The line isolation monitor is a critical component of an isolated power system. The line isolation monitor continuously monitors the isolated power system’s impedance from all conductors to ground. Impedance includes both resistive and capacitive readings. This value is then used to calculate the Total Hazard Current (THC), which dictates what current could flow if a patient were to come in contact with a conductor to ground. The THC reading provides advanced warning of issues that are present in the system.
Since the line isolation monitor is on an isolated power system, power interruption is not necessary and critical processes may continue to run. Continuity of power is maintained on systems where interruption cannot be tolerated. A single ground fault condition will also not trip the main circuit breaker. Appropriate actions may be taken while the system remains online.
The basic principle behind the system is that while a patient is anesthetized during treatment, and if there were a fault in the line, the patient would essentially be electrocuted and you wouldn’t have any way of knowing without the LIM installed.
The NFPA 99 states that a line isolation monitor (LIM) circuit shall be tested after installation , and prior to being placed into service. After installation the NFPA 99 requires that the line isolation monitor and ground fault circuit interrupter (GFCI) tests be conducted at regular intervals.
Medical Testing Solutions, can supply you with the industry leading monitors while ensuring that they are installed and tested correctly.
When is Testing of Line Isolation Monitor Required per NFPA 99 2012 and 2015 Edition?
- NFPA 99 220.127.116.11.2 says – “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 audible alarms shall be activated.”
- NFPA 99 18.104.22.168.5 says – “After any repair or renovation to an electrical distribution system, the LIM circuit shall be tested in accordance with 22.214.171.124.2.” See above. This is to make sure the integrity of the LIM is still working and has not been altered.
- NFPA 99 126.96.36.199.4 says – “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 test switch shall activate both visual and audible alarm indicators.” The MK IV LIM is a self -testing self-calibrating type LIM.
- NFPA 99 188.8.131.52.5 says – “Electrical safety test instruments shall be tested periodically, but not less than annually, for acceptable performance.” The LIM is a test instrument per 3.3.97 definitions, so needs to be tested to see if it is in the specifications of the manufacturer and NFPA requirements. When the LIM is defective or out of the panel the room must be shut down. Do you have a spare LIM in your stock?
- NFPA 99 184.108.40.206.2 says – “A permanent record shall be kept of the results of each of the tests.” Joint Commission will look for your test log to make sure it is being done on time and correctly.
- NFPA 99 220.127.116.11.1.2 says – “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.” Isolated Power Specialist can help you set up a maintenance log book that meet these Requirements.
Get the full NFPA 99 Health Care Facilities Code