Look at a typical RCBO label and you may find 20A, 6kA and 30mA printed within a few centimetres of each other. All three are currents. None of them are interchangeable, and each answers a different question.
Amps โ what it carries
The plain amp rating is the continuous current the device is designed to carry in normal service. A 32A isolator switches and carries 32A indefinitely at its rated voltage and utilisation category.
This is the number that has to suit the circuit: cable size, load, and the protective device coordinating with both.
kA โ what it can interrupt
Kiloamps describe prospective short circuit breaking capacity: the largest fault current the device can interrupt safely without failing.
A 20A MCB rated 6kA carries 20A in service and can clear a 6,000A fault. Fit a 6kA device where the prospective fault current is higher and it may not clear the fault at all โ it can fail destructively instead.
Prospective fault current is highest close to the supply and falls with distance and impedance, which is why breaking capacity requirements are usually tighter at the main switchboard than at a distribution board.
You will also see devices marked with two figures, such as 6kA and 10kA. These typically relate to different test standards or application conditions โ check the manufacturer's data rather than assuming which applies.
mA โ what makes it trip on leakage
Milliamps on an RCD or RCBO are the residual current sensitivity: the earth leakage at which the device operates.
- 10mA โ high sensitivity, used for particularly high risk situations
- 30mA โ the standard for personal protection on socket outlets and lighting circuits
- 100mA and 300mA โ too coarse for personal protection; used for fire protection and equipment applications
A 30mA RCD does not trip at 30 amps. It trips at three hundredths of one amp of leakage to earth. That sensitivity is what makes it a life safety device.
Why this matters when searching a catalogue
Product titles routinely contain all three numbers. A search or filter that treats "6kA" as a current rating will file a 6kA breaker under 6 amps โ and someone specifying a 6A circuit would be shown a device rated for an entirely different duty.
Our catalogue filters are built to keep these separate. The Current Rating filter carries only genuine load ratings; breaking capacity and residual sensitivity are deliberately excluded, so filtering to 40A returns devices that carry 40A, not devices that mention 40 somewhere in their name.
The other figure worth checking: utilisation category
Isolators and switches carry a category such as AC-21, AC-22 or AC-23, describing what they can make and break rather than merely carry. AC-23 covers motor and highly inductive loads. A correctly sized AC-21 switch in front of a motor is still the wrong device, because inrush and inductive break duty are what the category addresses.
Quick reference
- A โ continuous current carried in service
- kA โ fault current the device can safely interrupt
- mA โ earth leakage at which an RCD operates
- AC-2x โ the type of load it can make and break
- V โ the system voltage it is rated for
You can filter by current rating and voltage directly in our catalogue. Heavy Current 63A and Above covers mains and submains switchgear; Single Phase 240V and Three Phase 415V split the range by supply.
This is general guidance only. Device selection, coordination and fault level assessment in Australia are governed by AS/NZS 3000 and related standards, and electrical work must be carried out by a licensed electrician. Always verify prospective fault current and device suitability against the standard and the manufacturer's documentation for the specific installation.