Type A and Type B RCDs are often lumped together as “modern RCDs”, but they solve very different problems. Choosing the wrong one can mean nuisance tripping at best - or a circuit that fails to disconnect under fault conditions at worst.
This guide breaks down the actual, practical difference between Type A and Type B RCDs, when each is correct, and how to avoid over-specifying (or under-protecting) a circuit.
Quick Answer: Type A RCDs handle AC and pulsating DC leakage and are suitable for most modern domestic circuits. Type B RCDs also detect smooth DC leakage and are used where inverter-driven equipment may generate continuous DC fault current, or where the manufacturer or application specifically requires Type B protection.
Browse both ranges here: Type A RCDs | Type B RCDs
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What Type A RCDs Are Designed For
Type A RCDs are the default choice for modern domestic and light commercial installations. They are designed to cope with the leakage signatures produced by everyday electronic loads.
Type A RCDs detect:
- Standard AC leakage
- Pulsating DC leakage
- Distorted waveforms from appliances with electronic control
Where Type A is the correct choice
- General socket circuits
- Lighting circuits with LED drivers
- Boilers and heating controls
- Washing machines and white goods
- Induction hobs
For most household circuits, Type A provides the right balance of protection, stability and cost.
What Type B RCDs Add
Type B RCDs build on Type A protection by adding the ability to detect smooth (continuous) DC leakage and high-frequency fault currents.
This matters because smooth DC can blind Type A RCDs, preventing them from tripping during a fault.
Circuits that typically require Type B
- EV chargers (unless DC detection is built in)
- Solar PV inverters
- Battery storage systems
- Heat pumps with inverter compressors
- Variable speed drives (VFDs)
If the manufacturer mentions smooth DC fault current, variable frequency operation, or a specific Type B requirement, that is a strong sign Type B protection may be needed. Always check the equipment instructions and the fault current characteristics of the circuit before deciding.
When Type A Is Still the Right Choice
Type B is not the default answer for every modern circuit. In many cases, Type A remains the correct and more cost-effective option where the equipment does not generate smooth DC leakage or where equivalent DC fault detection is already built into the equipment.
This is why many standard domestic circuits, and some EV charging setups with built-in RDC-DD protection, can still be protected correctly using a Type A device.
Type A vs Type B – Practical Comparison
This side-by-side comparison shows exactly where Type A stops and Type B becomes necessary. Use it to quickly sanity-check your spec before ordering - especially on circuits involving EV charging, renewables or inverter-driven equipment.
| Feature | Type A | Type B |
|---|---|---|
| AC leakage | ✔️ | ✔️ |
| Pulsating DC | ✔️ | ✔️ |
| Smooth DC | ❌ | ✔️ |
| EV / renewable ready | ⚠️ Limited | ✔️ |
Compliance Note: Where smooth DC residual current may be present, the protective arrangement must account for it correctly. In EV charging applications, BS 7671 requires a Type B RCD unless suitable DC fault current protection is already provided by the equipment.
Installer Picks – Type A & Type B Options
Below are proven RCD options installers regularly use on compliant domestic, commercial and renewable installs. These picks cover standard Type A protection for everyday circuits, plus Type B options where smooth DC leakage must be accounted for.
Popular Type A RCDs
- 2-Pole Type A High-Immunity 63A
- 4-Pole Type A High-Immunity 63A
- 4-Pole Type A High-Immunity 80A
- 4-Pole Type A 100mA Time-Delay
When Type B Is the Better Choice
If the circuit involves EV charging, solar or inverter-driven equipment, step up to a Type B solution.
FAQs
These are the questions that come up most when choosing between Type A and Type B protection. If you’re weighing up cost, compliance or future-proofing, the answers below should help you make the right call quickly.
Can I use Type A instead of Type B?
Only if the equipment cannot generate smooth DC leakage. Many EV chargers and inverters require Type B or built-in DC detection.
Is Type B always required for EV chargers?
Yes - unless the charger includes certified DC fault current detection.
Why not just install Type B everywhere?
Type B offers broader protection, but it costs more and isn’t necessary on standard domestic circuits.
Can Type A RCDs be used on EV chargers?
Yes, in some cases. If the EV charger includes suitable DC fault current protection, a Type A RCD may be acceptable. If it does not, a Type B RCD is generally required.
👉 Not sure which RCD type suits your circuit? Compare all RCD options