By Tony Titre, EMEA Business Development Manager (Automotive), Future Electronics
The technology for detecting residual current faults in mains electrical wiring and mains-powered devices is mature, and is implemented in thousands of products offering fault monitoring and protection functions. Indeed, a type of residual current device (RCD) was invented as long ago as the 1950s by the Austrian physicist Dr Gottfried Biegelmeier.
So it is perhaps surprising that the market for residual current monitoring products is now undergoing considerable change: new product introductions are frequent, and a number of new suppliers have recently been drawn to the market. What is prompting such upheaval in this mature market?
The answer is the electric vehicle (EV).
Growth in the number of EVs on the road entails growth in the number of home charger installations, and this is where residual current detection technology plays an important part. Now, both competitive pressure and changing consumer tastes are leading manufacturers of residual current monitors (RCMs) for EV charge points to apply innovative thinking to the product offerings. This is enabling EV charger manufacturers to improve the product designs, increase production efficiency, and reduce bill-of-materials costs.
The function of the RCM in EV chargers
Over the past 10 years, a specialist market in RCMs for ac chargers has developed. The most common example of an ac charger is the familiar 7 kW charge point installed at EV car owner homes and in public road-side charge points. Mains wiring in residential or small office buildings is already protected by RCDs in the mains power distribution panel or consumer unit. But RCDs are only sensitive to ac residual faults.
An EV charger requires both ac and dc fault monitoring:
Both ac and dc residual current faults pose a high risk of shock to the user, of fire, or of damage to electrical circuitry. The causes of fault currents can include:
This means that EV chargers require a special kind of RCM that can detect both ac and dc faults as specified by the IEC 62752 standard, entitled ‘In-cable control and protection device for Mode 2 charging of electric road vehicles’, and IEC 62955, ‘Residual direct current detecting device to be used for mode 3 charging of electric vehicles’. Mode 2 charging is via an ordinary mains plug socket, and Mode 3 charging is via a dedicated wallbox.
Until recently, the annual European production volumes of residential EV chargers were numbered in only the tens of thousands. This means that the market for off-the-shelf RCMs attracted a small number of specialist manufacturers. The toroidal architecture of an RCM is simple, but the design of the magnetics and the signal-processing circuitry requires specialist technical know-how, so charger manufacturers have preferred to buy off-the-shelf RCMs rather than designing and building an RCM, see Figure 1. In the years up to 2022, supplies of these specialist off-the-shelf RCMs were limited, and price pressure on RCM manufacturers was muted.
Fig. 1: Typical three-phase RCM circuit. In a fault-free system, the sum of all currents is equal to zero so that no voltage is induced in the measuring current transformer. If a fault current flows via PE (earth) or other paths, the difference in current in the transformer generates a current flow which is detected by the RCM
Since the beginning of 2023, the market dynamics have changed dramatically. First, the EV market is starting to boom. Battery electric and plug-in hybrid electric cars made up just 3.0% of all new car registrations in Europe in 2019. By February 2025, that share had jumped to 22.6%. Some 255,489 battery electric cars were sold in Europe Union member states in the first two months of 2025 [1].
With sales volumes of EVs rising fast, the market for ac chargers is also set to boom. This is having two profound effects on the market for RCMs.
Now, thanks to moves by governments to encourage EV car ownership and to penalise fossil fuel-powered cars, the profile of the EV buyer is changing. EVs are now a mainstream product, and price has become a much more important factor in the buyer’s choice. The charger is generally seen as a commodity item, and is subject to intense price pressure, which is being passed on to the manufacturers of components including the RCM.
These two factors are prompting RCM manufacturers to innovate in both designs and business models, and are leading to a fertile period for new product introductions. Here are the most important new product developments in the market for RCMs.
Support for automated assembly
The typical product configuration of RCMs for EV chargers requires the power cable to be routed manually through the aperture in the transformer, shown in Figure 2. This manual assembly process can be awkward and time-consuming when the RCM is mounted inside the charger enclosure.
Fig. 2: The Broyce Control RCM-EV-03 has the traditional design configuration with an aperture through which the power cable runs
To enable streamlined, automated assembly, Broyce Control has introduced a new RCM, the board-mount RCM-EV-08/09, which features four integral primary conductors. Board connections are made via two 4-way male pin headers on the underside of the housing. The RCM detects ac and dc fault currents according to IEC 62752, and is configured with fixed 6 mA dc and 30 mA ac trip levels. It is suitable for Mode 2 and Mode 3 EV charging systems. In addition, a 6 mA-only RCMEV09 version is available for Mode 3 charging systems.
Fig. 3: The Broyce Control RCM-EV-08/09 simplifies assembly operations, eliminating the need to route the power cable through an aperture
Simpler board layout
Zettler Magnetics is a globally significant manufacturer of transformers, chokes and power modules, and is making an important move in the market for EV charger RCMs with the development of the APR00T0332WT and APE00T0332WT. Like the Broyce Control RCMs, this is a fluxgate type of current sensor, a technology which offers high measurement accuracy of typically ±0.1%, and high linearity over temperature. The APR00T0332WT RCM complies with the specifications of the IEC 62955 standard, and the APE00T0332WT complies with IEC 62752.
The innovation in the APR00T0332WT and APE00T0332WT is the new approach to the board layout. Popular RCMs on the market today require complex routing of traces between the power supply, the RCM and the load. The design of the APR00T0332WT and APE00T0332WT has been made with easy board layout in mind, while maintaining high sensor performance and compact dimensions.
Fig. 4: The Zettler APR00T0332WT and APE00T0332WT provide for easy routing of traces in an EV charger board layout
Lower bill-of-materials cost
The third trend in evidence in the market is manufacturer response to bill-of-materials (BoM) cost pressure on charger manufacturers. An instance of this is provided by Chinese manufacturer Hongfa. The company supplies a range of standards-compliant RCMs, the HFCA-Fxx family, which are attractively priced. These include the HFCA-F12 with analog output, and HFC-F15 with digital PWM, shown in Figure 5.
Hongfa can reduce the cost of these RCMs by reducing the functionality: the HFCA-Fxx family RCMs are fluxgate sensors with simple analog or digital PWM outputs. This eliminates the need for additional circuitry in the form of a microcontroller and its associated components. The software required to meet the requirements of the IEC 62955 and IEC 62752 standards, for the HFCA-F15, or just the IEC 62955 for the HFCA-F12, runs instead in the host microprocessor or microcontroller in the EV charger.
Fig. 5: The Hongfa HFCA-F15 RCM
New opportunity to reduce BoM and production cost of EV chargers
With a boom in EV car sales in full swing, the number of EV chargers required to satisfy the European market is set to grow fast. This is bringing more suppliers and much more competitive pressure to bear on the market. Innovations by manufacturers of RCMs, a crucial safety component, look set to help charger manufacturers to ramp up production efficiently while meeting consumer demand for more affordable charger products.
[1] Statistics from European Automobile Manufacturers Association (ACEA): www.acea.auto/pc-registrations/new-car-registrations-3-in-february-2025-year-to-date-battery-electric-15-2-market-share/
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