What is a Line Isolation Monitor?

A Line Isolation Monitor, commonly referred to as “LIM”, monitors the overall insulation of a “Line.” Line Isolation Monitors are used to monitor hospital electrical power systems typically found in critical patient areas such as ICUs and Operating Rooms.

When considering the word “Line” as it relates to operating rooms, one must consider all components in an ungrounded system. The goal of an ungrounded system is to isolate and insulate every electrical device from the grounded system. The ungrounded system is more than the outlets and wires behind the wall - everything that plugs into the outlets becomes part of the ungrounded electrical system.

Components typically found connected to “Ungrounded Systems” in operating rooms include:

1. Receptacles (electrical outlets) distributed throughout the operating room

2. Isolation transformer secondary winding (the transformer’s primary winding is attached to a different isolated electrical system)

3. Circuit Breakers (CB) in the Isolation Power Panel (IPP)

4. The Line Isolation Monitor (LIM) is also connected to the ungrounded electrical system

Other components:

1. Surgical lights within six feet of the patient
2. Power cords that have insulated copper conductors (the purpose of the cord’s insulation is to keep the copper from touching “Ground”)
3. Suction pumps, ventilators, Bobies - Bipolar electrocautery tools, heart and oxygen monitors
4. When plugged into a receptacle, the instruments used by the medical team