Iskra WM3M4C Three-Phase EV Charging Meter, 40 A, MID

WM3M4C is the Iskra three-phase, direct-connected DIN-rail energy meter built for EV charging stations. It has MID approval for class B active energy, a 40 A maximum current, 70 C ambient operation and a crypto engine that signs a billing dataset. The same data sheet covers the WM3M4 without the digital signature.

A charging-point meter that signs its own billing data

In an EV charger the meter must prove what was delivered. The WM3M4C measures energy, then adds a SHA-256 hash and a digital signature to a billing dataset written by the charger controller. The manual states that signing is hardware based, uses an ECDSA NIST P256 curve, finishes in under a second and keeps the private key inside the crypto chip where it cannot be read.

The billing dataset is compatible with OCMF 1.0. The public key is printed as a QR code on the front and can also be read through Modbus. The data sheet says the design follows requirements of PTB, VDE and OCMF, and the manual lists PTB approval for EV charging stations (PTB-A 20.1 and 50.7) as valid only for the WM3M4C.

Features stated in the data sheet

• Compact 3-module DIN-rail meter, direct connection, 40 A maximum, 5 A reference current.
• Class 1 active energy to EN 62053-21; MID class B to EN 50470-3.
• Two-row display with 6+2 digits (10 Wh resolution) and remote-controlled backlight.
• IR optical port and RS485 Modbus RTU; connection to one phase only (on L3) is possible.
• Sealable terminal cover; operating temperature up to 70 C.

Technical specification

Electrical and accuracy data

Communication, security and mechanics

Ordering codes

The data sheet lists two articles: 022433922000 WM3M4 230 (energy meter 40 A) and 022433922100 WM3M4C 230 (the same meter with digital signature). Confirm the exact article with the supplier before ordering.

The meter measures active, reactive and apparent power, import and export active energy, voltage per phase and phase to phase, current, phase angle, frequency, power factor and THD of voltage and current.

Installation and charger integration

The manual requires a qualified person for connection. Fit ferrules on stranded wire before mounting, connect the neutral wire, and use a 40 A line fuse as recommended in the data sheet. Communication terminals take 1 to 2.5 mm2 conductors with M3 screws at 0.7 to 0.8 Nm.

For a signed session, the charger control unit sets time, time zone and signature format, writes the billing dataset, sends Begin, may request intermediate or fiscal readings, then sends End. It reads the signature status register, the output message, the signature and the public key. Dataset and signature occupy more than 120 registers and must be read in sequence.

If the meter shows an error state on row 2, charging with a digital signature is blocked and the manual says the meter has to be replaced.

Where it fits

General engineering note: AC wallboxes and charging pedestals in car parks, hotels and fleet depots need a billing-grade, MID-approved meter in a small DIN footprint. The 70 C rating helps in enclosures that warm up in direct sun, which is a common issue in Gulf conditions; verify installation temperatures against the datasheet limit.

Related Iskra items

The IE38MD is an 80 A three-phase meter with NFC and Modbus, and the WM3-6 is a 65 A family with optional modules. Browse the power meters category for the full range.

EV charging notes for Oman and the GCC

Check with the charger maker and the local authority which billing and calibration rules apply, and confirm the cabinet’s internal temperature in summer stays within the meter’s rating.

Frequently asked questions

What does the C in WM3M4C mean?

In the data sheet the WM3M4C is the version with digital signature for charging events; the WM3M4 has the same high-temperature design without it.

Is the WM3M4C MID approved?

Yes. The data sheet states MID approval for class B active energy according to EN 50470-3 for both versions.

How is communication done?

Through RS485 Modbus RTU and an IR optical port that uses the WM-USB adapter; the meter can also connect to an Iskra SG smart gateway.

Can it be used on a single-phase charger?

Yes. The data sheet allows connection to one phase only, on L3, with neutral connected.

Does Seven Star LLC act as an Iskra distributor?

No. Seven Star LLC is not an Iskra distributor; it is an independent Muscat-based supplier that quotes Iskra products on request.

Documents and quotation

The official Iskra datasheet and user manual for WM3M4C are hosted on this page for download. Seven Star LLC is an independent supplier in Muscat; send your quantity and delivery location through the quotation form and we will quote this item. Please confirm the exact order code, supply voltage and output options against the documents before ordering. More related products: product category.