RJ-45 Pin Convention
RS-485 on the first pair, DC input on the second, earth on pin 8. Every cable, board and harness we make follows this. Standing decision, 2026-08-29.
Contacts facing you, latch down, pin 1 on the left · colours are T568B
The pinout
| Pin | T568B colour | Function | Notes |
|---|
Go by pin number, never by colour. These are T568B colours. Crimp T568A instead and the pins keep these functions, but the orange and green pairs swap colour — so a cable that looks wrong can be right, and one that looks right can be wrong.
Mapping to your inverter
Every brand numbers its own communication port differently, and none of them will match this socket. Go by the signal, never by the pin number — this is the single easiest thing to get wrong. Huawei is shown here as a worked example; look up your own brand in the documentation.
Note the inversion in this example: Huawei carries A+ on its pin 1, we carry it on pin 2. Wiring “pin 1 to pin 1” gets you a reversed pair — and it will be a different inversion, or none, on another brand.
Reversed A/B is silent, not destructive
The bus simply goes quiet — no damage, no error, nothing in a log. If a scan finds nothing, swapping the two is the first thing to try, and it costs nothing.
Power
Pins 3 and 4 carry 5.5–30 V DC, pin 4 positive.
Feed the RS-485 transceiver from 5 V, not 3V3. The module regulates internally and 3.3 V sits right at its dropout — it will appear to work on the bench and then fail under load or temperature.
Never plug this into a network port
This connector is RJ-45 shaped and is not Ethernet. Pins 3 and 4 carry DC: on 10/100, pin 3 is half of the receive pair; on gigabit, pins 4 and 5 are an active data pair. Plugging a Svitgrid cable into a switch, router or laptop puts up to 30 V onto a data pair.
Label both ends of every cable you make.
Earth, and the spare pins
Pin 8 carries the RS-485 earth — the earth contact on the inverter’s own communication port. It is assigned so the convention is fixed and every cable is made the same way. Whether it is actually landed is the installer’s call, site by site.
If you do connect it, connect it at one end only. Earthed at both ends it forms a loop between two different grounds, and current flowing in that loop is a noise source on the very pair it is there to steady.
Pins 5, 6 and 7 are the reserve. Do not repurpose one for a new signal without updating this convention and the firmware together — a cable made to an older convention is indistinguishable from a correct one until something misbehaves.
The firmware side
RS-485 lands on GPIO6 (TX) and GPIO5 (RX), on UART2.
Never GPIO43 / GPIO44
Those are UART0’s IOMUX pads. IOMUX overrides the GPIO matrix, and the transmitter dies partway through boot while the write call returns the full byte count and reports success. The wire stays silent and nothing reports an error.
When wiring and firmware disagree, run the pad scan. It transmits from every broken-out pad with the pad number in the Modbus slave byte, so a listener on A/B names the pad the firmware is actually driving. A meter cannot do that — it confirms a net without saying which pad is being driven.