> ## 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.

# Meter Phase Matching: RS485, Three-Phase CT Discipline

> Meter schemes vs direct CTs, RS485 A-on-A polarity, three-phase CT-to-conductor-to-terminal discipline, AC-coupled sites, and third-party GT limitations.

Meters extend what a bare CT can do on reach and on multi-source sites. Three-phase sensing adds a discipline that single-phase experience never teaches: every CT must match its conductor and its terminal pair — all three at once.

<Warning>
  **For trained and authorised installers only.** Meter wiring is live-side work. Isolate before connecting or modifying any meter terminals.
</Warning>

## When to use a meter instead of direct CTs

A supported energy meter carries its own CTs and reports over RS485 to the inverter. Use a meter scheme when:

* The grid connection point is beyond the CT lead's design reach \[KNB-VAL-23]
* The site design shipped with a meter scheme
* AC-coupled metering is required at a multi-source site

Run one sensing scheme per site — either direct CTs or a meter, not both simultaneously.

Platform-specific meter options, terminal maps, and kit ratios:

<CardGroup cols={2}>
  <Card title="Kent M1 CT & Meter" icon="bolt">
    Supported meters, terminal mapping, 3-CT single-phase schemes, and 6-CT three-phase AC-couple schemes are on the Kent M1 CT & Meter page.
  </Card>

  <Card title="Kent G3 CT & Meter" icon="bolt">
    Meter scheme, pin map, kit ratios, and installation location options (Grid side / Load side / Grid + PV inverter) are on the Kent G3 CT & Meter page.
  </Card>
</CardGroup>

## RS485 polarity — A on A, B on B

Meter communications fail on swapped polarity more than any other wiring error. Land **A on A and B on B** at every termination point, using signal name rather than pin number as your reference — on the Kent G3 the meter end and the inverter end use different pin numbers for the same signal pair.

| Symptom                                   | Likely cause                                                  |
| ----------------------------------------- | ------------------------------------------------------------- |
| Meter comm fault, no grid data on display | A/B swapped at one end, or meter supply circuit is dead       |
| Comm fault only during backup test        | Meter powered from a circuit that goes dead when grid is lost |

## Three-phase discipline: match everything, per phase

On a Kent G3 three-phase installation, three CTs must agree with three conductors and three terminal pairs simultaneously.

<Steps>
  <Step title="Match CT to conductor by phase">
    The L1 CT clamps on the L1 conductor. L2 on L2. L3 on L3. Right phases with crossed leads is still wrong.
  </Step>

  <Step title="Match CT leads to the correct terminals">
    The L1 CT's leads land on the CT-L1 terminal pair. L2 leads on CT-L2 terminals. L3 leads on CT-L3 terminals.
  </Step>

  <Step title="Check arrow direction on every CT">
    Every CT's arrow toward the grid — the universal Kent rule applies on all three phases.
  </Step>

  <Step title="Prove it per phase with a stepped load">
    Step a known single-phase load on L1 only. The display's L1 reading rises; L2 and L3 stay flat. Repeat for L2 and L3. Photograph each step.
  </Step>
</Steps>

<Warning>
  The classic three-phase mismatch signature is **one phase importing while another phase discharges** on the same display simultaneously. Treat that pattern as a phase-mapping error until the per-phase live test proves otherwise.
</Warning>

## AC-coupled and multi-source sites

Where an existing grid-tie PV inverter shares the site, the metering scheme must account for its generation:

* **Kent M1** AC-couple schemes place a CT on the grid connection **and** a second CT on the existing solar inverter's output — detailed on the Kent M1 CT & Meter page.
* **Kent G3** offers the *Grid + PV inverter* meter placement option for the same scenario.

<Note>
  **Retrofit expectation for third-party grid-tie inverters:** a third-party grid-tie inverter on the grid side has no control channel to the Kent hybrid. The system can meter its output but cannot command it to reduce generation. This has a direct impact on zero-export performance — plan export behaviour accordingly and engage Kent service before quoting a multi-source retrofit.
</Note>

## Common mistakes

<AccordionGroup>
  <Accordion title="A/B swapped at one end only — 'tested fine' with a continuity beep">
    A continuity test on swapped RS485 polarity passes because both wires are present. It fails at comm. Wire by signal name: A on A, B on B.
  </Accordion>

  <Accordion title="Meter powered from a circuit that is dead during backup operation">
    Grid data vanishes exactly when you need it most. Power the meter from a circuit that survives a grid outage.
  </Accordion>

  <Accordion title="Three CTs clipped in a hurry — right directions, wrong phases">
    Speed at the enclosure costs an hour of troubleshooting. Match conductor, leads, and terminals per phase before closing up.
  </Accordion>

  <Accordion title="Running both CTs and a meter simultaneously 'to be safe'">
    Only one sensing scheme per site. Two schemes conflict and produce corrupted grid data.
  </Accordion>
</AccordionGroup>

## Related pages

* [CT Basics](/ct-meter/ct-basics)
* [Direction & Location](/ct-meter/direction-and-location)
* [Energy-Flow Test](/ct-meter/energy-flow-test)
* [Kent M1 CT & Meter](/m1/ct-and-meter)
* [Kent G3 CT & Meter](/g3/ct-and-meter)