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

Quick Answer: EV chargepoint faults fall into four main categories: circuit faults (supply failure, RCD trip, earth fault), chargepoint hardware faults (control board, relay, cable damage), communication faults (CP signal, pilot signal errors), and smart/network faults (Wi-Fi, app, CPMS). Diagnose methodically: confirm supply voltage at the chargepoint terminals first, then test the CP signal, then check app/network status. Most "faults" reported by customers are actually scheduling issues or Mode 3 protocol mismatches rather than hardware failures.

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

Quick Reference Table: Fault Symptoms and First Checks

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Symptom First Check Common Cause
Chargepoint completely dead Voltage at terminals; RCBO in consumer unit RCBO tripped; supply fault; cable damage
Chargepoint powers on but won't start charge CP signal; vehicle state B confirmed; scheduling CP signal fault; scheduling window active; earth self-test fail
Chargepoint starts then stops immediately RCD type; DC leakage from vehicle Type AC RCD tripping on DC leakage
Intermittent RCD trips RCD type; insulation resistance of cable DC leakage; cable insulation degradation; RCD mechanical wear
Charging at wrong rate CT clamp reading; chargepoint current limit setting CT clamp fault; incorrect configuration
App shows offline Wi-Fi signal; router settings; chargepoint Wi-Fi module Wi-Fi dropout; DHCP lease expired; firewall
Over-temperature shutdown Chargepoint enclosure; cable conductor temperature Long cable run at full load; inadequate ventilation; loose connection

Detailed Guidance

Systematic Fault-Finding Approach

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

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:

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

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

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

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

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

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

Symptom: Solar divert mode not working

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:

OCPP commercial chargepoint not connecting to CPMS:

Over-Temperature Shutdown

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

Causes:

Checks:

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