Type A RCDs are now the standard choice for modern installations. They handle AC leakage and pulsating DC leakage from inverter-driven appliances - something older Type AC devices cannot safely detect. With heat pumps, EV chargers, induction hobs, washing machines and LED drivers now everywhere, Type A has become the minimum safe and compliant option in most UK installs.
Quick Answer: A Type A RCD detects AC and pulsating DC leakage, making it the correct choice for most modern domestic and commercial circuits. It is commonly selected where electronic equipment may introduce DC components into the residual current, while Type AC should only be used where it is known that no DC components will be present.
Browse all Type A options here: Type A RCDs.
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What a Type A RCD Actually Detects
Type A devices are designed to protect against the leakage signatures produced by modern electronic loads. They detect:
- AC leakage (standard residual current faults)
- Pulsating DC leakage
Why this matters
Most appliances today use internal rectifiers or inverters. These generate DC components that can blind a Type AC RCD, preventing it from tripping under fault conditions. Type A continues to operate correctly.
Type A vs Type AC – Practical Installer Breakdown
Type AC is the older RCD type. It only detects pure AC leakage and does not handle any DC component.
| Feature | Type AC RCD | Type A RCD |
|---|---|---|
| AC leakage detection | ✔️ Yes | ✔️ Yes |
| Pulsating DC leakage detection | ❌ No | ✔️ Yes |
| Handles inverter loads | ❌ No | ✔️ Yes |
| Current recommended by manufacturers | ⚠️ Rarely | ✔️ Standard |
Type AC is still sold, but in practice it should only be used on circuits that are known not to contain DC components. On modern installations, that makes Type A the more appropriate default choice for many circuits.
Regulation Reminder (BS 7671): There is growing industry guidance that Type AC should not be used on circuits supplying modern electronic appliances. Type A is becoming the default for domestic and commercial installations.
When Did Type A RCD Become Mandatory?
Type A RCDs are not described in BS 7671 as a universal blanket requirement for every circuit. However, current guidance makes it clear that Type AC devices should only be used where it is known that no DC components will be present in the load current. Because so many modern appliances now contain electronic controls, rectifiers or inverters, Type A has become the practical default choice on many new installations.
When a Type A RCD Is Required
You should use Type A whenever the circuit feeds equipment that uses electronic control, rectification or inverter technology. In other words - almost every modern appliance.
Common circuits that require Type A:
- EV chargers (if no Type B requirement)
- Heat pumps and hybrid systems
- Induction hobs
- Washing machines & dryers
- Dishwashers
- LED lighting drivers
- Boilers with electronic control boards
- Solar equipment with internal DC leakage monitoring
What about smooth DC leakage?
Type A detects pulsating DC up to 6mA. If smooth DC leakage is possible (EV, solar, VFD, battery systems), a Type B RCD must be used instead.
Installer-Favourite Type A RCDs
Below are the most commonly used Type A RCD options for domestic, commercial and industrial circuits - including standard, high-immunity and time-delay models.
High-Immunity Type A RCDs (2-Pole & 4-Pole)
- 4-Pole 63A Type A High-Immunity
- 4-Pole 40A Type A High-Immunity
- 4-Pole 80A Type A High-Immunity
- 4-Pole 100A Type A High-Immunity
- 2-Pole 63A Type A High-Immunity
- 2-Pole 80A Type A High-Immunity
- 2-Pole 100A Type A High-Immunity
Time-Delay (S-Type) Type A RCDs – 100mA
- 4-Pole 80A Type A 100mA Time-Delay
- 4-Pole 63A Type A 100mA Time-Delay
- 2-Pole 63A Type A 100mA Time-Delay
- 4-Pole 100A Type A 100mA Time-Delay
- 2-Pole 100A Type A 100mA Time-Delay
Explore the full range: View all Type A RCDs
FAQs
Installers ask these frequently when specifying Type A RCDs.
Are Type A RCDs now mandatory?
Not as a blanket rule for every circuit. However, BS 7671 requires the RCD type to be selected according to the presence of DC components, and Type AC should only be used where it is known that no DC components will be present. In practice, that makes Type A the normal choice for many modern circuits.
Do Type A RCDs detect smooth DC leakage?
No. They detect pulsating DC only. Smooth DC leakage requires a Type B RCD.
Can Type A RCDs reduce nuisance tripping?
Yes - especially high-immunity models - because they better tolerate distorted waveforms and leakage spikes from inverter-driven loads.
Where should I avoid Type AC?
Anywhere with electronic control boards, inverters, or rectification - which includes almost every appliance in a modern home.
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