Isolated Power Systems are designed to protect patients and caregivers from electric shock in critical care areas of healthcare facilities. Line Isolation Monitors (LIMs) are the most important component of all Isolated Power Panels. LIMs are the piece of the Isolated Power System that monitors the hazard current and provides both visual and audible alarm signals to alert the medical staff of the presence of a line-to- ground fault on any connected equipment.

LIM testing is vital to ensuring that the isolated power systems perform their patient protection and fault monitoring role as well as maintaining compliance with NFPA 70 and NFPA 99.

MainPro, Inc. offers LIM testing services in Alabama, Florida, Georgia, Illinois, Indiana, Kentucky, Michigan, North Carolina, Ohio, Pennsylvania, South Carolina, Tennessee, Virginia, West Virginia, Wisconsin.

What testing is required by the NFPA-99 standard for Line Isolation Monitoring Systems?
NFPA 99 defines a Line Isolation Monitor (LIM) as an electrical test instrument and requires that they be tested not less than annually for acceptable performance. This test is what is accomplished during our inspection process.

NFPA 99 also requires that the LIM test switch be actuated to test the LIM circuit, visual and aural alarm indicators monthly. However, for a LIM with self-test and self-calibration capabilities, the test needs only to be performed annually. The annual test of the LIM is included in our inspection process. We can provide a form to record your monthly tests.

What tests are performed during the testing of Line Isolation Monitoring Systems?

  •  Operation of LIM alarm function (
  •  LIM alarm point verification via simulated fault (
  •  LIM Remote Annunciator operation if present (
  • Record Voltage, THC and Alarm Trip Point of each system

Does your Line Isolation Monitoring System need to be tested after repair?
Yes, per NFPA 99 – LIMs must be tested after installation and after any “repair or renovation” to the system.

What documentation is required after testing your Line Isolation Monitoring System?

We provide a letter detailing our inspection along with a summary of all isolated power panels, a record of the values obtained and an individual page for each isolated power panel with pictures. If any isolated power panels do not meet the standards of NFPA 70 & NFPA 99, we also include a corrective actions report and can provide a quote to perform the necessary repairs.

Our certified isolated power system technicians have the necessary experience and qualifications and are available at short notice.

Contact us today to schedule your LIM testing. We offer line isolation monitor testing contracts, troubleshooting, repair, and LIM installation.