Siemens SINAMICS Drive Spares: G120, G120X and S120

SINAMICS is a family, not a product, and the differences between its members decide whether a spare you order will actually commission. A G120 control unit will not operate an S120 power module. A G120C is a single integrated unit with no separable control unit at all. And within G120 alone, the control unit, the power module and the operator panel are three separately ordered articles that must be compatible by firmware as well as by hardware. This guide covers how to identify what you have, what is interchangeable and what is not, and what to send a supplier so a drive spare arrives ready to run.

The families, and which one you are looking at

The identification shortcut: if you can see two separate modules clipped together with independent article numbers on each, you have a modular G120 or S120. If it is one box with one article number, it is a G120C, G120X or V20. This single observation determines whether you are ordering one part or two.

The article number is the order

Every SINAMICS component carries a Machine-Readable Product Designation in the familiar Siemens format - 6SL3210-1KE21-3UF1, 6SL3244-0BB12-1FA0 and so on. This is the orderable article and it is unambiguous. The three blocks matter differently.

• 6SL3 - the SINAMICS product family prefix.
• The next block identifies the component class: 3210 and 3211 ranges are typically power modules and integrated units, 3244 ranges are control units, 3255 ranges are operator panels, 3054 covers memory cards.
• The trailing characters encode frame size, power rating, supply voltage, filter class and variant. This is where a single character difference means a different voltage class or a built-in filter you do not want.

Never transcribe an article number by hand from a photograph if you can avoid it. The characters most often confused - 0 and O, 1 and I, 5 and S, B and 8 - all appear in these codes, and a single-character error produces a part that arrives, does not fit, and cannot be returned as an incorrect customer order.

The control unit is the part that carries your application

On a modular G120, the Control Unit holds the parameter set, the firmware and the communications configuration. The Power Module is, to a first approximation, dumb power electronics. This has a practical consequence that surprises buyers: if your drive fails and the fault is in the power stage, replacing the power module and moving your existing CU across restores the drive with its configuration intact. If the CU fails, the replacement arrives with factory defaults and the application has to be re-parameterised.

• CU240B / CU240E series - general-purpose, with variants for different fieldbus options and for Safety Integrated functions.
• CU250S - supports encoder feedback for closed-loop and positioning duty.
• CU230P - positioned for pump, fan and compressor applications with the associated function set.
• Fieldbus variant matters and is not field-changeable: PROFINET, PROFIBUS DP, USS/Modbus RTU and EtherNet/IP are different article numbers.

Compatibility rules that actually bite

1. 01Firmware version. A control unit shipped with newer firmware than the power module expects, or a parameter set exported from an older firmware, can refuse to commission. Record the firmware version from parameter r0018 before you order, and tell your supplier.
2. 02Voltage class. 200-240V, 380-480V and 500-690V units are physically similar and electrically incompatible. The article number encodes this; the casing does not make it obvious.
3. 03Filter class. Unfiltered, Class A and Class B EMC-filtered variants are different articles. Fitting an unfiltered unit where the installation required Class B can breach the site's electromagnetic compatibility compliance.
4. 04Frame size and mounting. Physical footprint changes across power ratings and generations. A like-for-like power rating in a newer generation may not match the existing backplate drilling.
5. 05Safety Integrated. If the existing drive implements STO, SS1 or SLS as part of the machine safety function, the replacement must carry the same safety capability, and the safety parameter set must be re-validated and the acceptance test re-run and documented. This is a functional-safety obligation, not an optional step.

Obsolete and phasing-out units

A large installed base still runs MICROMASTER 4 (MM420, MM430, MM440) and older SINAMICS generations. These reach end of product support in stages: end of new supply, then end of spare-part support, then end of repair. Being on the third stage is what turns a routine drive failure into an unplanned modernisation project.

When a direct replacement is no longer available, the practical migration paths are: a current-generation unit of matching voltage and power with a re-worked parameter set and new mounting; a refurbished-market unit, which we do not supply and generally advise against for anything on a critical duty; or a planned like-for-like modernisation of a group of drives at once during a shutdown, which is almost always cheaper per drive than replacing them individually as they fail.

The cabling, filtering and accessory items buyers forget

A drive RFQ that covers only the drive is incomplete more often than not. The items that routinely turn up as a second urgent order, days later:

• Line reactors and output reactors, where cable runs are long or the supply is weak.
• dv/dt filters or sine filters for motor cable runs beyond roughly 50-100 m, protecting motor winding insulation.
• Braking resistors and braking modules for overhauling loads.
• Operator panels - BOP-2 (basic) and IOP-2 (intelligent) are separate articles and are not interchangeable in their menu structure.
• Memory cards, and the correct one for the CU generation.
• PC connection kits and USB cables for commissioning - a genuine recent RFQ in our inbox was for exactly this and nothing else.
• Shield connection kits, without which the EMC installation is not compliant regardless of filter class.

What to send with a SINAMICS enquiry

1. 01Article numbers for every module, photographed rather than transcribed. On a modular drive that means both the CU and the PM.
2. 02Firmware version from r0018 if the drive is still powered and readable.
3. 03Motor rating in kW, rated current, and voltage.
4. 04Supply voltage and frequency at the drive input.
5. 05Whether Safety Integrated functions are in use, and which ones.
6. 06Fieldbus type in use.
7. 07Motor cable length between drive and motor.
8. 08Whether you need the parameter set restored, and whether you hold a backup or a memory card.

On authenticity

Drives are a heavily counterfeited category, and the counterfeits are increasingly good externally. The discriminators that hold up: an article number and serial that resolve in the manufacturer's system; correct and current label printing and holography; correct weight; and a documented supply chain. A counterfeit drive will often commission and run, then fail under thermal cycling or produce output waveforms that destroy motor insulation over months. We supply new and genuine only, with manufacturer documentation and serial traceability, and we will say no to an enquiry we cannot fill genuinely.

Thermal design: why drives fail in year three

The dominant physical failure mode in variable-frequency drives is thermal, and it is largely a function of installation rather than product quality. DC-link electrolytic capacitors age as a function of temperature, and cooling fans are consumable mechanical parts in a dusty environment. A drive installed in a sealed cabinet in a hot plant room will not reach the life of the identical drive in a ventilated cabinet at 25 C.

• Check the ambient rating and derate above it. Most drives are rated to 40 C without derating, with a published derating curve above that.
• Cabinet ventilation must actually move the heat the drive rejects - roughly 2-3% of rated power as heat. A 90 kW drive puts two to three kilowatts into the cabinet.
• Filters block. A cabinet filter maintenance schedule is a drive reliability measure, not housekeeping.
• Fans are replaceable and should be replaced preventively at the manufacturer's stated interval rather than on failure, because fan failure causes over-temperature trips and, if the trip does not act quickly enough, capacitor damage.
• Altitude derating applies above 1000 m, and it is significant at the altitudes found across Andean and highland installations.

A drive that has been running hot for years may fail shortly after an unrelated replacement elsewhere in the cabinet, because the capacitors were already near end of life. When a site reports several drive failures in a short window, the cause is usually environmental and common to all of them.

EMC installation: the part that is done badly most often

A drive is a deliberate generator of high-frequency electrical noise, and the installation practice around it determines whether that noise stays contained. The consequences of getting it wrong are not confined to the drive: nuisance trips on nearby instrumentation, corrupted fieldbus communications, and bearing currents in the driven motor all trace back to EMC installation.

1. 01Use screened motor cable, and terminate the screen through 360-degree glands at both ends. A screen pigtailed to a terminal is close to useless at the frequencies involved.
2. 02Keep motor cable runs as short as the layout allows, and separated from signal cabling.
3. 03Fit the correct filter class for the installation environment - Class B for residential and light industrial, Class A for industrial. Unfiltered units are for installations with their own upstream mitigation.
4. 04Bond the drive to the cabinet backplate on bare metal, not through paint.
5. 05Fit output reactors or dv/dt filters on long motor cable runs to limit voltage reflection at the motor terminals.

Commissioning a replacement: the realistic sequence

Replacing a drive is not a like-for-like electrical swap even when the article numbers match, because the parameter set defines the application.

1. 01Isolate, prove dead, and wait for the DC link to discharge. Drives hold a lethal charge after isolation for the time stated on the label.
2. 02Record the existing terminal wiring photographically before disconnecting.
3. 03Fit the replacement, restore wiring, and confirm the motor data against the motor nameplate.
4. 04Load the parameter set from the memory card or backup, or re-enter motor data and run the motor identification routine.
5. 05Verify direction of rotation uncoupled where the driven machine permits.
6. 06Verify the safety functions if Safety Integrated is used, and document the acceptance test.
7. 07Run up on load and confirm current, temperature and any application-specific behaviour before handing back.

The step most often skipped is the motor identification routine. A drive controlling a motor with default or estimated motor data will run, but the vector control model is wrong, and the symptoms - poor low-speed torque, instability, unexpected current - get misdiagnosed as a faulty drive.