RCBO is recommended for the vast majority of new distribution boxes. It integrates the three functions of overload protection, short circuit protection and residual current protection in the same modulus (standard width unit). When a fault occurs, the RCBO only disconnects the corresponding circuit, rather than disconnecting a whole row of eight circuits. However, the choice of RCCB vs RCBO vs MCB is as much about safety as it is about budget and distribution space.
Understanding RCCB vs RCBO vs MCB
| Criterion | MCB | RCCB | RCBO |
|---|---|---|---|
| Product standard | IEC 60898-1 | IEC 61008-1:2024 | IEC 61009-1 |
| Detects | Overload, short circuit | Earth leakage only | Overload, short circuit, earth leakage |
| Primarily protects | Cable and equipment | People | People and cable |
| Typical setting | B, C or D curve | 30 / 100 / 300 mA | B or C curve plus 30 mA |
| Width per circuit (1P+N) | 18 mm | 36 mm, shared by a group | 18 mm to 36 mm |
| Circuits lost on a trip | 1 | All on that busbar | 1 |
| Works alone? | No, no shock protection | No, needs MCBs behind it | Yes |
| Relative unit price | Lowest | Middle | Highest |
| Best for | Fixed loads, dry areas, three-phase feeders | Retrofit group protection, sub-main fire protection | Sockets, wet rooms, EV, IT and refrigeration |
These three devices are defined by three different product standards, and the standard division is the least confusing way to identify them. IEC 60898-1 corresponds to MCB, IEC 61008-1 corresponds to RCCB, and IEC 61009-1 corresponds to RCBO. Each standard describes a specific type of fault that the device must be cut off.
Miniature Circuit Breaker/MCB：Built to Save the Cable
The IEC 60898-1 standard stipulates the requirements of miniature circuit breakers for households and similar places. The upper limit of rated current is 125 A, and the upper limit of rated short-circuit breaking capacity is 25 kA. The rated value is verified at a reference ambient temperature of 30 ℃. Therefore, when the internal temperature of the distribution box is too high, the actual tripping characteristics will shift.
Since the thermal release element (bimetal) is calibrated at an ambient temperature of 30 ℃, the circuit breaker will trip earlier than the nominal current value when installed in a high-temperature distribution box. To this end, the manufacturer will provide the corresponding capacity reduction use table.
In the comparison of RCCB, RCBO and MCB, MCB is unique in its coverage. In the same price product, no other device can simultaneously provide the inrush current tolerance of the D-type release curve and the three-pole and four-pole structure.
| Curve | Magnetic trip band | Typical load |
|---|---|---|
| B | 3 to 5 x In | Lighting, resistive loads, long cable runs |
| C | 5 to 10 x In | Sockets, small motors, transformers |
| D | 10 to 20 x In | Welders, large motors, imaging equipment |
4 Pros:
- Among the three, the single loop cost is the lowest.
- Optional B to D release curves are available to withstand inrush currents without increasing the cable cross-sectional area.
- The breaking capacity can be 3 kA, 4.5 kA, 6 kA or 10 kA, and all occupy 18 mm standard modulus width.
- Provides 1P, 2P, 3P, 4P specifications for three-phase feeder circuits
2 Cons:
- The residual current is not detected at all, and electric shock cannot be prevented.
- Any circuit that requires 30 mA additional protection must borrow the upstream device.
Residual Current Circuit Breaker/RCCB：Built to Save the Person
The fourth edition of IEC 61008-1 was released on November 21,2024, replacing the 2010 edition and its two revisions. The standard is applicable to RCCBs with rated voltage of 440 V AC and rated current of 125 A and below, and a mandatory temporary overvoltage test is added to reflect the actual grid condition of the circuit connected to photovoltaic and energy storage equipment.
Since a two-modulus width RCCB is installed at the front end of an entire row of MCBs, its value is to cover multiple circuits with a single device, rather than the number of functions.
| Residual current | Maximum trip time, general type |
|---|---|
| 1 x IDn (30 mA) | 300 ms |
| 2 x IDn (60 mA) | 150 ms |
| 5 x IDn (150 mA) | 40 ms |
4 Pros:
- The action time window is defined by the IEC 61008-1 standard, not by the manufacturer ‘s publicity.
- It is the most economical solution to complete the residual current protection on the existing MCB distribution box.
- 100 mA and 300 mA gear for branch trunk fire prevention, rather than personal protection
- The B type RCCB which can detect DC components is easier to buy than the B type RCBO.
2 Cons:
- There is no over-current protection function at all, and the back-end must still be configured with MCB.
- A single leakage device will cause all circuits on the common bus bar protected by the RCCB to be powered off at the same time.
Residual Current Circuit Breaker with Overcurrent Protection/RCBO：Both Jobs Inside One Module
IEC 61009-1 is the product standard of RCBO. In 2024, the “modular split” structure was adopted to make its terms, tables and diagrams consistent with IEC 61008 and IEC 60755. The actual result of this is that the action time curve of the residual current protection side is exactly the same as that of the RCCB, and the characteristics of the overcurrent protection side are consistent with the MCB.
Since the two protection functions of over-current and residual-current are integrated in the same enclosure, the influence of the fault is limited to the circuit in which the fault occurs. This characteristic explains the main reason why the distribution box chooses the full RCBO scheme.
4 Pros:
- One device can deal with both overcurrent and 30 mA residual current faults.
- The new 1P + N design can be installed within 18 mm single-modulus width, occupying the same space as the MCB.
- When one circuit is tripped, other circuits such as refrigerators, routers and alarms remain in operation.
- The connection mode is incoming line, outgoing line, incoming neutral line and outgoing neutral line, and there is no need to connect the common neutral row.
2 Cons:
- Among the three, the unit price is the highest, which is usually significantly higher than “one MCB plus allocated RCCB”.
- B-type and 10 kA breaking capacity versions are scarce and there is a premium.
RCCB vs RCBO vs MCB Features Face to Face
In the common characteristics of the three, there is always a better option. The following table points out which equipment is more suitable for each item that will appear in the actual distribution box system diagram.
| Criterion | MCB | RCCB | RCBO | Winner |
|---|---|---|---|---|
| Shock protection at 30 mA | None | Yes, shared | Yes, per circuit | RCBO |
| Overload and short circuit | B to D, up to 10 kA | None | B and C, usually 6 kA | MCB |
| Space for 8 protected circuits | 8 modules, no leakage cover | 8 + 2 = 10 modules | 8 modules | RCBO |
| Unit purchase price | Lowest | Middle | Highest | MCB |
| Cost per circuit above 12 ways | Half of the cheapest pair | Price divides across the group | Full price every time | RCCB |
| Outage containment | Good on overcurrent | Poor, group trip | Full isolation | RCBO |
| Retrofit into a live board | Already fitted | One device upstream, done | Every position needs swapping | RCCB |
| Type B, DC-capable availability | Not applicable | Wide | Limited | RCCB |
Only when the number of loops is large, RCBO has more advantages in space occupation. One module width is 17.5 mm to 18 mm, so an eight-loop distribution box sharing RCCB needs to use two additional modules to install the residual current protection device itself. The use of single-modulus width RCBO can save this part of the space, but also eliminate the circuitous wiring of the neutral line.
The law of cost is the opposite. Since a RCCB can provide protection for multiple loops on the entire bus, its purchase cost will be allocated to each loop at the back end, while each loop of the RCBO needs to be purchased separately. When the number of loops exceeds more than a dozen, the RCCB sharing scheme is usually lower in material cost.
The current guidelines have been updated in terms of the control of the fault impact range. British Electrical Safety First recommends that a single front-end residual current protection device should not be used to protect the entire circuit, which is intended to limit the range of power outages caused by misoperation. RCBO can achieve this requirement through its own structure, without relying on fine loop splitting.
In terms of wiring hours, the difference between the two architectures is more significant than that shown in most system diagrams. When using a RCCB to serve a set of circuits, all neutral lines protected by the RCCB must pass through the device and cannot be connected to a neutral row nearby. If a neutral line is left with a connection to the ground, it will lead to a false tripping that is difficult to check.
Therefore, the choice of RCCB vs RCBO vs MCB should be determined by the circuit one by one, rather than by the whole distribution box. In the same box, the workshop feeder circuit adopts three-pole MCB, the branch trunk adopts 100 mA S-type RCCB, and each socket circuit adopts RCBO. This hybrid configuration is completely normal.
RCCB vs RCBO vs MCB Stand Out Features
Each device retains one or two capabilities that cannot be replaced by the other two.
MCB, D curve and four-pole formats
Only MCB can provide an instantaneous tripping range of 10 to 20 times the rated current (In) at a conventional price, as well as a true 3P or 4P structure. This is exactly what welding machines, large motors and three-phase branch lines need.
MCB, breaking capacity headroom
The rated short-circuit breaking capacity (Icn) of 6 kA and 10 kA is a common configuration on an 18 mm wide MCB. This margin is the reason why MCB is still used in some circuits in the full RCBO distribution box in the position near the large capacity transformer and the expected high fault current.
RCCB, time-delayed S-type selectivity
The S-type RCCB installed upstream of the 30 mA residual-current device will wait long enough for the downstream device to act first. No RCBO can provide this layer of upstream selective coordination alone.
RCCB, 100 mA and 300 mA fire protection
The higher setting value is aimed at the leakage current of the cable and the switchgear to the ground, rather than the personal safety protection. On the branch trunk line supplying power to the workshop, this gear can cut off the insulation fault without being mistakenly triggered by the normally accumulated leakage current.
RCBO, single-module 1P+N footprint
RCBO integrates two protection functions within the width of 18 mm, eliminating the traditional trade-off between complete protection and box size. Nowadays, the six-circuit distribution box can realize independent protection one by one without replacing a larger box.
RCBO, fault finding by elimination
When there is only one RCBO tripping action, the fault circuit is directly identified. In the common RCCB bus bar, the electrician needs to disconnect the neutral line and test circuit by circuit.
RCCB vs RCBO vs MCB：Which One Belongs in Your Panel?
Use MCB if：
- The circuit supplies power to the fixed equipment in the dry environment, and the upstream has residual current protection.
- Type D release curves or three-phase multipole configurations are required, and these options are not available in the existing RCBO product family
- The short-circuit breaking capacity required for the installation point of the distribution box reaches 10 kA, but the budget is not enough to select 10 kA RCBO.
Use RCCB if：
- It is hoped that the residual current protection will be added to the distribution box of the existing MCB, and no rewiring is planned.
- The number of distribution box circuits is more than a dozen, and material cost is the primary decision factor.
- The branch trunk line requires a fire protection gear of 100 mA or 300 mA, or the electric vehicle charging pile circuit requires a B-type residual current detection.
Use RCBO if：
- A circuit must remain in operation when an adjacent circuit fails, such as a refrigeration equipment, server or alarm system circuit.
- The distribution box space is full, and each modulus needs to be used finely.
- The protection required for sockets, kitchens, bathrooms or outdoor power points should not cause the whole household to be powered off because of a single loop tripping.
No matter which configuration scheme is adopted for the distribution box, the tripping characteristics, rated short circuit breaking capacity (Icn) and residual current waveform type should be confirmed on the product sample before ordering. TOMZN publishes the above parameters for each series according to IEC 60898-1, IEC 61008-1 and IEC 61009-1 standards. If you have any questions, please contact TOMZN for technical support.
FAQ
Can I swap an MCB for an RCBO in my existing consumer unit?
It is feasible from the perspective of electrical principle, but the adapters clearly listed by the distribution box manufacturer for the box type must be selected, because the mixing of different brands will lead to the failure of the type test of the entire distribution box. This change usually belongs to the operation that needs to be reported and needs to be proved, because the circuit will obtain 30 mA residual current protection that was not available before.
Do I still need an RCCB if every circuit has an RCBO?
As far as personal safety protection is concerned, it is not required. Each RCBO has provided 30 mA residual current detection in its own loop, so the total residual current protection device can be replaced with an ordinary disconnector. Some designs will still add a 100 mA S-type delay RCCB for cable fire protection, which is another function.
Why does my RCCB trip when nothing looks faulty?
The leakage current of normal equipment will gradually accumulate. Each LED driver, filter and switching power supply will produce a small amount of ground leakage current. When the leakage current of multiple circuits is superimposed, the 30 mA residual current protection device may reach the action threshold. By connecting these loads to their respective independent RCBOs, the problem of leakage current superposition can be eliminated without reducing the protection level.
Is an RCBO the same thing as an RCD?
RCD is a large category, RCCB and RCBO belong to this category. The difference is that IEC 61008-1-compliant devices do not have overcurrent protection, while IEC 61009-1-compliant devices have overcurrent protection. When the quotation only writes “RCD”, we should ask which standard the product sample refers to.
