C curve RCBOs are designed for circuits with higher inrush current - the kind of loads that briefly pull more current when they start up. EV chargers, motors, compressors, pumps, induction hobs, and some inverter-based equipment can all create startup conditions that make a B curve device more prone to nuisance tripping.
Quick Answer: Choose a C curve RCBO when the circuit supplies a load with medium to high inrush current. That includes EV chargers, heat pumps, motors, transformers, induction appliances, power tools and many inverter-driven units. B curve RCBOs trip too quickly on these loads, while C curve devices safely absorb the startup surge.
You can view the full range here: C Curve RCBOs.
This guide breaks down the differences between B and C curve trip characteristics, when installers switch curves, and which real-world loads require C curve protection.
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What Does a C Curve RCBO Do?
A C curve RCBO trips at around 5–10× its rated current - giving it enough headroom to tolerate inrush current without nuisance-tripping. The earth leakage characteristics stay the same as a B curve (30 mA for most domestic installs), but the magnetic trip curve is more forgiving.
Installers choose C curve RCBOs when the load momentarily spikes at startup. This covers a huge range of modern appliances and inverter-based systems.
You can browse all C curve options here: C Curve RCBOs.
B Curve vs C Curve RCBOs - What’s the Difference?
The difference comes down to the amount of magnetic inrush current the device expects before it trips.
| Curve Type | Trips At | Suitable For |
|---|---|---|
| B Curve | 3–5× rated current | Lighting, sockets, immersion heaters, general loads |
| C Curve | 5–10× rated current | Motors, pumps, EV chargers, compressors, inverter loads |
If a load has a motor, transformer, compressor, or higher inrush electronic start-up, installers will often consider C curve protection - but the final choice should still follow manufacturer guidance and confirmed circuit performance.
Loads That Require a C Curve RCBO
Here are some of the most common loads where installers often move from B curve to C curve protection to reduce nuisance tripping:
- EV chargers - inrush + switching electronics
- Heat pumps - inverter-driven compressors
- Air conditioning units
- Power tools (workshops, garages)
- Induction hobs
- Welding equipment
- Small motors or pumps (sump, circulation, booster pumps)
- 3-phase equipment with transformers or coils
- UPS / inverter systems
These loads spike briefly, pushing a B curve device into the magnetic trip zone far too easily.
When Installers Choose a C Curve RCBO
Most installers upgrade from B curve to C curve when:
- The load has a noticeable startup surge
- The circuit has tripped a B curve device incorrectly
- You’re wiring EV chargers or heat pump circuits
- You’re supplying pumps, compressors or motors
- The manufacturer explicitly requires C curve protection
- The circuit length and Zs values still meet disconnection times
Regulation note: Always verify that Zs values meet the required disconnection times when switching from B to C curve. A C curve demands lower Zs to operate within limits.
Explore the range here: C Curve RCBOs
Why Zs Still Matters When You Switch from B Curve to C Curve
Changing from B curve to C curve is not just about inrush tolerance. Because a C curve has a higher instantaneous magnetic trip threshold, the circuit still needs to meet the required disconnection performance for the earthing arrangement and protective measure being used.
That means installers should always verify fault loop impedance, confirm test results, and check the circuit remains compliant before swapping curves simply to stop nuisance tripping.
Recommended C Curve RCBOs
Here are some C curve models installers frequently choose, based on search data and real-world use:
- 32A Type A C Curve RCBO – WRT132C-030
- 6A Type A C Curve RCBO – WRT106C-030
- High Immunity 32A C Curve RCBO – WER32C-030
If you need B curve options for comparison:
- 40A Type A B Curve RCBO – WRT140B-030
- High Immunity 32A B Curve RCBO – WER32B-030
- High Immunity 20A B Curve RCBO – WER20B-030
View all curve types here:
FAQs
Installers regularly ask these questions when deciding between B and C curve RCBOs.
Can I replace a B curve with a C curve RCBO?
Yes - as long as Zs values meet the disconnection time for the C curve. Always test first.
Do all EV chargers need C curve protection?
Most do due to inrush current and switching electronics. Always check manufacturer requirements.
Is a C curve suitable for lighting?
Only if the lighting has high inrush (e.g., large LED drivers). Otherwise B curve is fine.
Does a C curve RCBO affect selectivity?
Not typically - but it can change Zs requirements. Test results must confirm compliance.
Can a C curve RCBO replace a B curve just to stop nuisance tripping?
Sometimes, yes - but only if the circuit is genuinely experiencing startup inrush and the installation still meets the required disconnection and fault loop conditions. A curve change should be justified, not used as a shortcut.
👉 Ready to spec the right curve for your circuit? Browse all C Curve RCBOs