Choosing between a 30 mA, 100 mA and 300 mA RCCB is not a matter of picking a ‘better’ sensitivity. The residual-current rating defines the leakage level at which the device is designed to operate, so each value serves a different protection objective within a coordinated electrical installation.
In many installations, 30 mA devices are used where additional protection against electric shock is required. Higher sensitivities such as 100 mA or 300 mA may be used for upstream residual protection or fire-risk reduction where the design and applicable rules permit. The correct choice still depends on the earthing arrangement, circuit purpose, normal standing leakage, time characteristic and the required discrimination between upstream and downstream devices.
This guide explains how to compare RCCB sensitivity without treating the milliampere value as a quality grade. It is intended for electrical designers, contractors and safety reviewers who need a selection that can be documented, tested and understood later.
Direct answer
A 30 mA RCCB is commonly associated with additional shock protection on selected final circuits. A 100 mA or 300 mA RCCB may be used further upstream for coordinated residual protection or fire-risk reduction where the project design and local requirements allow. Do not increase sensitivity simply to stop nuisance tripping; first measure standing leakage, review circuit subdivision and confirm manufacturer coordination data.
Quick comparison
| Rated residual current | Common design role | Main caution |
| 30 mA | Additional protection for selected final circuits | Standing leakage can cause unwanted operation |
| 100 mA | Upstream or equipment protection in a coordinated design | Does not replace required 30 mA protection |
| 300 mA | Fire-risk reduction or upstream residual protection | Not intended as additional shock protection |
Why RCCB sensitivity is not a quality grade
A lower rated residual current means the RCCB responds at a lower leakage level. It does not mean the device is universally safer or more suitable for every location. A distribution system can require different residual-current levels at different points because the protection objective changes from final-circuit additional protection to upstream coordination.
Treat the milliampere value as a design input. The specification must also define the waveform type, pole arrangement, time characteristic, rated current, upstream overcurrent protection and the test method. These choices work together; selecting only by 30 mA, 100 mA or 300 mA can create a false sense of completeness.
30 mA RCCB: where the lower sensitivity is used
30 mA is identified as a common design value where additional protection against electric shock is required. That makes it relevant to selected final circuits, but the final requirement still depends on the circuit type, location, earthing arrangement and applicable regulation.
The main design caution is cumulative leakage. Electronic power supplies, filters, long cables and surge protective devices can all contribute normal protective-conductor current. If many healthy loads share one 30 mA RCCB, their standing leakage can add together and cause unwanted operation. Better circuit subdivision is usually a more defensible response than raising the RCCB sensitivity without analysis.
100 mA RCCB: a coordinated upstream role
A 100 mA RCCB can serve an upstream or equipment-protection role in a coordinated design. It should not be treated as a substitute where 30 mA additional protection is required. The reason for choosing 100 mA must be stated in the protection design rather than inferred from convenience or device availability.
Where a 100 mA device sits upstream of lower-sensitivity protection, check whether the arrangement provides the intended discrimination. The residual-current rating alone does not prove selectivity. Time delay, device characteristics and manufacturer coordination information also matter.
300 mA RCCB: upstream residual and fire-risk functions
The source guidance associates 300 mA devices with upstream residual protection or fire-risk reduction where the design permits. This role is different from additional shock protection. A 300 mA RCCB should therefore not be presented as an alternative to a 30 mA device where lower-sensitivity additional protection is required.
For an upstream RCCB, the project should verify both sensitivity and time characteristic. Installing a 300 mA device upstream and a 30 mA device downstream does not automatically guarantee discrimination. Use the manufacturer’s coordination data and document the protection sequence.
How normal leakage changes the selection
Normal leakage is one of the most important reasons an apparently suitable RCCB can trip in service. Before choosing the sensitivity, list the connected electronic equipment, drives, filters, heating controls and equipment with DC links. Record the expected standing leakage and the protective-conductor current under representative operating conditions.
Several individually healthy loads can produce enough combined leakage to make one shared RCCB inconvenient. Separating circuits can improve fault localisation as well as reduce unnecessary loss of supply. Neutral conductors must also remain with their intended residual-current device; a borrowed or combined neutral can cause incorrect operation even when the RCCB itself is sound.
How to build discrimination between RCCBs
Discrimination means a downstream residual-current fault should preferably be cleared by the downstream device without the upstream device operating first. Achieving that outcome may require both a higher residual-current rating upstream and a selective time-delayed characteristic.
Do not rely on a simple ratio such as 300 mA upstream and 30 mA downstream as proof. Check the current BCH RCCB product range and the manufacturer coordination data for the exact devices before approving the arrangement.
A practical RCCB selection workflow
- Define the circuit purpose, connected load and required continuity of service.
- Record supply voltage, phase arrangement and earthing system.
- Identify where additional shock protection, upstream residual protection or fire-risk reduction is required.
- Measure or estimate normal standing leakage for the connected equipment.
- Choose the residual-current waveform type, sensitivity and time characteristic for a stated reason.
- Verify RCCB rated current and the associated overcurrent or short-circuit protection.
- Check upstream/downstream discrimination using manufacturer data.
- Review neutral segregation, pole arrangement and board space.
- Confirm the test procedure before energisation.
- Save the selected values, catalogue reference and test result in the panel record.
Worked application scenario
Consider a building with socket circuits, fixed equipment and an upstream distribution section where discrimination matters. Start with a one-page installation record: circuit purpose, connected equipment, normal current, expected leakage, supply details and the operational consequence of a trip.
Next compare the proposed RCCBs against four questions: Will each device remain stable during normal leakage? Will the downstream device operate before the upstream device for a downstream residual fault? Does the installation still have suitable overcurrent protection? Can the arrangement be tested and maintained without mixing neutrals or obscuring the fault location?
If one answer is uncertain, do not solve the problem by selecting a higher milliampere value automatically. The better correction may be circuit subdivision, different device characteristics, a change in wiring architecture or a verified selective arrangement.
Installation and commissioning checks
Good selection can be undone by poor installation. Confirm conductor sizes, terminal preparation, tightening requirements, protective-earth continuity and neutral routing against the approved drawing. The practical RCCB wiring guidelines are a useful companion when checking neutral segregation and connection discipline during installation.
Energised testing should be carried out by competent personnel using suitable instruments and protection. Record measured values under representative load, not only at no load. If nuisance tripping occurs, isolate circuits systematically and investigate cumulative leakage, moisture, damaged insulation, neutral-earth faults, shared neutrals and wiring errors before changing the protection level.
Using BCH product data in the application review
BCH’s RCCB product family and power-control portfolio give designers a direct path from application review to current product information. For a project specification, use the exact published device data for sensitivity, pole arrangement, rated current, coordination and test requirements rather than relying on a generic rating.
The useful value here is not a generic ‘best RCCB’ claim. It is the ability to connect the design requirement—sensitivity, pole arrangement, rated current, coordination and test procedure—to a documented product reference. For uncertain applications, the project brief should include the circuit data so BCH or a qualified panel builder can review the proposed arrangement.
Review the current BCH RCCB product range and broader power-control portfolio when finalising the specification.
Frequently asked questions
Will a 100 mA RCCB prevent fatal shock?
Do not treat a 100 mA RCCB as a substitute for additional protection where a 30 mA device is required. Basic protection, fault protection, earthing and automatic disconnection all remain necessary.
Why does a 30 mA RCCB trip with no obvious fault?
Possible causes include cumulative leakage, moisture, damaged insulation, neutral-earth faults, shared neutrals, wiring errors or a faulty appliance. A qualified person should isolate circuits and test systematically; BCH also covers common diagnostic patterns in its guide to causes of RCCB tripping.
Is 300 mA more suitable than 30 mA because it trips less often?
No. A higher residual-current setting serves a different protection role. Nuisance tripping should be investigated through leakage measurement, circuit subdivision and wiring checks rather than by increasing the setting without analysis.
Does 300 mA upstream and 30 mA downstream guarantee discrimination?
No. Sensitivity difference alone does not prove discrimination. The upstream time characteristic and manufacturer coordination data must also support the arrangement.
Does an RCCB provide short-circuit protection?
Residual-current protection does not replace overcurrent protection. The RCCB arrangement must include suitable associated or upstream overcurrent and short-circuit protection.
What should be recorded in an RCCB design review?
Record the protection objective, residual-current rating, time delay, normal leakage, earthing arrangement, upstream/downstream discrimination, product reference and commissioning test result.
Conclusion
The correct RCCB sensitivity comes from the protection objective, normal leakage, earthing arrangement and the required coordination between devices. Use 30 mA, 100 mA and 300 mA as engineering settings with different roles, not as a ladder of quality. Document the reason for each value, verify the exact product data and test the installed arrangement under representative conditions.
Where published data does not cover the proposed combination, send the circuit and panel details to BCH for application guidance before finalising the device selection.
