Type AC RCDs were once the standard choice for residual current protection. They’re simple, cheap, and designed for a time when electrical loads were largely predictable.
That world no longer exists. With EV chargers, solar PV, heat pumps, LED drivers and inverter-driven equipment now common, Type AC RCDs are increasingly unsuitable - and in many installs, unsafe.
Quick Answer: Type AC RCDs are not banned, but they are no longer suitable for most modern installations. Where DC leakage or inverter technology is present, Type AC can fail to trip. In these cases, Type B RCDs (or equivalent DC protection) are required under BS 7671.
If you’re working on EV, renewable or inverter-driven circuits, browse compliant options here: Type B RCDs.
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What Type AC RCDs Were Designed For
Type AC RCDs detect pure alternating current (AC) leakage only. They were designed for simple circuits supplying resistive or inductive loads.
Typical historic use cases included:
- Incandescent lighting circuits
- Basic socket circuits
- Resistive heating loads
- Motors without electronic control
At the time, these circuits did not generate DC leakage or distorted waveforms - so Type AC protection was adequate.
Why Type AC RCDs Fail on Modern Loads
Modern electrical equipment almost always contains some form of electronic control, rectification or inversion.
These technologies can introduce DC components into the fault current. When that happens, a Type AC RCD can become magnetically saturated and fail to operate.
Common modern sources of DC leakage
- EV chargers
- Solar PV inverters
- Battery storage systems
- Heat pumps with inverter compressors
- LED lighting drivers
- Variable speed drives (VFDs)
Once blinded by DC, a Type AC RCD may not trip even under dangerous fault conditions.
Compliance Note: BS 7671 recognises that Type AC RCDs are unsuitable for circuits supplying equipment that can generate DC fault currents.
Why Type B Replaced Type AC in Many Installs
Type B RCDs were developed to address the exact weaknesses of Type AC devices.
Unlike Type AC, a Type B RCD detects:
- AC leakage
- Pulsating DC leakage
- Smooth (continuous) DC leakage
- High-frequency fault currents
This makes Type B suitable for modern installations where inverter technology is present - and removes the risk of DC blinding.
Typical applications where Type B has replaced Type AC
- EV charger circuits
- Solar PV supplies
- Battery and hybrid systems
- Heat pump installations
- Industrial and commercial motor control
When Are Type AC RCDs Still Allowed?
Type AC RCDs are not explicitly banned, but their use is now extremely limited.
They may only be considered where the installer can be confident that:
- No DC leakage can occur
- No inverter or electronic control is present
- No future equipment upgrades are likely
In practice, these conditions are rare - especially in domestic installations.
For any circuit involving EV charging, renewables or modern appliances, Type AC should be avoided.
FAQs
Installers often ask whether Type AC RCDs are still permitted - and if so, where they actually make sense. The FAQs below explain the limits, the risks, and why Type B has become the preferred option on modern installations.
Are Type AC RCDs illegal?
No. They are still permitted, but only where their limitations are fully accounted for.
Why are Type AC RCDs being phased out?
They cannot reliably detect DC leakage from modern electronic loads.
Is Type B always required?
Type B is required where smooth DC leakage is possible. Otherwise, Type A may be sufficient.
Can Type AC cause failed inspections?
Yes. Inspectors increasingly expect Type A or Type B protection on modern circuits.
👉 Working on EV, solar or inverter-driven circuits? Use Type B RCD protection