M3-40
The Solax M3-40 is a three-phase smart meter rated at 40 A with 3 included 100A/40mA CTs, designed to enable export control, zero feed-in, and self-consumption optimization on Solax inverters. 50 ms refresh, RS485 Modbus RTU, plug-and-play CT, automatic phase and CT direction correction, remote configuration via SolaxCloud APP. For three-phase systems with a single inverter.
The Solax M3-40 is a three-phase smart meter rated at 40 A, designed for precise measurement of energy flows in residential and commercial three-phase photovoltaic systems. It is the component that allows Solax inverters to enable advanced functions such as export limitation (zero feed-in), self-consumption optimization, and intelligent battery management in storage systems. The package includes 3 CTs of 100 A / 40 mA with a plug-and-play terminal.
Why does the Solax inverter need a meter?
An inverter without a meter only knows how much it produces, but does not know what happens at the grid connection point. Without this information, it cannot:
- limit the power fed into the grid to comply with zero-injection requirements set by the grid operator
- decide when to charge or discharge the storage battery to maximize self-consumption
- provide accurate consumption data to the SolaxCloud monitoring system
The M3-40 measures in real time the power exchanged on all three phases and transmits it to the inverter via RS485 Modbus RTU, allowing the system to move from "a PV that produces" to "an intelligent energy system".
M3-40 Technical Specifications
| Product code | SOL-M3-40 |
| Type | Three-phase smart meter, single measurement channel |
| Network type | 3P3W / 3P4W (three-phase with or without neutral) |
| Voltage range | 220 - 415 V AC (40 - 400 V on a single phase) |
| CTs included | 3 CTs of 100 A / 40 mA |
| Compatible CTs (expansion) | 100 / 200 / 400 / 600 / 1000 / 1500 / 2000 A / 40 mA |
| Refresh rate | 50 ms (high sampling speed) |
| Communication | RS485 Modbus RTU |
| Wireless transmission | Compatible with Wi-BR (up to 200 m horizontal / 20 m vertical) |
| CT connection | Plug-and-play (single terminal for all 3 CTs) |
| Auto-correction | Automatic phase sequence and CT direction detection |
| Remote configuration | SolaxCloud APP |
| Safety | Electrical isolation between strong and weak current circuits |
| Display | Integrated LCD |
| Dimensions | 65 × 45 × 100 mm |
| Weight | ~500 g |
| Warranty | 24 months |
Compatible Solax Inverters
The M3-40 is compatible with almost all new generation Solax inverters, both three-phase and single-phase (in single-phase configuration, only L1 and N are connected):
- Three-phase hybrid inverters: X3-HYB G4, X3-HYB G4 PRO, X3-IES, X3-AELIO
- Three-phase retrofit inverters: X3-FIT G4
- Three-phase commercial inverters: X3-MEGA G2, X3-FORTH
- Single-phase inverters: X1-MINI G4, X1-BOOST G4, X1-SMART G2 (with L1 + N wiring)
For correct RS485 pin connection, refer to the meter's Quick Installation Guide, which provides a pin-out table for each inverter series.
Main Functions
- Accurate three-phase measurement of voltage, current, active/reactive power, power factor, frequency, and energy
- 50 ms refresh rate: very fast response time, essential for effective export control and for managing load transients in storage systems
- Plug-and-play CTs: the single terminal for all 3 CTs drastically reduces wiring time and connection errors
- Intelligent phase and CT direction adaptation: the meter automatically detects phase sequence or CT direction errors and self-corrects — fewer call-backs for the installer
- Remote configuration via SolaxCloud APP: change parameters remotely without being physically on site
M3-40, M3-40 Dual or M1-40: how to choose?
- Three-phase system with a single Solax inverter → M3-40 (this product)
- Three-phase system with two generation devices to monitor (e.g., Solax retrofit storage on existing PV from another brand, dual inverter) → M3-40 Dual
- Single-phase system (X1-MINI/BOOST/SMART inverter) → M1-40
Frequently Asked Questions
Is the M3-40 mandatory to enable export control on the Solax inverter?
Yes. To enable export control (zero feed-in or grid injection limitation) on Solax systems, a compatible meter is required. The M3-40 is the standard choice for residential and commercial three-phase systems with a single inverter. Without a meter, the inverter operates independently but cannot comply with a grid injection limit required by the grid operator.
Can I use the M3-40 on a single-phase system?
Yes, but it is an "oversized" solution. The M3-40 in single-phase configuration connects only to L1 and N (L2 and L3 ports remain unused) and uses only one of the three CTs. It works, but if the system is natively single-phase, the M1-40 model is preferable, as it has the same firmware but is less expensive and includes only one CT.
Are the CTs included in the package?
Yes. The package includes 3 CTs of 100 A / 40 mA, already pre-wired with a plug-and-play terminal. For systems with higher currents, CTs of 200, 400, 600, 1000, 1500, and 2000 A / 40 mA are available as accessories, to be paired with the meter while maintaining the same transformation ratio.
Can I configure the meter remotely?
Yes, via the SolaxCloud APP. Additionally, the meter features automatic self-correction of phase sequence and CT direction: once wired, it analyzes the data and reconfigures itself if it detects a reversal, drastically reducing the need for corrective interventions after installation.
What cable is needed for communication with the inverter?
Shielded twisted pair RS485 cable (recommended 0.5-1 mm² with shielding) or RJ45 Cat 5e cable depending on the communication port of the Solax inverter. The meter's Quick Installation Guide provides a pin-out table for each inverter series. Alternatively, the meter is compatible with the Solax Wi-BR module, which allows wireless connection up to 200 m horizontally.
How is the meter physically installed?
The M3-40 is mounted on a DIN rail or on the wall inside the electrical panel. The 3 CTs are clipped onto the 3 phases of the grid connection line (the arrow printed on the CT must point towards the load/inverter, with the grid side on the other). The RS485 cable connects the meter to the Solax inverter. Once powered, the meter starts automatic phase detection and configures itself.
