Isolated Power Systems for Hospitals

Many conflicting opinions prevail regarding isolated power systems (IPS), compounded by the confusion in the interpretation of codes. At the risk of beating a dead horse, I'll add to the discussion.

With the advent of the digital hospital, significant advances in medical technology and the elimination of flammable anesthetics, consulting engineers and hospital personnel are questioning the merits of IPS.

IPS were first mandated by the National Electrical Code (NEC) in the 1950s, for use in patient care areas where flammable anesthetics were used. These areas included operating rooms, intensive care units, coronary care units, cardiac catheterization labs, angiography labs, delivery rooms, dialysis units, and emergency rooms .

An IPS is an unground electrical distribution system. The typical IPS located within an operating room is comprised of a shielded isolation transformer, a line-isolation monitor (LIM), a 2-pole primary circuit breaker and several 2-pole secondary circuit breakers, as specified in NFPA 99 and NEC Article 517. The isolation transformer is most often either a 1:1 or a step-down transformer with the secondary windings not referenced to ground.

The LIM continuously monitors the isolated ungrounded system for any leakage current and activates an audible and visual alarm when the leakage current reaches 5-milliampere (mA), thus alerting the operating room staff. The alarm condition does not mean that hazardous current is flowing, and does not trip the upstream circuit breaker, which could be catastrophic in the event a life-sustaining device is in use. The alarm is just an indication to personnel to take corrective action. The LIM also gives continuous indication of the system's condition (in mA) and is a prediction of the magnitude of the leakage current that could possibly flow from either conductor of the isolated system to ground if a path was provided. A patient's body resistance, which is very low compared to a healthy individual, is susceptible to electric shocks.

With the phasing out of flammable anesthetics in the 1980s, the role of an IPS was reduced. With the advent of the digital hospital, consulting engineers, hospital facilities personnel and medical personnel started questioning the usage of these IPS, which are quite often a maintenance nightmare.

The National Electrical Code does not mandate the usage of IPS, except in wet locations. NFPA 99 defines a wet location as: A patient care area that is subject to wet conditions while patients are present. These include standing fluids on the floor or drenching of the work area, either of which condition is intimate to the patient or staff. Routine housekeeping procedures and incidental spillage of fluids do not define a wet location.

Furthermore, NFPA rules also state that in areas designated as patient care wet locations by the governing body of the facility, all receptacles and fixed equipment shall have ground fault circuit interrupter (GFCI) protection for personnel if interruption of power under fault conditions can be tolerated, or be served by an IPS if such interruption cannot be tolerated.