The difference is where your earth comes from. On a TN-C-S supply, the network operator provides the earth, and for part of its journey the earth and neutral share one combined conductor — the PEN conductor. On a TT supply, the installation makes its own connection to earth at the premises, separate from the supply neutral. Which one a property has changes which protective questions a charger installation must answer.
Key Takeaways
- TN-C-S takes its earth from the network on a combined PEN conductor; TT makes its own earth at the premises.
- The broken-PEN question belongs to TN-C-S; the local electrode and its protection carry the TT design.
- Identify the arrangement at survey, from records or the network operator — never by inference.
- No EVDANCE page claims earthing or PEN functions; the installation design answers those questions, confirmed in writing.
The Two Arrangements, Side by Side
| Dimension | TN-C-S | TT |
|---|---|---|
| Where the earth comes from | From the distributor’s network, delivered with the supply | From the premises itself — a local earth electrode |
| The neutral’s role | Earth and neutral travel combined as a PEN conductor for part of the route, then separate at the intake | Earth and neutral stay separate throughout |
| Who owns the earth connection | The network operator, up to the installation’s intake | The property — the electrode is part of the installation |
| The headline EV design question | What protects the car if the combined conductor fails upstream | Whether the local earth and the circuit protection together do their job |
| How it is identified | At the intake, by the installer; confirmed from network operator records where unclear | The same route — survey, records, and the installation certificate |
Why the Difference Matters More for a Car on Charge
A charging car is different from most loads: its metal body is bonded to the installation earth, outdoors, often within reach of true ground, for hours at a time. That makes the earth connection part of the charging design, not background.
On TN-C-S, the specific concern is the combined conductor. If the PEN conductor breaks upstream, earthed metalwork — including the car — can be left at a dangerous potential while everything appears to work normally. That failure mode is why EV installations on TN-C-S supplies are asked a protective question ordinary socket circuits are not — answered in the installation design, not assumed from the charger. On TT there is no combined conductor to fail that way; the design rests on the premises’ own electrode and the circuit’s protective device, so the condition of that local earth is an installer’s test item, not a guess.
How You Find Out Which One You Have
- Ask the installer to identify it at survey. It is read at the supply intake and recorded before the design is made — a design input, not a detail to discover mid-install.
- Check earlier paperwork. An existing electrical installation certificate names the earthing arrangement for the property.
- Confirm with the network operator where it is unclear. The distributor holds the record for the supplies it earths.
- Do not infer it. The age of the house, the street, or a neighbour’s arrangement is not evidence for your property.
Specifying the Charger Against Your Earthing
The earthing arrangement shapes the installation around the charger, not the charger’s headline specification. Take the EV-ACT3204PE wallbox (22 kW three-phase, tethered Type 2 cable, RFID and app, IP66, CE): EVDANCE’s page states no earthing-specific function and no built-in PEN fault protection, for this or any model. On a TN-C-S supply, the PEN question is answered by your registered installer’s design; on TT, the electrode and protection are verified the same way. If a supplier’s document claims a protective function, ask for it in writing for the exact model — and for UK work, confirm the UK version of the unit the same way, through contact us. Our residential charging range covers the hardware side.
Frequently Asked Questions
Can my earthing be changed from TT to TN-C-S, or the other way?
Not as a homeowner project. The arrangement belongs to the supply and the network; whether any change is possible is a question for the network operator. Your installer designs for the arrangement the property has.
Does a TT supply always need an earth electrode?
Yes — the local electrode is what makes it TT. Its design, position and testing are the installer’s work under the wiring standard; there is no figure a homeowner can check it against.
Does the earthing type change which charger I should buy?
Mostly it changes the installation design around the charger. Choose the unit on its stated facts, and let the installer confirm — in writing — how the protective questions for your arrangement are answered.
Related Reading
- RCD Protection for EV Chargers: Type A, Type B and DC Detection Explained
- Does an EV Charger Cable Need to Be Armoured? (UK)
- What Is a Standard EV Charger Installation?
- How to Become an Approved EV Charger Installer in the UK (OZEV)
