Siemens MM440: Changing P0305 Rated Current Post-Commissioning

Overview: The MM440 Parameter Access Model

The Siemens MICROMASTER 440 (MM440) is a sensorless vector / V/f inverter available in frame sizes A through F, with a 0.37 kW to 250 kW power range at 1-ph 200–240 V, 3-ph 380–480 V, and 3-ph 500–600 V supply. The drive organises its parameter database into groups (0…xx) and applies a state-machine filter (parameter P0010) that gates which parameters are visible and writable. The most common post-commissioning error reported by field engineers is: "P0305 is locked – I cannot edit the rated motor current after quick commissioning without losing everything."

This is by design. P0305 belongs to the motor data group (P0300…P0335) and is only writable while the drive is in Quick Commissioning state (P0010 = 1). Once the drive leaves that state via P3900, the value is stored in non-volatile memory and treated as a constant input to the motor-equivalent-circuit calculation. The good news: you do not need a factory reset (P0970 = 1) to re-edit the value. You re-enter the quick-commissioning state, change the parameter, and exit cleanly.

Prerequisites

1. Drive hardware: MM440, any frame size (A, B, C, D, E, or F). The procedure is firmware-version independent for firmware V1.x, V2.x, and V3.x families.
2. Operator panel access: either the Basic Operator Panel (BOP), Advanced Operator Panel (AOP), or a PC running STARTER V5.x commissioning software over USS / RS485 or PROFIBUS.
3. User access level: P0003 = 3 (Expert) to view and edit all commissioning parameters. Default is P0003 = 1 (Standard), which hides some motor data.
4. Drive state: drive must be in Ready or Run-disabled (not actively running the motor). Issuing parameter changes while the inverter is modulating will fault F0022 (Power stack fault) or F0035 (Auto restart after fault) depending on P1210 settings.
5. New motor nameplate data ready: rated voltage, current, power, power factor, frequency, and speed. The drive re-calculates the equivalent circuit (stator/rotor resistance, leakage reactance, magnetising current) from these inputs on P3900 exit.

Why P0305 Becomes Read-Only After Commissioning

The MM440 firmware maintains a parameter filter register (P0010) with the following allowed values:

After a successful quick commissioning sequence the firmware sets P0010 back to 0. From that moment, attempting to write P0305 via BOP simply returns the cursor without accepting the value; via STARTER the parameter shows a red padlock icon and the "Write" command is rejected with an "Access protection" status word (r2032 bit 0). The only legitimate re-entry path is to push P0010 = 1 again.

Step-by-Step: Change P0305 Without Factory Reset

The following procedure preserves all I/O configuration, BICO settings, and fieldbus mappings. It only re-runs the motor-equivalent-circuit calculation.

Step 1 – Lock the Drive

Open terminal 5 (DIN 1, default Enable) or clear control word bit 0 over the fieldbus. Confirm the drive status word bit 2 (Drive running) and bit 3 (Fault active) read 0. On BOP the display should show ready (top-left LED off, run LED off).

Step 2 – Raise Access Level

Navigate to P0003 and set to 3 (Expert). Press P on the BOP to save. On AOP/STARTER this is done in the Parameters > User Access dialog.

Step 3 – Enter Quick Commissioning Mode

Set P0010 = 1 and confirm. The drive display will cycle to comm (commissioning) for a few hundred milliseconds while the parameter filter is applied.

Step 4 – Select Motor Type (P0300)

If you also need to change motor technology, edit P0300:

Step 5 – Edit the New Motor Nameplate Data

Update the following parameters in any order. Save each with the P key.

Step 6 – Set the Calculation Source (P0340)

Although optional, set P0340 = 1 to force a complete re-calculation of the motor equivalent circuit (stator resistance P0350, rotor resistance P0354, stator leakage reactance P0356, magnetising inductance P0360). If you skip this and rely on P3900, the drive still re-computes – P0340 is mostly a diagnostic flag for engineering review.

Step 7 – Exit Quick Commissioning with P3900

This is the most important step. The exit mode determines whether I/O and BICO wiring survives.

P3900 Exit Mode Comparison

Step 8 – Wait for EEPROM Cycle

After writing P3900, the drive displays busy for 1–8 seconds while it computes the equivalent circuit and writes all changed values to non-volatile memory. Do not remove power during this window – a power-down cycle here can corrupt parameter storage and trigger F0039 (EEPROM checksum) on next power-up.

Step 9 – Verify P0010 Returns to 0

After the busy period, the drive automatically resets P0010 to 0. Confirm by reading r3996 (commissioning status word): bit 0 = 0 indicates exit completed.

Verification: Confirming the New Motor Data is Active

1. Read r0206 (rated inverter power) and r0207 (rated inverter current). These should match the new motor data within ±10 % of inverter rating.
2. Read back P0305 via BOP or STARTER and confirm the new value is stored.
3. Run a static motor identification: set P1910 = 1 (motor data identification, with rotating measurement disabled). Issue a Run command. The drive will inject a short magnetising pulse and update P0350, P0354, P0356, P0360. When the panel returns to "ready", identification is complete and the new motor model is active.
4. For full equivalent-circuit identification with rotation, set P1910 = 3 (rotating measurement). The motor must be uncoupled – rotating measurement will spin the shaft at approximately rated speed with no load. The duration is 30–90 seconds depending on motor size.
5. Save the parameters permanently with P0971 = 1 (transfer RAM to ROM) or via STARTER Copy RAM to ROM. This guarantees the new values survive a power cycle.

STARTER / TIA Portal Alternative Procedure

When the drive is online in STARTER V5.x or TIA Portal with the SINAMICS G120 / MM440 HSP:

1. Open the project and go online to the drive.
2. Right-click Drive > Parameterization > Commissioning.
3. In the wizard, select Modify motor data (not Restore factory settings).
4. The wizard pushes P0010 = 1, exposes the motor data screen, lets you edit P0304…P0311, then exits with P3900 = 3 automatically.
5. Click Save to ROM in the toolbar (Ctrl+E) to commit.

The STARTER wizard is the safest path because it forces P3900 = 3 – a common operator error is to click "Factory reset" by mistake, which sets P0970 = 1 and wipes the I/O configuration.

Troubleshooting Matrix

Frame Size and Hardware Notes

The frame-size designator affects the r0207 inverter rated current range – not the procedure itself. For Frame B MM440 (the most common in 0.55–1.5 kW 3-ph 400 V applications), r0207 is typically 2.0 A (0.55 kW) up to 4.0 A (1.5 kW). The motor rated current entered into P0305 should never exceed r0207 × 1.05 (a small margin above the inverter rating will trip F0001 on first modulation cycle). If a motor change pushes P0305 above this limit, an up-sized inverter frame is required.

Related Parameters to Audit When Changing Motors

If the new motor is a different frame size, runs in a different ambient, or has a different cooling arrangement, the thermal model parameters above will produce nuisance trips if not updated at the same time as P0305.

Field-Proven Caveats

1. Power-loss risk window: the P3900 = 3 sequence takes 1–8 s to compute and store. A power interruption in this window can leave a partially-flashed EEPROM. Always ensure the upstream DC bus capacitor is fully charged (DC bus voltage > 430 V on a 400 V drive) before initiating the exit sequence, and the 24 V control supply is on a UPS if available.
2. Do not edit P0304…P0335 outside P0010 = 1. The drive silently ignores writes when P0010 = 0 even though the parameter appears editable in some older BOP firmware (V1.5 and earlier). Always confirm by reading the value back after writing.
3. PM motors (P0300 = 2): the firmware V3.0+ enforces an additional check on P0305 × P0310 × P0311 = derived torque. If the new motor nameplate values are inconsistent (e.g. 50 Hz, 1480 RPM, 2-pole, 2.2 A all entered, but P0305 = 22 A), the firmware will raise F0011 (Motor data inconsistent). Always cross-check power, current, and speed against the manufacturer data sheet.
4. Frame B vs Frame C inverter swap: if the underlying drive was swapped during a motor change, you may also have to re-verify the fan run-time counter (r0037) and the capacitor aging counters. The motor-change procedure does not reset these.
5. Connected BOP vs AOP behaviour: AOP will show a full motor-data screen during P0010 = 1; BOP will only show one parameter at a time and you must scroll through P0300, P0304, P0305, P0307, P0308, P0309, P0310, P0311 in turn. There is no difference in the underlying state machine.

Frequently Asked Questions