Iskra WM3M4

Compatibility

Compatible with EpiSensor Edge over Modbus RTU

Iskra documents Modbus RTU on the RS-485 port of every WM3M4 and WM3M4C and publishes the input register table with addresses, lengths and data types. This is documented compatibility, without a physical Edge test.

Iskra WM3M4 and WM3M4C (V2), read with appendix 9 of user manual version 2.13, valid from firmware 2.12. The measurement addresses used here are the same in manual version 1.14 for earlier meters. Read-only monitoring of the input registers: no writes to settings, passwords, the Change Lock control or the WM3M4C charging-transaction registers.

Connect it with

• Modbus Interface ZMB-3X From €399 ex VAT Configure
• Gateway ZGW-20 From €899 ex VAT Configure

Models

Specifications

The WM3M4 suits a three-phase or single-phase EV charging point, sub-circuit or tenant supply up to 40 A where a MID-approved meter with a local display and RS-485 readings is wanted. It connects directly, with no current transformers, and draws its supply from the measured voltage.¹

Models

WM3M4 and WM3M4C. The WM3M4C adds digital signing of charging transactions and PTB approval for EV charging stations.^1, 2

Connection

Direct connection to a four-wire three-phase network, or single-phase on L3. The neutral must be connected.¹

Current

Reference 5 A, maximum 40 A, minimum 0.25 A, transitional 0.5 A, starting current 20 mA.¹

Voltage and frequency

3 × 230/400 V (-20% to +15%), 50 Hz or 60 Hz. Consumption below 8 VA and 0.6 W per phase.¹

Accuracy

Active energy class 1 (EN 62053-21) and class B (EN 50470-3), with MID approval for class B. Voltage and current ±1%, active power ±1%, reactive and apparent power ±2%, frequency ±0.5%, within the stated current ranges.¹

RS-485

Modbus RTU on terminals 16 (A) and 15 (B); 1200 to 115200 bit/s (default 115200), 8 data bits, no, odd or even parity, one or two stop bits (default 8N1). Default address 33, settable from 1 to 247.¹

Infrared port

Modbus RTU at 19200 bit/s 8N1, address 33, through the WM-USB adapter. Its settings are fixed.¹

Terminals

Main terminals 2.5 to 25 mm² rigid (16 mm² flexible), M5, 3 Nm; communication terminals 1 to 2.5 mm², M3, 0.7 Nm.¹

Housing

Three DIN modules on a 35 mm rail, 53.6 × 84 × 69.4 mm, 228 g. IP50 (IP51 when mounted in an IP51 cabinet), protection class II, 300 V CAT III.¹

Environment

Operating -25 to +70 °C, storage -30 to +80 °C, non-condensing humidity, indoor use, mechanical class M1 and electromagnetic class E2.¹

Interface

Documented measurements and integration boundaries for WM3M4.

• Iskra prints each address as the 30000 memory reference plus the register offset, and lists register 30000 itself (device group). Subtract 30000 for the zero-based address sent on the wire; a client that expects one-based 3xxxx numbers enters the table value plus one. Read the input registers with function 04.
• T5 (unsigned) and T6 (signed) are two registers: the top byte of the first register is a signed power-of-ten exponent and the remaining 24 bits are the value. Iskra's example stores 123456 × 10⁻³ as FD01 E240. The table has no unit column, so check the first decoded value of each quantity against the display or a known value before relying on base units (Hz, V, A, W).
• Frequency at 30105 to 30106: T5, Hz.
• Phase voltages U1, U2 and U3 at 30107, 30109 and 30111 and line voltages U12, U23 and U31 at 30118, 30120 and 30122: two registers each, T5, V.
• Phase currents I1, I2 and I3 at 30126, 30128 and 30130: two registers each, T5, A. Calculated neutral current at 30132 from firmware 2.12.
• Total active power at 30140 and phase active power at 30142, 30144 and 30146: two registers each, T6 signed, W. Total reactive power at 30148 (T6) and total apparent power at 30156 (T5).
• Total power factor at 30164 and phase power factor at 30166, 30168 and 30170: T7, where the first byte flags import or export (00 or FF), the second inductive or capacitive (00 or FF), and the second register is the value with four decimal places.
• Voltage THD at 30182 to 30184 and current THD at 30188 to 30190: one register each, T16, unsigned with two decimal places, %.
• Energy counter 1 (imported active energy) at 30418 to 30419 and counter 2 (exported active energy) at 30420 to 30421: T3, signed 32-bit, each with its own T2 exponent register at 30414 and 30415. Counters 3 and 4 are squared-current totals for cable-loss calculation, not energy.

Setup

1. Identify the meter and firmware

   Check the front label for WM3M4 or WM3M4C. The firmware identification screen at power-up shows the main firmware version, which is also readable at input register 30013 (100 = 1.00). Manual version 2.13 is valid from firmware 2.12; record the version with the configuration.

2. Give every meter its own address

   Every WM3M4 leaves the factory at Modbus address 33, so meters on a shared bus must be readdressed first. Iskra's MiQen software does this over the infrared or RS-485 port; the address is holding register 40202 (1 to 247).

3. Match the serial settings

   The default is 115200 bit/s, 8 data bits, no parity and one stop bit. Enter the installed values in Edge. If the installer changes speed, parity or stop bits, those settings are only kept after the save command, so confirm them on the meter before commissioning.

4. Wire the RS-485 line

   Connect A to terminal 16 and B to terminal 15 as in Iskra's connection diagram, using 1 to 2.5 mm² conductors in the M3 communication terminals. Keep the bus a single daisy chain.

5. Confirm the address convention

   Read one input register at zero-based address 0 with function 04. It should return 4, the WM device group, which confirms that the table addresses are offset from 30000. Then read the model number string at 30001 to 30008.

6. Start with the frequency read

   Read frequency with the example below and compare it with the supply. Then add voltages, currents, power and the energy counters with their exponent registers, checking each new point against the meter display.

Common questions

Why send 0x0069 when the table says 30105?

Iskra's table starts each section with a memory reference of 30000 and lists register 30000 itself as the device group, so the printed address is the reference plus the register offset. 30105 is offset 105, or 0x0069, read with function 04. A client that takes one-based 3xxxx numbers subtracts 30001, so it needs 30106 to reach the same register. Reading the device group at offset 0 (value 4) is a quick check of which convention your client uses.¹

How is a T5 or T6 value decoded?

Read both registers in one request. The top byte of the first register is a signed 8-bit exponent and the remaining 24 bits are the value: unsigned for T5, signed for T6. Multiply the value by ten to the power of the exponent. Iskra's examples are FD01 E240 for 123456 × 10⁻³ (T5) and FDFE 1DC0 for -123456 × 10⁻³ (T6). Because the exponent travels with each reading, do not apply a fixed scale.¹

Which counters are energy, and how fine is the Modbus resolution?

Counter 1 is imported active energy and counter 2 exported active energy; counters 3 and 4 accumulate squared current for the cable-loss calculation. All four are fixed in production and cannot be reset. Iskra states that the display shows energy in 10 Wh steps while the Modbus registers carry 1 Wh resolution, and holding register 47099 can change that to 10 Wh. Read each counter with its exponent register and check the scaled result against the kWh display before storing it.¹

Can Edge read a WM3M4C used in a charging station?

The WM3M4C has the same measurement registers as the WM3M4. Its charging transactions, time setting and signed datasets live in the holding registers from 47000 and are driven by the charging station controller. Edge needs only the input registers; never write to the transaction, time or Change Lock control registers from Edge.¹

Is the WM3M4 approved for billing?

Iskra's manual gives MID approval for class B to EN 50470-3 for both models, and PTB approval for EV charging stations for the WM3M4C. Treat Edge readings as monitoring data; where billing is required, use the approved meter's own register and, on the WM3M4C, its signed dataset.¹