Connecting a Three-Phase Eastron Meter to Single-Phase Sunsynk and Deye Inverters

Key Takeaways

• The Eastron SDM630MCT three-phase meter can be deployed on single-phase Sunsynk and Deye 3.6kW and 5kW Ecco inverters to overcome analogue CT distance constraints.
• Single-phase terminal bridging requires linking terminal 5 (LA) to Phase 1 (connection 4) and terminal 6 (NA) to neutral (connection 1).
• Only one current transformer is used, clamped with its directional arrow pointing towards consumer loads and terminated into Phase 1 S1 and S2 inputs.
• RS485 communication connects terminal 14 (TX+A) to Pin 5 (485-A) and terminal 13 (TX-B) to Pin 4 (485-B) on the inverter Meter port.
• Isolate the main distribution board switch and test conductors with a calibrated voltage tester before modifying wiring in compliance with national wiring standards.

Why Use a Three-Phase Meter on a Single-Phase Inverter

In residential and light commercial solar installations throughout South Africa, single-phase hybrid inverters represent the vast majority of installed systems. While standard installations utilize a single analogue current transformer (CT) plugged directly into the inverter chassis, installations often encounter physical layout challenges. When the hybrid inverter is located in an outbuilding, garage, or dedicated plant room tens of meters away from the main utility service entrance, analogue CT extension leads suffer from electromagnetic noise and signal degradation.

To resolve this distance challenge, solar technicians often deploy digital energy meters over an RS485 serial communication link. While dedicated single-phase digital meters exist, many commercial distributors and installers standardize on the robust Eastron SDM630MCT multi-phase platform. It is fully supported and possible to use the three-phase meter with single-phase inverters, provided the auxiliary power terminals, reference voltage inputs, and current sensing channels are configured to account for a single incoming active conductor.

This technical guide provides the exact terminal bridging, CT termination, and RS485 wiring protocols required to connect an Eastron SDM630MCT to single-phase Sunsynk and Deye hybrid inverters.

Technical Advantages of Multi-Phase Metering on Single-Phase Supplies

Deploying a three-phase digital power meter on a single-phase installation offers significant practical advantages:

1. Supply Chain Consistency: High-capacity solar distributors across South Africa routinely stock the Eastron SDM630MCT in volume. Utilizing a single unified meter model across both single-phase and three-phase client portfolios streamlines inventory and replacement stock.
2. Future Three-Phase Expansion: Many residential properties in suburban areas of Johannesburg, Pretoria, Cape Town, and Durban currently operate on 60A or 80A single-phase Eskom or municipal feeds, but plan future upgrades to three-phase 400V supplies. Installing a three-phase meter today ensures that if the supply is upgraded and two additional inverters are paralleled, the metering hardware requires zero replacement.
3. Severe Distance Capability: Standard analogue CT wires are vulnerable to voltage drop and radio frequency interference when extended beyond 10 to 15 meters. The digital RS485 Modbus interface of the Eastron meter allows communication cables to run over long distances with complete signal fidelity.

Terminal Bridging Scheme for Single-Phase Supply

The Eastron SDM630MCT features separate measurement inputs for three independent phase voltages (L1, L2, L3) and neutral (N), alongside dedicated auxiliary power terminals (LA and NA) that energize the meter's internal logic controller and backlit LCD screen.

When connected to a single-phase 230V alternating current supply, the meter will not power up or measure current accurately unless auxiliary power is bridged correctly. Installers must execute a precise bridging scheme across the main terminal block:

1. Auxiliary Phase Bridge: Fabricate an insulated copper jumper link and create a bridge from connection 5 labelled LA to phase 1 (connection 4). This links the internal power supply phase terminal directly to the active Phase 1 voltage sensing circuit.
2. Auxiliary Neutral Bridge: Fabricate a matching insulated copper jumper link and create a bridge from connection 6 labelled NA to the neutral (connection 1). This completes the return circuit to the distribution board neutral busbar.
3. Reference Connections: Connect the incoming single-phase utility live conductor directly to connection 4 (Phase 1 / L1). Connect the incoming utility neutral conductor directly to connection 1 (Neutral). Terminals 2 and 3 (Phase 2 and Phase 3 voltage sensing) remain completely empty and unpopulated.

```
EASTRON SDM630MCT SINGLE-PHASE TERMINAL BRIDGING
+-----------------------------------------------+
| [1] [2] [3] [4] [5] [6] |
| Neutral (Empty) (Empty) L1 LA NA |
+---|-----------------------|------|------|-----+
| | | |
| +------+ |
| Phase 1 Bridge |
+-------------------------------------+
Neutral Bridge
```

All connections must conform to national wiring regulations for low-voltage wiring inside distribution enclosures. The phase supply to connection 4 must be tapped from an appropriately rated miniature circuit breaker (MCB) to ensure the meter can be isolated safely without de-energizing the entire building.

Current Transformer Installation and Phase 1 CT Terminations

Because a single-phase supply delivers power through a single live conductor, only one current transformer is required. Attempting to install multiple CTs on the same conductor or wiring CTs into the Phase 2 or Phase 3 channels will confuse the meter firmware and cause the inverter to report zero load or communication fault states.

CT Clamp Placement and Directional Orientation

1. Locate the incoming utility live conductor between the main municipal electricity meter / service fuse and the main distribution board isolator.
2. Fasten the split-core CT clamp securely around the incoming live conductor.
3. The CT clamp has an arrow that must point towards the loads (consumer unit / distribution board circuits) and away from the incoming utility meter.
4. If the CT arrow is installed pointing in reverse towards the grid, the inverter interprets normal domestic consumption as power export, triggering reverse-power alarms or throttling solar output.

Secondary Terminal Wiring

The secondary wiring leads from the current transformer must terminate exclusively into the Phase 1 measurement terminals on the Eastron meter:

• The white cable should then be connected into S1 1 on the upper terminal array.
• The black cable should be connected into S2 1 on the upper terminal array.
• Terminals S1 2, S2 2, S1 3, and S2 3 (corresponding to Phase 2 and Phase 3 current inputs) must remain completely disconnected and open.

```
CURRENT TRANSFORMER SECONDARY WIRING
+--------------------------------------+
| [S1 1] [S2 1] (S1 2) (S2 2) |
| White Black (Open) (Open) |
+------|----------|--------------------+
| |
+----------+
Phase 1 CT Leads
```

RS485 Communication Cable and RJ45 Termination

The digital communication link between the Eastron SDM630MCT and the hybrid inverter relies on a two-wire differential RS485 serial bus running over twisted-pair data cabling.

Cable Selection and Preparation

• Use a high-quality Cat5e or Cat6 shielded twisted-pair (STP) cable.
• Preserve the bare foil shielding and drain wire along the entire cable run to suppress electromagnetic interference from nearby AC power circuits.
• Strip the cable jacket back at the meter end, selecting a matched color pair (for example, Blue and Blue/White, or Brown and Brown/White).

Meter Terminal Termination

• Connect the solid colored conductor into terminal 14 (designated as TX+A).
• Connect the striped white conductor into terminal 13 (designated as TX-B).

Inverter RJ45 Plug Pinout

At the inverter side of the cable run, terminate the twisted pair into a standard 8P8C RJ45 modular connector according to the manufacturer's serial pinout:

• The serial port pinout requires that Pin 4 = 485-B and Pin 5 = 485-A and plug RJ45 into Meter/RS485 Port.
• This definition applies to the 3.6kW and 5kW Ecco inverter units.
• Connect the wire from meter terminal 14 (TX+A) to Pin 5 on the RJ45 jack.
• Connect the wire from meter terminal 13 (TX-B) to Pin 4 on the RJ45 jack.
• Terminate the RJ45 modular plug firmly into the port clearly labelled Meter or RS485 on the bottom connection panel of the hybrid inverter chassis.

```
+---------------------+-------------------+---------------------+

+---------------------+-------------------+---------------------+

+---------------------+-------------------+---------------------+
```

Meter Programming and Inverter Setup Menu

Once all mechanical terminations and communication leads are completed, both the Eastron meter and the single-phase inverter must be configured to communicate.

Programming the Eastron SDM630MCT

1. Energize the distribution board and observe the meter display. The LCD panel should illuminate.
2. Press and hold the navigation push button for 3 seconds until the password entry screen appears.
3. The password is 1000. Use the front scroll buttons to set each digit from left to right, confirming each entry.
4. Navigate to the Address parameter and verify it is configured to 001.
5. Navigate to the Baud rate parameter and ensure it is configured to 9600.
6. Navigate to the CT1 setting and input the primary rating of your current transformer (for example, 100 or 200).
7. Navigate to the CT2 setting and confirm it matches the secondary rating of the coil (typically 5A).
8. Save and exit the programming menu.

Inverter Operating Mode Configuration

1. Tap the touchscreen on the single-phase Sunsynk or Deye inverter to wake the LCD display.
2. Navigate to Settings > Advanced Settings > Others.
3. Under the external sensor options, enable Ex_Meter for CT.
4. In the meter selection drop-down list, select Eastron 3P (or Eastron). Even though the inverter is a single-phase unit, selecting the three-phase driver instructs the processor to parse the multi-channel Modbus data registers generated by the SDM630.
5. Save the settings and exit the configuration menu.

Commissioning Checks and Verification

Verify operational integrity through direct system observation:

• Inverter Telemetry Check: Within 10 to 30 seconds of saving the inverter settings, the home display screen will update. The grid load indicator should reflect real-time domestic consumption.
• Load Response Verification: Switch on a high-power domestic appliance (such as an electric kettle, induction cooktop, or geyser). The active power recorded on the Eastron LCD display should increase immediately, and the inverter screen should report a matching increase in home load.
• Troubleshooting W04 Alarms: If the inverter displays warning W04_Meter_Comm_Fail, immediately verify that Pin 4 (485-B) and Pin 5 (485-A) have not been inverted, confirm the meter Modbus address is set to 1, and ensure the baud rate matches 9600 bps.

By utilizing this single-phase bridging methodology, solar technicians can install the high-reliability Eastron SDM630MCT on standard single-phase residential properties with complete confidence, ensuring robust zero-export management and seamless compatibility across South African electrical networks.