What Is SINAMICS G120? Drive Family Explained

The SINAMICS G120 is one of the most widely deployed variable frequency drives in industrial automation. You'll find it on conveyors, pumps, fans, compressors, and general-purpose machinery across virtually every industry. If you're new to it—or inheriting a system that uses it—here's what you need to know before you touch a parameter or pull a module.

What Is SINAMICS? The Broader Family

SINAMICS is Siemens' unified drive platform covering everything from fractional-horsepower single-axis drives up to multi-megawatt regenerative systems for heavy industry. The family is organized into letter-number codes:

• G-series — general-purpose variable speed (G110, G120, G130, G150)
• S-series — servo and vector control for high-dynamic motion (S110, S120, S210)
• V-series — economical drives for basic pump/fan/conveyor duty (V20, V90)

The G120 sits in the middle of the G-series: more capable than the entry-level V20 or G110, but focused on single-drive general-purpose duty rather than the cabinet-drive G130/G150 or multi-axis S120 chassis.

Modular Architecture: Control Unit + Power Module

The G120's defining feature is that the brains and the power stage are physically separate modules.

Control Unit (CU) — contains the processor, I/O terminals, fieldbus interface, and parameter memory. Common variants include CU240B, CU240E, CU250S (for Safety Integrated and encoder feedback), and others. The CU variant determines your I/O count, safety level, and communications protocol support (PROFINET, PROFIBUS, EtherNet/IP, etc.).

Power Module (PM) — contains the rectifier, DC bus, IGBT inverter, and heatsink. The PM variant determines your voltage class and current/power rating. Common PM series include PM240 (with integrated brake chopper for hoist/positioning duty), PM240-2 (compact footprint), PM250 (energy recovery to the supply), and PM260 (for medium-voltage supply with integrated transformer). The active PM lineup changes over time as variants are introduced, updated, or superseded—confirm which series are current in the Siemens catalog before specifying.

This matters practically: if a CU fails, you replace only the CU and keep the power stage wired in place. If a PM fails, you replace the PM and the CU retains all parameters on its internal memory card. That modularity reduces downtime significantly compared to a monolithic drive.

G120 Power Range

The G120 family covers a wide span of motor ratings. Rather than stating specific endpoints that vary by voltage class and PM variant, understand the general positioning:

• The low end of the PM240/PM240-2 range is suitable for small conveyor and pump duty.
• The upper end of the G120 PM series handles substantial industrial machinery—well above what the smaller V20 or G110 can address.
• For the exact kilowatt and ampere rating of any specific PM part number and voltage class (200–240 V, 380–480 V, 500–600 V, 660–690 V), consult the Siemens Industry Online Support portal or the official catalog.

Exact power range endpoints vary by voltage class and PM variant—do not rely on generic numbers. Always confirm against the current SINAMICS G120 catalog for the specific part number you are sizing or replacing.

Overload Capability: What the Parameter Controls

The G120's overload behavior is one of the first things a commissioning engineer sets. The drive supports two standard overload modes, often selected through a parameter in the commissioning wizard:

High Overload (HO) — intended for applications with high starting torques: hoists, compressors, conveyors with heavy loads. The drive is derated in base current to allow a significant short-term overload current multiple for a defined period. The exact multiple and duration vary by PM variant—confirm in the relevant PM datasheet before sizing.

Low Overload (LO) — intended for pump, fan, and centrifugal applications where the load torque curve is quadratic and large starting transients are rare. The base current rating is higher (you can use a smaller PM for a given motor), but the overload headroom is reduced.

In the parameter set, look for the parameter that selects the operating mode or application class (fan/pump vs. constant torque). The exact parameter number varies by CU firmware version—refer to the CU parameter manual on support.industry.siemens.com for the version installed on your hardware.

Getting this wrong causes nuisance trips on startup. If your drive faults on overcurrent during motor acceleration, check whether LO mode is selected on a constant-torque load.

Commissioning in TIA Portal: Startdrive

Siemens commissions G120 drives inside TIA Portal using an add-on engineering package called Startdrive. This is separate from STEP 7 / WinCC logic—it's a drive-specific tool that integrates into the same TIA Portal project.

1. Install Startdrive — Download the Startdrive version that matches your TIA Portal installation. Compatibility between Startdrive and TIA Portal versions is version-specific—confirm the correct pairing in the compatibility notes on support.industry.siemens.com before downloading. Install it as an add-on to an existing TIA Portal installation.
2. Create or open a TIA Portal project — Add the G120 drive to the project in the device view. Select the exact CU part number so the parameter set matches your hardware.
3. Connect online — Via PROFINET, PROFIBUS, or USB (using the PC connection kit). The drive must be powered but does not need to be running.
4. Run the commissioning wizard — Startdrive walks you through motor data entry (nameplate data), application class (HO vs. LO), control mode (V/f or vector), and I/O assignment. Exact wizard screen names and menu paths vary by Startdrive version.
5. Motor identification run — With the motor wired and able to rotate freely, perform the motor identification (stationary and/or rotating measurement). This calibrates flux and slip models. Do not skip this step on vector-controlled applications—it materially affects performance and thermal protection.
6. Download parameters — Transfer the full parameter set from the engineering tool to the drive. Verify the download completes without errors.
7. Test run — Jog the motor at low speed first, verify rotation direction, then ramp to full speed and check current against nameplate.

Common Problems with G120 Drives

• F001 / Overcurrent on startup — Wrong overload mode selected (LO on a constant-torque load), or motor data entered incorrectly. Re-run the commissioning wizard and verify nameplate data.
• A070x Alarm: CU not communicating with PM — Often caused by a dirty or damaged connector interface between CU and PM. Remove the CU, clean the backplane connector, reseat firmly.
• Parameter loss after power cycle — Memory card loose or failed. Reseat the card. If parameters are truly gone and no backup exists, the motor identification run must be repeated.
• Drive runs but motor overheats — Thermal model not initialized (motor identification skipped), or wrong motor data entered. Also check that output frequency is not too low for too long on a self-cooled motor.
• Fieldbus communication faults — CU variant does not match the network. A CU240E-2 PN is PROFINET; a CU240E-2 DP is PROFIBUS. You cannot change this in firmware—you need the correct CU hardware for the network.

When Replacement Makes More Sense Than Repair

G120 Power Modules are robust, but IGBTs fail—especially in environments with voltage spikes, heavy cycling, or poor cooling maintenance. If the PM has a confirmed IGBT fault, gate driver failure, or DC bus capacitor degradation (shown by ripple faults or bus voltage alarms), repair cost often exceeds replacement cost for mid-range units. CU failures are less common but do occur, especially from ESD damage during field wiring or lightning-induced transients on analog inputs.

Disclaimer: This guide is provided for general information only. Procedures vary by model, series, and firmware version. Industrial equipment can cause serious injury, equipment damage, or downtime if serviced incorrectly. Always consult the manufacturer's official documentation and a qualified professional before performing work, and follow your facility's lockout/tagout and safety procedures. PLC Department is an independent surplus supplier and is not affiliated with or endorsed by the manufacturers referenced. Use this information at your own discretion.