RCDs – Residual Current Devices

The Importance of Testing & Tagging

Why do I need to have power tools and portable electrical equipment inspected and tested when the site is protected by RCDs?

This is a common question asked by builders and subbies. So, let’s start from the beginning. Residual Current Devices (RCDs), commonly known as safety switches, are designed to shut off the electrical supply when electricity leaking to the earth is detected at high levels. It is used to prevent a fatal electrical shock.

OHS law requires the duty holder to eliminate risks, including the risk of electric shock, if reasonably feasible. If the risk or part of the risk cannot be eliminated, the risks must be reduced.

Unfortunately, many in the construction industry incorrectly assume RCDs eliminate the risk of electric shock. In fact, RCDs only reduce the risk from the electric shock if the electric current goes through the person to earth. RCDs are designed to trip at a current low enough to prevent a person from receiving a permanent injury or death from an electric shock. The electric shock still occurs but the RCD shuts off the power in less than ½ second to prevent a fatal event.

“Unfortunately, many in the construction industry incorrectly assume RCDs eliminate the risk of electric shock. In fact, RCDs only reduce the risk from the electric shock if the electric current goes through the person to earth.”

However, RCDs may not provide protection against other types of electric shocks where there is no path between the person and earth such as when the person makes contact between two live wires (active and neutral).

While RCDs reduce the risk of electric shock, duty holders still have a responsibility to eliminate the risks of electric shock. This may be achieved through an inspection regime which includes inspection and testing of equipment before it’s first used, and periodic inspections and testing every three months thereafter. This is known as testing and tagging. A fixed RCD, which may be found in a construction switchboard, must be tested monthly.

“A fixed RCD, which may be found in a construction switchboard, must be tested monthly.”

During the periodic inspections, the equipment’s electrical insulation and earthing should be tested to ensure they have not failed or deteriorated. Periodic inspections also include visual inspection for damage or wear and checks on the correct operation of triggers, switches and guards to ensure they work correctly.

Between periodic inspections, the duty holder should have users undertake visual inspections prior to use, as electrical equipment is constantly in danger of being damaged due to the nature of construction work.

“Between periodic inspections, the duty holder should have users undertake visual inspections prior to use.”

Detecting faulty electrical equipment and removing it from service before it’s plugged into power, eliminates the risk of electric shock from that equipment.

For more information see WorkSafe Victoria’s industry standard – Electrical installation on construction sites.