RCBO breaking capacity must be selected from the prospective short-circuit current at the installation point, the supply arrangement, the manufacturer’s test conditions and any approved backup or cascading arrangement. It is not the same as rated current and it cannot be chosen from the load nameplate alone. Obtain the calculated maximum fault current, verify the RCBO short-circuit capacity and confirm coordination with upstream protection before approval.
Decision table
| Selection input | Why it matters | Evidence |
|---|---|---|
| Prospective fault current | Sets required interruption duty | Fault study at the RCBO |
| Rated current | Protects the circuit in normal service | Cable schedule and load calculation |
| Backup combination | May affect declared short-circuit capability | Exact manufacturer table |
| Source mode | Fault level can change with generator or transfer | All operating-mode calculations |
Use the table as a screening aid, then verify each row against the exact product documentation and project study. The parent circuit-breaker guide gives broader context, while rccb selectivity coordination and rccb sensitivity 30ma 100ma 300ma cover related RCCB selection questions.
Separate rated current from fault duty
Rated current protects the circuit in normal service; breaking capacity addresses whether the device can interrupt the prospective fault current under its declared test conditions. Identify the highest and lowest fault levels at the RCBO, including utility, generator and transfer modes. Check the device marking, manufacturer table and the applicable standard scope. Do not silently substitute a higher-current device if the cable, enclosure or coordination study has not been reviewed.
Check the complete protection chain
Compare the RCBO with upstream fuses, breakers, busbars and conductors. If a manufacturer declares a backup or cascading combination, record the exact model codes, ratings and conditions. A nominal “10 kA” statement without the installation voltage, pole arrangement and tested combination is incomplete evidence. Confirm terminal withstand, enclosure short-circuit rating and the project fault study.
Record the approval boundary
At handover, retain the fault-current calculation, exact RCBO code, breaking-capacity evidence, coordination table, settings and commissioning result. Recheck after a transformer, generator, cable, busbar or source change.
Start with the installation duty
An RCBO combines residual-current protection with an overcurrent function, but the two functions still have different design questions. State the system voltage and frequency, phase and neutral arrangement, rated current, prospective fault current, earthing system, residual-current objective, required disconnection time, enclosure and operating mode. The exact catalog code, poles, curve, residual-current type, accessories and terminal arrangement then become part of the approval record.
Do not choose from a photograph or a short product label alone. Keep the single-line diagram, cable schedule, fault study, device coordination information, manufacturer instructions and commissioning record together. If the offered product differs from the study, treat the quotation as conditional until the responsible engineer reviews the change.
Use evidence and an RFQ checklist
Ask for the complete model code, rated current, voltage, short-circuit capacity, trip curve, residual-current sensitivity and type, pole arrangement, neutral treatment, line/load markings, terminal torque, accessories and test method. Ask which claims are tested for the exact combination and which depend on installation conditions. Record the datasheet revision with the purchase order.
IEC 61009-1:2024 gives general requirements and tests for RCBOs within its stated scope. HSE electrical-safety guidance reinforces competent work and safe isolation. These references do not approve a particular SUTON model or project; apply the adopted standard and manufacturer instructions.
Commission and preserve the as-left state
Before energization, verify identity, terminals, conductor routing, neutral path, barriers, labels, settings, test-button operation and isolation boundaries. Record the instrument, method, operating mode, measured result and drawing revision. A test button exercises a defined internal circuit; it does not replace inspection, insulation testing, fault verification or safe isolation.
After a load, cable, source, setting, firmware or accessory change, repeat the relevant review. Keep normal, standby, transfer, generator, bypass and maintenance modes visible. If evidence is missing, mark the item conditional and obtain engineering approval instead of assuming a similar-looking RCBO has the same behavior.
Review the circuit before accepting a quotation
List each outgoing circuit, its conductor size and length, protective-earth arrangement, connected load, expected inrush and maximum fault current. Identify whether the circuit is single phase or three phase, whether the neutral is distributed, and whether the panel includes a busbar, comb connection or flexible link. These details affect the physical installation as well as electrical performance. Ask the supplier to state compatible terminal sizes, tightening torque, stripping length, accessory positions and enclosure conditions rather than relying on a generic catalogue image.
For a new panel, compare the RCBO schedule with the schematic, panel layout and cable schedule line by line. For a replacement, save a before snapshot of the existing device, model code, terminal positions, settings and date. A change that appears small—such as moving a feed to another busbar position or adding an auxiliary contact—can change the isolation boundary, neutral route or available fault duty. Record the reason for the change and the person who approved it.
Use controlled tests and clear acceptance criteria
Define the acceptance test before energization: visual inspection, conductor identification, connection check, protective-conductor continuity, insulation or leakage test where applicable, residual-current test, overcurrent function test where specified, and verification of labels and barriers. State which values come from the product manual, which come from the project calculation and which come from the local installation rules. A test result without its method and instrument range is difficult to audit.
When a test fails, keep the failure visible and investigate one variable at a time. Do not change the device type, setting, wiring and load simultaneously. Check whether the device is the quoted code, whether the neutral is routed through the intended sensor, whether the incoming and outgoing terminals match the diagram, and whether the source is in the expected mode. If the corrective action changes a drawing or setting, issue a revised document and repeat the affected tests.
Keep maintenance information usable
At handover, give the owner the final model code, rating, curve or characteristic, residual-current type and sensitivity, breaking capacity, pole arrangement, terminal diagram, accessory list, test result, drawing revision and maintenance limitations. Label the device and its circuit so a future technician can identify the isolation point without guessing. Where the device is part of a selective or backup arrangement, keep the coordination table with the panel record.
Reassess the selection after a transformer, generator, inverter, charger, motor drive, cable route, firmware, enclosure or source change. Also reassess after a repeated trip, unexplained test failure or a change in the local rules. A new device with a similar front label may have different sensing, switching, electronic supply or short-circuit behavior. Treat the replacement as a new technical decision until the evidence shows otherwise.
Supplier questions that close common gaps
- What exact model code and option package is being offered?
- Which terminals are line, load and neutral, and is reverse feed permitted?
- What residual-current type, sensitivity and delay are declared?
- What rated current and short-circuit capacity apply at the project voltage?
- Which backup, cascading or selectivity tables cover the proposed combination?
- What test method and instrument limits are required at commissioning?
- Which ambient, enclosure, busbar and accessory restrictions apply?
- What document revision should be retained with the purchase order?
Keep the acceptance record readable for procurement, commissioning and maintenance teams. If a value is conditional on a source, cable, enclosure or accessory, write that condition beside the value. A clear limitation is safer than a blank field that later appears to be approval.
For fault-duty decisions, keep both the maximum and minimum calculated values and state the calculation date. For wiring decisions, keep the terminal diagram and a photo of the completed panel where site rules permit. For testing decisions, retain the instrument identity and the exact procedure used.
Review the record whenever site conditions or equipment change, and date the review for traceability now.
Keep the final approval with the panel documents so future inspections can confirm the same assumptions, terminals, settings and test boundaries.
Product and related resources
Use the SUTON RCBO product page as a quotation starting point. The circuit-breaker types guide is the parent overview; the related guides below cover adjacent selection decisions.
Educational video
This neutral electrical-safety lesson provides background on residual-current protection. It does not replace the project calculation, product manual or safe-work procedure.
Watch the residual-current safety lesson on YouTube.
Frequently asked questions
Is breaking capacity the same as RCBO rated current?
No. Rated current is a continuous load value; breaking capacity is the declared fault-interruption capability under specified conditions.
Can I use a higher breaking-capacity RCBO without review?
Only after confirming current rating, cable protection, dimensions, terminals, coordination and the approved installation design.
Does a backup fuse automatically increase breaking capacity?
No. A backup or cascading claim requires the exact tested combination and conditions from the manufacturer.