Line Isolation Monitor

Fig. 82.1

  1. 1.

    What does the image show? Describe its function.


  2. 2.

    What are leakage currents?


  3. 3.

    What are line isolation monitors (LIM)?


  4. 4.

    List the locations where line-isolated electrical systems are required in a health-care facility.


  5. 5.

    What are the effects of differing current strengths?


  6. 6.

    Explain situations that enhance risks of electrical shock.



  1. 1.

    It shows an isolation transformer whose function is to allow electric power transmission between two circuits without a direct connection. On the left is the main power supply which is grounded and looped around the primary coil of the isolation transformer. The current flowing through this generates a magnetic field which creates an electrical potential difference in the secondary coil allowing current to flow from the primary to the secondary coil. By this arrangement an electrical fault on one side cannot spread to the other side. The isolation transformer transmits only the potential difference across the primary coil and not the absolute voltage. Hence a fault in a device plugged into the isolated power supply, which is not grounded, does not lead to an electric shock.


  2. 2.

    Perfectly working electrical equipment may yet produce leakage currents. This is defined as any current, not intended to be applied to a patient, but may pass from exposed metal parts of equipment to ground or to other parts of the instruments.


  3. 3.

    LIM detects electrical potential and leakage currents between the two lines of the isolated secondary system and ground. It is designed to alarm with audible and visual warnings when the secondary system degrades to the extent that there would be a 5 mA or greater electric shock with the next electric fault.

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Sep 23, 2017 | Posted by in Uncategorized | Comments Off on Line Isolation Monitor

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