As electric vehicles (EVs) continue to gain global popularity, the demand for safe and reliable charging infrastructure is rising at an unprecedented pace. With more households, businesses, and public facilities installing charging equipment, electrical safety has become a critical consideration. One of the most important components in ensuring safe charging is the Residual Current Device (RCD) — a protective device designed to prevent electric shock and reduce fire risks by rapidly disconnecting power when abnormal current leakage is detected.
While RCDs have been used for decades in residential and industrial electrical systems, EV charging introduces new challenges due to modern power electronics, variable charging loads, and the presence of direct current (DC) leakage. Understanding which type of RCD is required, how it interacts with EV chargers, and why it is essential is fundamental for installers, EV owners, and anyone designing charging infrastructure.
This article provides an in-depth look at what an RCD is, how it works, the different types available, and why specific types are required for EV charging applications. It also covers installation best practices, international regulations, and maintenance guidelines to ensure long-term safety and compliance.
A Residual Current Device (RCD) is an electrical safety mechanism designed to disconnect power when it detects that some of the electrical current is leaking from the intended circuit. Normally, the current flowing through the live conductor and the neutral conductor should be equal. If a difference occurs — known as residual current — it indicates that electricity may be escaping into unintended paths.
These leakage paths can include:
A person accidentally touching an energized component
Damaged insulation or wiring inside a charger
Moisture entering electrical equipment
A fault occurring within an EV’s onboard charging system
When such an imbalance is detected, the RCD cuts power within milliseconds, helping prevent:
Severe electric shock
Electrical fires caused by overheating
Damage to charging equipment and the vehicle
Thanks to these protective capabilities, RCDs have become mandatory in many countries for EV charging installations, especially as the charging environment combines high power levels with close human interaction.
While RCDs have long been used in households, EV charging adds complexity. Electric vehicles contain power converters, onboard chargers, and battery management systems that can generate smooth DC residual currents. These currents can saturate and effectively “blind” traditional AC-type RCDs, rendering them unable to trip when dangerous faults occur.
Because of this, EV charging regulations worldwide specify that chargers must be protected by RCDs capable of detecting DC leakage currents or by chargers that include built-in DC fault monitoring.
Reasons EV chargers require RCD protection include:
Residential outlets normally handle modest loads, while EV chargers can draw from 3.3 kW up to 22 kW in AC applications. Higher currents increase the risk of ground faults and electrical shock.
Wallboxes are frequently installed outdoors, exposing them to humidity, rain, and temperature fluctuations. Moisture intrusion is a common source of leakage current.
Modern EVs use switching power electronics, creating components of DC leakage that older RCDs cannot detect.
Regulations in the UK, EU, U.S., Australia, and many other regions require proper RCD protection for EV charging to meet safety certifications and building codes.
Not all RCDs are suitable for EV applications. Different types of RCDs detect different waveforms of residual current, and selecting the wrong type can compromise safety.
Here is a breakdown of the major types of RCDs and their suitability for EV charging.
Detection capability: Alternating sinusoidal currents only
Suitability for EV chargers: Not recommended
Type AC is the most basic form of RCD. It can detect residual alternating currents under simple fault conditions but cannot detect pulsating DC or smooth DC leakage. Because EV chargers generate complex current patterns, Type AC RCDs are no longer recommended for modern charging installations.
In fact, current UK wiring regulations (BS 7671) advise against using Type AC RCDs for EV chargers. Several European countries have phased them out entirely in favor of more advanced types.
Some RCBOs (combined RCD + circuit breaker), such as the FuseBox Mini, include both AC and A-type functions in one unit, but even then, the AC function alone is insufficient for EV charging.
Detection capability:
AC sinusoidal currents
Pulsating DC residual currents
Suitability for EV chargers: Suitable only when the charger includes internal 6 mA DC fault protection
Type A RCDs are among the most commonly used devices for EV chargers that already integrate a DC leakage detection module. Many modern home wallboxes include built-in 6 mA DC monitoring, which blocks dangerous DC currents from reaching the external RCD.
In such cases, a Type A RCD is sufficient to provide the required protection.
Cost-effective
Widely available
Adequate for chargers with DC monitoring
Limitation:
If a charger does not provide internal DC fault protection, a Type A RCD alone is not enough.
Detection capability:
AC residual currents
Pulsating DC residual currents
Smooth DC residual currents
High-frequency currents
Suitability for EV chargers: Required for chargers without built-in DC fault detection
Type B RCDs offer the highest level of protection and are therefore used when the vehicle or charger may generate DC leakage that other RCDs cannot detect. They are designed for power converters, inverters, and high-frequency electronics — all of which are common in EV charging.
Universal protection
Covers all known residual current types
Required in IEC 61851-1 for chargers without 6 mA DC detection
More expensive than Type A
Despite the higher cost, Type B is often the safest and sometimes the only compliant option for certain installations.
Detection capability:
AC sinusoidal currents
Pulsating DC currents
High-frequency leakage currents up to 1 kHz
Suitability for EV chargers: Rarely used
Type F RCDs are designed for appliances equipped with variable frequency drives, such as heat pumps, air conditioners, and some modern washing machines. They provide protection against high-frequency currents that Type A cannot detect.
While technically capable of detecting some DC-related faults, Type F devices are not commonly used for EV charging, largely because their protection range does not fully meet EV requirements, especially regarding smooth DC detection.
Regulations vary by region, but the following international guidelines apply broadly:
Requires DC fault protection of at least 6 mA.
Allows the DC protection to be built into the charger or provided by an external RCD (Type B).
Discourages the use of Type AC RCDs.
Requires Type A or Type B depending on whether the charger includes DC monitoring.
EV charging installations must ensure “protection against DC residual currents,” making Type B or Type A+DC monitoring mandatory.
Requires leakage current detection within the charger itself; external RCDs aren’t commonly used, as U.S. EVSE usually integrates GFCI functions.
In most international installations, the key requirement is simple:
EV chargers must be protected from smooth DC leakage of 6 mA or higher.
Proper installation is essential to ensure RCDs function as intended. Because EV charging circuits involve high power levels and sensitive electronics, installation should always be performed by a qualified electrician familiar with EV charging standards.
If your charger includes 6 mA DC protection: Use Type A.
If your charger does not include DC detection: Use Type B.
Selecting the wrong type can result in dangerous fault conditions going undetected.
Countries differ in their requirements, and compliance is often checked during safety inspections.
RCD performance depends heavily on a reliable grounding system. Earthing faults can lead to false trips or failure to trip when needed.
EV chargers should be connected to a dedicated electrical circuit to avoid interference with other appliances.
Extension leads increase resistance and could create ground faults, overheating, or insufficient protection.
To protect sensitive charger electronics from voltage spikes, SPDs are recommended — and in some regions, required.
Even the best RCD can fail if not regularly tested and maintained.
Qualified electricians should perform checks at intervals recommended by local electrical standards. Many regions mandate testing every 6–12 months.
Most RCDs include a “TEST” button. Pressing it simulates a fault condition and should immediately disconnect power. EV owners should perform this test monthly unless otherwise specified.
Checking for Nuisance Tripping
Occasional nuisance tripping can occur due to:
Moisture entering outdoor installations
Voltage fluctuations
Faulty household wiring
A malfunctioning charger
A qualified electrician can diagnose and resolve such issues.
Check for signs of:
Overheating
Corrosion
Cracked housing
Water ingress
Any abnormality requires professional attention.
Residual Current Devices (RCDs) play a crucial role in ensuring safe and reliable EV charging. As electric vehicles become more widespread, understanding the function and importance of RCDs is essential for homeowners, installers, property developers, and charging network operators.
EV chargers can produce complex residual currents — including smooth DC — that traditional RCDs may not detect. Therefore:
Type A RCDs are suitable only when the charger includes built-in DC fault protection.
Type B RCDs provide the most comprehensive protection, especially for chargers lacking internal DC monitoring.
Type AC RCDs are outdated and no longer recommended for EV charging.
Proper installation, regular testing, and adherence to local standards ensure that EV charging systems remain safe, reliable, and fully compliant.
As the EV ecosystem continues to grow, RCD technology will remain a fundamental component in shaping a safe and sustainable future of electric mobility.
