EV charger tripping or showing an earth fault: what it means

Why a chargepoint trips, and why that is usually good news

Think about what a home charger is protecting. Someone is standing on a wet drive with a hand on a metal car and a cable running into it. Nothing else in the house is used like that, and the wiring rules treat it accordingly. On the earthing arrangement most British houses have, one conductor from the street does two jobs — it carries the neutral and it provides the earth — and if that conductor breaks upstream, every earthed metal surface in the property, the car included, can float up to mains voltage. The rules therefore require a chargepoint on that kind of supply to detect the break and disconnect. Manufacturers generally build the detection into the unit instead of driving an earth rod, and myenergi describe the effect of theirs operating in careful terms: the zappi cuts itself off from the incoming supply entirely, so that nothing at the socket or on the cable — live, neutral, earth or the control signals — can present a shock. They cite BS 7671:2018 Amendment 1:2020 as the requirement it meets.

The practical consequence is that a charger which drops out and will not restart is, more often than not, telling you about the mains arriving at your house rather than confessing to a fault of its own. That is the distinction this guide turns on, and it is the reason the reflex of resetting it each evening is the wrong one.

The voltage window

Ohme are the one manufacturer that publishes the actual figures, and they account for the pattern most owners describe. When the mains rises above 253 V or falls below 207 V, their units suspend the session, flash a red error, record an overvoltage or undervoltage event, and carry on again once the reading is back in range. Mains voltage is not constant: sunny afternoons with a street full of solar panels exporting push it upwards, the evening peak drags it down, and a drop-out that recurs at the same hour each day is a fingerprint of the supply rather than of the charger.

You do not have to guess. The Ohme app displays the live mains reading for a Home or Go; on a Home Pro, with the car connected, two taps of Next View bring up the energy screen with the voltage highlighted. What you do with the number is the part Ohme are unusually clear about: the call goes to your distribution network operator — the company that owns the cables into your house, as distinct from the supplier that bills you — not to Ohme. The operator can measure at your property and correct the level at the local substation, at no cost to you. Ohme ask two things of that process: that the operator logs the voltage over several days rather than taking one reading, since the level moves around through the day and night, and that you keep charging as normal in the meantime, because each interruption is the protection doing its job. Only if the errors persist after the operator has confirmed the correction does the case go back to Ohme, with the operator's report attached.

The earth codes

PE Fault, code 25, on a zappi. The charger continuously tests the earth path it relies on, and this code means the test has failed — in myenergi's words, the earth is either disconnected or its impedance is too high. Nothing inside the unit has broken. Typical causes are a terminal disturbed during work on the consumer unit or the charger circuit, corrosion or a loosened connection, or an earth rod that has dried out; myenergi also name a configuration case, where a supply that is IT earthed needs the Supply Grid and Earthing menu setting checked. The action they publish has three parts — unplug the EV, check the earth connection to the zappi, hold the button to reset — and the middle one belongs to a registered electrician, not to you. It involves opening a permanently connected mains enclosure, and the same manual says the device must be disconnected from the supply before the cover comes off and that only suitably qualified people may maintain or service it. A chargepoint that has found a poor earth and refused to charge has behaved exactly as designed. Leave it until it has been looked at.

PEN Fault, code 29 is the open-PEN protection described above having operated. myenergi's action has a clause most owners skip: unplug the EV, make sure the fault has been removed, then press and hold the button to reset. If the condition is still present the unit simply trips again, and if the supply's PEN conductor has genuinely failed that is a distribution network operator emergency, not something to work around. An earlier revision of the same manual used code 29 for an RCD trip, so on an older zappi the same number may mean earth leakage somewhere in the charging path.

The RCD

Residual current protection exists to interrupt a leakage path through a person. Ohme build it into the unit and publish the reset — one of very few owner actions any manufacturer in this category sanctions: unplug the vehicle and re-plug; if that does not clear it, switch off at the dedicated breaker, wait five seconds, switch on. A single event that never returns was a transient; looking at the plug and socket for water or damage while the cable is out is this site's addition, because moisture in a connector is a common cause of one.

A pattern is not a transient. A device that trips repeatedly is detecting something, and resetting past it removes the protection rather than the fault. The leakage may be anywhere along the charging path — the unit, the lead or the car — and finding which is a registered electrician's job. When you call, mention what kind of RCD sits upstream in the consumer unit. Ohme ask for Type A at minimum, because a Type AC device can be saturated by the small smooth DC currents (under 6 mA) that vehicle charging can produce, and a saturated RCD may fail to trip when it should — so an installation with the wrong device is unpredictable in both directions.

The one fault that is inside the charger

Contactor Fault, code 28, is the most serious thing a zappi reports about itself, and the wording is worth reading for what it reveals about the design: the relay inside has a welded contact, and the secondary relay is open to make sure the supply to the EV is isolated. A contactor is the heavy switch that connects the mains to your car, and one that has welded shut has stopped being a switch. The unit is built with two in series so that one failing closed does not leave the output live; it has detected the weld, held the other relay open, and reported it. That is a contained failure rather than an emergency. myenergi's action is the standard one — unplug the EV, press and hold to reset — and it is worth one attempt, because the detection can fire on a condition that is not a genuine weld. If it comes straight back, it was, and that is a manufacturer call: free under warranty, which is where many of these fall, and a contactor replacement or a unit swap outside it. Codes 26 and 27 — the built-in protection components failing to communicate or failing their pre-charge self-test — are the same class of problem and the same call.

Right now

If the charger keeps tripping, do not keep resetting it. Switch it off at its own breaker in the consumer unit rather than waiting for a call. If you can smell burning, see scorching, or find a cable or plug that has overheated, leave it isolated and do not use it again until it has been looked at. Do not open the enclosure: there are no user-serviceable parts on any brand, and bp pulse's advice for any sign of damage is to power the unit down at the distribution board.

Who to call

• Your distribution network operator for anything about supply voltage or the PEN conductor: overvoltage and undervoltage errors, a PEN Fault that returns after a reset, a pattern by time of day, or several houses affected at once. They resolve it at the substation and do not charge.
• A registered electrician for anything about the earth, the RCD or the installation: a PE Fault, an RCD that trips repeatedly, the type of protective device upstream. Installing a chargepoint normally means a new circuit from the consumer unit, which is notifiable electrical work under Part P of the Building Regulations in England and Wales and is normally done by an electrician registered with a competent-person scheme; that is the accurate claim, and it is not the same as the criminal restriction that applies to gas.
• The manufacturer for a fault the unit reports about itself: a Contactor Fault, a self-test failure, flashing yellow on an Ohme Home or Go that survives both resets. Within warranty, this should cost nothing.

What it costs

The brackets are those the code pages on this site carry.

• Nothing for a supply voltage problem or a PEN fault on the supply side — the network operator's to resolve — or for a single RCD event that never returns.
• An electrician's visit to test and correct the earth: £80 to £260, with a loose or corroded terminal at the low end and work involving the supply earth or a new earthing arrangement well above it. An RCD that recurs: up to about £240, more if the consumer unit needs a suitable protective device fitted.
• A charger that keeps tripping for a reason in the installation: up to about £300 for the electrician, or a manufacturer call-out if it proves to be the unit.
• A contactor replacement or unit swap outside warranty: up to about £400. Establish which before agreeing to anything, and check the warranty first.

If the charger is simply doing nothing with no trip and no fault message, it is far more likely to be obeying its schedule than protecting you: EV charger not charging? has the regulations that make it look broken.

Sources

• myenergi zappi v2.1(G) user manual revision 1.7 (July 2023), section 22 Fault Codes: codes 23 to 32 including PE Fault (25), Comms Fault (26), SelfTest Failed (27), Contactor Fault (28) and PEN Fault (29), the reset actions, the qualification and disconnect-before-opening statements; the June 2022 revision 2.1.5 for the earlier code 29; myenergi product support on open-PEN isolation and BS 7671:2018 722.411.4.1 (v).
• Ohme UK support, "Troubleshooting: Voltage Errors" (253 V / 207 V, error logging, Home Pro Next View, the DNO route and monitoring period), the Ohme ePod product manual (PEN detection, Type A recommendation, 6 mA smooth DC) and the Ohme Home and Go product manual v2.0; fetched 3 September 2026.
• BS 7671:2018 Amendment 1:2020, section 722 (electric vehicle charging installations), as cited by myenergi; Building Regulations Approved Document P (England) and the Welsh Government equivalent.
• bp pulse and EO published safety wording, as cited on the "Red light" code page.
• Cost brackets are those published on the code pages for Charger keeps tripping, PE Fault, PEN Fault, RCD activation and Contactor Fault, each with its own sourcing.