Huawei Smart Meter — DDSU666-H Single-Phase vs DTSU666-H Three-Phase

Without a smart power meter on the grid tie, your Huawei SUN2000 hybrid system is half-blind. It can produce, store, and consume — but it cannot tell how much is flowing to or from the utility, which means no accurate self-consumption analytics, no export limit control, and no zero-export configuration. The Huawei DDSU666-H (single-phase) and DTSU666-H (three-phase) smart power sensors fill that gap, talking RS485 Modbus back to the inverter and feeding FusionSolar the import/export numbers that everything else hangs off. This guide covers the difference, the wiring, and the commissioning trap that catches new installers.

DDSU666-H vs DTSU666-H — One Decision

The decision is your service entrance, not your inverter.

• DDSU666-H Smart Power Sensor (Single-Phase): single-phase 230 V residential service, direct-connection meter (the meter itself is wired in series — no external CT). Class 1 accuracy, RS485 Modbus RTU output. Paired with single-phase SUN2000-2KTL/3KTL/4KTL/5KTL/6KTL-L1.
• DTSU666-H (100A): three-phase 400 V residential or small-commercial service up to 100 A per phase. CT-clamp installation — split-core CTs clip around each phase conductor without breaking the cable. Class 1, RS485 Modbus RTU. Paired with three-phase SUN2000-5/6/8/10/12KTL-M1 and KTL-M0 series.
• DTSU666-H (250A): same as 100A variant but with 250 A CTs for larger C&I services where the cable bundle will not fit through 100 A CTs.

Choose by counting the phases at the main isolator. Three live conductors (L1/L2/L3) plus neutral = DTSU666-H. One live plus neutral = DDSU666-H. Forget what the inverter is — match the service.

What the Meter Actually Measures

The Huawei smart meter sits on the grid side of the system — between the main isolator and the consumer unit. It measures the net flow of power across the connection: positive when you are importing from the utility, negative when you are exporting solar back. It reports per-phase voltage, current, real power, apparent power, and power factor over RS485 to the SUN2000 inverter every 200 ms. The inverter uses this to:

• Compute real-time self-consumption percentage and feed it into FusionSolar's energy flow diagram.
• Enforce zero-export when the customer is on a non-export tariff (the inverter throttles solar production to match house load, never feeding the grid).
• Cap export at a fixed kW limit per the connection agreement (DEWA in Dubai, ADDC in Abu Dhabi, SEC in Saudi Arabia all enforce export caps on rooftop PV).
• Drive time-of-use battery dispatch — knowing whether the meter is currently importing tells the battery whether to discharge.

DDSU666-H — Single-Phase Installation

The single-phase meter is direct-connect: the line conductor passes through the meter itself, not via an external CT. Wiring sequence:

1. Isolate the main supply.
2. Mount DDSU666-H in the consumer unit on DIN rail (it is a 1-module 18 mm wide unit).
3. Connect the incoming line (L) from the main isolator to L_IN on the meter; outgoing line to L_OUT toward the consumer unit busbar.
4. Connect neutral (N) through-pass on the dedicated N terminals.
5. Wire RS485+ and RS485- to the SUN2000 inverter's COM terminal (typically pins 1 and 2 of the COM connector — verify against the inverter quick-start sheet).
6. Restore power; the meter LCD shows live import/export.

Crucially, the DDSU666-H is rated for 60 A direct-connection. If the service is above 60 A (rare on single-phase residential but possible for villa-with-pool loads), step up to a CT-clamp meter or add an external CT — the DDSU666-H is not built for higher direct current.

DTSU666-H — Three-Phase CT Installation

The three-phase meter uses external split-core CT clamps. This is the more forgiving install because you do not interrupt the main cable.

1. Isolate the main supply (or fit while live with appropriate PPE — split-core CTs allow live install but verify local code).
2. Mount DTSU666-H on DIN rail (typically 4 modules wide).
3. Clip one CT around each phase conductor (L1, L2, L3) at the service entrance. The CT has a polarity arrow — the arrow points toward the load (consumer unit), not toward the grid.
4. Connect each CT's S1/S2 secondary leads to the corresponding phase terminals on the meter (CT1 -> L1, CT2 -> L2, CT3 -> L3) and twist the secondaries together if you have spare length (don't let them dangle as antennas).
5. Connect voltage taps: L1, L2, L3 from the busbar through 1 A fuses into the meter's voltage terminals. N to the neutral terminal.
6. Wire RS485 to the SUN2000 COM port the same as the single-phase version.
7. Restore power. Confirm the meter LCD shows positive values when loads are running and the sun is down (import) and negative values when the sun is up and solar exceeds the house load (export). If signs are reversed, flip the CT or swap S1/S2 — do NOT swap phase voltage taps.

The CT-Direction Trap

The most common DTSU666-H commissioning fault is CT direction. Every CT has a stamped arrow indicating current flow direction; if you clamp it backward, the meter reports negative when the house is importing and positive when exporting — completely inverted. The symptom in FusionSolar is unmistakable: the energy flow animation shows solar feeding grid at midnight, and grid feeding house when solar is producing. The fix is to physically reverse the CT clamp on the affected phase. If you cannot get to the CT (sealed enclosure), you can swap S1/S2 leads on the CT secondaries — same electrical effect.

If only one phase is wrong, the symptom is subtler: per-phase totals look fine individually but the three-phase sum is off. Always verify all three phases agree on direction by walking through the meter LCD per-phase view before sealing the meter cover.

Setting the Modbus Address

Each meter ships with a default Modbus address. Before wiring multiple meters on the same RS485 bus (rare but possible — e.g., one for grid metering, one for genset metering), set unique addresses 1-247. Configure via the meter's front-panel buttons under the SET menu. Match the address you enter in the SUN2000 inverter's FusionSolar Installer device-config screen.

FusionSolar Integration and Export Limit

Once the meter is wired and the inverter recognises it, the FusionSolar app surfaces the meter as a device under the inverter. Configure the export limit in Settings -> Grid Connection:

• Zero export: Solar production limited to instantaneous house load. The meter reports zero at the grid tie. Used in jurisdictions that prohibit any export.
• Limited export: Enter the max kW the utility permits (e.g., 5 kW under DEWA's small-system tariff). The inverter throttles when meter export exceeds the cap.
• Unlimited export: No throttling. Used where the utility has a feed-in tariff or a net-metering arrangement that pays for export.

The closed-loop response time from meter measurement to inverter throttle is approximately 200 ms — fast enough to prevent a measurable export pulse on transient cloud-clearing events.

Modbus Register Map for Customer SCADA

Beyond feeding the SUN2000, the DDSU666-H and DTSU666-H both speak standard Modbus RTU on RS485 and can be polled by a third-party SCADA on the same multi-drop bus. The registers you will typically read are: per-phase voltage, per-phase current, per-phase active/reactive/apparent power, per-phase power factor, system frequency, and accumulated energy counters split into import kWh and export kWh. The energy registers persist across power cycles via flash. If you wire a SCADA in parallel with the inverter, give it lower polling priority (1-5 seconds rather than 200 ms) so the inverter's faster polling for export-limit control is not crowded out. Multi-drop RS485 supports up to 32 devices per segment with 120 ohm termination at each end.

The meter's Modbus map matches the published Acrel-derived format, so retrofitting into a site that previously used Acrel or Eastron usually needs no firmware change — only address and baud rate must match.

Meter Accuracy and Class 1 Compliance

The DDSU666-H and DTSU666-H are both Class 1 accuracy meters under IEC 62053-21, meaning the measured energy is within 1 percent of the actual value across the rated current range. Utility billing meters in DEWA, ADDC, SEC, KAHRAMAA, and most GCC distribution networks are Class 0.5 — twice as accurate and tested against tighter calibration drift over time. The practical implication is that the Huawei meter is good enough to drive export-limit control and energy analytics inside FusionSolar, but the customer's invoice from the utility will always be the authoritative number. If the FusionSolar import kWh for a month and the utility bill differ by a percent or two, that is within stack tolerance — it does not mean either meter is faulty.

Installing the DTSU666-H With Existing Utility Meter

The DTSU666-H is a self-consumption meter, not a fiscal billing meter. It does not replace the utility's licensed cyclometer or smart billing meter. In the typical retrofit, the utility's billing CT cabinet stays exactly where it was — at the service entrance, sealed, owned and inspected by the distribution network operator. The DTSU666-H goes downstream of that cabinet, between the utility meter and the consumer unit, on the customer side of the demarcation point. Both meters see the same current; the utility's reading is the legal record and the Huawei meter is the operational telemetry feeding the inverter and FusionSolar.

Two practical consequences: first, do not break utility seals during installation — open only the customer-side enclosure. Second, the two meters will show slightly different totals over a month because of their different accuracy classes and because they sample at different intervals. The customer should be told up front that the FusionSolar number is for analytics and the utility number is the bill.

Time-of-Use Tariffs and Meter Integration

Several GCC distribution networks now apply time-of-use tariffs to large residential and small commercial accounts — DEWA's Slab tariff, SEC's commercial bands, and Mobily-region commercial schedules in Saudi Arabia all charge different rates by hour of day. FusionSolar uses the live meter feed to time battery charge and discharge against those tariff windows. The inverter charges LUNA2000 from solar during cheap midday hours, holds through peak-rate evening hours, and discharges into house load during the most expensive band — minimising import exactly when each kWh costs the most. Without the meter the inverter can cycle on time-of-day rules but cannot validate the actual flow direction.

Common Wiring Errors Beyond CT Direction

CT direction gets all the attention because it is the most common fault, but several other wiring errors produce confusing FusionSolar readings:

• Voltage taps swapped between phases: If the L1 voltage tap is connected to the L2 busbar (and vice versa), per-phase power readings will be wildly wrong even though CT direction is correct. Symptom: one or more phases show negative power factor at all times, or per-phase totals do not match a clamp-meter reading on the same phase.
• Neutral missing: Three-phase meters need a neutral reference for accurate phase-to-neutral voltage. A missing or loose neutral causes phantom readings — voltage drifts, power factor jumps around. Always confirm the N terminal is landed and torqued.
• Blown fuse on a voltage tap: The 1 A fuses on each voltage tap protect the meter from a short. If one blows, that phase reads zero volts on the meter LCD even though the load is energised. Replace the fuse and investigate why it blew (usually a pinched conductor or a stripped insulation against an enclosure wall).
• Polarity reversed on the RS485 pair: A and B (RS485+ and RS485-) swapped causes the inverter to fail to detect the meter entirely. Symptom: FusionSolar device list shows no meter, even though the meter LCD is live. Swap the pair.
• Termination missing on long RS485 runs: Without 120 ohm termination at the far end of the bus, longer cable runs (over 20 m) produce intermittent reads. Add a termination resistor across A and B at the end-of-line device.

Meter Replacement Without Re-Commissioning

Meters fail. When you replace a DDSU666-H or DTSU666-H in the field, the inverter does not need to be re-commissioned from scratch — the inverter binds to the Modbus address, not the meter serial number. Procedure: isolate the meter, swap the physical unit, set the same Modbus address on the new meter via the front-panel buttons, restore power. The inverter polls the bus, finds the meter at the expected address, and resumes normal operation within seconds. FusionSolar logs a brief meter-offline event but no manual intervention is required after the swap.

This is a meaningful operational advantage versus inverter brands that require a full re-commissioning sequence each time a meter is replaced. Keep one spare DDSU666-H and one spare DTSU666-H on the service van for any sites running Huawei.

What to Verify Before Leaving Site

• FusionSolar live view shows current import or export consistent with the house load (lights on, AC running -> importing or self-consuming; sunny noon with low load -> exporting or capped at the configured limit).
• Per-phase voltage on three-phase installs reads 230 V (±5%) phase-to-neutral, 400 V phase-to-phase.
• Power factor reads close to 1.0 for resistive loads, lagging for AC compressors.
• Export limit, if configured, is being respected — turn off house loads and confirm the inverter throttles when meter export approaches the cap.
• Modbus address recorded in the install dossier so a future meter replacement can be done without re-commissioning.
• Sealing cover snapped closed over the terminal block on both single-phase and three-phase variants.