Eastron SDM630MCT vs v2 Comparison & CT Selection Guide

Key Takeaways

• The Eastron SDM630MCT and SDM630MCT v2 deliver identical operational functionality and Sunsynk/Deye compatibility, differing solely in how CT ratios are configured.
• Original SDM630MCT models configure primary current under CT1 and secondary current under CT2, while v2 models require setting CT2 and a computed CT Rate quotient.
• Physical installation distances greater than 15 meters between the supply boundary and inverter mandate an external digital power meter to avoid analogue signal distortion.
• Standard Eastron meters support only 1A or 5A secondary coils; millivolt coils (40mA/100mA) require the specialized SDM630MCT-MV model.
• Always disconnect mains power and adhere to national wiring safety isolation procedures before installing or servicing current transformers on live busbars.

Hardware Comparison: Eastron SDM630MCT vs SDM630MCT v2

Both the SDM630MCT and the SDM630MCT v2 are compatible with our inverters. These meter models both provide the same functionality. With only one notable difference. This is how the CT ratio is set.

From an electrical integration standpoint, both units feature:

• Identical 4-module DIN-rail mounting chassis width.
• Identical measurement voltage ranges across standard three-phase line-to-line and line-to-neutral AC supplies.
• Identical auxiliary power bridging requirements (connection 5 LA bridged to phase voltage, connection 6 NA bridged to neutral).
• Identical RS485 Modbus RTU communications interface on terminal 14 (TX+A) and terminal 13 (TX-B), polling at 9600 baud with default slave address 1.
• Identical bidirectional measurement capability, tracking forward active energy (import), reverse active energy (export), reactive power, and per-phase power factors.

The distinction lies entirely within the internal setup menu used by technicians to define the transformation ratio of the external current transformers clamped over the main incoming utility phase conductors.

When Does a System Require an External Meter

Most residential Sunsynk and Deye installations initially rely on small split-core current transformers supplied inside the inverter carton. These standard CTs connect directly into analogue RJ12 or terminal block ports on the underside of the inverter chassis. However, analogue current signals are low-power electrical representations that degrade rapidly over physical distance.

When installing a system with a CT run of greater than 15m* you will need to install an external CT meter.

In commercial buildings, shopping centers, agricultural packhouses, and expansive residential estates throughout Gauteng, KwaZulu-Natal, and the Western Cape, the main incoming Eskom or municipal distribution board is often situated in an external boundary kiosk or main electrical intake room, while hybrid inverters and lithium batteries reside in an internal power room.

Attempting to extend analogue CT wiring beyond 15 meters introduces severe line resistance, signal attenuation, and electromagnetic interference from adjacent high-voltage AC cables. The resulting signal distortion prevents the inverter from accurately detecting reverse power flow, which frequently trips sensitive municipal prepaid meters. Installing an external Eastron meter directly at the distribution board and transmitting packetized digital data over an RS485 shielded twisted-pair cable resolves this challenge, supporting reliable data transmission across extended installation distances.

Programming CT Ratios on the Original SDM630MCT

On the original Eastron SDM630MCT hardware revision, the firmware menu prompts the installer for two distinct, direct parameters: primary current and secondary current.

On the SDM630MCT: you will have a setting for both CT1 and CT2.

Parameter Definitions

• CT1 (Primary Current): CT1 should be set to the primary current of your CT coil. This represents the maximum rated primary alternating current designed to pass through the central aperture of the CT clamp (for example, 100A, 200A, 300A, 500A, or 1000A).
• CT2 (Secondary Current): CT2 should be set to the secondary current of your CT coil (this meter is compatible with CTs that have a 1A or 5A secondary current ONLY). Standard commercial current transformers in South Africa output either 5A or 1A across their secondary terminals when operating at full primary current.

Programming Example

Consider a commercial site equipped with a 300A main three-phase utility breaker, utilizing 300/5A split-core current transformers:

• Example – for a 300/5A CT coil, CT1 should be set to 300 and CT2 should be set to 5.
• The internal microprocessor calculates the scaling factor automatically (300 divided by 5 equals 60) and applies this multiplier to all instantaneous current and active power registers transmitted across the RS485 bus.

```
ORIGINAL SDM630MCT SETUP MENU STRUCTURE
+---------------------------------------------+
| Parameter | Value Setting | Description |
+---------------------------------------------+
| CT1 | [ 300 ] | Primary (Amps) |
| CT2 | [ 5 ] | Secondary (A) |
+---------------------------------------------+
Scaling factor computed internally by meter: 60x
```

Programming CT Ratios on the SDM630MCT v2

On the second-generation Eastron SDM630MCT v2, the internal programming routine eliminates the direct primary current setting, replacing it with a mathematical ratio quotient termed CT Rate.

On the SDM630MCT v2: you will have a setting for CT2 and CT Rate.

Parameter Definitions

• CT2 (Secondary Current): Defines the secondary output rating of the physical CT coil (configured as either 5A or 1A).
• CT Rate (Transformation Ratio): CT rate should be set for the CT ratio. Rather than entering the primary amperage directly, the installer must mathematically divide the primary current rating by the secondary current rating and input the resulting integer into the CT Rate menu field.

```
CT Rate = Primary Current Rating / Secondary Current Rating
```
(Formula: CT Rate equals Primary Current Rating divided by Secondary Current Rating)

Programming Example

Applying the same 300/5A current transformers on a v2 meter:

• Example – for a 300/5A CT coil, CT2 should be set to 5 and CT rate should be set to 60 (300/5=60).
• If a technician inadvertently inputs the primary rating 300 into the CT Rate field, the meter applies a 300x multiplier instead of 60x. The inverter will interpret a physical 10kW building load as an immense 50kW demand, completely distorting system operation and triggering false overload alarms.

```
SDM630MCT v2 SETUP MENU STRUCTURE
+---------------------------------------------+
| Parameter | Value Setting | Description |
+---------------------------------------------+
| CT2 | [ 5 ] | Secondary (A) |
| CT Rate | [ 60 ] | Ratio (300 / 5)|
+---------------------------------------------+
Installer must compute ratio prior to data entry!
```

CT Coils Selection: Current Ratings and Secondary Limits

Selecting the correct physical current transformer is as vital as programming the digital meter. Connecting an incompatible coil type results in measurement saturation or thermal failure.

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

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

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

Standard 1A and 5A Secondary Coils

Standard SDM630MCT and SDM630MCT v2 meters are designed to sample alternating current directly through internal low-impedance shunt resistors rated for 1A or 5A nominal inputs. Current transformers rated for 5A secondaries (such as 100/5A, 200/5A, 400/5A, or 600/5A) are the industry standard for South African low-voltage commercial distribution boards.

Millivolt (mV) Model Exceptions

Installers frequently encounter miniature split-core CTs producing millivolt outputs (such as 333mV, 100mA, or 40mA). Standard SDM630 meters cannot read these coils:

• The SDM630MCT-MV is compatible with CTs that have a secondary current of 40mA/100mA.
• Attempting to connect a 40mA or 100mA secondary coil to a standard 5A meter results in negligible signal detection, causing the meter to register zero amps under normal household loads.

Single-Phase 120 Series Constraint

Installers working across mixed residential portfolios should note that single-phase equipment has strict hardware bounds:

• The single-phase (120 series) only meters are compatible with the Eastron 120A/40mA CT.
• These compact single-phase units cannot be paired with commercial 5A industrial current transformers.

Compliance with South African Grid Standards (NRS 097-2-1:2024)

In South Africa, small-scale embedded generation (SSEG) systems connected to municipal distribution networks (such as City Power Johannesburg, City of Cape Town, eThekwini, and Eskom) must comply strictly with South African standard NRS 097-2-1:2024.

Under NRS 097-2-1:2024 regulations:

1. Reverse Power Export Limitation: Embedded generators operating under zero-export agreements must prevent power export into the municipal grid. The response time of the power control system depends entirely on the speed and accuracy of the external energy meter.
2. Phase Balancing: Three-phase grid connections enforce phase unbalance limits. The Eastron SDM630 records active power per phase independently, enabling the Sunsynk or Deye inverter's phase-balancing algorithm to dynamically supply asymmetrical power, matching the exact consumption of each independent phase.
3. Overcurrent and Isolation Safety: In accordance with national wiring standards, all reference voltage sensing lines supplying the Eastron meter must originate from a dedicated, locked miniature circuit breaker to prevent accidental contact during switchboard maintenance.

By verifying hardware generations, calculating CT Rate quotients correctly, and adhering to strict secondary current compatibility, installers ensure robust compliance, flawless telemetry, and optimal performance across all South African solar installations.