Are Type AC RCDs Still Allowed? Type AC vs Type A Explained
Quick answer: Type AC RCDs have not been banned in the UK. However, their permitted use is now limited to fixed equipment where it is known that the load current contains no DC components.
For circuits supplying socket outlets, electronic equipment or loads capable of producing pulsating DC residual current, a Type A RCD or RCBO is normally the more appropriate choice. Type B or another specialist RCD type may be required where the equipment can produce residual currents that Type A is not designed to detect.
Type AC was once the standard residual-current device across domestic and commercial installations. Modern equipment has changed the selection process.
LED drivers, appliance controls, switch-mode power supplies, inverters and other electronic equipment can produce residual-current waveforms that a Type AC device is not designed to detect reliably.
The important question is therefore not simply whether Type AC is still legal. It is whether Type AC is suitable for the exact fixed equipment connected to the circuit.
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Are Type AC RCDs Still Allowed in the UK?
Yes. Type AC RCDs and RCBOs have not been completely banned.
However, Regulation 531.3.3 of BS 7671 restricts their use. A Type AC RCD should only serve fixed equipment where it is known that the load current contains no DC components.
This means Type AC is no longer a general-purpose choice for an unknown mix of modern loads.
Before specifying one, the designer needs to know:
- Exactly what fixed equipment the circuit will supply.
- Whether that equipment contains rectifiers, electronic controls or power-conversion components.
- Whether its normal load current can contain a DC component.
- Which RCD type the equipment manufacturer specifies.
Regulation reminder: Type AC should not be selected simply because no obvious inverter or EV charger is connected. Its use depends on knowing that the fixed equipment’s load current contains no DC component.
What Does a Type AC RCD Detect?
A Type AC RCD is designed to operate for residual sinusoidal alternating currents.
It does not provide the wider residual-current detection available from Type A, Type F or Type B devices.
Electronic equipment commonly converts, switches or controls the incoming AC supply. Depending on the equipment, this can produce pulsating DC components or other residual-current waveforms.
A DC component can desensitise or blind an unsuitable Type AC device. Its operation may be delayed, or it may not operate as required under the relevant fault condition.
This is why the connected equipment must determine the RCD type rather than cost, habit or what was traditionally installed on similar circuits.
What Is the Difference Between Type AC and Type A RCDs?
Type A provides wider residual-current detection than Type AC.
| Feature | Type AC | Type A |
|---|---|---|
| Sinusoidal AC residual current | Detected | Detected |
| Pulsating DC residual current | Not within its intended detection characteristics | Detected within the device specification |
| Permitted application | Fixed equipment known to contain no DC component in its load current | Many modern circuits containing single-phase electronic equipment |
| Suitable as a general default? | No | Often selected for modern general-purpose circuits, subject to the connected equipment |
Type A is not automatically suitable for every electronic load. Equipment capable of producing smooth DC, mixed-frequency or other residual-current characteristics may require Type F, Type B or another specified protective arrangement.
👉 Compare our Type A RCBOs for modern domestic and commercial circuits.
When Can a Type AC RCD Still Be Used?
A Type AC device may still be selected where all the following points can be established:
- The circuit supplies fixed equipment rather than an unrestricted socket outlet.
- The exact connected load is known.
- The equipment’s load current contains no DC components.
- The manufacturer does not specify another RCD type.
- The circuit is not likely to be repurposed for unknown electronic loads.
- The selection meets all other relevant BS 7671 requirements.
The key phrase is known fixed equipment.
A circuit should not be treated as suitable for Type AC merely because its present load appears simple. The equipment specification and internal electronics need to support that decision.
Can Type AC Be Used for a Basic Resistive Load?
Potentially, yes, where the fixed equipment is confirmed not to contain electronic controls or other components introducing DC into the load current.
However, many apparently simple appliances now contain displays, control boards, electronic thermostats or power supplies. The product documentation should be checked before assuming the load is purely resistive.
Can a Type AC RCD Be Used on Socket Circuits?
A socket circuit can supply an unrestricted range of portable equipment, including computers, televisions, chargers, appliances and switch-mode power supplies.
Because the future connected loads are unknown, it is generally not possible to establish that the load current will contain no DC components.
Type AC is therefore not an appropriate general selection for a socket circuit supplying unknown equipment under the current requirements.
Can a Type AC RCD Be Used on Lighting Circuits?
Modern lighting circuits commonly supply LED drivers, dimmers, emergency-lighting equipment and electronic controls.
These loads should not automatically be treated as suitable for Type AC. The RCD must be selected according to the actual equipment and the residual-current characteristics identified by its manufacturer.
A dedicated circuit supplying specifically identified fixed equipment may be assessed differently from a general lighting circuit whose fittings and drivers can change over time.
What RCD Type Is Used for Modern Electronic Equipment?
RCD selection must follow the characteristics of the equipment rather than a broad assumption based on the circuit name.
| RCD Type | Residual-Current Capability | Selection Principle |
|---|---|---|
| Type AC | Sinusoidal AC residual current | Only for qualifying fixed equipment known to contain no DC load-current component |
| Type A | AC and pulsating DC residual current | Commonly selected for modern single-phase electronic loads |
| Type F | Type A characteristics plus defined mixed-frequency capability | Certain single-phase frequency-controlled equipment where specified |
| Type B | Includes smooth DC and wider waveform/frequency capability within its specification | Equipment or installations capable of producing residual currents beyond Type A or Type F capability |
A Type B RCD is not automatically required for every EV charger, photovoltaic inverter, battery system or variable-speed drive. The equipment manufacturer may permit another arrangement where the required DC protection or separation is provided within the equipment.
👉 Browse Type B RCDs for applications whose residual-current characteristics require wider DC detection.
What Do the Type AC and Type A RCD Symbols Mean?
The markings on an RCD or RCBO identify its residual-current detection type.
- Type AC symbol: A sinusoidal waveform, indicating detection of sinusoidal alternating residual current.
- Type A symbol: A sinusoidal waveform together with a pulsating rectified waveform, indicating detection of AC and pulsating DC residual current.
- Type B symbol: Additional waveform markings identifying its wider DC and frequency response.
The marking may appear on the front or side of the RCCB or RCBO alongside its rated residual operating current, current rating and applicable product standard.
Do not confuse the RCD type symbol with:
- The B or C overcurrent curve printed on an RCBO.
- The rated current, such as 32 A, 40 A or 63 A.
- The residual operating current, such as 30 mA or 100 mA.
For example, a B32 Type A RCBO has a B-curve overcurrent characteristic, a 32 A rated current and Type A residual-current detection. The “B” in B32 does not make it a Type B RCD.
Does a Type AC RCD Fail an EICR?
No. The presence of a Type AC RCD does not automatically make an Electrical Installation Condition Report unsatisfactory.
The inspector must assess:
- The circuits supplied by the device.
- The fixed and portable equipment likely to be connected.
- Whether DC components could affect the Type AC device.
- The installation standard and requirements applicable when the work was completed.
- Whether there are aggravating factors creating an immediate or potentially dangerous condition.
Where a Type AC RCD is present but no immediate or potential danger is identified, an improvement recommendation may be appropriate. Where connected equipment makes the device unsuitable and creates a greater safety concern, the inspector must apply engineering judgement to the classification.
Inspection note: An existing installation does not automatically become unsafe because a later edition of BS 7671 changed the requirements. The condition, suitability and risks present at the time of inspection determine the EICR observation and code.
There is therefore no universal “Type AC EICR code” that applies to every circuit.
Should Existing Type AC RCDs Be Replaced?
Replacement should be considered where the existing device is no longer suitable for the connected or foreseeable equipment.
Examples include:
- A socket circuit supplying modern electronic equipment.
- A lighting circuit containing LED drivers and electronic controls.
- A new appliance or fixed load whose manufacturer requires Type A or another RCD type.
- An alteration that introduces inverter-driven or power-electronic equipment.
- An upstream Type AC device that could be affected by DC residual current from downstream equipment.
- A consumer-unit upgrade where the protection is being redesigned for modern loads.
Replacement should not be treated as a simple like-for-like device swap without checking:
- Rated current and conditional short-circuit rating.
- Residual operating current.
- Number of poles and neutral switching.
- Overcurrent protection and selectivity.
- Compatibility with the consumer-unit manufacturer.
- Earth-leakage levels across grouped circuits.
Installer summary: Type AC remains permitted only in a narrow, defined application. For general modern circuits, the device should be selected according to the electronic equipment likely to be connected rather than automatically repeating the legacy Type AC specification.
Browse RCD and RCBO Protection
Select the RCD type according to the connected equipment, expected residual-current waveform and manufacturer’s instructions.
Type AC RCD FAQs
Are Type AC RCDs banned in the UK?
No. Type AC RCDs are not banned, but their use is limited to fixed equipment where it is known that the load current contains no DC components.
Can you still install a Type AC RCD?
Yes, but only where the connected fixed equipment meets the permitted conditions and another RCD type is not required by its residual-current characteristics or manufacturer.
What is the difference between Type AC and Type A?
Type AC detects sinusoidal AC residual current. Type A detects sinusoidal AC and pulsating DC residual current, making it suitable for a wider range of modern electronic equipment.
Is a Type AC RCBO the same as a Type AC RCD?
Type AC describes the residual-current detection characteristic. An RCBO also includes overcurrent protection, while an RCCB provides residual-current protection without integrated overload protection.
Does a Type AC RCD automatically receive a C2 on an EICR?
No. The classification depends on the circuit, connected equipment, risks and the inspector’s engineering judgement. Type AC does not receive an automatic C2 solely because it is present.
Can Type AC receive a C3 on an EICR?
A C3 improvement recommendation may be appropriate in some circumstances, but there is no automatic code. Aggravating factors and evidence of unsuitable connected loads may affect the inspector’s decision.
Can a Type AC RCD protect socket outlets?
Type AC is restricted to fixed equipment known to contain no DC components in its load current. A socket circuit can supply unknown electronic loads, so Type AC is generally unsuitable as its protective device.
Are Type A RCDs mandatory?
Type A is not universally mandatory for every circuit. The appropriate type must be selected according to the connected equipment, DC components and AC frequencies that may be present.
Does solar PV always need a Type B RCD?
No. Where an RCD is required, Type B may be needed unless the inverter or installation provides suitable separation or the manufacturer confirms that another RCD type is appropriate.
Is Type B always better than Type A?
Type B has wider detection characteristics, but RCD selection should follow the equipment and installation requirements. Installing a higher-specification type does not remove the need to coordinate ratings, frequency response, upstream devices and manufacturer guidance.
What does the Type AC RCD symbol look like?
It is represented by a sinusoidal waveform. Type A includes both the sinusoidal waveform and a pulsating rectified waveform marking.
Is a C-curve RCBO a Type AC device?
Not necessarily. C-curve describes the overcurrent trip characteristic. The residual-current type will be marked separately as Type AC, A, F or B.
Should You Still Use Type AC?
Type AC has not disappeared from BS 7671, but its role is now tightly restricted.
It may be used for fixed equipment where it is known that the load current contains no DC components. It should not be treated as a low-cost default for socket circuits, modern lighting or unknown electronic loads.
For each circuit:
- Identify the connected equipment.
- Check for electronic controls and power conversion.
- Review the manufacturer’s RCD requirements.
- Select the device according to the expected residual-current waveform.
- Check upstream and downstream RCD compatibility.
👉 Specifying protection for modern loads? Compare Type A RCBOs, high-immunity RCBOs and Type B RCDs.