How to choose an RCD sensor for a wallbox or EV charger

Choosing a residual current sensor looks simple: every EVsense model detects Type A + DC 6mA residual current. But a sensor that is electrically correct can still be the wrong part if the conductors do not fit, the mounting style does not suit your assembly line, or you end up adding a separate current transformer that a different model already integrates. This guide gives charger and wallbox designers a step-by-step checklist.

Step 1: Charger mode, market and target standard

Begin with what you are building and where it will be sold. This decides which standard the protection must satisfy:

• Mode 2 portable charger (in-cable control box). The in-cable control and protection device must meet IEC 62752 (IC-CPD). The device itself must detect both AC and smooth DC residual current. See our guide to IEC 62752 IC-CPD.
• Mode 3 wallbox or AC charging station. IEC 61851-1 requires handling of DC fault current above 6 mA. The common route is a Type A RCD in the installation plus a residual direct current detecting device (RDC-DD) to IEC 62955 inside the charger. See IEC 62955 RDC-DD explained.
• China market AC charging piles. The equivalent references include GB/T 40820 for RDC-DD and GB/T 22794 for Type F and Type B RCCBs. See GB/T vs IEC leakage protection.

EVsense sensors are designed with these IEC and GB references in mind. The selection guide also marks which models are positioned for Mode 2 only (4R2Z and CT1719, IEC 62752) and which cover both Mode 2 and Mode 3 applications.

Step 2: Phases and rated current

Next, check how much current passes through the sensor and how many conductors there are.

• Single-phase portable or small wallbox. Pre-wired sensors are attractive here because the line and neutral jumpers are already part of the sensor. The 4R2Z is pre-wired for single-phase use. The CT1719 magnetic core is pre-wired for single-phase 20 A, and the CT2728 for single-phase 32 A.
• Three-phase wallbox (for example 11 kW or 22 kW). All three phase conductors and neutral must pass through the sensing core, so you need an aperture large enough for four conductors with their insulation. The 1R20 Series with its 20 mm aperture is the typical starting point, and our application material includes a three-phase 22 kW charger using it.

Step 3: Aperture vs conductor size

For through-hole sensors, measure the bundle of conductors you will route through the core, including insulation, and leave assembly clearance. Published apertures from the EVsense selection guide:

Model	Aperture or wiring	Mounting
1R20X	20 mm aperture	Harness connection
1R20Z	20 mm aperture	PCB-mounted
CT1836	18.5 mm aperture	Harness connection (core for chip solution)
5R15Z	15 mm aperture	PCB-mounted
3R14X	14 mm aperture	Harness connection
2R4Z	2 × 4.5 mm apertures	PCB-mounted
4R2Z	Pre-wired, 1 phase	PCB-mounted
CT1719	Pre-wired, 1 phase 20 A	PCB-mounted (core for chip solution)
CT2728	Pre-wired, 1 phase 32 A	PCB-mounted (core for chip solution)

If your conductors are close to the limit of an aperture, choose the next size up. Forcing cables through a tight window makes assembly slower and can stress the insulation.

Step 4: PCB-mounted or harness connection

The mechanical format affects your production process as much as your schematic.

• PCB-mounted sensors (1R20Z, 2R4Z, 4R2Z, 5R15Z) solder directly to the controller board. This suits compact designs and automated assembly, and keeps the signal wiring short.
• Harness-connected sensors (1R20X, 3R14X) sit in the cable path and connect to the controller with a short wire harness (the 1R20X standard harness is 200 mm). This gives more freedom when the power conductors do not run near the control PCB.

Whichever format you choose, remember the datasheet guidance: install the sensor at the output side of the charger and keep it more than 3 cm from the relay. Our PCB integration guide covers layout in more detail.

Step 5: How much integration do you need?

Many chargers also need to measure voltage and load current for metering, power management or display. Instead of adding separate magnetic parts, you can choose a sensor that integrates them:

• 2R4Z integrates both a voltage transformer and a current transformer with the residual current detection.
• 6R2Z integrates a current transformer.
• CT2728 integrates a 32 A current transformer with accuracy class 0.2 (rated output 16 mA into a 10 Ω burden), useful when the charger needs energy metering.
• CT1719 integrates a 20 A current transformer (rated output 20 mA into a 40 Ω burden).

Fewer separate components usually means a smaller board and simpler assembly.

Step 6: Packaged sensor or chip + magnetic core?

EVsense offers two architectures:

1. Packaged sensors (1R20, 2R4Z, 3R14X, 4R2Z, 5R15Z, 6R2Z). A complete module with a simple interface: 5 V supply, a digital TRIP output and a CLK&CHK input for self-test and zero calibration.
2. Chip + magnetic core (CT1836, CT1719, CT2728 with the external ILM2112TQC IC). You place the IC and a small peripheral circuit on your own PCB, using the reference design in the datasheet. This gives you more layout control and is suited to high-volume designs where the engineering team wants to own the circuit.

Quick selection table

Your project	Good starting point
Three-phase 22 kW Mode 3 wallbox	1R20 Series (20 mm aperture)
Mode 3 charger needing voltage and current measurement	2R4Z (integrated VT + CT)
Mode 2 portable charger, single phase	4R2Z or CT1719
GB-standard AC charging pile in China	5R15Z
Compact controller PCB, harness connection	3R14X
Single-phase 32 A charger with metering, own PCB layout	CT2728 + ILM2112TQC
Chip solution with a larger conductor bundle	CT1836 + ILM2112TQC

Treat this table as a shortlist, not a final decision. Confirm the mechanical drawing and pinout in each datasheet, then validate a sample in your own charger.

Step 7: Send your project details

The fastest route to the right model is to share your constraints. Useful information includes:

• Charger mode, target market and standard
• Number of phases, rated current and conductor size
• Available PCB space or enclosure drawing
• Preferred mounting (PCB or harness) and controller interface
• Prototype schedule and expected annual volume

You can compare all EVsense models side by side or send your project details and our engineers will recommend a model and arrange datasheets and samples. If you are still deciding between architectures, read Type A vs Type B RCD for EV chargers first.

Frequently asked questions

What is the most important parameter when choosing an RCD sensor?

Start with the charger type and target standard (Mode 2 IC-CPD to IEC 62752, or Mode 3 charger with RDC-DD to IEC 62955), then check that your conductors physically fit the sensor aperture or match its pre-wired current rating. Electrical trip thresholds are similar across EVsense Type A + DC 6mA models.

Do all EVsense RCD sensors have the same trip thresholds?

The packaged sensors share the same published typical thresholds: smooth DC trip at 3 mA min, 4.5 mA typical and 6 mA max, and 50 Hz AC trip at 15 mA min, 22 mA typical and 30 mA max. The main differences are mechanical format, aperture, mounting style and integrated transformer functions.

When should I choose a chip + magnetic core solution instead of a packaged sensor?

Choose a magnetic core such as CT1836, CT1719 or CT2728 with the external ILM2112TQC IC when you want to place the detection circuit directly on your own controller PCB and control the layout yourself. Choose a packaged sensor when you want a ready-made module with a simple 5 V, TRIP and self-test interface.

What information should I send to get a model recommendation?

Send the charger mode, target market and standard, number of phases, rated current, conductor diameter or busbar size, available PCB space, preferred mounting (PCB or harness), output requirements and expected annual volume.

Need help choosing a sensor?

Send your charger platform, target standard, rated current and PCB space. Our engineers reply with a model recommendation, datasheets and sample options.

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