Why does starting at offset 2 fail?

L1-N voltage begins at offset 1 and is two registers long. Siemens warns that reading from the second register of a multi-register value produces an error. Read the complete value at its starting offset.

Can write protection stay enabled during monitoring?

The hardware switch prevents writes while measured values remain readable. It must be changed locally; do not disable it just to collect readings.

Why is an energy value a thousand times too large?

The documented double energy counters use Wh. Divide by 1000 when presenting kWh, once only. Also verify tariff, direction and the full four-register decoder before attributing an error to unit scaling.

Siemens PAC3220 Modbus TCP register map

Compatibility

Compatible through Modbus TCP

Edge reads the documented local Modbus interface through the connection path below. This is protocol compatibility, not a claim of a built-in device mapping.

PAC3220 non-MID family covered by the July 2024 PAC3120/PAC3220 manual. Check the full 7KM3220 order number and supply variant. PAC3120, PAC3220 MID and optional expansion modules have separate interface or certification scope.

Connect it with

Gateway ZGW-20
From €899 ex VAT Configure Gateway

For the standard PAC3220 Ethernet interface

Modbus
Edge
Platforms

Configure the meter’s IP settings and Modbus TCP port, normally 502. Its two Ethernet ports have an integrated switch; they are not two separately addressed meters. Record the configured unit identifier and confirm device identity before using the map. The customer-platform output is optional; Edge remains the local system of record.

Models

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Models	Interface	Route into Edge
PAC3220	Built-in Ethernet with two switched ports and Modbus TCP	Use this guide for the non-MID meter and its matching manual.
PAC3220 with RS-485 expansion	Optional module adds a serial path	Use the expansion module manual and its actual settings; PAC3120 serial defaults are not evidence for this module.
PAC3120 / PAC3220 MID	Different native interface or metrological certification scope	Use the exact model manual and approval requirements rather than inferring them from PAC3220.

Specifications

The PAC3220 separates commissioning access from routine collection with a physical write-protection switch. Once ratios and network settings are correct, read-only monitoring can continue with changes blocked. Its Modbus tables use offsets, and the device checks complete multi-register access: a request beginning halfway through a value is an error.¹

Current inputs: External 1 A or 5 A secondary current transformers¹
Built-in network: Two Ethernet interfaces with an integrated switch; Modbus TCP, web readings and time synchronisation¹
Serial option: RS-485 requires an expansion module on PAC3220¹
Active energy: Class 0.5S to IEC 62053-22 in the cited manual; installation and CT error are separate¹
Write protection: Rear hardware switch blocks writes through communications and cannot be disabled remotely¹
Enclosure: Device front IP65; rear IP20; install within a suitable panel¹

Interface

Documented measurements and integration boundaries for SENTRON PAC3220.

L1/L2/L3 voltage and current in two-register Float values.
Total active power in W at offset 65; instantaneous power is not cumulative energy.
Frequency at offset 55, power factor and total harmonic distortion.
Import and export energy by tariff; the double-precision counters occupy four registers and report Wh.
Demand values and diagnostics for distinguishing electrical changes from configuration or communications faults.
Model and configuration information, including CT ratios and wiring topology, retained with the connection.

Assessment

PAC3220 non-MID family covered by the July 2024 PAC3120/PAC3220 manual. Check the full 7KM3220 order number and supply variant. PAC3120, PAC3220 MID and optional expansion modules have separate interface or certification scope.

InteroperabilityWell supported: The manufacturer publishes functions, literal measurement offsets and complete value lengths for local Modbus TCP.¹
AccuracySupported with conditions: CT-connected active-energy measurement has specified class and wiring modes; CT selection and ratios remain part of the result.¹
SecuritySupported with conditions: Physical write protection and a dedicated cybersecurity chapter support controlled read-only operation on a protected network.¹
ReliabilitySupported with conditions: The manual documents diagnostics, supply conditions and maintenance; clients must preserve stale state during outages.¹
RuggednessSupported with conditions: IP65 front and IP20 rear define panel installation protection, not an outdoor rating for the whole meter.¹
ScalabilitySupported with conditions: Switched Ethernet supports connected panels; unique network configuration and complete reads remain necessary per meter.¹
LifecycleSupported with conditions: Siemens publishes a revised 2024 manual and firmware maintenance guidance; recheck the applicable model after replacement.¹

Setup

Read one complete phase voltage

The July 2024 manual specifies L1-N voltage at offset 1, two registers, Float in V, readable with FC03 or FC04. The request below uses FC03.

Function: FC03 Read Holding Registers
PDU start address: 1 decimal, 0x0001; the manual already calls this an offset
Quantity: 2 registers, four data bytes; never start at the second register of the Float
Request PDU: 03 00 01 00 02
Response structure: 03 04 followed by the four value bytes; transport headers are separate
Decode and unit: 32-bit Float, volts. Establish the multi-register word order against the simultaneous meter display before accepting it.
Independent decoder example: The ordered IEEE-754 bytes 43 66 00 00 represent 230.0 V. This arithmetic example does not establish the device’s returned byte order.

Acceptance: Accept the reading only after the endpoint identity, full four-byte response and configured byte/word ordering agree with the meter display. The request is derived from the manufacturer table; the 230 V bytes are a synthetic decoder example, not a claimed device capture.

Record the complete order number
Distinguish the standard PAC3220 from PAC3220 MID and PAC3120. Record firmware, auxiliary supply variant, wiring system and external CT primary/secondary values before creating the Edge device.
Set the Ethernet endpoint
Set or reserve an appropriate IP address, subnet and gateway and record the Modbus TCP port. Use the protected local network; the two switched ports belong to one meter. Do not assume an optional serial module is installed.
Use the table’s literal offset
The manual labels measurement addresses as offsets. L1-N voltage starts at offset 1 and spans two registers. Send offset 1, not zero, and read the full value. A client that asks for a one-based display reference may need reference 2 to produce PDU address 1.
Verify decoding against the display
Read a stable voltage and inspect all four returned bytes. Select the 32-bit Float decoder and establish its word order by comparison with the meter’s simultaneous display. Keep that verified ordering with the device configuration; do not scale a float as if it were an integer.
Protect configuration and check counters
After authorised commissioning, use the rear write-protection switch where appropriate. Read the complete four-register double energy counter, retain import/export and tariff meaning, and convert Wh to kWh only once. Check an interval delta and keep unavailable readings distinct from zero.

Common questions

Why does starting at offset 2 fail?: L1-N voltage begins at offset 1 and is two registers long. Siemens warns that reading from the second register of a multi-register value produces an error. Read the complete value at its starting offset.¹
Can write protection stay enabled during monitoring?: The hardware switch prevents writes while measured values remain readable. It must be changed locally; do not disable it just to collect readings.¹
Why is an energy value a thousand times too large?: The documented double energy counters use Wh. Divide by 1000 when presenting kWh, once only. Also verify tariff, direction and the full four-register decoder before attributing an error to unit scaling.¹

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Siemens SENTRON PAC3220