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 inverter-based equipment all trigger higher startup currents that can nuisance-trip a B curve device.
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 device has a motor, transformer, or inverter-driven electronics, it almost certainly needs C curve protection.
Loads That Require a C Curve RCBO
Here are the most common loads that must not be put on B curve protection due to the risk of 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
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.
👉 Ready to spec the right curve for your circuit? Browse all C Curve RCBOs