Which Eastron Meter Do I Need? SDM230 vs SDM72D-M vs SDM630MCT
Share
The short answer: if your supply is single phase, buy the Eastron SDM230. If it is three phase and 100A or less, and you can wire the meter in line, buy the Eastron SDM72D-M. If it is three phase and bigger than 100A, or you can't break into the cables, buy the Eastron SDM630MCT with clip-on CT clamps. All three are MID approved, fit a standard DIN rail and talk Modbus RS485, so any of them will read into Home Assistant, ESPHome, Victron and most solar inverters.
The rest of this guide explains how to tell which of those you are, and the few details that catch people out.
The three meters side by side
| SDM230 | SDM72D-M | SDM630MCT | |
|---|---|---|---|
| Supply | Single phase | Three phase | Three phase (or single phase) |
| Maximum current | 100A | 100A | Set by the CT clamps: 100A, 150A or 200A |
| How it connects | Wired in directly | Wired in directly | Clip-on CT clamps, no need to break the circuit |
| Measures import and export separately | Yes | Yes | Yes |
| MID approved for billing | Yes | Yes | Yes |
| Output | Modbus RS485 and pulse | Modbus RS485 and pulse | Modbus RS485 and pulse |
| OmniKit price | £36.99, or £209.99 for six | £60.99 | £124.99 meter only; £154.99, £160.99 or £170.99 with 100A, 150A or 200A clamps |
Step one: single phase or three phase?
Most UK homes have a single-phase supply: one main fuse at the incoming cable, 230V. Three-phase supplies are common on commercial and industrial sites, farms, larger homes and buildings with big heat pumps or fast EV chargers. A three-phase supply has three main fuses where the cable comes in, and the meter the electricity company fitted will say three phase on it.
If you are sub-metering a single circuit, such as one EV charger, one solar inverter or one annexe, what matters is that circuit, not the building. A single-phase EV charger in a three-phase building still only needs an SDM230.
Single phase: the Eastron SDM230
The Eastron SDM230 is the meter most people want. It measures one single-phase circuit up to 100A, and the live and neutral wire straight into it, so there are no clamps to buy or fit. It is two modules wide on a DIN rail, so it fits in most consumer units and small enclosures.
Typical uses are solar inverter output, EV chargers, heat pumps, annexes and sub-let rooms, and whole-house monitoring on a single-phase supply. Installers doing several at once usually buy the six-pack.
Three phase up to 100A: the Eastron SDM72D-M
The Eastron SDM72D-M does for three phase what the SDM230 does for single phase. All three phases wire directly into it, up to 100A, with no clamps. It is the cheapest way to meter a three-phase circuit properly, and it measures import and export, so it works for three-phase solar as well as consumption.
Choose it when you can isolate the circuit and wire the meter in line. If you can't, go to the SDM630MCT below.
Three phase over 100A, or where you can't break in: the Eastron SDM630MCT
The Eastron SDM630MCT uses current transformers, usually called CT clamps. Each clamp opens and closes around one cable, so you can meter a supply without disconnecting anything and without the current passing through the meter itself. That is why it handles supplies well above 100A.
Choose the clamp size by the main fuse or breaker, not by the load you expect. A 100A set suits most smaller three-phase supplies. The 150A and 200A sets are for larger services and heavy commercial loads. A clamp that is too small for its circuit will stop reading accurately once the current goes past its rating.
The clamps must match the meter. The SDM630MCT works with clamps that have a 5A (or 1A) output, and the sets we supply with it are 5A. Clamps with a 333mV output will not work with it. Those belong with a different model, the SDM630MCT-MV, which we sell as a complete set with three 100A 333mV clamps. If you already own clamps and want the meter on its own, email us with the clamp you plan to use and we'll confirm it suits.
What MID approval means
MID is the measuring instruments standard that UK law uses for meters people are charged against. A MID-approved meter has been tested to show its readings are accurate enough to put on a bill. If you are charging a tenant, a neighbouring unit or an EV driver for electricity, use a MID meter. All three meters in this guide are MID approved, with Class 1 accuracy or better. Our guide What does MID approved mean? explains when you need one.
Reading the meter in Home Assistant
All three meters talk Modbus RTU over two wires, labelled A and B. Connect those to a USB to RS485 adapter plugged into the computer running Home Assistant, add the Modbus integration, and the readings appear as sensors you can use in the Energy dashboard. ESPHome and Victron GX work over the same connection.
Our step-by-step guide How to connect an Eastron SDM230 to Home Assistant has the settings to copy and paste. Weighing an Eastron up against a Shelly? See Shelly or Eastron for Home Assistant.
These are Eastron's factory settings, taken from the manufacturer's manuals. Eastron Europe's own pages for the SDM230, SDM72D and SDM630MCT have the full specifications.
| Address | Baud rate | Parity | Stop bits | |
|---|---|---|---|---|
| SDM230 | 1 | 9600 | None | 1 or 2 |
| SDM72D-M | 1 | 9600 | None | 1 |
| SDM630MCT | 1 | Check the meter's menu | None | 1 or 2 |
All three use 8 data bits, and every setting can be changed from the buttons on the front. If a meter has been set up before, check its own menu first, because the values may have been changed.
If you would rather buy it all in one box from one UK supplier, OmniKit's Home Assistant Energy Monitoring Kit (£179.99) puts a Raspberry Pi 4 8GB, an SDM230, the adapter, an industrial power supply and a card with Home Assistant already installed together.
Installation
All three meters connect to mains wiring, so they must be fitted by a competent person to the current UK wiring regulations. The two-wire data connection can be run afterwards. Keep the data cable away from mains cables where you can, as running them together is a common cause of lost readings.
Common questions
Can I use the SDM230 on one phase of a three-phase supply?
Yes, if you only want to measure a single-phase circuit, such as one charger or one inverter, fed from that supply. To measure the whole three-phase supply you need the SDM72D-M or the SDM630MCT.
Which meter for three-phase solar?
If the inverter's output is 100A or less and can be wired through a meter, the SDM72D-M. Otherwise the SDM630MCT with clamps. Both measure import and export separately. Check your inverter's documentation for which meter model it expects.
Do the meters come with a warranty?
Yes. All three come with a one-year OmniKit warranty against faults, on top of your legal rights as a consumer.
How quickly will it arrive?
All three meters are held in UK stock. Order before 2pm on a working day and your order is dispatched the same day.
Still not sure which one you need? Email customersupport@omnikit.co.uk with the rating of the fuse feeding the circuit and what you want to measure, and we'll tell you.