The isolated power system incorporates the use of monitors, called Line Isolation Monitors. These are informally called LIMs by technicians in the field. The line isolation monitor replaces the circuit breaker. It will alarm, instead of tripping a circuit breaker, during most ground-fault occurrences.

Section 3.3.9 of NFPA99 defines a Line Isolation Monitor as A test instrument designed to continually check the balanced and unbalanced impedance from each line of an isolated circuit to ground and equipped with a built-in test circuit to exercise the alarm without adding to the leakage current hazard. In an isolated power circuit, a ground fault would result in an alarm, but power would not be interrupted.

Section 6.3.2.2.1.2(C) of NFPA99 addresses isolated power with regard to Critical Care Areas and states Where used in locations such as critical care areas, isolated power panels shall be permitted in those locations.

Section 3.3.184 of NFPA99 defines a Wet Procedure Location as The area in a patient care room where a procedure is performed that is 'normally subject to wet conditions while patients are present', including standing fluids on the floor or drenching of the work area, either of which condition is intimate to the patient or staff.

Section 6.3.2.2.8 of NFPA99 addresses Wet Procedure Locations.

Section 6.3.2.2.8.1 of NFPA99 states Wet procedure locations shall be provided with special protection against electric shock.

Section 6.3.2.2.8.4 of NFPA99 states Operating rooms shall be considered to be a wet procedure location, unless a risk assessment conducted by the health care governing body determines otherwise.

This is the most controversial section. A risk assessment by the health care governing body can in fact deem an operating room not to be a wet procedure location. This would be contingent on interpretation of the mopping of the floor which occurs between cases as "drenching", as defined in Section 3.3.89 above.

Section 6.3.2.2.8.7 of NFPA99 states Operating rooms defined as wet procedure locations shall be protected by either isolated power or ground fault circuit interrupters.

Section 6.3.2.2.8.7 of NFPA99 states "Operating rooms defined as wet procedure locations shall be protected by either isolated power or ground fault circuit interrupters.

Section 6.3.2.2.8.6 of NFPA99 states The use of an isolated power system (IPS) shall be permitted as a protective means capable of limiting ground-fault current without power interruption. When installed, such a power system shall conform to the requirements of 6.3.2.6.

Section 6.3.2.2.9 of NFPA99 addresses Isolated Power

Section 6.3.2.2.9.2 of NFPA99 states The system shall be permitted to be installed where it conforms to the performance requirements specified in 6.3.2.6.

Section 6.3.2.6.2.2 of NFPA99 addresses Line Isolation Monitors

Section 6.3.2.6.3.2 of NFPA99 states The monitor shall be designed such that a green signal lamp, conspicuously visible in the area where the line isolation monitor is utilized, remains lighted when the system is adequately isolated from ground; and an adjacent red signal lamp and an audible warning signal (remote if desired) shall be energized when the total hazard current (consisting of possible resistive or capacitive leakage currents) from either isolated conductor to ground reaches a threshold value of 5.0 mA under normal line voltage conditions. The line isolation monitor shall not alarm for a fault hazard current of less than 3.7 mA.

This is interesting, as many of the Line Isolation Monitors still in use are older, often analog units that are set to alarm at only 2 mA. These units must be replaced immediately, as it is a violation of code to use them.

Section 6.3.3.3 of NFPA99 addresses Performance Criteria and Testing for Isolated Power System Testing Servicess.

Section 6.3.3.3.2 of NFPA99 Line Isolation Monitor Tests states The line isolation monitor (LIM) circuit shall be tested after installation, and prior to being placed in service, by successively grounding each line of the energized distribution system through a resistor whose value is 200 x V (ohms), where V equals measured line voltage. The visual and alarms shall be activated.

Section 6.3.4.1 of NFPA99 addresses Maintenance and Testing of the Electrical System.

Section 6.3.4.1.4 of NFPA99 states The LIM circuit shall be tested at intervals of not more than 1 month by actuating the LIM test switch. For a LIM circuit with automated self-test and self-calibration capabilities, this test shall be performed at intervals of not more than 12 months. Actuation of the test switch shall activate both visual and audible alarm indicators.

Section 6.3.4.2 of NFPA99 addresses Record Keeping.

Section 6.3.4.2.1.1 of NFPA99 states A record shall be maintained of the tests required by this chapter and associated repairs or modification.

Section 6.3.4.2.1.2 of NFPA99 states "At a minimum, the record shall contain the date, the rooms or areas tested, and an indication of which items have met, or have failed to meet, the performance requirements of this chapter.

Section 6.3.4..2.2 of NFPA99 Isolated Power System Testing Services (Where Installed) states A permanent record shall be kept of the results of each of the tests.