Safety Switches/Residual Current Devices
Residual Current Device, RCD, is an electrical wiring device, a safety switch, which has become a mandatory part of Australian housing electrical codes since 1991. The use of Residual Current Devices will be mandatory in workplaces by January 1, 2013, increasing the safety of workers using electricity to perform their job duties. The safety switches, RCDs, are designed to shut off the electrical supply when a leakage or change in current occurs. A difference of electrical current of 0.3mA between the active and neutral conductor causes the current to be shut off, thereby averting the chance of injury by electrical shock.
Purpose of the Residual Current Device
The purpose of the Residual Current Device is the prevention of electrocution of people while manipulating electrical cords, tools and appliances. The most common cause of death by electrical shock can occur within 25-40 milliseconds, so a Residual Current Device detects a leakage of current before it can pass into the operator. RCDs measure the current between the live and neutral conductor. When the sum of the current changes or does not remain zero, leakage is detected and the device opens its contacts to stop accidental electrocution.
RCDs, Better Than Circuit Breakers
Prior to 1991, a large safety switch protected a group of circuits which caused the loss of power to all circuits, not just the defective line. Residual Current Devices also have a built-in test button which allows the operator to prove functionality at the connection instead of the main circuit breaker box.
Danger, Will Robinson, Danger!
A Residual Current Device cannot remove all risk of electrocution or fire due to human error factors. The device cannot protect against electrical shock when current flows through a finger touching both live and negative contacts in a light fixture.