IEC 61851-1 defines four charging modes for conductive EV charging, distinguished not primarily by speed but by where the control pilot (CP) function lives, what protects the circuit, and how the EVSE and vehicle communicate. Mode 2 puts the CP function inside a portable in-cable control box plugged into a general-purpose socket. Mode 3 puts it inside a dedicated, fixed AC charging station. Mode 4 hands the whole AC-to-DC conversion to an external station and shifts the vehicle-charger conversation to a digital protocol. Knowing which mode you're standing in front of tells you which circuit, protection device and test instrument you actually need.
Mode 1: why it barely enters the conversation
Mode 1 is direct connection between an EV and a standard socket outlet, with no control pilot communication at all between vehicle and supply, meaning no electronic negotiation of available current, no way to confirm the connection is safely made before power flows, and no dedicated fault detection specific to EV charging. This absence is exactly why Mode 1 is restricted or effectively unused in most developed charging frameworks, Singapore's included; it's worth naming only so the numbering makes sense, since almost nothing you test in the field will be Mode 1.
Mode 2: the control pilot lives in the cable, not the wall
Mode 2 charging uses a portable EVSE, commonly called an in-cable control box or IC-CPD (In-Cable Control and Protection Device), plugged into a standard general-purpose socket outlet rather than a dedicated charging point. The defining feature is where the control pilot function physically sits: inside a control box moulded into the charging cable itself, not a fixed wallbox. This is the "travel charger" or "granny cable" many EVs are supplied with, typically limited to a single-phase current of 10–13 A to stay within what an ordinary domestic socket circuit can safely and continuously supply. Electrically, the socket the IC-CPD plugs into was very likely designed and tested as a general-purpose circuit, not a dedicated EV charging circuit: its earth fault loop impedance, RCD protection and cable sizing were verified against ordinary intermittent loads, not several hours of continuous near-maximum current draw. The IC-CPD's own control pilot function provides some protection, negotiating a safe current limit and detecting basic faults, but cannot retroactively upgrade the fixed circuit's design margin.
What this means for testing: two things need checking. First, the general-purpose socket circuit needs verification as suitable for sustained near-maximum draw over hours, which can mean re-checking loop impedance and cable thermal performance rather than assuming a standard periodic domestic test is sufficient. Second, the IC-CPD device itself needs its control pilot behaviour verified independently, confirming it correctly negotiates state transitions and enforces its current limit, exactly the kind of simulation the Fluke FEV300 test adapter kit and FEV350 analyzer are built to exercise.
Mode 3: the control pilot lives in a dedicated, fixed station
Mode 3 is what most people picture when they say "EV charger": a dedicated AC EVSE, wall- or pedestal-mounted, hard-wired into its own circuit, with the control pilot and proximity pilot functions built into the fixed unit rather than the cable. This is the mode a Fluke FEV350 is designed around, carrying single or three-phase power commonly up to 32 A per phase, giving AC charging power up to roughly 7.4 kW single-phase or 22 kW three-phase. Because Mode 3 uses a dedicated circuit rather than a shared socket, that circuit can, and under Singapore's SS 638 and IEC/HD 60364-7-722 must, be designed specifically for the sustained current and duty cycle of EV charging from the outset (see our guides to earth loop impedance testing at EV charging points and insulation resistance testing for EV charging circuits): a dedicated design load, a protective device sized for the actual current and disconnection time required, and RCD protection (Type A minimum, Type B where the system could produce smooth DC fault currents) matched to that installation. For testing, the full FEV350 sequence applies, PE earth pre-test, 30 mA RCD plus 6 mA RDC-DD trip testing, nominal voltage and phase sequence, control pilot testing with waveform analysis, proximity pilot verification and error condition testing, alongside earth bond, insulation and loop/line impedance via a compatible multifunction installation tester. Because the control pilot function is built into the fixed station rather than a swappable cable, a fault found here points at the charging station itself, not a portable accessory that could simply be swapped out.
Mode 4: the vehicle's own onboard charger is bypassed entirely
Mode 4 hands AC-to-DC conversion to the external charging station itself rather than the vehicle's onboard charger, delivering DC current directly to the battery, allowing it to reach power levels an onboard charger could never handle since the conversion electronics live in the much larger, more heavily cooled station. CCS2 is the connector standard Singapore's regulatory framework favours for public Mode 4 charging, and the Fluke FEV500 is built specifically to test this mode. Mode 4 does not rely on a simple analogue PWM control pilot signal the way Mode 2 and 3 largely do; instead it uses a full digital communication channel, established through SLAC power-line communication followed by ISO 15118 or the earlier DIN SPEC 70121 protocol, to negotiate and manage the session. The station, not the vehicle's onboard converter, does the heavy electrical lifting, which is why FEV500 needs to verify power electronics, insulation resistance on both DC polarities, PE continuity at high test current, IMD response, and digital protocol negotiation, an entirely different test surface from a Mode 3 station's control pilot and RCD checks. A Mode 4 fault is more likely to show up as a SLAC or ISO 15118/DIN SPEC 70121 handshake failure, an insulation or IMD response problem on the DC power path, or a load test discrepancy in delivered voltage, current or power, rather than control pilot waveform distortion you'd chase on a Mode 3 AC station.
The differences, side by side
| Mode 2 | Mode 3 | Mode 4 | |
|---|---|---|---|
| Where CP function lives | In-cable control box (IC-CPD) | Fixed dedicated EVSE | Fixed DC charging station |
| Connection point | General-purpose socket outlet | Dedicated hard-wired circuit | Dedicated high-power circuit |
| Typical power | ~2.3 kW to 3 kW (single-phase, limited current) | Up to ~7.4 kW single-phase or ~22 kW three-phase | Tens to hundreds of kW, station-dependent |
| Who converts AC to DC | Vehicle's onboard charger | Vehicle's onboard charger | The external charging station |
| Communication method | Analogue PWM control pilot | Analogue PWM control pilot | Digital: SLAC + ISO 15118 / DIN SPEC 70121 |
| Typical connector | Type 1 / Type 2 (with domestic plug on supply side) | Type 1 / Type 2 | CCS2 (Combo 2) |
| Test focus | Underlying socket circuit's suitability + IC-CPD's own CP behaviour | Full FEV350 sequence: PE pre-test, RCD/RDC-DD trip, CP/PP, loop impedance | FEV500 sequence: RISO both polarities, RLO, IMD no-trip/trip, comms negotiation, load test |
| Fluke instrument | FEV300 / FEV350 (CP simulation) | FEV350 | FEV500 |
Why the mode, not just the connector, should be the first question you ask
Two Type 2 connectors, one on a Mode 2 travel cable and one on a Mode 3 wallbox, look almost identical but represent fundamentally different electrical realities. Testing the Mode 2 setup without recognising the underlying socket circuit was likely never designed for sustained EV charging load misses the actual risk, and testing a Mode 3 station's control pilot the same way you'd test a Mode 4 station's digital communication link would be testing the wrong layer entirely. Identifying the mode first, before reaching for an instrument, determines whether you're testing a portable accessory plugged into a kitchen socket, a purpose-built AC charging station, or a DC power conversion plant, three genuinely different jobs wearing similar-looking connectors.