Realistically, in order for Ground Detectors or Line Isolation Monitors to properly detect or sense leakage current which compromises (or grounds) the isolated power system, there must be a low impedance equipment ground path from the point of equipment use, or patient ground, back to the isolated power panel where the LIM or Ground Detector is located and attached. If this circuit has high impedance, the LIM or Detector may not sense the "real" level of leakage current circulating in the O.R./patient vicinity.

As in "normal" electrical systems, grounding in a patient care or anesthetizing area is important for protection against shock and electrocution. Proper grounding dissipates static charges and diverts fault currents and normal leakage currents away from patients and personnel.

The grounding conductor in equipment power cords prevents static charges from reaching dangerous levels on non-current carrying parts such as cases, housings and boxes of electrical instruments. If these instruments are not properly grounded, a static charge could build up. This charge could then discharge as a static spark. This static charge could be a hazard to the patient and personnel if it ignited some flammable gas, or if it discharged into the patient as a shock (microshock).

This grounding conductor also provides a path for leakage current which could be conducted to the case of an appliance or instrument. The level of this leakage current depends on the nature of the instrument and its’ insulation. This leakage current could establish potential differences between pieces of equipment and could flow through vital organs of the patient, if a current path is established. For example, during cardiac catheterization, small amounts of current could lead to ventricular fibrillation.

All electrical instruments and appliances with good, solid internal grounding characteristics need an equally solid and low impedance ground circuit to be plugged into: ie – the hard-wired ground system between the isolated power panel and the O.R., and receptacles contained therein.

Current codes and standards require that all conductive surfaces within the patient vicinity be properly grounded. A high-integrity grounding system allows the intermingling of electric instruments and appliances located near or attached to the patient without the risk of leakage or fault current to the patient. A low impedance ground circuit in the O.R. ensures that potential differences between conductive surfaces and multiple instruments will be kept to a minimum.

Not necessarily. Many old systems, even though they were not wired with dedicated ground wires and rely only on "conduit grounds", still have low impedance ground circuits – less than 0.2 ohms as currently required by NFPA 99 for existing systems.

However, ground circuit impedance values can "climb" with age. Over time, receptacles can become loose in their boxes - causing higher resistance to the box/conduit ground circuits. Additionally, receptacles "wear" with age. Not only do the L1 & L2 power pins become loose with reduced spring tension, so do the equipment ground pins and contacts. These conditions have to be addressed in order to assure a low impedance ground circuit. Occasionally, O.R.s are rewired or reconfigured without adequate attention paid to the ground circuit between the isolated power panel and the room/new room it feeds.

The impedance testing of ground systems in operating rooms and critical care areas is best performed while conducting the required periodic testing of the associated Isolated Power Systems (IPS) . Not only is it important to verify this low impedance value between each receptacle ground pin and the IPS ground bus – it is very important to also test the tension of the ground pin receptacle. If this tension is deficient due to excessive wear (particularly on straight-blade receptacles), a high impedance connection can result. In these cases the receptacles should be replaced.

NFPA 99 Section 3 takes a very strong position with respect to ground conductor testing in older systems which do not meet the performance levels of modern day Isolated Power Systems with Line Isolation Monitors:

Specifically, refer to NFPA 99 (1999 Edition) Section 3-3.2.1.2(f)1 Wet Locations found on page 25: