ABB B21 energy meter
The ABB B21 is a single-phase energy meter for DIN rail mounting (2TE) with RS485 Modbus RTU communication. The meter is the single-phase variant of the popular B23/B24 series and is available in different versions with varying functionality.
ABB follows the TIA-485 standard where A = inverting (negative) and B = non-inverting (positive). This is opposite to most other devices such as the Currentt Navigator, Eastron, Huawei, and SolarEdge, where A = positive and B = negative.
Therefore, connect the ABB meter as follows:
| ABB terminal | Currentt Navigator terminal |
|---|---|
| 37 (A) | B- |
| 36 (B) | A+ |
| 35 (C/GND) | G |
If you do not swap the wires, communication will not be possible.
Make sure each device on the RS485 bus has a unique Modbus address.
🔀 Variants
The ABB B21 is available in three variants:
| Variant | Direction | Description |
|---|---|---|
| Silver | Bidirectional | Measures import (+A) and export (-A) |
| Bronze | Bidirectional | Measures import (+A) and export (-A) |
| Steel | Unidirectional | Measures import (+A) only |
Identifying the Steel variant
The Steel variant can be identified by the type designation: B21 1xx-xxx (the first digit after "B21" is a 1). This variant only measures import consumption and is not suitable for installations where feed-in needs to be measured, such as with solar panels.
If you need bidirectional measurement (for example, to measure feed-in from solar panels), use the Silver or Bronze variant.
🔌 Connecting the meter
The meter is connected to the Currentt Navigator using a twisted pair data cable (for example CAT5 or CAT6 UTP). The cable contains two signal lines (A+ and B-) and optionally a ground connection. Always use a twisted pair for the signal lines — the twisting suppresses electromagnetic interference (EMI) and is essential for a reliable RS485 connection.
The RS485 connection is located at the bottom of the meter on terminals 35, 36, and 37.
ABB B21: RS485 terminals (35=C/GND, 36=B, 37=A)
Connection to the meter
| Terminal | Label | Function (ABB/TIA-485) | Description |
|---|---|---|---|
| 35 | C | Ground | Reference (earth) |
| 36 | B | Non-inverting (+) | Data line B (positive per TIA-485) |
| 37 | A | Inverting (-) | Data line A (negative per TIA-485) |
Connection to the Currentt Navigator
| ABB B21 terminal | Currentt Navigator terminal | Wire color (T-568B) |
|---|---|---|
| 37 (A) | B- | Blue/white |
| 36 (B) | A+ | Blue |
| 35 (C/GND) | G | Optional (see below) |
ABB uses the reverse A/B naming compared to the Currentt Navigator.
Always use a twisted pair for the A and B signal lines. The twisting suppresses electromagnetic interference (EMI) and is essential for a reliable RS485 connection.
Connect the ground on one side only: either to the Currentt Navigator or to the meter — but never on both sides. Connecting ground on both sides can cause a ground loop, leading to communication errors.
Bus topology
Preferably use a daisy-chain (series) topology. At short distances (< 25 meters), a star topology often works as well. Connect a maximum of 32 devices to a single RS485 bus. Place a 120 Ohm termination resistor at both ends of the bus.
The Currentt Navigator has a built-in termination resistor that can be enabled or disabled via software. By default, it is enabled.
⚙️ Configuration in the Currentt Navigator
After physically connecting the meter, the device must be added in the Currentt Navigator. This can be done in two ways:
Via the setup wizard (recommended)
- Go to Settings > Setup wizard
- Follow the on-screen steps
Manual configuration
- Click the settings icon (top right of the screen)
- Go to Components
- Click the + button in the Meters section
- Select ABB
- Choose the model B21
- Specify what the meter will measure:
- Consumption and generation — the meter measures both consumption and feed-in (bidirectional)
- Consumption only — the meter measures consumption only
- Generation only — the meter measures generation only (for example, behind an inverter)
- Specify which phase the meter is connected to (L1, L2, or L3)
- Under Communication, select RS-485
- Set the communication parameters. The meter's default settings are pre-filled in the Navigator (see settings summary)
Additional options
- Measurement range: If possible, specify the measurement range in amperes that will be measured.
- Reverse meter direction: If the meter is physically installed in the wrong direction, the measurement direction can be reversed in software. This prevents the meter from registering consumption as generation (or vice versa) without physically reversing the meter.
- Use as PAP: This meter can also be used to measure the main connection (PAP, primary allocation point). In that case, select the "Use as PAP" option during configuration.
📋 Settings summary
| Parameter | Value |
|---|---|
| Type | Single-phase |
| Direction | Bidirectional (Silver/Bronze) or unidirectional (Steel) |
| Baud rate | 19200 |
| Data bits | 8 |
| Parity | None |
| Modbus address | 1 (default) |
| Cable | CAT5/CAT6 UTP (twisted pair) |
| ABB terminal 37 (A) → | Navigator B- |
| ABB terminal 36 (B) → | Navigator A+ |
🔢 Configuring the Modbus address
The default Modbus address of the B21 is 1. If multiple meters are connected to the same RS485 bus, each meter must have a unique address.
The address can be changed via the menu on the meter's display:
- Navigate to Settings > RS485
- Change the Modbus address to the desired number
- Confirm the setting
🛟 Troubleshooting
| Problem | Possible cause | Solution |
|---|---|---|
| No communication | A/B wires not swapped | ABB A (37) → Navigator B-, ABB B (36) → Navigator A+ |
| No communication | Wrong Modbus address | Verify that the address matches in both the meter and the Navigator |
| No communication | Wrong baud rate | Verify that the baud rate is 19200 on both sides |
| No communication | Parity is not set to None | Set parity to None on the meter |
| No export values | Steel variant (unidirectional) | Steel (B21 1xx-xxx) only measures import; replace with Silver or Bronze |
| Intermittent communication | No twisted pair used | Use a twisted pair for A and B |
| Intermittent communication | Ground connected on both sides | Connect ground on one side only |
| Intermittent communication | Poor cable connection | Verify that wires are securely fastened in the terminal block |
| Meter shows values but Navigator does not | Communication parameters do not match | Verify baud rate, parity, and address on both sides |