> ## Documentation Index
> Fetch the complete documentation index at: https://learning.kent.co.in/llms.txt
> Use this file to discover all available pages before exploring further.

# CT Basics: Current Transformer Role and Clamp Rules

> How the CT drives self-use and zero-export logic, the single-conductor clamp rule, ratio discipline, lead-length limits, and CT vs meter scheme.

The CT is the hybrid system's eyes on the grid connection. Every smart function — self-use, export limiting, and the energy figures on the display — is only as accurate as the clamp on that one conductor. Get this right and the system controls correctly; get it wrong and the symptoms can look like an inverter fault.

<Warning>
  **For trained and authorised installers only.** Isolate the AC conductor before clamping anything around it.
</Warning>

## What the CT is for

A current transformer (CT) clips around a grid conductor and reports the current flowing through it. The inverter uses that signal to determine whether the site is importing or exporting, and by how much. That information drives:

* **Self-use logic** — directing PV and battery to cover the load before buying from the grid
* **Zero-export control** — throttling PV output when the site would otherwise export
* **Energy display figures** — grid import, export, and load values on the screen and the app

Without a healthy CT signal, none of these functions work correctly. The system has no reliable way to know what is happening at the meter.

## The clamp rule

* The CT clamps around **one conductor: the live**. Clamping around the live and neutral together cancels the magnetic fields — the CT reads 0 W and the control logic goes completely blind.
* Close the clamp until it **clicks** fully shut. A half-latched CT under-reads consistently and the fault is nearly invisible until someone moves the cable.
* Where the CT sits and which way its arrow faces are separate disciplines — both are covered on [Direction & Location](/ct-meter/direction-and-location).

## Ratio discipline

The CT reports a scaled-down version of the conductor current. The **ratio setting tells the inverter the scale factor**. A wrong ratio means every power figure on the display is wrong by a large factor — and export limits are enforced against numbers that have nothing to do with the actual grid flow.

<Warning>
  **Pending Kent validation.** \[KNB-VAL-08] The shipped CT scheme and ratio per Kent SKU are under confirmation. Until published here: **read the ratio from the shipped CT's nameplate and enter exactly that value — never assume a default.** On the Kent G3, the box-kit CT and the meter-scheme CT carry different ratios; the kit table is on the Kent G3 CT & Meter page.
</Warning>

## Lead length — the quiet killer

The CT's output is a millivolt-class analog signal. Long or improvised lead extensions pick up electrical noise, and that noise reads as phantom import or export that the control loop continuously chases.

* The Kent G3 box kit ships with a **1 m, 2.3 mm² CT lead** — that is the design lead length for that kit.

<Warning>
  **Pending Kent validation.** \[KNB-VAL-23] The approved CT lead extension method per Kent SKU is under confirmation. Until published here: **do not extend CT leads.** If the supplied lead cannot reach the grid connection point, use the platform's **meter scheme** instead — never a spliced-on length of flex.
</Warning>

## CT scheme vs meter scheme

Both Kent platforms can sense the grid either directly with CTs on the conductor, or through a supported energy meter that carries its own CTs and communicates over RS485 to the inverter. You choose one scheme per site — not both.

<Info>
  On the Kent G3, if CTs are connected directly, a separate smart meter is not required for grid sensing. The platform-specific wiring options are on the Kent M1 CT & Meter and Kent G3 CT & Meter pages.
</Info>

## Common mistakes

<AccordionGroup>
  <Accordion title="CT clamped around live and neutral together">
    The magnetic fields cancel. Load reads 0 W and all control logic is blind. Reclamp on the live conductor only.
  </Accordion>

  <Accordion title="CT ratio entered from memory instead of the nameplate">
    Ratios vary by CT model and SKU. Always read it off the physical CT you installed.
  </Accordion>

  <Accordion title="CT lead extended with random cable 'just two metres'">
    Even a short extension on an analog millivolt signal introduces noise. Use the meter scheme if the lead cannot reach.
  </Accordion>

  <Accordion title="Half-latched clamp that never audibly clicked">
    The CT under-reads until disturbed. Always confirm the click before closing up the enclosure.
  </Accordion>
</AccordionGroup>

## Related pages

* [Direction & Location](/ct-meter/direction-and-location)
* [Wrong-CT Symptoms](/ct-meter/wrong-ct-symptoms)
* [Kent M1 CT & Meter](/m1/ct-and-meter)
* [Kent G3 CT & Meter](/g3/ct-and-meter)