrical hazards

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 (operating room) table is connected to the ground and therefore a part of the electrical ground system in the operating room. This is also true for 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 depend 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 the ground. As we will discuss later, “Grounded Systems” only require one fault to result in electrical current flow through the ground.



Components often found connected to “Ungrounded Systems” in operating rooms:
  • Circuit Breakers in the Isolation Power Panel (IPP)
  • The Line Isolation Monitor (LIM)
  • Most receptacles (electrical outlets) distributed throughout the operating room
  • The surgical lights
  • Isolation transformer secondary winding. (Note that the transformer’s primary winding is attached to a different isolated electrical 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
  • Suction pumps, ventilators, Bobies - Bipolar electrocautery tools, heart and oxygen monitors

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

What is monitored in a grounded system
  • Anesthesiology cart and or Anesthesia Boom
  • The floor - may be conductive and therefore grounded
  • The patient’s bed/table
  • The patient and hospital staff - 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


Nearly anything a person can touch in an operating room should be connected to the 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 the ground. It is essential to remember that “Ground” still exists throughout the operating room. The ground always exists, but in an ungrounded system, the output of an isolation transformer is not intentionally attached to the ground.

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

There’s another massive 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.

For more information about this application or to learn more about Bender technology related to your specific application, contact our team of experts.


This article is for informational purposes only. Bender provides the information "as is" without warranty and is not responsible for its accuracy or reliability. No warranties are given regarding its suitability for any specific circumstances.