What is the difference between an RCD and a Circuit Breaker?
Sometimes there is a misconception regarding the difference between an RCD (Residual Current Device) and a Circuit Breaker. Let’s explain…
An RCD is typically known as a Safety Switch, designed to protect against electrocution and will detect any disruption of electrical flow through an electrical circuit. If the flow of electricity returning through the circuit does not exactly match the amount of electrical flow entering the circuit, the RCD will ‘switch off,’ due to electricity leakage (leakage to earth). The RCD ‘thinks’ that the leakage to earth is electricity going through a person and into the ground, therefore switching off the power supply to prevent any form of an electric shock.
A Circuit Breaker on the other hand is an electrical switch, designed to protect an electrical circuit from damage, caused by an excess electrical flow (current draw), due to an overload or short circuit.
Circuit Breakers will not ‘switch off’ the power to the circuit in the event of an earth leakage fault. They will activate by switching the power ‘off,’ in the event of a high current fault, short circuit or overload, such as when too many appliances are plugged into a single power point, or when one of the appliances is faulty.
How does an RCD work?
An RCD constantly monitors the current flowing in both the ‘active’ and ‘neutral’ wires supplying a circuit or an item of equipment; which under normal circumstances should be an equal current flow in both wires. When an earth leakage occurs, it creates an imbalance, the RCD detects this and will automatically ‘cut off power’ before damage or injury transpires. RCDs must disconnect power supply (switch off) within 30 milli-seconds of leakage detection. RCD’s in Patient Protected Areas (such as hospitals) must ‘cut off power’ within 10 milliseconds of detecting a leakage.
“Even a 30mA of current could be enough to cause a person to go into cardiac arrest or cause irreversible damage to their body.”
Fixed RCDs can be identified by the ‘Test’ button. Portable RCD’s (plug into a socket outlet) and Socket Outlet RCD’s (incorporated into an outlet) also have a ‘Test’ button. If you can’t identify a ‘Test’ button, then it’s likely to not be an RCD.
Are RCDs compulsory? Do all circuits require RCDs?
All circuits rated 32A or less that are supplying socket outlets, lighting, hand held equipment or equipment that present as an increased risk of an electrical shock must be RCD protected (unless labelled otherwise for a specific item of equipment). All new circuit installations require RCDs to be installed, or when the circuit installations require additional protection (30 Amps +).
For Commercial and Industrial installations RCDs must be installed within a switchboard at which the final sub-circuit originates. This is a mandatory requirement of the AS/NZS 3000:2018 Wiring Rules Standard. Even though the standard calls for RCDs on all sub-circuits up to and including 32 Amps, exemptions apply. If a single item of electrical equipment (e.g. light) which isn’t RCD protected is to be replaced with an equivalent item within the same location, then the exemption may apply.
When switchboards are altered or replaced, RCDs are required for final sub-circuits. RCDs are also required to protect socket outlets when they’re added to an existing circuit. However, RCD protection only needs to be installed at the origin of the additional wiring. When all circuit protection within a switchboard is replaced, then additional RCD protection is required for the final sub-circuits supplied by that switchboard.
Looking to upgrade a switchboard? Call Prolux Electrical Contractors on 1800 800 880 and let us ensure your commercial and industrial buildings run safe and efficiently.