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.
- Ensures all equipment is earthed at the same low potential
- Red sockets
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
- 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