How to wire two single-phase inverters to a 3x220V network without a neutral wire

The 3x220V network without neutral: understanding the configuration

What is a 3x220V network without a neutral?

In Belgium, some installations (particularly older or industrial ones) use a 3x220V three-phase network without a neutral connection . Here are the characteristics:

• 3 phases available: L1, L2, L3
• Voltage between phases: 220V (L1-L2 = 220V, L2-L3 = 220V, L1-L3 = 220V)
• NO neutral wire distributed in the installation
• It is impossible to measure a phase-to-neutral voltage (the neutral does not exist).

Why this configuration is complex

Connecting a single-phase inverter to a standard network with a neutral wire is simple:

• Inverter terminal "L" → Phase (e.g., L1)
• Inverter "N" terminal → Neutral (the true neutral of the network)

But on a network without a neutral , there are only 3 phases. To connect a single-phase inverter, you must use 2 phases :

• Inverter terminal "L" → One phase (e.g., L1)
• Inverter "N" terminal → Another phase (e.g., L2) which will serve as a reference

Crucial point: The terminal marked "N" on the inverter is connected to a phase (not a neutral). This is technically incorrect, but that's how the system works.

The cabling convention: L2 = common reference

Why impose an agreement?

On a 3x220V network without a neutral, the inverter could theoretically be connected between any two phases (L1-L2, L2-L3, or L1-L3). However, for the energy meter (Chint DTSU666) and the inverters to communicate, they must share the same voltage reference .

The solution: impose a convention .

Configuring the Chint DTSU666 counter in Aron mode

What is the Aron (3-wire) mode?

The Chint DTSU666 meter can operate in several modes. For a 3x220V network without a neutral wire , the Aron mode (Net ID 33) is used:

• 2 clamps (ampere clamps) instead of 3
• Clamp 1 on phase L1
• Clamp 3 on phase L3
• No clamp on L2 (it serves as a reference).

How Chint Measures Power

The meter performs two independent measurements:

The counter calculates:

• Element 1: _P1 = _IL1 × _UL1-L2 (current measured on L1, voltage between L1 and L2)
• Element 3: _P3 = I _L3 × U _L3-L2 (current measured on L3, voltage between L3 and L2)
• Total power: P _total = P ₁ + P ₃

Crucial point: All voltages are measured relative to L2 . This is why L2 must be the common reference for the entire system.

Inverter wiring: the absolute rule

The wiring diagram (Wattuneed convention)

This is the only wiring permitted to guarantee the proper functioning of the system:

Case with 1 single-phase inverter

If you only have one single-phase inverter (e.g., Sofar ESI 3kW):

• Inverter terminal "L" → Phase L1
• Inverter "N" terminal → Phase L2 (reference)
• Clamp 1 of the counter → On L1
• Meter clamp 3 → On L3 (to measure other loads)

Case with 2 single-phase inverters

If you have two single-phase inverters (e.g., 2× Sofar ESI 3kW = 6kW total):

Crucial points:

• Both inverters share the same L2 reference.
• L2 has no clamp (it serves only as a voltage reference)
• Inverter 1 injects power into L1, inverter 2 injects power into L3
• The meter measures the total production: P _total = P _inverter1 + P _inverter2

Why the wiring MUST be respected (technical explanations)

How the inverter measures its production

A single-phase inverter (like the Sofar ESI) calculates its injected power according to the formula:

P _inverter = I _L × U _LN × cos(φ)

It measures:

• The current coming out of its "L" terminal
• The voltage between its terminals "L" and "N"
• The phase shift between current and voltage (cos φ)

For an inverter wired according to the convention (L→L1, N→L2):

• Measured voltage: U _L1-L2 = 220V
• Current injected onto L1
• Calculated power: P = I _L1 × U _L1-L2

How the meter measures production

The Chint counter (Element 1) calculates:

P _element1 = I _L1 × U _L1-L2 × cos(φ)

It measures:

• Current on L1 (via clamp 1)
• The voltage between L1 and L2 (reference L2)
• The phase shift between current and voltage

Why it works: Reference alignment

Both devices measure exactly the same thing :

• Same reference voltage (U _L1-L2 )
• Same current (I _L1 )
• Same phase shift

➡️ Result: The inverter displays 1000W, the meter reads 1000W. The system is working perfectly.

The fatal mistake: reversing the connections

Worst-case scenario: L connected to L2, N connected to L1

Imagine you wire Inverter 1 backwards :

• Inverter terminal "L" → L2 (instead of L1)
• Inverter terminal "N" → L1 (instead of L2)

Concrete consequences

• The inverter thinks it is producing 1000W, the meter displays -1000W (consumption).
• The system becomes totally unstable : the inverter tries to correct it by increasing its output.
• Risk of overvoltage on the domestic network (up to 250-260V).
• Massive injection into the public grid (instead of self-consumption).
• Premature wear of the inverter and meter.
• Unusually high electricity bill (the supplier's electricity meter counts the injection as consumption).

"My inverter shows 2500W of production, but my home meter is running backwards and my Chint meter says I'm consuming 2000W from the grid." — Classic symptom of reversed wiring.

Pre-commissioning checklist

Before switching on your installation, check each point individually :

1. Network configuration

• ☑️ My network is indeed three-phase 3x220V WITHOUT NEUTRAL
• ☑️ I only have 3 phases available (L1, L2, L3)
• ☑️ No neutral wire is distributed in my installation

2. Configuring the Chint DTSU666 counter

• ☑️ The counter is in Aron mode (Net ID 33)
• ☑️ Clamp 1 is installed on L1
• ☑️ Clamp 3 is installed on L3
• ☑️ No clamp on L2
• ☑️ Modbus communication is working (RS485 connection inverter ↔ meter)

3. Inverter 1 wiring (if present)

• ☑️ Inverter terminal "L" → L1
• ☑️ Inverter "N" terminal → L2
• ☑️ Voltage measured with a multimeter: U _L1-L2 ≈ 220V

4. Inverter 2 wiring (if present)

• ☑️ Inverter terminal "L" → L3
• ☑️ Inverter "N" terminal → L2
• ☑️ Voltage measured with a multimeter: U _L3-L2 ≈ 220V

5. Additional checks

• ☑️ All connections are tightened to the recommended torque
• ☑️ The protective devices (circuit breakers, surge protectors) are correctly sized
• ☑️ The inverter firmware is up to date
• ☑️ Network parameters are configured (nominal voltage 220V, frequency 50Hz)

Functionality test (commissioning)

Once the wiring is complete and verified, follow this testing procedure:

Step 1: Gradual power-up

1. Activate the power supply for the Chint counter (wait for the display on the screen).
2. Check that the meter displays 0W (or close to 0, standby consumption).
3. Activate the inverter (let it start up and synchronize with the grid).
4. Wait for the inverter to start injecting (green light or production display).

Step 2: Verification of measurements

1. On the inverter: Note the displayed power (e.g., 1500W).
2. On the Chint meter: Check that the displayed power is positive and close to that of the inverter (e.g., 1480W, the difference is normal).
3. If the meter displays a negative value : WIRING ERROR. Disconnect immediately and check the connections.

Step 3: Load Test

1. Switching on a power-hungry appliance (e.g., a 2000W kettle) to the mains.
2. Check that the Chint meter detects the increase in consumption.
3. Check that the inverter adjusts its production (if configured in self-consumption mode).

Frequently Asked Questions (FAQ)

1. Why can't I use the neutral wire in my network?

Because your electrical system doesn't have one. A 3x220V system without a neutral wire only distributes three phases. There is no neutral wire available in your electrical panel. If you had a neutral wire, you would have a different system (single-phase or three-phase with four wires).

2. Can I connect the inverter directly between L1 and L3?

No, that's dangerous. Between L1 and L3, the voltage is 380V (line voltage = √3 × 220V). A single-phase inverter is designed for 220-230V. You would instantly destroy the inverter. You must always connect between two adjacent phases (L1-L2 or L2-L3), and adhere to the convention L2 = reference.

3. What if I have 3 single-phase inverters?

Not possible with 2 clamps. The Aron setup (2 clamps) can only measure a maximum of 2 inverters (one on L1, one on L3). If you have 3 single-phase inverters, you must:

• Either switch to 4-wire mode (3 clamps) on the Chint (Net ID 30 or 31), but this requires a neutral.
• Either use a three-phase inverter instead of three single-phase ones.
• Either add a second meter for the 3rd inverter (complex solution).

4. My Chint counter displays "Err 01". What should I do?

The error "Err 01" usually indicates a configuration problem :

• Check that the Net ID is indeed 33 (Aron 3-wire mode).
• Check that the nominal voltage is set to 220V (not 230V or 400V).
• Restart the meter (cut off the power for 30 seconds).
• If the error persists, please contact our technical support .

5. Can I use L1-L3 instead of L1-L2 and L2-L3?

No, this is not compatible with the Aron configuration. In Aron mode, phase L2 is the common reference. All inverters must have their "N" terminal connected to L2. If you connect an inverter between L1 and L3 (bypassing L2), the voltage measurements will be incorrect.

6. What cable cross-section should be used for inverters?

It depends on the power and the distance. For a 3 kW single-phase inverter:

• Rated current: I = 3000W / 220V ≈ 13.6A
• Minimum recommended cross-section: 2.5 mm² (if distance < 20m)
• Recommended cross-section: 4 mm² (if distance > 20m or planned extension)

Consult our cable cross-section calculator for accurate sizing.

Summary: the 3 absolute rules

Golden rule: In a 3x220V network without neutral with Chint DTSU666 meter (Aron mode), the "N" terminal of the single-phase inverter must ALWAYS be connected to phase L2 (common reference), never to L1 or L3.

If you follow these 3 rules, your installation will work perfectly: the inverters will produce, the meter will measure correctly, and you will fully enjoy your solar self-consumption in complete safety.

To go further

Now that you've mastered 3x220V network wiring without a neutral, check out our other guides:

• Sofar inverter configuration for self-consumption
• Setting up the Chint DTSU666 counter: a complete guide
• Modbus communication: RS485 cabling between inverter and meter
• Troubleshooting: 10 common mistakes in photovoltaic installations

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Photovoltaic specialist in Belgium since 2015
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