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Regulations for Type AC RCDs (Residual Current Devices)

When carrying out Electrical Installation Condition Reports for your property, Electrical installation Condition Report (EICR / Periodic Inspection), your Electrical Engineer can often flag up an issue with Type AC RCD’s

The issue is often coded to C3, where the installation met the conditions at the time of the initial installation. We have a separate Article on the Examples of the Use of Classification Codes which will be a usefull read for you to understand.

Although the Type AC RCD’s met the electrical installation at the time, it should be noted to you that it is recommended that this Type AC RCD’s, should be upgraded/replaced.

The electrical regulations are updated regularly, when Safety is concerned & Technology has improved.

The typical cost of replacement of two Type AC RCD’s into a Dual split load Consumer unit including parts & Labour is in the region of  £275 - £375 +VAT with around 1 hour installation & Testing + the power is SWITCHED OFF, the prices vary due manufacturers supplied parts. (Date of this article September 2025).

Bright Spark Electrical Services can provide this installation / upgrade for your property.

Regulations for Type AC RCD’s (Residual Current Devices)  BS7671:2018+A2:2022 restrict their use to circuits with no DC components, such as basic heating elements or filament lighting, because DC can desensitize or "blind" them. For new installations, it is recommended to use Type A RCD’s as a minimum, Type A RCD's incorporate a filtering device to provide protection against transient surges in the supply to the unit, thus reducing the occurrence of unwanted tripping. and a Type B RCD for equipment like Electric Vehicle Charging Points. The change reflects modern electrical loads often containing electronic devices that can introduce DC leakage, making Type AC RCDs unsuitable and potentially dangerous. 

Key Regulations and RCD Types

• BS 7671:2018+A2:2022: This is the current standard for electrical installations in the UK. 
• Type AC RCDs: These are designed only for purely sinusoidal AC waveforms and are unsuitable for loads with any DC components. 
• Type A RCDs: These offer broader protection, being sensitive to AC waveforms and residual pulsating DC currents. 
• Type B RCDs: These provide the widest protection, detecting AC, pulsating DC, and smooth DC residual currents, and are necessary for equipment like EV chargers. 

Why Type AC RCDs Are Restricted

• DC Blinding: Electronic devices, such as those with switch-mode power supplies (SMPS), can introduce small amounts of DC onto the circuit. 
• Failure to Operate: The presence of DC can cause a Type AC RCD to become desensitized and fail to trip within the required timeframe during a fault. 

Practical Applications

• Type AC: Only for circuits with known purely resistive loads (e.g., simple filament lighting, some electric heaters). 
• Type A:A minimum requirement for new installations and for most modern circuits containing electronic devices. 
• Type B: Essential for circuits supplying electric vehicle supply equipment (EVSE) and other equipment known to generate smooth DC leakage. 

Bright Spark Electrical Services can provide this installation / upgrade for your property, it should be noted that if other issues are noted on your Electrical installation Condition Report (EICR / Periodic Inspection), it may be more cost effective to upgrade & replace the complete Consumer Unit.

Thanks for reading! We hope this article was of use to you. If you have any questions or suggestions, please feel free to let us know.

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Email: karen@brightsparkelectrician.co.uk