After years of neglect, this fascinating topic has finally founds its way into the fellowship exam in the form of Question 22 from the first paper of 2016.

Microshock: small current delivered via electrodes directly into the body, bypassing the resistance of the poorly conductive skin.

Equipotential earthing

  • Ensures all equipment is earthed at the same low potential

Residual current devices (RCDs)

  • Detect current leak
  • Breaks circuit if the leak is detected

Line isolation monitors (LIMs)

  • Monitor escess current
  • Alarm when excess current detected

Uninterruptible power supply

  • Connected to battery banks or diesel generator.
  • Blue sockets for battery UPS, red sockets for generator backup

Protected areas:

  • Cardiac protected electrical area
    • Areas where microshock is likely, eg. areas where patients have intravascular devices
    • These areas have equipotential earthing and RCDs/LIMs
  • Body protected electrical area
    • Areas where microshock is unlikely (eg. outpatient clinics, anywhere there is ECG monitoring)
    • RCDs/LIMs are used

Equipment electical safety is classified by the permitted current leak:

  • Type B devices can leak all they want
  • Type BF devices can only leak a maximum of 5mA
  • Type CF devices can only leak a maximum of 50μA


O'HARA Jr, JEROME F., and THOMAS L. HIGGINS. "Total electrical power failure in a cardiothoracic intensive care unit." Critical care medicine 20.6 (1992): 840-845.


Olson, Walter H. "Electrical safety." Medical instrumentation. Boston: Houghton Mifflin Co (1978): 667-707.

Χριστοδούλου, Χριστόφορος. Recommendations and standards for building and testing an Intensive Care Unit (ICU) electrical installation. Diss. 2011. - This is a fascinating masters thesis dissertation on the standards of electrical equipment in ICU. It is not exactly a canonical source- as I expect the CICM engineers use other, locally validated guidelines -but it is an interesting read nonetheless, particularly because the author makes his recommendations on the basis of published evidence. Thus, this is the nearest thing I can find to "evidence-based ICU design".