A residual-current device (RCD), or residual-current circuit breaker (RCCB), is a type of AC electrical switch that instantly breaks an electric circuit to prevent serious harm from an ongoing electric shock. An RCD is often referred to as a “Safety Switch” because it is designed to disconnect the power if a person makes contact with a live part of a circuit and earth at the same time.
THERE ARE THREE GENERAL CATEGORIES OF CIRCUIT PROTECTION: – FUSES, CIRCUIT BREAKERS AND RCDS.
THE PURPOSE OF FUSES AND CIRCUIT BREAKERS IS TO PROTECT WIRING AND APPLIANCES, NOT PEOPLE. THE PURPOSE OF RCDS IS TO PROTECT PEOPLE, NOT WIRING AND APPLIANCES.
ALWAYS REMEMBER THERE ARE SITUATIONS WHERE THE RCD WILL NOT PROTECT YOU!
In Australia residual current devices have been mandatory on power circuits since 1991 and on light circuits since 2000. All socket outlets and lighting circuits are required to be distributed over circuit RCDs. A maximum of three subcircuits may be connected to a single RCD.
Australian regulations require that standard RCD’s (type 2) activate within 300 milliseconds, and RCDs designed for medical use (type 1) must activate within 40 milliseconds.
Leakage can indicate a shock hazard (or shock in progress) which is a potential danger to a person. This condition can occur if someone comes into contact with the active supply wire while being in contact with earth.
Even though the purpose of RCDs is to protect people not wiring and appliances, ALWAYS REMEMBER there are situations where the RCD will not protect you!
RCDs can be of either the Fixed or Portable variety.
A Fixed RCD is one that is permanently wired to terminals in a circuit or equipment. The only testing AS/NZS 3760:2010 requires for fixed RCDs is using the RCD test button, and observing the operating time, which should be ‘without undue delay’. However, the state-of-the-art- PAT testers used by Jez Test and Tag also allow us to perform the same Trip Test that is generally only performed on Portable RCDs.
A Portable RCD is one that, as the name suggests, is NOT permanently wired to terminals in a circuit or equipment and can be relocated as required. Portable RCDs generally look similar to powerboards but with a manual trip and reset switch, they are also several times more expensive than standard powerboards. The standard AS/NZS 3760:2010 requires that portable RCDs’ manual trip function is checked, then to measure both current level and trip time a Trip Time test is conducted. This is done using a PAT tester that introduces a current, equal to the rated tripping current, that is ‘suddenly’ applied between active and protective earth and the operating time measured.
If the Portable RCD has multiple sockets (outlets), similar to a powerboard, the Trip Time test will be conducted on each socket.