• What you should know

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 6.3.3.3.2 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 6.3.4.1.5 says – “After any repair or renovation to an electrical distribution system, the LIM circuit shall be tested in accordance with 6.3.3.3.2.” See above. This is to make sure the integrity of the LIM is still working and has not been altered.
  • NFPA 99 6.3.4.1.4 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 6.3.3.1.5 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 6.3.4.2.2 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 6.3.4.2.1.2 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

  • Common Questions:

    Whats The Cost: Cost varies by the number of LIM’s installed throughout the facility.  We can usually give you an estimate over the phone, just call 1+(844) 768-5744 or fill out the call back form on this page.

    When can we do it: If you need an emergency certification or calibration of your line isolation monitors, we’ll be happy to get it done. Just call 1+(844) 768-5744 or fill out the call-back form on this page and we’ll be there when you need us.

    What to do if a LIM is in alarm: Scroll down to our line isolation monitor alarm checklist for important information on how take action should any LIM be in alarm.

Line Isolation Monitor Alarm Checklist:

  • If you just plugged a piece of equipment in and the panel alarms, unplug the equipment. If the panel stops alarming, red tag the equipment and remove from operating room.
  • If the panel alarms during the operation, visually look around the operating room. Do you see a cord laying in fluids, or a cart on top of a line cord?  If the equipment is not maintaining the life support of the patient, can you unplug it? when you unplug the equipment does the panel stop alarming? If so, replace the equipment and red tag it for maintenance to inspect for damage.
  • If the panel alarms during the operation and you can’t see any visual reason, silence the line isolation monitor (LIM) and call maintenance. When the panel alarms it does not mean there is an unsafe condition. It means that if another fault happens while in the alarm condition there could be a possibility of a shock. once the case is completed the patient can be safely removed from the room. The room must be closed down until the problem is resolved. Make note of what equipment was on when panel alarmed so all equipment can be checked.
  • With the patient out of the room maintenance can now turn one breaker off, one breaker at a time, while watching the line isolation monitor to see when it drops out of alarm. Once the LIM drops out of alarm note which circuit was causing the alarm. Locate all equipment on that circuit. turn the breaker back on. The LIM should alarm again. Unplug each piece of equipment one at a time until the LIM drops out of alarm. Red tag the defective equipment and remove from operating room. Notify all that have a need to know, that the problem has been resolved.
  • If the panel will not drop out of alarm, after all circuit breakers are turned off, the LIM is defective. Remove and replace the LIM. With the LIM defective the operating room is down until the defective LIM is replaced. It is also best practice to have a spare LIM in stock.
  • Call Medical Testing Solutions or fill out the form to your right if the problem cannot be solved or for replacement LIM’s and parts.

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