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 often unsuitable for modern circuits. In many cases, Type A RCDs or RCBOs are now the better choice because they can detect pulsating DC residual currents. Type B RCDs are used where smooth DC leakage may be present, such as certain EV, inverter and renewable applications.
Working out what protection suits the circuit? For many modern final circuits, Type A RCBOs are the practical upgrade from older Type AC devices. Where smooth DC leakage is possible, browse our 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 Can Be Unsuitable 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.
Type AC vs Type A vs Type B RCDs
If you are choosing protection for a modern circuit, the real question is usually not whether Type AC is banned. It is whether Type AC is still suitable, or whether the circuit now calls for Type A or Type B protection instead.
That matters because many circuits that once used Type AC now include electronic equipment that changes the type of residual current protection required.
| RCD Type | Detects | Typical Use | Best For |
|---|---|---|---|
| Type AC | Pure AC residual current only | Older, simpler circuits with no DC-producing electronics | Limited legacy applications |
| Type A | AC and pulsating DC residual current | Many modern domestic and commercial final circuits | General modern installs |
| Type B | AC, pulsating DC, smooth DC and higher-frequency leakage | Certain EV, PV, battery, inverter and specialist applications | Circuits where smooth DC leakage is possible |
For many electricians, Type A is now the practical step up from Type AC. Type B comes into play where the circuit characteristics go beyond what Type A can safely cover.
Why Type B RCDs Are Used on Certain Modern Circuits
Type B RCDs are designed for applications where residual currents may go beyond what Type AC or even Type A devices are intended to detect.
Unlike Type AC devices, Type B RCDs can detect:
- AC leakage
- Pulsating DC leakage
- Smooth (continuous) DC leakage
- Higher-frequency fault currents
That makes them suitable for certain modern installations where inverter technology, power conversion or specialist equipment increases the risk of DC-related fault currents.
Typical applications for Type B RCDs
- Some EV charger circuits
- Solar PV supplies
- Battery storage and hybrid systems
- Inverter-driven equipment
- Specialist commercial and industrial applications
When Are Type AC RCDs Still Allowed?
Type AC RCDs are not banned in the UK, but they should only be used where the circuit does not involve equipment likely to generate pulsating DC or smooth DC residual current.
That usually means only simpler circuits with predictable loads and no inverter-driven or electronically controlled equipment. In real-world installs, that leaves Type AC with a much narrower role than it once had.
- No DC-producing equipment on the circuit
- No inverter-driven loads
- No EV charging equipment
- No solar, battery or similar power electronics
- No expectation that the circuit will later be upgraded with modern electronic loads
That is why many electricians now treat Type A as the safer default on general modern circuits, with Type B reserved for applications where smooth DC leakage may be present.
Does a Type AC RCD Fail an EICR?
A Type AC RCD does not automatically mean an installation fails inspection. The real issue is whether the device is suitable for the circuit and connected equipment.
If a Type AC RCD is protecting a circuit that includes equipment capable of producing pulsating or smooth DC residual current, that may be flagged as an issue because the protective device may no longer be appropriate for the actual risk present.
Inspection Note: The coding outcome depends on the circuit, the connected load, and the inspector’s judgement. The practical question is not simply “Is Type AC present?” but “Is Type AC appropriate here?”
That is one reason many installers now default to Type A RCBOs on modern circuits, and use Type B RCDs where the application demands it.
FAQs
These are the questions electricians and buyers usually ask when deciding whether a Type AC device is still acceptable, or whether it is time to move to Type A or Type B protection.
Are Type AC RCDs banned in the UK?
No. Type AC RCDs are not banned, but they are often unsuitable for modern circuits with electronic loads or DC-producing equipment.
What is the difference between Type AC and Type A RCDs?
Type AC detects pure AC residual current only. Type A detects AC and pulsating DC residual current, which makes it more suitable for many modern circuits.
When should I use Type B instead of Type A?
Type B is used where smooth DC leakage may be present, such as certain EV charging, inverter, PV, battery and specialist commercial applications.
Does a Type AC RCD fail an EICR?
Not automatically. The issue is whether the device is suitable for the connected circuit and equipment. If it is protecting a circuit it is not appropriate for, that may be flagged during inspection.
Is Type AC still suitable for domestic installations?
Only in limited cases. Many modern domestic circuits now include equipment that makes Type A the more suitable choice.
👉 Need the right protection for a modern circuit? Browse Type A RCBOs for general modern installs, or explore Type B RCDs for EV, inverter and renewable applications.
👉 Working on EV, solar or inverter-driven circuits? Use Type B RCD protection