> ## 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.

# Battery Comm Cable Checks: The 4–5 Crossover Pin Rule

> The 4–5 crossover pin card, three pre-power-up checks, the field fallback for re-terminating on site, and multi-pack addressing rules.

One cable determines whether a Kent lithium installation communicates at all. A straight RJ45 patch lead looks identical to the correct cable — and fails every time on this pairing. Run these checks before every power-up.

<Warning>
  **For trained and authorised installers only.** Comm-cable work happens adjacent to live battery terminals. Battery Safety rules apply throughout — see [Battery Safety](/battery/safety).
</Warning>

<Warning>
  **A straight RJ45 patch lead will never communicate on a Kent lithium pairing.** The Kent battery carries CAN-L on pin 4 and CAN-H on pin 5; both Kent inverters expect the opposite. You must use the labelled Kent battery comm cable — pins 4 and 5 are swapped end-to-end. The symptom of a straight cable is a battery comm fault at first power-up, every time.
</Warning>

## The pin card

Pins 4 and 5 cross between the battery end and the inverter end. All other pins run straight.

| RJ45 pin | Kent battery end | Inverter BMS end (G3 and M1) |
| -------- | ---------------- | ---------------------------- |
| **4**    | CAN-L            | CAN-H                        |
| **5**    | CAN-H            | CAN-L                        |

The correct cable is straight on all pins **except** 4 and 5, which swap — that is the labelled Kent crossover cable. One such cable per bank, running from the **master pack's CAN port** to the inverter BMS port.

## Before power-up: three cable checks

Run all three checks with the system isolated and the cable connectors accessible.

<Steps>
  <Step title="Label check">
    Confirm the Kent crossover label is physically on the cable in use. A generic LAN patch lead anywhere in the battery comm path is an automatic fail — remove it and replace it with the labelled Kent cable. Photograph the label in place.
  </Step>

  <Step title="Continuity check">
    With the cable off-line and both connectors in hand, meter it against the pin card above:

    * Pin 4 on one end must read continuity to pin 5 on the other end.
    * Pin 5 on one end must read continuity to pin 4 on the other end.
    * All other used pins must read straight (pin 1 to pin 1, and so on).
  </Step>

  <Step title="Seating check">
    Both RJ45 connectors must click fully home — at the master pack's CAN port and at the inverter BMS port. Confirm the run is strain-relieved and routed away from DC power cable pinch points.
  </Step>
</Steps>

## Field fallback — re-terminating one end on site

If no labelled Kent cable is available, both source manuals authorise the same fallback: **cut off the RJ45 at one end, re-crimp it with pins 4 and 5 swapped**, then re-run the continuity check and mark the cable clearly as a crossover.

<Warning>
  **Never attempt to fix a comm fault through the menus.** No battery-model selection, protocol entry, or settings change compensates for a wrong cable. Cable first, settings second — in that order, always.
</Warning>

<Warning>
  **Pending Kent validation.** \[KNB-VAL-05] The F1 cable-kit contents and the exact battery-brand label shown on the Kent M1 screen are under confirmation with the Kent battery team. The pairing, minimum-pack matrix, and the 4–5 crossover rule are confirmed. Until published here: use only the labelled Kent battery comm cable, and verify any field-made crossover cable against the pin card above before power-up.
</Warning>

## Multi-pack banks

When running more than one pack in parallel, follow these rules:

* Each pack needs a **DIP-switch address** set before power-up. Record the address map on the commissioning sheet.
* Only the **master pack** connects to the inverter — one crossover cable per bank, regardless of pack count.
* The maximum bank size is **16 packs**.

<Tip>
  Set every pack's address before any pack is connected to another. Addressing live packs mid-installation is a preventable mistake.
</Tip>

## Common mistakes

<AccordionGroup>
  <Accordion title="Using a straight LAN patch lead 'because it fit'">
    Physical fit is irrelevant — the pinout is wrong. A straight patch lead guarantees a comm failure on this pairing.
  </Accordion>

  <Accordion title="Re-terminating both ends of the cable">
    The swap belongs at one end only. Re-terminating both ends makes the cable straight again, which fails the continuity check and fails at power-up.
  </Accordion>

  <Accordion title="Routing the crossover cable between packs instead of pack-to-inverter">
    The inter-pack link follows the battery wiring guide, not this pin card. The crossover cable runs from master pack to inverter only.
  </Accordion>

  <Accordion title="Not labelling a field-made crossover cable">
    An unlabelled field-made cable will be "fixed" back to straight by the next technician on site. Mark it clearly and permanently.
  </Accordion>
</AccordionGroup>

## Related pages

* [BMS Comms Basics](/battery/bms-comms-basics)
* [Kent M1 Battery Wiring](/m1/battery-wiring)
* [Kent G3 Battery Wiring](/g3/battery-wiring)