An EV charging circuit needs residual-current protection designed for the faults the charging system can produce. Common solutions are Type A protection combined with suitable 6 mA DC detection, or Type B protection. The wallbox manual, upstream devices and national wiring rules decide the correct arrangement. A qualified electrician must design and test it.
What does an RCD do?
An RCD monitors current in the live conductors and responds when the outgoing and returning values differ beyond its design conditions. That difference can indicate current flowing through an unintended path. The device disconnects according to its type, sensitivity and operating requirements.
An RCD is not the same as an overcurrent protective device. A circuit breaker or fuse deals with overload and short-circuit conditions. Some products called RCBOs combine residual-current and overcurrent functions in one unit.
EV charging adds power electronics in the car and charging equipment. Faults can therefore create different residual-current waveforms, including a smooth DC component. Protection must be chosen for that application, not copied from a general household circuit.
Why does smooth DC matter?
A Type A RCD is designed for specified alternating and pulsating DC residual currents. A smooth DC residual current can affect an RCD that is not designed to handle it. The EV protection design therefore needs a way to address that possibility.
One approach detects smooth DC residual current in the charging equipment and disconnects before it can impair upstream Type A protection. IEC 62955 covers residual direct-current detecting devices, called RDC-DDs, for permanently connected Mode 3 charging stations.
Another approach uses a Type B RCD. IEC 62423 specifies additional requirements and tests for Type B devices, including response to specified smooth DC residual currents. Type B is a protection classification, not a statement that every Type B device suits every circuit.
What is Type A plus 6 mA DC detection?
This arrangement combines upstream Type A residual-current protection with EV charging equipment that provides suitable 6 mA smooth-DC detection. The DC detection may be built into the wallbox or provided as equipment designed for that function. The manual should state exactly what is included.
The phrase “6 mA DC protection” is often shortened in product pages. Ask whether the device is an RDC-DD compliant with the applicable standard and what action it takes. Also ask which RCD and overcurrent protection remain required upstream.
An RDC-DD does not automatically replace all residual-current protection. It addresses a particular DC residual-current condition within the coordinated installation. The electrician still has to apply IEC 60364-7-722 as adopted locally, national rules and the wallbox instructions.
Read the exact installation manual
Do not assume that every wallbox with “DC detection” needs the same upstream device. Give the electrician the model-specific manual before the distribution-board design is agreed. Marketing copy is not enough for protective-device coordination.
What is a Type B RCD?
Type B RCDs cover a wider set of residual-current waveforms than Type A, including specified smooth DC. This can make Type B part of an EV charging design where the equipment does not provide the alternative DC detection route. IEC 62423 defines requirements and tests for Type B household and similar RCDs.
That does not make Type B a universal add-on. Its current rating, residual-current sensitivity, number of poles, coordination and installation conditions still have to be correct. Upstream and downstream devices also need to work together.
Do not replace a specified Type B device with Type A because the plugs look similar. Do not add Type B without checking the full design either. The installer should document why the selected route meets the applicable rule and manufacturer requirement.
Where do Type AC and Type F fit?
Type AC responds to sinusoidal AC residual current under its specified conditions. EV charging protection has to consider waveforms created by power electronics, so Type AC alone is not the normal solution described by IEC 60364-7-722 for an EV connection point.
Type F adds capabilities for certain frequency-converter loads beyond Type A. IEC 62423 covers Type F as well as Type B. Type F alone must not be treated as protection against smooth DC residual current. Local rules may permit it when coordinated with suitable DC detection, but the installer must verify that exact design.
The device letter is only one part of selection. The exact product standard, markings and installation arrangement matter. Ask the installer to identify every protective device by full specification, not colour or brand.
Does built-in protection mean no external RCD?
No general statement is safe. “Built in” may refer to an RDC-DD, residual-current monitor or a complete switching function. Those terms do not all mean the same thing.
Read the wallbox installation manual for the required upstream protection. It should describe whether DC residual-current detection is included and which external RCD types remain necessary. IEC 61851-1 also requires equipment information that supports coordination with the fixed installation.
The electrician should check that built-in and upstream devices do not leave a protection gap. They should also consider what happens after a detected fault and whether the wallbox can restart automatically.
Does each charging point need separate protection?
IEC 60364-7-722 contains requirements for circuits supplying EVs and protection at connection points. How those requirements appear in enforceable local wiring rules depends on national adoption. Multi-point and load-managed installations need a designed arrangement, not a casual shared circuit.
Separate protection can help isolate one fault without disabling unrelated circuits. Yet the exact architecture may differ when equipment contains multiple controlled outputs. The installer must check the standard and instructions for that system.
For a home with one wallbox, ask the installer to show which device protects that charging circuit. For several wallboxes, ask for a simple single-line diagram and a description of fault isolation.
What should you ask the installer?
Use questions that produce verifiable answers:
- Which locally adopted wiring rule applies to this EV connection point?
- What residual-current waveforms must the design detect?
- Does the wallbox contain an IEC 62955 RDC-DD or another DC function?
- Which upstream RCD type and rating does the manufacturer require?
- Which device provides overcurrent and short-circuit protection?
- How are the devices coordinated with existing upstream RCDs?
- Which commissioning tests will be recorded?
Keep the answers, product manual, circuit schedule and test record. If the wallbox or distribution board changes later, the next electrician needs those design assumptions.
What are the warning signs of a poor proposal?
Be cautious if an installer never asks for the exact wallbox model. Also question a quote that says only “RCD included” without a type, standard or location. A confident one-line answer may hide missing coordination.
Do not accept bypassed protection because a wallbox trips. Repeated tripping is evidence to diagnose, not a setting to defeat. Stop using the point until a qualified person finds the cause.
The safe public message is not that one RCD type always wins. It is that EV residual-current protection is a coordinated design. Type A plus verified 6 mA DC detection and Type B are different valid routes when the equipment and local rules support them.
Frequently asked questions
Does a wallbox need a Type B RCD?
Not always. One common design uses a Type A RCD with suitable 6 mA DC residual-current detection in the charging equipment. Another uses Type B protection. The exact choice depends on the wallbox manual, upstream installation and local rules.
What does 6 mA DC detection do?
It detects a specified level of smooth DC residual current so the charging equipment can disconnect. IEC 62955 covers RDC-DD devices for permanently connected Mode 3 charging equipment. It does not replace every other required protective function.
Is an MCB the same as an RCD?
No. An overcurrent protective device responds to overload and short-circuit conditions. An RCD responds to specified residual current. An RCBO can combine functions, but its exact type and ratings still matter.
Can I reuse an existing household RCD?
Only after a qualified installer checks the wallbox requirements, circuit arrangement, selectivity and local rules. A label saying Type A does not prove that the complete EV protection design is correct.
