Configuring Siemens G120 CU230E-2 Auto-Restart on Power-Up

Overview

The Siemens SINAMICS G120 modular drive system, when populated with a CU230E-2 control unit, is typically configured for safety-first operation: after a power cycle the drive boots, reads its parameter image, and waits for a fresh rising edge on the ON/OFF1 command source before it will run the motor. In many OEM and process applications (pumps, fans, conveyors, refrigeration compressors) this default behavior is undesirable. The application requires the drive to start the motor automatically as soon as the line and control voltage are healthy, using the last analog setpoint or a 4-20 mA process reference.

This reference documents three field-proven methods to achieve automatic restart on the G120 / CU230E-2 after a mains power interruption or a complete power-up:

1. Method 1: Built-in automatic restart using p1210 in combination with p840 and the standard digital input wiring.
2. Method 2: Free Function Blocks (FFB) — specifically a delay-on-make timer driven by the parameter r20160 — to synthesize a valid ON command a few seconds after the CU has finished booting.
3. Method 3: External power contactor interlock that uses the contactor's own auxiliary NO contact to re-issue the run command only after the contactor has been latched and the line is stable.

Each method has different implications for EMC, safety integrity, restart behavior after a fault, and the response of external safety circuits. Select the method based on the SIL/PL requirement of the machine, whether STO is wired, and whether the application is attended or unattended.

Prerequisites

Before You Begin

Confirm three things before changing any parameter:

1. The motor data identification (p1910) and any rotating measurement (p1960) have been completed and saved to the active parameter set.
2. The drive was commissioned with the analog setpoint, and the ramp-up/down ramps in p1120 and p1121 are appropriate for an unattended restart.
3. The application is rated for automatic starting; check the relevant product standard (e.g. EN 60204-1 §5.3 for unexpected start, NFPA 79 §6.4 for industrial machinery).

Understanding the G120 / CU230E-2 Power-Up Sequence

The CU230E-2 control unit executes a defined sequence on every power-up. The relevant steps for the auto-restart behavior are:

The critical detail is in the line labelled p840 (the ON/OFF1 command). Even if digital input DI 0 is held at logic 1 the entire time the control unit is booting, the SINAMICS firmware only accepts a 0→1 edge on this signal as a valid run command once the drive has reached the "ready" state. With the DI held continuously high, no edge exists, so the drive remains in the OFF1 state (r52.0 = 0) and the motor does not start.

Method 1: Built-In Automatic Restart (p1210)

Parameter p1210 defines the automatic restart behavior. Setting it to a non-zero value allows the drive to self-clear certain faults, re-acknowledge them, and issue a fresh run command after a mains power interruption or a black-out, using the last valid setpoint and the wired command source.

Required Parameter Set

p1210 Settings — Reference

Wiring Requirement for Method 1

The 24 V supply to DI 0 must be sourced from a stable point that is energized whenever the drive should be running. The source may be the 24 V output on the CU230E-2 (terminal 9) or an external 24 VDC rail that is energized with the line. The DI 0 common must be configured to match the source — set p0728 to 0 for sink (PNP) with the internal 24 V, or to 1 for source (NPN) with an external rail. Holding DI 0 high continuously is acceptable; the firmware's p1210 = 2 (or 4/5) logic reissues a synthetic run command internally at the end of the restart window.

Method 2: Free Function Block (FFB) Timer

The CU230E-2 firmware includes a bank of Free Function Blocks (FFBs) — digital timers, AND/OR gates, comparators, and latches — that can be used to synthesize a delayed run command. The standard approach is a delay-on-make timer that holds the output low during the CU boot phase and then drives it high after a configurable delay, providing the required 0→1 edge on p840.

FFB Parameters Used

Step-by-Step via BOP-2

1. Press ESC to enter the parameter menu, navigate to P20158, press OK.
2. Set index .0 to 722 (this is the BICO source for the status of DI 0 — confirm with the List Manual for your firmware).
3. Navigate to P20159, set to 5000 (5 seconds in ms).
4. Navigate to P20161, set to 5 (delay-on-make mode; refer to the FFB documentation if the mode number differs for your firmware build).
5. Navigate to P0840, set index .0 to 20160 (route the FFB output to the ON/OFF1 command).
6. Set p840 = 20160 to clear the original direct DI 0 wiring, leaving only the FFB in command.
7. Save to the active parameter set: p0971 = 1 or use the SAVE soft key on the BOP-2.

FFB Signal Flow (SVG)

Why the FFB Method Works

The CU230E-2 finishes its boot in roughly 20-60 seconds (depending on the parameter set size and any plugged-in option boards). The FFB timer stays at 0 for the configured delay and then produces the missing 0→1 edge on the ON/OFF1 command source. The drive sees a valid rising edge, exits the OFF1 state, ramps to the analog setpoint, and runs.

Method 3: Power Contactor Interlock

When the drive should not energize the motor on a brief control-power blip, but should resume automatically only after a full re-close, an upstream power contactor is the most deterministic approach. The contactor's own auxiliary NO contact (one of its normally-open blocks wired back to a free DI on the CU) provides the rising edge required for the next run command.

Wiring Diagram (Conceptual)

Sequence of Operation

1. Control logic energizes coil of contactor K1. Line is applied to the SINAMICS G120 power module.
2. K1's auxiliary NO closes simultaneously with the main contacts. DI 0 on the CU sees a 0→1 transition.
3. CU230E-2 boots. The rising edge on DI 0 is latched in the parameter r722.0; once the drive reaches the ready state, it issues the ON command.
4. On a mains power interruption, K1 drops out, line is removed, DI 0 falls back to 0. When the line is re-applied and the control logic re-energizes K1, the cycle repeats — fresh 0→1 edge, fresh run command.

Parameter Reference (Quick Copy)

; === Method 1: p1210 auto-restart ===
p0840   = 722.0      ; ON/OFF1 from DI 0 (rising edge)
p1000   = 2          ; Setpoint from analog input
p1210   = 4          ; Auto-restart on mains failure
p1211   = 3.0        ; Wait time before first restart (s)
p1212   = 10.0       ; Wait time between restart attempts (s)
p1213   = 3          ; Max restart attempts

; === Method 2: FFB timer ===
p20158  = 722.0      ; Timer input from DI 0 (or use 1 to ignore DI)
p20159  = 5000       ; Delay in milliseconds
p20161  = 5          ; Delay-on-make mode
p0840   = 20160.0    ; Route FFB output to ON/OFF1

; === Method 3: contactor interlock ===
; No parameter change vs. Method 1. The rising edge comes from K1's NO aux contact.

Enter these via STARTER, Startdrive, or the BOP-2. Save to non-volatile with p0971 = 1 and then cycle the control power to verify the values were stored.

Safety Considerations

Verification Procedure

1. With the drive running, capture r52.0 (status word 1 bit 0 = "Drive ready") and r53.0 (bit 0 = "Run") in the STARTER trace.
2. Open the upstream disconnect or de-energize the line (do this in coordination with a safe state of the driven equipment).
3. Wait at least 30 seconds. The CU230E-2 will power down, the bus caps on the power module will discharge, and the line monitoring will drop out.
4. Re-apply the line. With the chosen method, the drive should ramp to the analog setpoint within the time window defined by p1211 (Method 1), the FFB delay (Method 2), or the contactor close time (Method 3).
5. Verify motor rotation direction, current, and frequency match the expected operation. Confirm r0021 (smoothed actual speed) tracks the setpoint.
6. If the drive does not start, capture the active fault buffer r0945[] and warning buffer r2122[] before cycling power again.

Troubleshooting Matrix

Related Parameters Worth Knowing

Field Commissioning Checklist

• [ ] Confirm the application permits unattended restart (safety file updated, ISO 7010-W026 label applied).
• [ ] Run motor data identification and save.
• [ ] Verify analog input wiring and scaling on p756–p759.
• [ ] Wire the E-stop to a separate DI (DI 1 or DI 2) routed to p2102 and/or p848.
• [ ] Apply the chosen method's parameters and save with p0971 = 1.
• [ ] Power cycle the drive, observe the trace, and verify the drive runs within the expected time window.
• [ ] Test an E-stop trip and confirm the drive stops in OFF1/OFF2 as required.
• [ ] Document the wiring and parameter set in the cabinet drawing set and the controller's tag database.