A Type A RCD trips on two fault shapes: ordinary AC leakage, and pulsating DC leakage — DC that rises and falls. What it cannot see is smooth, steady DC, and that one gap decides its place on an EV circuit. Type A is enough for EV charging only in combination: where the charging equipment states, in its maker’s documentation, a detection function for the smooth DC faults the RCD is blind to. Standing alone, it leaves that shape uncovered.
Key Takeaways
- A Type A RCD detects AC and pulsating DC residual current — but not smooth DC.
- It is enough for EV charging only with the charger’s stated DC detection, where the wiring rules accept that combination.
- No EVDANCE listing states DC detection, so the circuit’s device carries the answer in the design.
- “Type A fitted” alone is not evidence a circuit is EV-ready; the combination is what counts.
What an RCD Actually Measures
Every RCD runs the same balance test: all the load conductors pass through one sensing core, and current out should cancel current back exactly. If some leaks away — through damaged insulation or a person — they no longer cancel. The leftover, the residual current, is what the device measures, and at its rated level it disconnects the supply. The types differ in which shapes of leftover current they can register.
The Waveforms, Type by Type
| Device | Fault shapes it detects | The gap that matters for EV charging |
|---|---|---|
| Type AC | Sinusoidal AC residual current only | Blind to every DC shape — not an EV answer |
| Type A | AC, plus pulsating DC residual current | Smooth, steady DC passes unseen |
| Type B | AC, pulsating DC and smooth DC residual current | None — it watches the DC shapes itself |
The distinction between pulsating and smooth DC is the whole story. A pulsating fault current still changes — it rises and falls — so a sensing core built on change can register it. A smooth fault current flows steadily, produces no change to sense, and can bias the core, weakening its response to a later AC fault. That is blinding: the device looks healthy and cannot do its job. A car’s onboard charger can, in a fault, put exactly that steady shape onto the supply side — which is why our guide to RCD protection for EV chargers treats DC separately.
When Type A Is Enough — and When It Is Not
Type A earns its place on an EV circuit when two conditions hold together:
- The charger covers the smooth DC side itself. Its manufacturer’s documentation states a detection function for smooth DC fault current — a stated line in the manual, not a sales claim.
- The wiring rules accept the combination. The code your installer works to must allow that pairing for EV circuits.
It is not enough when either condition fails. If the charger’s documentation is silent about DC detection, the charger is treated as having none, and a Type A device alone leaves the smooth DC shape unwatched — the design then puts detection in the circuit instead: the Type B route. Beware the shortcut: “a Type A RCD is fitted” is not evidence that a circuit is EV-ready. The label says what the device sees; the combination is what the design must show.
Reading an EVDANCE Listing for the Answer
Apply that test to our own range: no EVDANCE listing states a built-in RCD or a DC fault detection function, for any model. An installation built around the EV-ACT3204PE wallbox (22 kW three-phase, Type 2, RFID and app, IP66, CE) or the hardwired EV-ACT5006T (up to 48 A, NACS, 25 ft, IP66, ETL/FCC/CE) starts from “detection not stated”, and the installer specifies the circuit’s protection accordingly — the Type B route. The same applies to a portable such as the EV-ACS4005T (9.6 kW, NACS, adjustable 16–40 A, IP66): the question attaches to the circuit it plugs into. If a model’s documentation ever states one, ask for that line in writing.
Frequently Asked Questions
Is Type A better than Type AC?
It sees more: pulsating DC as well as AC. But neither type sees smooth DC, which is the shape EV charging adds — so “better” only matters inside the combination above.
Can a Type A RCD be blinded even if it never trips?
Yes — a steady DC fault can bias the core without tripping it. That hidden failure is what charger-side detection, or a Type B device, prevents.
My charger’s manual never mentions DC detection. What then?
Treat the charger as having none stated, and let your electrician design on that basis — the route where the circuit’s own device watches the DC shapes.
Related Reading
- RCD Protection for EV Chargers: Type A, Type B and DC Detection Explained
- Mode 2 vs Mode 3 Charging: What IEC 61851 Means for Portable EV Chargers
- What Size Breaker Do I Need for an EV Charger?
- IP Ratings for EV Chargers: IP54, IP65 and IP66 Compared
