Electrical Safety Devices

Revised and reviewed 11 December 2014

OVERVIEW

Electrical safety devices include a range standard electric components that are mandatory to ensure patient and staff safety

USE

• prevent electrical fires
• maintain operation of life-sustaining, electrically powered equipment
• prevention of macroshocks (e.g. 5mA can cause pain and increasing amounts lead to sustained muscle contraction, respiratory arrest then VF arrest)
• prevention of microshocks (conduction of unearthed current from electrical devices directly into the patient along conductors such as pacing wires and intravascular catheters with induction of VF – may be associated with current as low as 100 microamperes)

DESCRIPTION

• Equipotential earthing system
  • electrical wiring of areas to ensure all equipment is earthed at the same low potential
  • points allowing device connection to this system are coloured differently (e.g. red) to standard mains points (e.g. white)
• Equipotential earth points (or studs)
  • installed adjacent to plug sockets to allow equipment at risk of current leak to be connected to the equipotential earthing system
• Residual current devices (RCDs)
  • if excess current leakage is detected a switch will trip and the panel of connected points will lose power
• Line isolation monitors (LIMs)
  • monitor for excess current and alarm if this is detected, but do not shut down power in response to this
• Uninterruptible power supply (UPS)
  • a self contained source of power (e.g battery bank) located independent of other electrical power circuits that will continue to function, without interruption, if mains power is lost
• Emergency electrical generator
  • another source of electrical power (e.g. diesel powered) distinct from the mains power supplied by a power station

METHOD OF INSERTION / USE

• Equipotential earth points
  • becoming redundant as equipment used in areas with these points must be checked before to use to ensure function, ensure  minimal current leak, and devices must be connected to other points that have equipotential earthing
• RCDs
  • if the switch is tripped all devices connected to the panel should be turned off, the switch reset and then devices plugged in turn to see which one is problematic
  • if a new device is plugged in and trips the switch it should be removed
  • devices suspected of malfunction should be sent for electrical testing
• LIM
  • if the alarm is triggered the attached equipment should be removed and checked
• UPS
  • life-sustaining devices where an interruption to power would be deemed clinically significant are connected to these circuits (e.g. blue points)
• Emergency electrical generator
  • usually will activate automatically after a short delay (e.g. 20–30 seconds)
• Other measures for maintaining safety including the banning of double adaptors, extension cords and unapproved power boards

COMPLICATIONS

• Patient injury – effects depend on current type, density, frequency, impedence to flow and the nature of the exposed tissue
• Microshock
• Macroshock with electrocution and burns
• Electrical fires
• Critical device failure with clinical adverse consequences

References and Links

LITFL

• CCC — Electrical injury
• CCC — Electrical Concepts and Definitions

FOAM and web resources

• HowEquipmentWorks.com — Electricity Basics
• HowEquipmentWorks.com — Electrical Safety
• RCH Melbourne — Electrical Safety