RCD, RCBO, MCB, MCCB and fuse in Australia
Common protective-device terms used in Australian testing, protection and switchboard schedules.
What The Device Terms Mean
RCD, RCBO, MCB, MCCB and fuse are protective-device terms used in Australian switchboard schedules, testing worksheets and protection review. They should not be collapsed into one generic label.
Each term points to a different function or product family. RCD and RCBO wording is often near residual-current testing. MCB, MCCB and fuse wording is often near overcurrent, short-circuit, breaking-capacity and I2t review.
Residual-Current And Overcurrent Functions
An RCD is residual-current protection. An RCBO combines residual-current protection with overcurrent protection in one device. MCB and MCCB wording belongs to circuit-breaker overcurrent and fault-current review. Fuse wording belongs to fuse protection and let-through context.
That difference matters because the value being reviewed changes: rated residual current in mA, measured trip time in ms, normal current rating in A, breaking capacity in kA, or let-through energy in A2s.
| Term | Main use | Do not confuse with |
|---|---|---|
| RCD | Residual-current protection and timed test rows. | Overcurrent protection rating by itself. |
| RCBO | Combined residual-current and overcurrent device context. | A generic safety-switch label without product data. |
| MCB | Miniature circuit breaker context for overcurrent and fault review. | RCD trip-time test rows. |
| MCCB | Moulded-case circuit breaker context, often with higher-current product data. | Generic MCB assumptions. |
| Fuse | Fuse protection, breaking capacity and let-through context. | Circuit-breaker curves or RCBO test data. |
Which Check Belongs To Which Device
| Task | Use | Keep visible |
|---|---|---|
| RCD or RCBO test-value comparison | RCD test checker and testing record fields. | Rated residual current, test value, criterion, circuit and device label. |
| Fault-current estimate | Short-circuit current calculator and fault-current chart. | Location, voltage basis, source impedance or transformer data. |
| Breaking-capacity comparison | PSCC and manufacturer device rating. | Device type, product label, kA rating and location. |
| Cable withstand check | I2t cable withstand calculator. | Fault current, clearing time, conductor data and k-value source. |
Safety Switch Wording
Australian public wording such as safety switch can help people recognise the topic, but technical review should still identify whether the installed device is an RCD, RCBO or another product. The public term is not a substitute for the device label or product data.
When fault current, I2t or RCD test values are involved, keep those checks separate. The same circuit may involve more than one protective-device question, and each one uses different inputs.
Next checks
- Use the protection device terms table to keep abbreviations clear.
- Use the RCD test checker for entered test values and criteria.
- Use short-circuit current and I2t calculators only when those protection checks are the actual task.
Boundaries
- This terminology page does not select a device.
- It does not provide test procedures or pass criteria.
- Current product data, standards context, site conditions and competent verification remain controlling inputs.