Exclusive - Inside the EV charger which doesn't need an earth rod

The Zappi charger from Myenergi is packed full of smart features including a unique safety circuit which removes to need for electricians to fit an earth rod. We lift the lid to discover more.

Words by Gordon Routledge
Video review by Gary Hayers & Joe Robinson
Friday 20th September 2019

Myenergi and the Zappi EV charger were born from a recognition that in the future home energy is going to get more complex. Driving this complexity are the megatrends of electric cars and more renewables in the electricity supply network. More renewables, such as wind and solar panels, means that the supply of electricity can swing wildly between scarcity and excess.

A driver who chooses an electric vehicle will typically see their home electricity bill double. So instead of watching the Petrol price at local filling stations, drivers become acutely aware of the cost of electricity used at home.

This link between renewables and electric vehicles allows users to profit or be penalised by the energy market. Charge your car using an off-peak tariff, and you can pay 5p per kilowatt-hour. Opt to charge during peak hours then expect to pay 15p. For a Nissan Leaf with a 40kW battery, this is the difference between paying £2 or £6 for a full charge. Homes with solar panels installed are the real winners as they can divert generated energy to charge for free.

Managing this complexity is where the Zappi steps in unless you want to spend hours watching your electricity meter. At its heart, Zappi is a combination of EV charger plus energy manager. The Zappi, depending upon user choice, will choose between available energy sources to charge at the lowest cost or within the fastest time.

Find out how the Zappi 2 EV charger works.

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Installer friendly features

Myenergi have designed the Zappi with the installer in mind. The solidly build housing contains some handy features to cope with real-life installation challenges.

Load monitoring

Perhaps the most useful feature is the multiple current transformer (CT) inputs. Installing a current transformer on the incoming supply protects against the car charger overloading the installation. This feature is useful for properties with existing high current electric appliances, e.g. induction hobs, electric showers and heating. Or the same approach can be used on properties with a 60 amp incoming supply, avoiding the need to upgrade.

Fitting a second CT on sub-mains enables Zappi installation in remote buildings to prevent overloading the circuits and share power with existing appliances.

Current transformers can be hard-wired to the unit or linked wirelessly using the Harvi CTs available from Myenergi.

PME fault monitoring

PME or TNCS electricity supplies posing particular challenges for installers. The practical solution adopted in most installations is to convert the EV charger to a TT supply and fit an earth rod. Fitting earth rods are time-consuming and hitting buried services such as drains, water or gas pipes is always a risk.

The 18th edition wiring regulations included a specific clause for a device which would disconnect the charger if a PME fault was detected. When the regulations were published, no such device existed. It now does in the Zappi. The clever bit is a current transformer which monitors any earth leakage in the earth connection to the vehicle. Used in conjunction with over and under-voltage detection sensing can detect all scenarios related to a PME fault. .

On board RCD

Incorporated in the main circuit board is RCD protection. Having this function within the charger removes the need for an external type B or A device. The RCD circuit self tests when the Zappi is powered up

Off peak tariff sensing

As mentioned earlier, it's much cheaper to charge using an off-peak electricity tariff. However, the exact time that economy seven switches over can vary by time and location. The Zappi includes a sense input which detects when the off-peak tariff is available. This signal usually comes from a change over contact within 5 terminal electricity meters.

Charging cable lock

We tested a non-tethered unit in which the user plugs in their own charging cable. To avoid someone unplugging the car mischievously a solenoid locks the cable in place during charging.

Our verdict

The Zappi 2 charger is the Swiss Army knife of electric vehicle chargers. It's well built, delivers loads of useful functions for the owner and solves just about every installation issue an electrician could face.