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Energy Meters

RS485 Wiring

Connecting HPzenAi energy meters to the HPzenAi gateway over an RS485 Modbus RTU bus.

RS485 Terminal Identification​

Locate the RS485 terminal block on the energy meter — it is marked A and B (sometimes A+/B− or D+/D−). Terminal A is the positive differential line; terminal B is the negative. Swapping A and B is the most common wiring error and prevents communication entirely.

Single Meter Wiring​

Steps​

  • Run shielded twisted-pair cable from the energy meter RS485 terminals to the HPzenAi Gateway.
  • Connect: Gateway RS485 A → Meter RS485 A.
  • Connect: Gateway RS485 B → Meter RS485 B.
  • Connect the cable shield to earth at the gateway end only — do not earth the meter end.
  • Use twisted-pair cable for all runs, even short ones — single-core cable picks up noise from nearby power wiring.

Multiple Meters on One Bus​

Steps​

  • Daisy-chain all meter A terminals together and all B terminals together — run the bus from the gateway to each meter in sequence.
  • Do not use a star topology — all devices must be on a single linear bus.
  • Each meter must have a unique Modbus RS485 address (1–32) — configure via the meter DIP switches or configuration menu.
  • Fit a 120 Ω termination resistor between A and B at the furthest meter on the bus.
  • Maximum cable run: 1200 m at 9600 baud; reduce to 800 m or lower baud rate in high-interference environments.

Cable Specification​

Steps​

  • Use 2-core shielded twisted-pair (STP) RS485 cable — Belden 9842 or equivalent.
  • Minimum conductor size: 0.2 mm² (24 AWG) for runs up to 300 m; use 0.5 mm² (20 AWG) for longer runs.
  • Cable impedance: 120 Ω (matched to the RS485 standard).
  • Route RS485 cables in a separate duct from 230V / 415V power cables — maintain at least 100 mm separation.
  • Avoid routing near VFDs, inverters, and motor starters — these are major sources of RS485 interference.

Powering the Energy Meter​

RS485 carries communication only — it does not supply power. Each energy meter requires a dedicated 12V DC supply connected to its power input terminals. Use an HPzenAi PWR-1P-12V-15W or PWR-3P-12V-12W adapter mounted in the same panel. Ensure the 12V supply is rated for the total load of all connected devices.

Modbus Address Configuration​

Steps​

  • Factory default Modbus address is 1 — suitable for a single meter on the bus.
  • For multiple meters, assign a unique address to each before connecting to the shared bus.
  • Address configuration is done via the meter front panel buttons or DIP switches — refer to the meter label for the procedure.
  • In the HPzenAi app, the RS485 Scan automatically detects addresses — no manual address entry is needed in the app.