Monitoring a three-phase workshop: machines, a compressor and the input limit

A small workshop on a three-phase supply: a bank of machine tools, an air compressor, an office, the lighting and the ventilation. Work runs Monday to Friday, eight to six. The questions here are less about the price per kWh and more about the supply: how close does the workshop get to what the connection allows, which circuit is working hardest, and what keeps drawing power after everyone has gone home?

This guide builds that workshop on a real RBgrid hub. An rbAmp STD-U3I3, a precise energy meter, measures the three-phase input, phase by phase. Three Basic modules, one per phase, measure five circuits. The app shows it all in the Business view: the input against its limit, the phases, each line against its rating, and a single-line diagram. It's the same workshop as the Workshop site in the live demo, so you can look at the finished result before you build anything. The screenshots in this guide are from the demo and show demo data.

What you'll have at the end

• The input's power against your input limit, with the headroom left.
• Each phase of the input, measured: power, current, voltage and the load against the breaker.
• Each circuit against its own rating, with the lines that go above it flagged.
• A single-line diagram of the installation, with your groups as switchboards.
• History for every circuit, kept on the hub, in energy, power or money: by hour for 60 days, by day for about 13 months, by month for 3 years. You can download any of it as CSV.
• Notes from the app, among them the base load at night.

Already monitoring in Home Assistant? The hub can send each point's power and energy to Home Assistant over MQTT as well; your existing setup can stay as it is. The per-phase readings of the three-phase input, the groups and the money stay in the RBgrid app, with the input against its limit, the line ratings, the history views and the notes. → A power meter for Home Assistant

What you need

The STD-U3I3 is a precise energy meter: on the input it gives exact metering of the whole workshop, phase by phase. It comes as a 60 A or a 100 A kit; for a 63 A main breaker, the 60 A kit reads correctly up to about 75 A (measured by rbAmp); for more headroom take the 100 A kit. Its sensors are paired with the module and aren't replaceable, so there's no clamp to buy for the input and no current sensor to choose in the app.

One Basic module per phase. A Basic module works out each channel's power from its own single voltage input. A clamp on a circuit of another phase would measure wrong. So each Basic module's voltage input goes on one phase, and its clamps go only on circuits of that phase:

On L1 a Basic UI3 works too, and leaves room for more L1 circuits.

Machine tools and compressors are often three-phase. Meter such a machine like the heat pump in the three-phase house: one clamp per conductor, one point per phase, grouped.

Choose each circuit clamp as the smallest rating at or above the circuit's breaker (see Choosing the clamp sizes).

The demo workshop has the same layout: the STD-U3I3 on the input, the Basic UI1 on L1 and a Basic UI3 on each of L2 and L3, with the same circuits on the same channels. It fits an SCT-013-050 on the machine tools and an SCT-013-030 on every other Basic channel; choose yours by the breaker, as above. Not sure which clamp you have? See Which SCT-013 do you have?

Safety. For any work inside an electrical panel, call a qualified electrician.

Clamp one conductor only (L) per circuit, never the whole cable: the currents in L and N cancel out.

A three-phase load gets one clamp on each of its L1, L2 and L3 conductors, each on the Basic module of that phase; no clamp on N.

1. Wire, flash, connect

1. Wire the modules: the STD-U3I3, the Basic UI1 and the two Basic UI3, their voltage inputs and sensors.
   • The STD-U3I3: its voltage inputs are wired like a Basic module's: AWG26–22 wire, a fuse of up to 0.1 A in each L line, and it needs the neutral (terminals N, L1, L2, L3). Its three sensors go on the three input conductors, each with its arrow in the import direction, from the grid towards the workshop.
   • Each Basic module: its voltage input to its own phase and N through its fuse; its clamps on that phase's circuits (the table above), each with the arrow pointing towards the load. A Basic module counts one direction only, so a clamp the wrong way round reads nothing.

The conductor you call L1 must be the same one everywhere: the STD-U3I3's L1 sensor and L1 voltage terminal, the L1 Basic module's voltage input, and the clamps on that module. The same for L2 and L3. The check in step 5 confirms it.

Place each module within 15 cm of the hub. For longer runs see the bus-length section of the rbAmp wiring guide. The modules' I²C cables are connected to the hub one at a time later, during Add a module, with the hub off.

2. Connect only the STD-U3I3 to the hub for now (power, GND, SDA, SCL), at its factory I²C address 0x50. → Quick start, step 1
3. Flash the hub, join it to your Wi-Fi and open the app, at webapp.rbgrid.io or installed on the hub: follow the Quick start steps 2–4, then come back here.

A new hub makes the module at 0x50 your grid input by itself, plus a voltage point. There's nothing to bind for it. In step 3 you turn it into a three-phase input.

2. Run the setup wizard

The app opens with a banner, The hub still has its factory settings. Choose Set up →. → The setup wizard

• Security: set an API token and write it down.
• Site & time: a site name (the demo uses "Workshop (demo)"), your time zone; check that the clock shows synchronized. The scenario is set in step 6.
• Sensors: the grid input is already there. Leave the rest for step 5.
• Tariff: the quick form fits the demo's plan. Enter the day price, switch on There is a night rate (23:00–07:00) and enter the night price. Leave Price as on the bill — incl. VAT on if your bill prices include VAT, and check the VAT, %: a new hub starts at 21 %. Leave The grid pays per exported kWh empty: the workshop has no solar.

The demo uses Day 07:00–23:00 at 0.36 and Night 23:00–07:00 at 0.18 per kWh including 20 % VAT (its plan stores them without VAT, as 0.30 and 0.15, which is what the Tariffs screenshot shows). Use your own bill's prices. Costs in RBgrid are energy-based: the demo's monthly "Standing charge" isn't included, so don't copy it. Leave Net metering off on the Tariffs page: the workshop exports nothing.

3. Make the input three-phase

A three-phase input is supported on one STD-U3I3. Open Points: the STD-U3I3's card shows the grid input.

1. On the module card, press Use as the three-phase input.
2. Confirm Use as the input. The input keeps its history.
3. Press Restart now.

After the restart the input is one point, L1–L3, with a reading for each phase. → Use as the three-phase input

Then open Settings → Mains and choose Three phase. Mains system applies at once, and the Phase list on each point now offers L1, L2 and L3. Nominal voltage and frequency, if you change them, apply after a hub restart (Save and restart). The defaults are fine for a 230/400 V supply. → Settings

On the grid input, open Point setup and set:

• Input limit, kW: what your supply contract allows; without a contracted figure, use the main breaker (A × 230 V × 3). 43 kW in the demo. This is the figure the Business view measures the input against;
• Input breaker, A: 63 A in the demo.

The STD-U3I3's sensors are calibrated with the module at the factory, so there's no current sensor to choose.

The Business view takes the smaller of the input limit and what the breaker passes (63 A × 230 V × 3 = 43.47 kW). Here that's 43 kW. → Grid input vs limit

4. Add the three Basic modules

Connect the Basic modules one at a time, with Points → Add a module. Every module from the box answers at the same address, 0x50. So each time, the module answering at 0x50 is moved to a free address first, and the new module is then connected at 0x50. On the first round that's the STD-U3I3: it moves, and keeps its points, history and settings. → Adding modules

For each Basic module (the UI1 for L1, then the UI3 for L2, then the UI3 for L3):

1. The app offers a free address, for example 0x51, and moves the module now at 0x50 there.
2. Switch the hub off and connect the new module's I²C cable to the hub. It answers at 0x50.
3. Switch the hub on, open Add a module again and press Scan, then Add.

Each module's channels now show under Free sensors. The final addresses depend on the order you add the modules in, and they don't matter: points are known by their names. The demo's Points page shows a different set of addresses.

5. Bind the five circuits

First make two groups: Settings → Consumer groups → Add group, "Production" and "Building", then Save. In the single-line diagram they become the switchboards. → Consumer groups

Then Bind each free sensor with its name, role, phase and line rating. Open each new point's Point setup for the breaker, the current sensor and the group.

• Line rating is what the circuit's breaker allows: breaker × 230 V (for example 10 A → 2.3 kW, 16 A → 3.68 kW, 25 A → 5.75 kW). The Business view compares every line against it. The demo uses its own figures: 9, 3, 3, 2 and 6 kW, in the order of the table.
• Role Heating/cooling keeps the ventilation out of the app's base-load estimate, because it runs on its own schedule.
• Phase: the phase of the module's voltage input; every channel on a module is on that phase.
• Current sensor must match the clamp actually fitted. → Points

The short names in the screenshot, "Machines" and "HVAC", are each point's Short name, set in Point setup.

Restart the hub (Settings → Administration). A newly bound point shows live values at once and starts keeping history after the restart; nothing measured before is lost. The hub keeps history for up to 12 points; the workshop has six. A three-phase load measured per conductor uses three of the 12 history slots, so plan for growth.

Check it: switch on a load you know, such as a kettle on the office circuit. Its point should read about the kettle's rated power, and the input's L2 should rise by about the same amount.

6. Switch to the Business view

Open Settings → Site scenario, choose Business and confirm Change. It needs the API token, if you've set one. It applies at once, for everyone who opens this hub. Just preview shows it in this browser only. → Site scenario

7. What the app shows

The Overview in the Business scenario opens in power. → The Overview

• Grid input vs limit: the input's power against the 43 kW limit, with a bar and the headroom left.
• Phases, measured at the input, with "breaker 3 × 63 A (per phase)": each phase's power, current and voltage, a bar against the breaker, and the current unbalance. On a real hub the card also reports the phase rotation.
• Load lines: each circuit with its power, its cost per hour, current, today's energy and its Load against its rating.
• Needs attention: the lines that need a look, each linked to its point.
• Single-line diagram: the input, the main bus, then the "Production" and "Building" switchboards with their lines.

In money, each circuit's cost is its energy at the zone's buy price: an hour in the Day zone at the day price, an hour in the Night zone at the night price.

History for 7 days, in money, shows the working days, a quiet weekend, and today so far. In the screenshot (Tuesday to Monday) that's four full working days, two low weekend bars, and Monday morning, still incomplete. Today in power, for the compressor alone, shows its working-hours pattern. → History

History steps by the hour at its finest; live values update every 3 seconds on the Overview (and over MQTT). Energy on modules that count on board moves in 15-minute steps.

Details adds the hourly chart, the points table and Insights. The Business scenario words them for a business. In the demo, on a Monday evening after work (19:30), they read:

• Expensive now: Day — 2.0× the "Night" rate, with the app's note that flexible loads (heating, charging, batches without a fixed schedule) are cheaper to run in the "Night" zone;
• Where the energy goes today and Month consumption forecast;
• Today uses ≈ 503% more than yesterday by this hour: a Monday compared with a Sunday. It's a weekday/weekend artefact of the demo;
• Base load outside working hours ≈ 1,060 W, with the app's line Check what can be switched off on a schedule. It's the app's night-time floor, from the quiet hours 01:00–05:00: the same estimate as Standby use in the Home view, shown under the Business name. There's no working-hours setting. The ventilation isn't counted in it, because it runs on its own schedule.

These are the app's estimates at your current rates, marked with ≈. RBgrid doesn't switch anything: what you turn off, and when, is up to you. → Insights

The compressor above its rating

The demo's compressor line is rated 3 kW. In working hours the compressor alternates: about 3.8 kW in the even hours (08, 10, 12, 14, 16) and about 1.5 kW in the odd ones. 3.8 kW on a 3 kW line is about 127 % of the line's rating; the screenshot at 10:00 caught 3.75 kW, 125 %.

The demo exaggerates this to show the flag. 3.8 kW on a 16 A line is more than a real 16 A breaker would carry for long.

The app flags it in three places while it lasts:

• Load lines: the compressor's status reads above limit;
• Needs attention: "3.8 kW — 127 % of the line's rating", tagged above rating;
• the Points table under Details: above rating.

At an odd hour the flag clears, and after 18:00 the compressor stops. In History, today by hour in power, the compressor draws a saw-tooth through the working day.

On a real site the same flag means the line's rating as entered is lower than what the machine draws. RBgrid only shows the figure; the rating you enter decides when the flag comes on. This is a line-rating flag, not a clamp flag: 3.8 kW is about 16.5 A, inside a 20 A clamp's range, so the clamp raises no sensor limit or clipping.

Choosing the clamp sizes

A clamp has a range, and both ends matter. Too small, and its readings are cut off above its rating; too big, and small currents read as zero on a Basic module. A clamp rated at the circuit's breaker stays inside that range, which is why the table matches each clamp to its breaker. → Choosing the clamp sizes

Known issue in app 1.1.4: the point's settings check the breaker against a limit below the clamp's rating (90 % of it), so the lighting's 10 A clamp on a 10 A breaker shows "The line breaker 10 A is above the sensor's limit (9 A)…". The clamp reads correctly at its rating; the check will be corrected in an upcoming release.

Demo data vs your workshop

• In the demo every working day is the same, and the compressor's pattern follows the clock (even and odd hours), not the air pressure.
• The demo's phases are a fixed split of the input's power, not measured per phase. On a real hub the STD-U3I3 measures each phase at the input, and the per-phase remainders follow your real wiring.
• The demo's line ratings (9, 3, 3, 2 and 6 kW) are its own figures, and its compressor is set to go above its line to show the flag.
• The demo fits an SCT-013-030 on every Basic channel except the machine tools; choose your clamps from your own breakers.
• The demo's money history leaves out VAT. Its module firmware update is simulated.
• History starts when you set the hub up; data from other systems isn't imported.
• Your numbers depend on your circuits and your work pattern; nothing in this guide promises a figure.

If something's wrong

• Use as the three-phase input isn't offered: the STD-U3I3 must be present and the input not three-phase already. → Sensors and modules
• Add a module finds nothing new: check that only one new module is connected, and that the hub was off while you connected it. → Adding modules
• "Input limit is not set" on the Overview: set the input's Input limit, kW in its Point setup.
• A circuit reads 0 while its load runs: the clamp may face the wrong way (the point says sensor reversed — not metered).
• A circuit reads implausible power: check that its clamp is on the module whose voltage input is on the same phase.
• Sensor limit or clipping on a point: the circuit draws more than its clamp's rating; see Choosing the clamp sizes.
• Business view not saved ("Admin token required."): enter the API token in Settings → Security.

Next

• Add more circuits: the L2 and L3 modules each have a free channel for a circuit of their phase; a hub takes up to eight modules, and keeps history for up to 12 points. → Sensors and modules
• Read the data into your own tools (for experienced users). Besides the CSV downloads in History, your tools can read the history of any point that keeps history (up to 12 points) over the hub's REST API: GET /api/v1/history?unit=…&period=hour|day|week|month|year&type=energy|electrical|economics, with a read token if you set one. Or over MQTT: the cmd history, with the answer on cmd/resp. The MQTT commands don't check a read token yet, so use a broker with its own users. → MQTT
• Check how much of the input your circuits cover: Balance: input and lines. → Economics
• Refine the tariff: more zones, per-kWh fees. → Tariffs
• Send the data to Home Assistant. → A power meter for Home Assistant
• Look around the finished workshop: demo.rbgrid.io, Workshop