How to wire a solar CT clamp for smart EV charging

Helpful video reference. Nick Bundy's "EV Solar Charging (Wiring)" on the N Bundy Electrical channel (published January 2023) covers the wiring side of solar EV charging in practical detail. Nick is a qualified UK electrician registered with NAPIT and based in Staffordshire. His channel has over 100,000 subscribers and covers domestic installation work with consistent attention to Part P and BS 7671 requirements.

1. Confirm your charger supports solar-aware charging

Not every EV charger has a CT clamp input. Before buying or fitting one, check the charger's specification:

• MyEnergi Zappi — CT clamp supplied, essential part of the installation.
• Ohme Home Pro — uses a CT clamp or inverter API integration.
• Andersen A2 — CT clamp optional, enables solar mode in the app.
• Wallbox Pulsar Plus — CT clamp available as an accessory.
• Pod Point — solar mode via inverter API rather than CT clamp on most models.

Some chargers integrate directly with the solar inverter via its API or a proprietary protocol, meaning a CT clamp is not needed at all. Check your charger's documentation before going near the consumer unit.

2. Understand what the CT clamp measures

A current transformer clamp works by induction. When alternating current flows through a conductor inside the clamp jaw, it induces a proportional tiny signal in the CT's coil. The charger reads this signal and knows, in real time, how much current is flowing through that conductor.

Fitted on the grid import line conductor, the CT measures the current the home is drawing from the grid. When the solar panels are generating surplus power that the home is not using, the grid import current falls toward zero (or even reverses direction if the system is net exporting). The charger sees this and ramps up its charging current to absorb the surplus, so the car charges from the panels rather than the grid.

The CT clamp does not connect to the mains. The signal cable carries millivolt-level signals back to the charger.

3. Locate the grid import cable

On a standard UK domestic installation, the path from the grid runs: DNO service head (the sealed grey box) → meter tails → electricity meter → meter tails (consumer side) → 100 A main switch in the consumer unit.

The CT clamp goes on the meter tail between the meter and the consumer unit main switch — or, where there is no accessible section of meter tail, on the line conductor entering the main switch itself. Your consumer unit enclosure needs to have enough space to fit the clamp without fouling the lid or any busbar.

4. Check space and access around the cable

Meter tails in UK domestic premises are typically 25 mm² single-core insulated cables. The CT clamp jaw needs to close fully around this cable — check the supplier's maximum cable diameter specification. The clamp also needs enough slack in the tails to be positioned without pulling on the meter terminations.

Look at the direction of the tails and plan where the CT body will sit once clipped. It should not obstruct the consumer unit lid closing, and the signal cable exit should point toward where you plan to route it to the charger.

5. Fit the CT clamp around the grid import live conductor

Open the clamp jaw and pass it around the brown (line) meter tail only. Do not clip around both live and neutral together — the fields cancel out and the clamp reads zero, so the charger never sees any grid current at all.

Check for a direction arrow printed or moulded onto the CT clamp body. This arrow must face toward the consumer unit (in the direction that current flows when the home is importing). Close the jaw firmly until it clicks or the two halves meet cleanly. Secure the clamp body with a cable tie through its mounting lug so it cannot slide.

6. Route the CT signal cable to the charger

Run the thin signal cable from the CT clamp along the wall to the EV charger. Clip it at regular intervals and keep it away from parallel mains cable runs where possible. Long parallel runs alongside 230 V cables can induce noise into the low-level signal, causing inaccurate readings.

Most charger manufacturers supply enough signal cable for the CT clamp to reach from the consumer unit to a charger installed on the same wall or the adjacent wall of a garage. If you need a longer run, check the manufacturer's maximum signal cable length before extending it.

Connect the signal cable to the charger's CT input terminal — usually a 3.5 mm jack socket or a screw terminal block labelled CT or Solar. Refer to the charger installation manual for the correct connector type and polarity.

7. Commission the solar mode and verify it works

In the charger's app, navigate to the solar or eco charging settings and enable solar mode. Plug the car in with the battery not full. On a day with reasonable generation, watch the charger's output current on the app — it should track the available surplus, ramping up when the sun is strong and stepping down when a cloud passes.

If the charger does not respond to solar: check the CT clamp direction arrow is pointing the right way, confirm the clamp is fully closed on the correct conductor (line only, not neutral), and check in the app that the CT clamp is shown as connected rather than absent.

Some chargers have a minimum solar threshold — they will not start charging below, say, 1.4 kW of surplus. If your panels are small or the day is overcast, the charger may never trigger solar mode even with the CT clamp wired correctly. This is normal behaviour, not a fault.

When to call us

Richard commissions solar-aware EV chargers across east Kent, including CT clamp fitting, signal cable routing, and app commissioning. If the original charger installer left the solar integration unfinished, or you are adding solar panels to an existing charger setup, a half-day visit is usually all it takes to get everything talking.