The Sunsynk SDM120CT-M digital meter is a single-phase, CT-operated Eastron energy meter specified by Sunsynk for installations where the run between the grid mains incomer and the inverter exceeds around 10 metres — a distance at which the inverter's built-in CT can start returning inaccurate power readings. Wiring in this external meter restores precise, real-time import/export measurement regardless of cable run length, feeding accurate data back to the Sunsynk inverter for load and export management.
Supplied with a 120A/40mA current transformer, the meter clips around the incoming supply conductor for non-invasive installation and communicates over RS485 Modbus directly to the Sunsynk inverter. It is MID certified (Class B and D), giving bi-directional kW/kWh measurement accurate enough for billing as well as system monitoring.
Class 1
Active energy accuracy
MID B+D
Certified for billing
RS485
Modbus communication
>10m
Recommended run length
CT ratio must match — 120A/40mA only
Sunsynk specifically requires the 120A/40mA CT clamp variant of the SDM120CT for use with its inverters. Fitting a meter with a different CT ratio (such as the 100A/100mA variant used by some other inverter brands) will produce inaccurate readings, so always confirm the model and CT ratio before ordering a replacement or spare.
When to add this meter
This meter is intended for installations where the cable run between the grid mains incomer and the Sunsynk inverter exceeds roughly 10 metres. Over shorter runs, the inverter's own internal CT is normally sufficient; this external meter corrects the measurement error that longer cable runs can introduce.
Purpose-matched to Sunsynk inverters
Specified directly by Sunsynk to correct power-reading inaccuracy on installations with a long grid-to-inverter cable run, ensuring the inverter's export and consumption data stays accurate.
120A/40mA CT clamp included
Supplied with the correct CT clamp for Sunsynk systems — a non-invasive clip-on sensor that measures current without breaking into the live conductor.
MID certified for billing
Certified to MID Class B and D, so readings are accurate enough for formal energy billing as well as inverter monitoring and export control.
Bi-directional energy measurement
Measures import and export kW/kWh independently, with configurable pulsed output for total, import, or export energy.
RS485 Modbus communication
Communicates with the Sunsynk inverter over RS485 Modbus, with an M-bus variant also available where that protocol is required.
Compact DIN rail meter
Simple to set up and operate, mounting on a standard DIN rail within the consumer unit or inverter enclosure alongside other system components.
Electrical
Measurement type
Single-phase, CT-operated
CT clamp ratio
120A / 40mA
Rated voltage
230V AC, single phase
Power consumption
< 2W / 10VA
Accuracy
Active energy
Class 1 (better than Class 1 overall)
Voltage
0.5% of range maximum
Frequency
0.2% of mid-frequency
Communication & output
Interface
RS485 Modbus RTU (M-bus variant also available)
Baud rate
1200 / 2400 / 4800 / 9600 bps (default 2400)
Modbus address range
1–247 (default 001)
Pulse output 1
Configurable — total / import / export / nett kWh
Pulse output 2
Fixed, 1000 imp/kWh
Certification & standards
Billing certification
MID Certified, Class B and D
Reference standard
IEC 62053-21 / EN 50470-1/3
Installation category
CAT II
Physical & environmental
Dimensions (W x H x D)
18mm x 118mm x 64mm
Display
White backlit LCD
Operating temperature
-25°C to +55°C
Relative humidity
0–95%, non-condensing
Protection rating
IP51 (indoor use)
Frequently Asked Questions
Why would I need this meter with my Sunsynk inverter?
It is needed where the cable run between the grid mains incomer and the inverter exceeds roughly 10 metres. Over that distance, the inverter's built-in CT can return inaccurate power readings; this external meter restores accurate measurement.
Can I use a different Eastron SDM120CT meter instead?
No — Sunsynk specifically requires the 120A/40mA CT clamp variant. Other Eastron SDM120CT meters use different CT ratios (such as 100A/100mA) and are not compatible with Sunsynk's expected calibration, which will result in inaccurate readings.
Is this meter suitable for billing purposes, or just monitoring?
It is MID certified to Class B and D, so it is accurate enough for formal energy billing as well as day-to-day inverter monitoring and export control.
How does the meter communicate with the inverter?
Over RS485 Modbus RTU, wired directly to the Sunsynk inverter's meter input; an M-bus communication variant is also available where that protocol is preferred.
Who should install this meter?
Installation involves working on the live incoming supply and should be carried out by a qualified electrician, in line with current UK wiring regulations (BS 7671).
