Next generation EV charge points don't need earth rods

Electric vehicle charge point manufacturers are adding intelligent electronics to remove the need for earth rods.

By Gordon Routledge
Monday 29th April 2019

Now that the 18th edition wiring regulations have bedded into our minds, we've quickly establish some rules of thumb that apply to typical installations. For electric vehicle (EV) charge points, in residential projects, we would expect to be fitting an earth rod next to the charge point.

Why earth rods?

Fitting an earth rod is the most cost-effective and quickest way to comply with regulation 722.411.4.1. This regulation seeks to avoid a shock hazard which could occur if the fault develops within the supply network of TNCS (PME) earthing systems, i.e. most domestic supplies in the UK. Isolating the EV charger earth from the TNCS system and creating a localised TT earthing arrangement is relatively straightforward. A glance at the twitter feeds of contractors focussing on the EV market shows how you can easily sneak an earth rod into an adjacent flower bed.

However, earth rods aren't without their challenges. It can be physically challenging to get the rod in the ground, especially on rocky terrain or close to building foundations. Driving the rod through other services such as drains, gas or water pipes is always a risk. Achieving a low enough resistance to trigger the RCD is not guaranteed, and resistance can change with ground conditions or corrosion of the rod over time. Plus ,aesthetically, it's another ugly pipe on the wall which won't go down well with many clients.

Earth rods and TT supplies are fine if you're the first to install, but what if the neighbouring property already has a charge point. You then need to think about the separation distance between earthing systems. This is a grey area which was flagged up in the recent Western Power Distribution EV strategy document.

UPDATE: - The 18th edition wiring regulations have now been updated with amendment 1 - see this article for the latest information.

The earthing considerations for the connection of electric vehicle charge points are firstly the type of earthing arrangement (PME, SNE or TT) and secondly the required segregation between these different earthing types. The requirements of the Code of Practice for the installation of EV charging equipment makes the use of protective multiple earthing (PME) prohibitive and steers installations towards a TT setup. However the IET Wiring Regulations (Guidance note 7) requires segregation of a minimum of 10m between the PME and TT earthing systems. We understand that this requirement will restrict installations in the street and therefore we have recalculated the requirement using modelling specifically for a street side application. As a result we can reduce the distance so that a balanced three phase demand utilising a TT earthing system will require segregation from the WPD earthing system by a minimum of 0.3m and a single phase or unbalanced connection would require a segregation of 3.6m.

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What's the alternative?

One alternative solution is to provide electrical separation by using an isolation transformer. However, these are more expensive than the charger itself and an extra bit of bulky kit to accommodate in the installation.

Isolation transformers for EV installations can take up valuable floor space (picture: SRG Electrical)

Another option included within 722.411.4.1 (iii) is just starting to be exploited

722.4.4.1 (iii)

"Protection against electric shock is provided by a device which disconnects the charging point from the live conductors of the supply and protective earth in accordance with Regulation 543.3.3.101(ii) within 5s in the event if the voltage between the circuit protective conductor and Earth exceeding 70v rms. The device shall not operate if the voltage exceeds 70v rms for less than 4 s. The device shall provide isolation. Closing or resetting of the device shall be by manual means only. Equivalent functionality could be included within the charging equipment."

In other words, a piece of intelligent electronics which monitors the incoming supply and disconnects the charger including the earth path if a fault condition is detected.

Necessity drives demand

Manufacturers are responding to the challenges of earth rods and utilising this clause to introducing new charge points with PEN fault monitoring which mitigate the need for earth rods.

Myenergi - Zappi

The Zappi charger from Myenergi already includes sophisticated electronics to balance loads, charging schedules and renewables. Adding extra circuitry and software to monitor earth faults allows for much easier installs.

See full product review >>>

Andersen A2

Andersen is targeting high-end residential installations with sleek architectural inspired designs. The paint finish and front panel can be tailored to match almost any building style. The updated A2 model now no longer requires an earth rod, making it easy to keep up appearances with the overall installation.