STD-U3I3 — three-phase meter
Member of the rbAmp STD family; everything on the family page applies.
What it is
A three-phase energy meter module: three voltage and three current inputs with synchronous sampling,
the full STD feature set, and a choice of I²C or Modbus RTU. Variant code 0x63.
It works as a sub-meter / smart-meter front end for a master (ESP32, Arduino, Raspberry Pi, PLC), or directly on a Modbus RTU network (through an external RS-485 transceiver) as a meter, including the SDM630-compatible profile for inverters and monitoring systems that read the points of an Eastron-type meter.
The module ships with a current sensor for every channel: each channel is calibrated together with its sensor from the kit, and every sensor is labelled with its channel. The kit includes a current sensor in one of two ratings: 60 A or 100 A.
Voltage connection
The voltage terminal block has four positions: N, L1, L2, L3. The module measures phase-to-neutral voltages, so the neutral must be connected. Wire and fuse rule: Hardware.
Three-phase features
- Per-phase U / I / P / Q / S / PF plus grand and per-phase totals, all from one coherent measurement window.
- Signed import/export energy by the phase balance (the standard meter convention) — correct totals on sites that export on one phase while importing on another.
- Phase angle of each voltage input and the phase sequence (forward / reverse / abnormal) — check the wiring before trusting per-phase readings.
- Eight independent snapshot banks.
- Hourly history: the last 7 hourly records (energy per phase and an electrical summary) kept on the module; records are written once the master has set the time, and a part-hour record is flagged. See Energy and periods.
- Sampling about 3 kHz per channel, windows of whole mains cycles.
Measured characteristics
Measured on one production module per kit (60 A and 100 A), each channel individually calibrated together with its sensor, against a reference meter on a resistive load. Current is given as the primary current with one pass of the wire through the sensor; figures cover all three channels.
| Parameter | 60 A kit | 100 A kit |
|---|---|---|
| Current error | ±0.25 % from 1.15 A to 76.7 A (single worst point −0.45 %) | ±0.19 % from 1.16 A to 99.5 A |
| Upper end of the range | the reading saturates from 79–80 A (−1 % at 81.4–82.3 A) | linear up to 131.5 A (±0.25 %) |
| Voltage error | ±0.25 % (measured at 205–228 V) | ±0.25 % (measured at 194–229 V) |
| Power factor, resistive load | 0.998–1.000 | 0.999–1.000 |
| Energy, one 15-minute run (deviation from the reference) | +0.044 % | +0.179 % |
| Reads from | 4.9 mA | 4.9 mA |
| Noise with no current | 0.15–0.35 mA | 0.4–0.7 mA |
The 100 A figure for the upper end is the limit of the test setup (about 131 A), not a limit of the module.
Typical uses
- The main meter of a three-phase home, a building, a production floor or a workshop.
- Three-phase sub-metering: a feeder, a workshop, an EV charger.
- Solar self-consumption: separate import and export energy, SDM points for a Modbus master.
- Feeder monitoring in a distribution cabinet.
Where to go next
Hardware · Getting started · Real-time polling · Energy and periods · Technical reference