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 required for EV chargers, solar PV, batteries, heat pumps and other inverter-driven systems where continuous DC fault current is possible.
Browse both ranges here: Type A RCDs | Type B RCDs
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 (up to 6mA)
- 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 DC fault current, inverter technology or variable frequency operation, Type B is usually the correct answer.
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 leakage may exceed 6mA, BS 7671 requires Type B RCD protection or an equivalent DC detection method.
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.
👉 Not sure which RCD type suits your circuit? Compare all RCD options