EV Charger Fault Finding: No Communication, Earth Fault, Pilot Signal Issues and CT Clamp Errors

Summary

EV chargepoints combine standard electrical installation with embedded electronics and software. Fault-finding requires both electrical test skills and an understanding of the IEC 62196 Mode 3 charging protocol. A chargepoint that "won't charge" may have a supply fault, a pilot signal fault, a vehicle compatibility issue, or simply be waiting for its scheduled charging window to open.

This article provides a systematic fault-finding approach for electricians called back to a site after commissioning, or attending a new fault on an installation they didn't originally fit.

Key Facts

• Control pilot (CP) signal — 12V PWM signal on pin 5 of the IEC 62196 Type 2 connector; communicates supply current availability from chargepoint to vehicle; faults in CP signal prevent charging from starting
• Proximity pilot (PP) signal — pin 4; communicates cable rating to chargepoint; resistor fault (wrong resistance, open circuit) causes chargepoint to refuse to start
• State A–E — the IEC 62196 / IEC 61851 charging states: A = disconnected, B = vehicle connected, C = charging, D = ventilation required, E = fault/no power, F = chargepoint fault
• RCD nuisance trip — a common call-back fault; usually caused by DC leakage from the vehicle OBC; Type AC RCDs are sensitive to DC-offset leakage current; Type A or Type F RCDs are more tolerant
• Earth fault at chargepoint — most modern chargepoints perform a self-test checking earth continuity before allowing charging to begin; an earth fault prevents charging start
• PME earth fault — if the chargepoint is not correctly earthed (TT electrode not fitted, or TT electrode gone high resistance), the chargepoint may trip or refuse to charge
• CT clamp errors — incorrect CT orientation or polarity causes wrong import/export readings; chargepoint may throttle incorrectly or display implausible readings
• Wi-Fi disconnected — most smart chargepoints will still charge on a default schedule if Wi-Fi is lost, but dynamic tariff features and remote monitoring stop working
• Firmware update failure — a chargepoint attempting a firmware update may appear unresponsive for 5–15 minutes; do not power-cycle during an update

Quick Reference Table: Fault Symptoms and First Checks

Detailed Guidance

Systematic Fault-Finding Approach

Step 1: Gather information from the customer Before attending site, ask:

• What is the chargepoint doing (or not doing)? What does the LED/display show?
• When did the fault start? Any recent changes (new router, power cut, software update)?
• Does the same fault happen with any vehicle, or only one specific vehicle?
• Is the chargepoint showing any error codes?

This narrows the diagnosis significantly before you arrive.

Step 2: Confirm supply Measure voltage at the chargepoint's L/N/E terminals. If 230V is present and stable, the circuit is intact. If no voltage:

• Check the RCBO in the consumer unit: has it tripped?
• If tripped: reset and monitor; if it trips again immediately, there is a fault on the circuit (proceed to insulation resistance test)
• If RCBO is on but no voltage at chargepoint: continuity fault in the cable (break; loose connection; damaged cable)

Step 3: Test the circuit If the RCBO is tripping repeatedly, disconnect the chargepoint and test the cable insulation resistance:

• 500V DC between L-E, N-E, L-N
• If insulation resistance is low (<1MΩ), the cable is damaged (physical damage, water ingress in an outdoor conduit, or failure of a connector/junction)
• If insulation resistance is good with chargepoint disconnected, reconnect chargepoint and retest — the fault is in the chargepoint electronics (contact manufacturer; warranty claim if within warranty period)

Step 4: Check the CP signal If supply is present but charging won't initiate, check the control pilot:

• Use an EVSE tester or oscilloscope at the Type 2 connector (for socketed units) or at the vehicle connector (for tethered units)
• Expected: 12V idle; PWM at approximately [rated_amps/0.6]% duty cycle when vehicle is connected (e.g., 32A = ~53% duty cycle per IEC 61851)
• If CP is stuck at 0V or +12V with no PWM: chargepoint control board fault or cable break
• If CP duty cycle is incorrect: chargepoint configuration error (check current limit setting in the app)

Step 5: Confirm vehicle compatibility If the EVSE tester shows the chargepoint working correctly but a specific vehicle won't charge:

• Try a different vehicle; if the second vehicle charges, the fault is vehicle-specific (vehicle OBC fault, cable issue, vehicle charging limit setting)
• Check the vehicle's own charging menu for error messages
• Confirm the vehicle is not in a charge scheduling mode that is preventing charging

RCD Nuisance Trips

A common fault: the RCBO or RCD trips intermittently or after a few minutes of charging. This is almost always caused by DC leakage from the vehicle's onboard charger.

How it happens: Vehicle onboard chargers (particularly from some manufacturers, notably some older Renault Zoe models and various Chinese imports) can produce DC current offset on the AC supply. Standard Type AC RCDs are designed to trip on pure AC residual current — they are also sensitive to DC-offset leakage. This can cause nuisance trips even though the leakage is within the vehicle's Type 2 specification.

Solution: Replace the Type AC RCBO with a Type A or Type F RCBO. Type A devices respond to sinusoidal AC and pulsating DC residual current (but not pure smooth DC). Type F adds Type A characteristics plus additional protection against high-frequency leakage from variable-frequency drives.

Most modern OZEV-approved chargepoints include an integral DC leakage detector (equivalent to BS DD IEC/TS 62955) which satisfies the BS 7671 requirement for RCD protection more precisely. If the integral DC detection is present and functioning, the circuit RCBO can be a standard Type A rather than Type F.

Note: Always check whether the chargepoint includes integral DC detection before specifying the RCBO type. Some chargepoints' documentation specifies the required RCBO type.

CT Clamp Faults

Where load management or solar divert is fitted, CT clamp errors cause incorrect chargepoint behaviour:

Symptom: Chargepoint barely charges despite headroom available

• CT reading shows inflated import current
• Cause: CT clamp reversed (arrow pointing wrong direction); polarity inverted in app
• Fix: Reverse CT clamp orientation or invert polarity setting in the chargepoint app

Symptom: Chargepoint doesn't throttle during high-load events

• CT reading shows low or zero current even when other loads are running
• Cause: CT clamp not fully closed; clamp not on the correct conductor; signal cable break
• Fix: Check CT clamp is fully locked; confirm it is on the main incomer live (not neutral); test signal cable continuity

Symptom: Chargepoint shows impossible CT reading (e.g., 200A on a 100A fuse)

• Cause: CT clamp on a sub-circuit rather than the main incomer; or incorrect CT ratio configured in the app
• Fix: Confirm CT is on the main incomer tails; check CT ratio configuration in the app (some chargepoints require the CT ratio to be entered manually)

Symptom: Solar divert mode not working

• CT reading is always positive (showing import) even when PV is generating
• Cause: CT clamp direction is wrong — it is showing all current as import
• Fix: Reverse the CT orientation; or invert the CT polarity in the app and retest

Wi-Fi and App Faults

Chargepoint shows offline in app:

1. Confirm the chargepoint's Wi-Fi LED or status indicator is active
2. Check the router: is it broadcasting on 2.4GHz? (Most chargepoints require 2.4GHz, not 5GHz)
3. Check the router's connected devices list — is the chargepoint shown?
4. If not connected: power-cycle the chargepoint (switch off the MCB for 30 seconds); the chargepoint should reconnect automatically
5. If still not connected: router channel or security settings may have changed (some routers update firmware and reset settings); re-enter Wi-Fi credentials via the chargepoint's setup process

App not showing charge history:

• Often a cloud sync delay; force-refresh in app
• Check the chargepoint firmware version; if out of date, a firmware update may resolve app sync issues
• Contact manufacturer support if the issue persists after reconnection

OCPP commercial chargepoint not connecting to CPMS:

• Confirm OCPP server URL, port, and password in the chargepoint configuration
• Check network firewall: commercial networks often block non-standard ports; OCPP typically uses WebSocket on port 443 or 9000
• Test OCPP connection using a test CPMS (several free OCPP test servers are available online)

Over-Temperature Shutdown

Symptom: Chargepoint starts charging then stops with an over-temperature error after 10–30 minutes

Causes:

• Long cable run at full 32A load causing conductor temperature rise
• Loose connection at consumer unit or chargepoint terminals causing resistance heating
• Chargepoint mounted in an enclosed space without ventilation
• Ambient temperature very high (summer, south-facing wall)

Checks:

• With charging running, feel the cable close to the consumer unit, midway along the run, and at the chargepoint: any section that is hotter than others indicates high resistance at that point (check connections either side)
• Confirm the cable size is appropriate for the run length (6mm² for runs over ~15m; 10mm² for very long runs)
• Move the chargepoint to a shaded or ventilated location if over-temperature is ambient-related

Frequently Asked Questions

The chargepoint worked fine for 6 months and has suddenly started tripping the RCD. What has changed?

Two likely causes: (1) the customer has changed vehicle (new vehicle has higher DC leakage characteristics); (2) the cable insulation or a connection has degraded, causing increased leakage to earth. Test insulation resistance first (quick check). If insulation is fine, the cause is likely the vehicle — try another vehicle to confirm, then replace the RCD with a Type A or Type F as appropriate.

A customer says the app shows the chargepoint charging but the car isn't gaining charge. What do I check?

The chargepoint may be in a paused state (eco mode with insufficient solar) or the app may be showing a stale state. Check the physical chargepoint LED: is it showing "charging" or "paused"? If paused, switch to fast mode manually and see if charging begins. If the chargepoint shows charging but the car doesn't respond, check the tethered cable or Type 2 socket for damage.

Can I fault-find an EV chargepoint I didn't install?

Yes. You need a copy of the installation manual for the specific model (available from the manufacturer's website). You also need access to the chargepoint's configuration app — if the previous installer registered it under their account, the customer may need the manufacturer to transfer ownership. Most manufacturers have a process for this on request from the property owner.

Regulations & Standards

• BS 7671:2018+A2:2022 — Chapter 722: protection and testing requirements

• IEC 61851 — EV charging system; CP signal States A–F definitions

• IEC 62196 — Type 2 connector; CP and PP pin assignments

• BS DD IEC/TS 62955 — DC leakage current measurement for EV chargepoints

• IET Guidance Note 7 — EV Charging — fault-finding principles

• Myenergi technical support — Zappi fault codes

• Ohme technical support — Home Pro fault diagnosis

• ev charger testing commissioning — commissioning and baseline test values

• bs 7671 ev wiring requirements — Chapter 722 protection requirements

• ct clamp load management — CT clamp fault-finding

• pme earthing ev charging — earthing fault diagnosis