Most Brisbane homeowners know they’ve got “safety switches” on the switchboard, but far fewer can say exactly what’s protecting which circuit, or why a single fault sometimes kills power to half the house. The short answer is that older switchboards and current-standard switchboards handle this very differently – and the difference comes down to RCDs versus RCBOs.
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What a circuit breaker actually does
A standard circuit breaker protects wiring and equipment from overcurrent – too much current flowing for too long, usually from an overloaded circuit or a short. It trips on excess current, full stop. It does nothing to protect a person from electric shock, because a fault current small enough to pass through a human body is nowhere near large enough to trip a standard breaker.
What an RCD adds
A residual current device (RCD) – what most people mean by “safety switch” – monitors for current leaking to earth, the kind of leakage that happens when a person contacts a live part or an appliance develops an insulation fault. It trips in milliseconds on a leakage far too small to worry a circuit breaker, which is what makes it the device that actually prevents electrocution. Since 2021, the Queensland Electrical Safety Regulation has required RCD protection on all power and lighting circuits in homes – see our guide to safety switch requirements in Queensland for the detail on what’s mandatory and when.
The catch with older RCD setups
Many Brisbane switchboards installed or upgraded years ago meet the letter of the rule with just one or two RCDs shared across the whole board – one covering all power circuits, another covering all lighting. It’s compliant, but it means a single earth leakage fault anywhere in the house – a dodgy appliance, a nicked cable, a wet outdoor power point – trips every power circuit at once. Fridge, aircon, alarm system and every power point in the house go dead together, and finding which single circuit actually caused it means switching things back on one at a time until it trips again.
What an RCBO does differently
An RCBO (residual current circuit breaker with overcurrent protection) combines both jobs – overcurrent protection and earth leakage protection – in a single device, fitted per circuit rather than shared across several. That means:
- Only the faulty circuit trips, not the whole power or lighting group
- The fridge, security system and lighting in the rest of the house stay on
- Fault-finding is immediate – the tripped RCBO tells you exactly which circuit has the problem
- Nuisance trips from one appliance (a fridge compressor, an older aircon unit) don’t take out circuits that have nothing to do with it
This is why RCBOs are now the standard fitout on new switchboards and full switchboard upgrades across Brisbane, even though the older shared-RCD arrangement still technically complies with the regulation.
Should you upgrade?
If your switchboard still runs on one or two RCDs covering everything, it’s not a compliance problem – but it is a liveability and fault-finding problem, especially in a household with a home office, security system or medical equipment that can’t afford to drop out every time an unrelated appliance faults. It’s also worth checking if you’re adding a high-draw circuit such as an induction cooktop, EV charger or three-phase upgrade, since that’s the natural point to move to per-circuit RCBOs rather than adding more load onto a shared RCD. See our guide to switchboard upgrade costs and warning signs for what a full board replacement involves.
As a rough guide, retrofitting RCBOs circuit-by-circuit into an existing switchboard with room to spare typically starts from around $180-$280 per circuit, while a full switchboard replacement with RCBOs throughout – the more common approach when several circuits need it – usually runs from $1,800-$3,500+ depending on the number of circuits and board condition. We test every safety switch we install or work on – see our guide to RCD testing frequency for how often that should happen regardless of which type you have.
Get your switchboard checked
If you’re not sure whether your home has shared RCDs or per-circuit RCBOs, it’s a five-minute check for one of our licensed electricians next time we’re on site. See our electrical services or get in touch for a free switchboard assessment.
Related guides
- Switchboard upgrades in Brisbane: costs & warning signs
- Do I need a safety switch in Queensland?
- RCD safety switch testing in Brisbane
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