Short answer: choosing a DIN-rail energy meter comes down to four answers — single-phase or three-phase, direct-connect or current-transformer (CT) operated, billing/sub-metering grade or monitoring grade, and whether the panel wants a communication bus. Fix those and the model follows: direct-connect single-phase meters for small loads, CT-operated three-phase meters where the main current is too high to pass through the meter, and a MID-certified version when the reading is used for billing or tenant sub-billing inside the EU.
This page sets out how to read that decision, what MID B+D certification actually covers, and which CHINT meters we can quote — DDSU666, DTSU666, DSSU666 and the CT-operated DTSU666-CT. It is written from the position of an independent trading company, not a manufacturer and not an appointed distributor of any brand: certificates are stated per exact ordering code, never for a whole range.
The four questions that fix the meter
| Question | Option A | Option B | What decides it |
|---|---|---|---|
| Phase | Single-phase | Three-phase (3-wire or 4-wire) | What the load actually is; mixed panels often need both |
| Current path | Direct connect | CT operated | Whether the load current can pass through the meter’s own terminals |
| Purpose | Monitoring | Billing / sub-billing | Whether the reading has legal or contractual weight |
| Communication | Pulse / local display | RS485 Modbus-RTU | Whether the meter reports into a BMS, SCADA or energy dashboard |
Direct connect versus CT operated
A direct-connect meter carries the whole load current through its terminals, so its rating is expressed as a current range such as 5(60) A or 10(100) A — the first figure is the basic current, the bracketed figure the maximum. This suits a single-phase final circuit or a small three-phase supply where the current stays within the meter’s terminal rating.
Above that, the load does not pass through the meter at all. A current transformer steps the primary current down to a 5 A or 1 A secondary, and a CT-operated meter reads that. The meter’s own current input is then small — on the DTSU666-CT it is a 0.015–1.5(6) A input — and the primary current is set by the CT ratio. This is the standard arrangement for a main incomer, a sub-distribution board, or any point where the current is too high to run through a meter.
Getting this wrong is the most common metering error: a direct-connect meter installed on a feed that exceeds its terminal rating, or a CT meter ordered without the CTs and without a stated ratio.
What MID B+D actually certifies
MID stands for the EU Measuring Instruments Directive, 2014/32/EU. A meter placed on the EU market for a legal purpose — billing a tenant, apportioning energy in a building, charging for consumption — must be MID-certified. The certification is run in modules, and the relevant ones for a meter are:
- Module B — EU-type examination. A notified body examines the design and confirms the type meets the directive.
- Module D — conformity to type based on quality assurance of the production process. The manufacturer’s production quality system is audited so that every unit matches the examined type.
So “MID B+D” means the design was type-approved and the factory that makes it is under quality assurance for that type. That combination is what lets a landlord or a facility operator bill on the meter’s reading. A meter offered for monitoring only does not need MID, but a MID meter is a safe default when the purpose might become billing later — which is exactly why the CT-operated DTSU666-CT carries MID B+D certification to EN 50470-1/-3.
| Signal | Where it comes from | Why it decides the purchase |
|---|---|---|
| Accuracy class | The datasheet, split into active and reactive | Class 1.0 active and 2.0 reactive is monitoring grade; a billing meter is offered to a tighter class such as 0.5S |
| MID B+D | Type examination plus production quality assurance | Required when the reading is used for legal billing inside the EU |
| CT input range | e.g. 0.015–1.5(6) A | Tells you it is CT operated, not direct connect |
| Bus | RS485 Modbus-RTU | Whether it can report to a building or energy management system |
Reading the model code
The confirmed CHINT DIN-rail meters:
| Model | Configuration | Notes that matter |
|---|---|---|
| DDSU666 | Single-phase DIN-rail meter | Direct connect ranges such as 5(60) A / 10(100) A; RS485 Modbus-RTU; about four modules wide |
| DTSU666 | Three-phase four-wire | Direct connect or CT input; RS485 Modbus-RTU |
| DSSU666 | Three-phase three-wire | For three-wire distribution, same family and bus |
| DTSU666-CT | Three-phase CT-operated | CT input 0.015–1.5(6) A; EN 50470-1/-3; MID B+D; accuracy class to 0.5S; IP20 |
The DDSU666 / DTSU666 / DSSU666 family is specified to the GB/T 17215 series, with export variants aligned to EN 62053 and EN 50470. Nominal voltage for the three-phase versions is 3×220/380 to 3×240/415 V at 50/60 Hz, so the same meter covers a 220 V and a 240 V market — one reason to state the grid at enquiry rather than assume it. The older DDS238 / DTS238 platform exists too, but its supply status is best confirmed per order rather than assumed.
Beyond the meter: the rest of the panel
A DIN-rail meter is usually one line in a metering section. Pair it with the breakers that feed it and, where a local readout or a legible face-level indication is wanted, with panel instruments: the PA/PZ666 series digital ammeter/voltmeter and the PD666 multi-function meter, both with RS485 Modbus-RTU and available in 48 / 72 / 96 mm panel sizes. Keep the metering CTs and the breaker ratings in the same schedule — a CT ratio that does not match the recorded primary current is a silent error.
FAQ
Q: Do I need MID certification on my DIN-rail meter?
A: Only if the reading is used for a legal or contractual purpose inside the EU, such as billing a tenant or apportioning energy. For internal monitoring it is not required, but a MID-certified meter is a safer default if billing might follow later.
Q: How do I know whether to use a direct-connect or a CT meter?
A: If the load current can pass through the meter’s terminals within its rated range, use direct connect. If the current is higher, or the point is a main incomer, use a CT-operated meter and specify the CT ratio alongside it.
Q: What does the (6) in 1.5(6) A mean?
A: It is the ratio of maximum to basic current. The figure before the bracket is the basic current; the bracketed figure is the maximum continuous current the meter’s input is rated for. On the DTSU666-CT the CT-side input is 0.015–1.5(6) A.
Q: Can one meter cover both 220 V and 240 V markets?
A: The three-phase DTSU666/DSSU666 family is rated 3×220/380 to 3×240/415 V at 50/60 Hz, so the same series spans those nominal voltages. State the destination grid so the exact variant is quoted.
Q: Does the meter talk to a building management system?
A: Yes — the DDSU666/DTSU666/DSSU666 family and the PA/PZ666/PD666 instruments use RS485 Modbus-RTU, which is the common input for BMS, SCADA and energy dashboards.
Q: Is certification stated for the whole meter family?
A: No. Certification is stated per exact ordering code. The DTSU666-CT carries MID B+D to EN 50470-1/-3; other variants are confirmed individually against the documentation for the code being quoted.
What to send us for a quotation
Phase and wires (1P, 3P3W or 3P4W) · direct connect or CT (with ratio if CT) · purpose (monitoring or billing) · grid voltage and frequency · communication requirement · destination country · quantity. You get unit price, packing data and the certificate document for the exact ordering code. Request a quotation.
Related: Boards and enclosures · Choosing an MCCB: frame, breaking code, trip unit · How to size a distribution board · How to import circuit breakers from China · How to verify genuine product · Electrical import certificates by country