Isolated electrical power systems have been in use in hospital operating rooms and critical care areas since the 1930’s. Their primary purpose was to prevent the possibility of electrical arcs and sparks which could provide a source of ignition for flammable anesthetics. The use of flammable anesthetics was discontinued in the U.S. in the 1970’s, however, the use of isolated power systems has continued because of the superior protection they also provide against electric shock in "wet locations".

The techniques and devices utilized for monitoring the "electrical isolation" of these power systems have evolved over time due to technological advances as well as experience factors with electrical safety for patients and personnel within the operating room and critical care areas.

Systems placed into service prior to 1971 typically used some variation of electromechanical devices which formed a balanced bridge. These units, called Ground Detectors, were simple in design, inexpensive to build and performed reliably within their limited sensing range. Common units were made by Crouse-Hinds (their GDA M2 and GDP devices) and Hevi-Duty (their Dynatector devices). The very notable disadvantage of these devices is their inability to detect balanced resistive and capacitive faults. In other words, if the ungrounded isolated power system became partially grounded through leakages that were equal in each conductor of the system, the Ground Detector would not recognize or sound an alarm in response to this fault condition. These inherent sensing limitations led to the design of subsequent generations of newer devices called Line Isolation Monitors or LIMs.

The aforementioned "experience factors" have progressively instigated many significant changes and new requirements in the NEC – NFPA 70 Article 517 and NFPA 99 – Standard for Health Care Facilities Section 3. Installation and periodic testing requirements have become significantly more stringent in the areas of line-to-ground fault detection and annunciation; grounding and ground system impedance; system leakage levels; and applied fault testing.

IPS HISTORY - MILESTONES:

1920's and 1930's: concern developed over large number of fires and explosions in operating rooms caused by the ignition of explosive anesthetics due to sparks from electrical systems as well as static electricity.

1930's: studies began and safety standards were considered, but delayed due to World War II activities.

1940's: NFPA published "Safe Practices in Hospital Operating Rooms".

1949: NFPA "Safe Practices in Hospital Operating Rooms" was revised and republished as NFPA No. 56 - which was the basis for the current NFPA standards.

1959: the National Electrical Code (NEC) officially established the use of  ungrounded isolated electrical distribution systems in areas where combustible gases were in use.  At the same time, the NEC incorporated the provisions of NFPA No. 56 into the code.  NFPA No. 56 was known as the "Standard for the Use of Inhalation Anesthetics.

1970 - 1978:  NFPA 56A continued to evolve with several major revisions. The use of explosive anesthetics was phased out in the United States.

1971:  the use of static ground detector technology was no longer allowed in new construction with the introduction of new line monitoring devices known as Dynamic Ground Detectors.

1970's:  Dynamic Ground Detectors were replaced by new design devices known as Line Isolation Monitors (LIMs).  These LIMs were vastly superior in their sensing characteristics - especially the detection of balanced simultaneous faults.

1982: NFPA 56A, along with a variety of other healthcare standards, was incorporated into a much broader new standard called "NFPA 99 - Health Care Facilities".

1980's:  with the phasing out of explosive anesthetics, the sole purpose of isolated power  was now considered to be its' superior protection against electrical shock to patients and personnel in "wet locations".  Today, this remains the purpose for continued application of isolated power systems.

1984 - 1999:  NFPA 99 received regular updating.

1980 - Present: Line Isolation Monitor technology has continued to evolve with new self-diagnosing digital LIMs being the current standard.

Application of Isolated Power Systems:

These systems can be found in a number or areas throughout a hospital or surgical center:  Operating Rooms, Cath Labs, Urology, Labor & Delivery, ICU/CCU, Emergency Rooms, Radiology, Special Procedures.

They supply 120 volts to receptacles as well as 208, 240 and 480 volts (single and three-phase) to X-Ray and Laser receptacles.  The IPS panels may be located inside the room they serve or they may outside the room in a corridor, in a central location in a corridor, or in an electrical closet in the vicinity.  When an IPS panel is located outside the room it feeds, a remote alarm unit will be installed inside the room to provide audible and visual indication of a problem.

Simply stated, Isolated Power Systems provide an additional level of electrical safety above and beyond a regular grounded power system.  This additional protection is essential in protecting patients in a wet location who might be especially vulnerable to electrical shock.  Hospital personnel also receive a higher degree of protection in these wet locations.