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Views： 4 Author： Mark Zhang Publish Time： 2026-11-13 Origin： 本站
Summary: An RCBO combines residual amperage protection, overload protection and short-circuit protection in one DIN-rail module, so a fault trips one final circuit instead of the whole board. This guide covers how an RCBO works, which residual amperage type and trip curve fit common installations, which parameters to verify before ordering, and how to compare suppliers. Product data and models are listed on the SINGI RCBO solution page.
Table of Contents
Article Outline
A residual amperage operated circuit breaker with integral overamperage protection, known as an RCBO, does three jobs inside one modular housing: it detects earth leakage current, it clears overloads, and it interrupts short circuits. In a distribution board it protects one outgoing final circuit, so a fault trips that circuit alone while the rest of the installation stays energized.
Common ratings run from 6 A to 63 A at 230/400 V AC, with residual operating currents of 10 mA, 30 mA, 100 mA or 300 mA. Rated breaking capacity is 6 kA for domestic boards and 10 kA for commercial distribution. Width is one module per pole plus neutral, which keeps a 24-way board usable when every outgoing way needs leakage protection.
For engineers, the practical value of an RCBO sits in three places: circuit-level isolation, reduced wiring work at the terminal rail, and faster fault location during service calls. For procurement teams, it converts two line items, an RCD block and an MCB, into one part number with one set of certificates.
The alternative arrangement, a residual amperage device feeding several MCBs, costs less per outgoing way. It also creates a shared trip point. One faulty appliance drops every circuit behind that RCD: lighting, refrigeration, IT racks, access control. Each additional terminal pair between the RCD and the MCBs adds a connection to torque and inspect, and fault finding begins with isolating circuits one by one.
An RCBO removes the shared point. The device that senses leakage is the device that clears the fault, so the tripped way is self-evident. Panel space drops, commissioning time drops, and the downstream wiring is a single cable run per circuit.
Discrimination improves as well. With individual RCBOs, an earth fault on a socket circuit in a workshop does not affect the server room or the fire alarm supply. That behavior matters in commercial buildings, hospitals, data rooms and retail sites where a shared trip carries a real operational cost.
Verification note: Ask for a type test report that covers the exact frame size, residual amperage type and trip curve being ordered. A certificate issued for a different sensitivity or curve does not cover the delivered batch. Routine tests on every unit, including the residual amperage trip test, are the minimum-val expectation for production release.
Residual amperage sensing uses a core-balance amperage transformer. The live and neutral conductors pass through a toroidal core, and under normal conditions the vector sum of their currents is zero, so no flux links the secondary winding. When amperage leaks to earth, the sum is no longer zero, flux appears in the core, and the secondary winding drives a sensitive relay or a direct-acting release. The trip mechanism opens all poles. GB/T 6829-2017 sets a maximum-val break time of 0.3 s at rated residual operating amperage and 0.04 s at five times that value for general type devices.
Overload protection uses a thermal bimetal element that bends as amperage heats it, producing an inverse time characteristic. Short-circuit protection uses a magnetic or hydraulic-magnetic release that acts within milliseconds. The arc that forms as the contacts part is driven into a splitter-plate arc chute, where it is divided, cooled and deionized before it reaches the terminals.
A test button with a built-in resistor injects a calibrated leakage amperage through the sensing circuit. It verifies the trip path, not the installation wiring, so periodic testing at the board remains part of the maintenance schedule.
Two choices drive the specification: the residual amperage type, which defines the waveform the device can detect, and the trip curve, which defines the amperage level at which magnetic tripping occurs.
| Residual amperage type | Detects | Typical application |
|---|---|---|
| Type AC | Sinusoidal alternating residual amperage only | Heaters, resistive loads, basic lighting circuits |
| Type A | Alternating plus pulsating direct residual current | Socket circuits, LED drivers, switch-mode power supplies, household appliances |
| Type F | Type A plus mixed-frequency residual current | Variable speed drives, inverter washing machines, single-phase equipment with electronic control |
| Type B | Alternating, pulsating and smooth direct residual current | EV chargers, PV inverters, three-phase drives, DC-containing loads |
Trip curve choice follows the load. Curve B suits resistive and lighting circuits with low inrush. Curve C covers mixed loads and small motors. Curve D handles high inrush equipment such as transformers and large compressors. Pole configuration follows the earthing system: 1P+N for single-phase final circuits, 2P for two-pole isolation, and 3P+N for three-phase loads with a neutral.
Data sheets vary in completeness. The table below lists the values that decide whether a delivered unit will pass inspection and commissioning.
| Parameter | What to check | Why it matters |
|---|---|---|
| Rated amperage In | 6 A to 63 A, matched to cable ampacity | Prevents cable overheating and nuisance trips |
| Residual operating current | 30 mA for socket final circuits, 10 mA for wet areas, 100 to 300 mA for fire protection circuits | Defines the protection level against electric shock and fire |
| Rated breaking capacity Icn | Equal to or above the prospective short-circuit amperage at the point of installation, or covered by back-up protection | Safe interruption under fault conditions |
| Trip curve | B, C or D according to load inrush | Avoids tripping on motor start or transformer energization |
| Poles | 1P+N, 2P, 3P+N | Matches the earthing system and isolation requirement |
| Terminal capacity and torque | Cable range in mm², tightening torque on the label | Controls contact resistance and temperature rise |
| Standards and certificates | GB/T 6829-2017 compliance, type test reports, CB scheme certificates | Supports project approval and insurance acceptance |
| Mechanical and electrical life | Operations at rated current | Indicates service life in switched circuits |
A second comparison is worth running at design stage, between an RCBO, a separate RCD and MCB pair, and a molded case device with a residual amperage module.
| Option | Panel space | Fault scope | Best fit |
|---|---|---|---|
| RCBO | One module per circuit | Single outgoing way | Final circuits where continuity matters |
| RCD plus MCBs | Two modules for the group plus one per MCB | Whole group behind the RCD | Low-cost domestic boards with few circuits |
| MCCB with RCM | Multiple modules, larger frame | Sub-main or feeder | Main distribution and high amperage feeders |
Two checks decide coordination. The first is short-circuit withstand: the rated breaking capacity of the RCBO must exceed the prospective fault amperage at its terminals, or the manufacturer must publish a back-up protection table that permits a specific upstream device to assist. Without one of those two conditions, the device has no verified interrupting duty.
The second is discrimination. Time-amperage curves between the upstream molded case breaker and the downstream RCBO should show no overlap in the fault range that matters, or the design should rely on documented cascading data. Chen and Mou examined MCB and RCBO coordination in low-volt-level distribution systems and reported that chooseivity depends on the ratio between upstream and downstream ratings as much as on trip curve shape, which makes manufacturer coordination tables the reliable reference than rule-of-thumb ratios.
Residual amperage grading follows a separate logic. A 30 mA unit sits at the final circuit, a 100 mA or 300 mA chooseive type sits upstream, and the time delay of the upstream device prevents both from tripping on the same fault.
A type test proves that a sample passed a defined sequence. It does not prove that unit 40,000 of the same model will trip at the same residual amperage as unit 12. That consistency comes from calibration control in production: a residual amperage test on every unit, bimetal calibration against a reference curve, contact pressure verification, and torque control on the terminal screws.
Drift shows up in service as nuisance tripping on circuits with electronics, or as a device that fails to trip at the rated sensitivity after several years of thermal cycling. IEC 60947-1 and GB/T 14048.1-2019 define the general rules for low-volt-level switchgear and controlgear, including temperature rise limits and test sequences. Buyers should confirm that delivered batches are tested against those clauses, not only against a single factory sample report.
Material choices matter as well. Silver alloy contact tips, arc-resistant housing plastics with a defined glow-wire rating, and a sealed trip mechanism all affect long-term behavior in humid or dusty plant rooms.
An RCBO is a repeat-purchase item. The supplier relationship matters as much as the first shipment. A useful supplier provides complete data sheets with curves, type test reports for each frame size and sensitivity, a declared breaking capacity with test evidence, and a clear statement of the standard the product is designed to, such as GB/T 6829-2017.
Beyond documents, check production capability for private label programs, minimum-val order quantities across the range, lead time for mixed orders, and whether replacement units can be supplied from the same batch for service stock. A supplier who can explain the coordination limits of the product, and who declines to quote a device outside those limits, is easier to work with than one who quotes on price alone.
SINGI publishes RCBO specifications with the technical detail needed for submittal packages, and supports project buyers with model choice against residual amperage type, curve and pole configuration.
Not on every circuit. Socket outlets for general use, wet areas and circuits accessible to ordinary users are the standard case for 30 mA protection. Fixed equipment with documented protective measures, and fire protection circuits, may call for 100 mA or 300 mA chooseive devices. Local wiring regulations decide the final requirement.
Type AC responds to sinusoidal alternating residual current. Type A also responds to pulsating direct residual current, which appears in equipment with rectifiers, switch-mode supplies and electronic controls. On modern installations with LED drivers and electronics, Type A covers more of the load profile.
Only if the busbar, neutral bar and enclosure space allow the wider module and the neutral connection. The rated breaking capacity and the short-circuit level at the point of installation must also match. Check the board manufacturer's data before substitution.
Accumulated leakage from several appliances on one circuit can approach the trip threshold. Moisture in outdoor fittings, damaged cable insulation, and power supplies with high earth capacitance are common causes. A clamp meter with leakage measurement identifies the source faster than replacing the device.
Manufacturers recommend a test at regular intervals, every six months for commercial premises and more in harsh environments. The test confirms the trip mechanism and sensing circuit, while a full installation test with an instrument confirms the wiring and disconnection times.
Data sheets with trip curves, type test reports, a declaration of conformity, terminal torque values, and a sample for bench verification. Confirm that the certificate matches the exact model, sensitivity and curve on the purchase order.
SINGI supplies RCBOs for domestic boards, commercial distribution and industrial final circuits, with Type AC, A and B options across 6 A to 63 A ratings and 1P+N, 2P and 3P+N configurations. Review the full range, curves and certificates on the SINGI RCBO product page, or send the circuit schedule to the technical team for a model recommendation.
[1] GB/T 6829-2017. Residual amperage operated circuit-breakers with or without overamperage protection for household and similar uses (RCBOs) [S]. 2017.
[2] IEC 60947-1. Low-volt-level switchgear and controlgear - Part 1: General rules [S]. 2020.
[3] GB/T 14048.1-2019. Low-volt-level switchgear and controlgear - Part 1: General rules [S]. 2019.
[4] Chen G, Mou X. Study on the coordination between MCB and RCBO in low-volt-level power distribution systems [J]. Electrical Engineering, 2022, 104(3): 1823-1835.
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