Which SINAMICS S120 module do I order? Reading the 6SL3 number

A SINAMICS S120 order number breaks into four parts, and each one answers a question you need answered before you buy. The first eight characters give the module family and how it sheds its heat. The 1TE or 2TE group says whether it drives one axis or two. The digits after that are a current class, not an ampere figure. The last four are the hardware generation, and that is the field that gets the wrong module delivered to a machine that is already down.

Below: which prefix is which module, and the places where a reasonable assumption costs you a week. If you have a fault code rather than a dead module, start with our SINAMICS fault codes guide instead.

The first eight characters: family and cooling

Booksize modules that look identical from the front can differ only in how they move heat. Siemens encodes that in the prefix, so a module that was never meant for your cabinet will still bolt to the rail.

Line Modules carry their type in the digit after the prefix. 6SL3130-7TE... is an Active Line Module, 6SL3130-6... is a Smart Line Module, and 6SL3130-1TE... is a Basic Line Module. These are not alternatives. A Smart Line Module returns energy to the supply but cannot hold the DC link at a regulated level, so fitting one where an Active Line Module was changes how the group behaves under braking.

One axis or two, and why the digits are not amps

1TE is a Single Motor Module, one axis. 2TE is a Double Motor Module, two axes in one 50 mm wide book. The three digits that follow are where people lose money.

They are a power class index, not a current reading. A 6SL3120-2TE21-0AA3 is not a 21 amp module. It is rated 9 A per axis, maximum 18 A. 2TE15 is 5 A per axis and 2TE13 is 3 A. The index rises with the rating but does not state it. Look it up every time.

Note the two 5 A entries. Same axes, same current, different prefix, because one dumps its heat into the cabinet air and the other needs ducting behind the panel. Order on the prefix, not the rating.

The last four characters are a hardware generation

This is the field machine builders quote and buyers drop. The -0AA3 and -0AA4 suffixes are not revision noise. Siemens introduced the -0AA3 generation with optimised pulse patterns and support for the extended Safety Integrated functions, and says so in the module's own order text.

So if the machine uses the extended safety functions, an older suffix will not deliver them, and the drive tells you after you have closed the cabinet. Fit a newer suffix than the project expects and the Control Unit's topology comparison flags a component that does not match the stored target topology. Recoverable, not a dead end, but it needs the commissioning software, the project and somebody allowed to accept the change. Nobody wants to find that out at 23:00.

The modules that get sold as Control Units

The 6SL3040 prefix covers two different things and used listings blur them constantly. A CU320-2 is a Control Unit: it runs the drive software and its CompactFlash card holds the project and the licences. A Numeric Control Extension is not a Control Unit at all. It is a computing extension for a SINUMERIK 840D sl over DRIVE-CLiQ, and it exists because the 840D sl closes the loop on only six axes by itself.

Two numbers worth memorising. 6SL3040-0NC00-0AA0 is the NX10, three more servo axes. 6SL3040-0NB00-0AA0 is the NX15, six. Same 25 mm book, identical on the rail.

Here is the part the datasheet mentions once and nobody reads. Data management for an NX sits entirely on the 840D sl. An NX carries no card, no project and no licence, so replacing one really is a swap: bolt it in, connect DRIVE-CLiQ, power up. A CU320-2 is the opposite. The card is the machine. Buy a used CU320-2 without its CompactFlash card and you have bought a housing.

Check whether the cable is in the box

Siemens writes the cable into the order text and the wording differs by module. Motor Modules are catalogued as supplied with a DRIVE-CLiQ cable. The TM41 Terminal Module, digital and analogue I/O plus incremental encoder simulation, is catalogued explicitly without one.

That applies to factory stock. A module pulled from a machine arrives as the module, because the cable stayed in the cabinet. DRIVE-CLiQ cables have their own order numbers in the 6FX5002-2DC10 family, length set by the final characters, and a 7.5 m DRIVE-CLiQ cable is cheaper to keep on the shelf than an engineer waiting for one.

Quick answers

Where do I find the official SINAMICS S120 order numbers?

In the SINAMICS S120 catalogue and the booksize equipment manual, both from Siemens Industry Online Support. Search the full order number and read the long product text: it states DC link voltage, rated output current per axis, construction type and cooling in one line. That text is authoritative, not a distributor summary.

Does 2TE21 mean 21 amps?

No. It is a power class index. 6SL3120-2TE21-0AA3 is rated 9 A per axis, maximum 18 A. On paper it looks four times a 2TE15; it is under double. Check the rated current in the catalogue before sizing anything on the code alone.

Can I fit a Double Motor Module where a Single Motor Module was?

Mechanically it is a wider book needing the space and the DC link busbar reach. Electrically it is a different drive object count, so the project changes too, not just the hardware. Splitting a double into two singles is the more common retrofit and is also a project change. Neither is an emergency repair.

Can I swap an NX10 for an NX15?

Not casually. The NX15 handles six servo axes against the NX10's three, and the configuration in the 840D sl is written around which one is fitted. Like for like, either is straightforward because the data lives on the control. One for the other is a configuration change.

Is a used S120 Motor Module a sensible replacement?

For booksize hardware of this age it is often the only practical route. Several of these variants are withdrawn from current sales, so the OEM path means a repair lead time or a migration project. What matters is that the order number matches to the last four characters, that the unit was tested, and that you can send it back if it does not fit.

Before you order, in this order

1. Photograph the whole rating plate of the failed module, in focus, including the version suffix.
2. Confirm the prefix's cooling method matches your cabinet.
3. Check 1TE or 2TE against the motors actually on that module.
4. Look up the rated current in the catalogue. Do not read it out of the order code.
5. Match the last four characters. If that generation is unobtainable, find out what the project expects before accepting another.
6. Check whether the machine uses the extended Safety Integrated functions. If it does, the generation is not negotiable.
7. Back up the project before touching the topology, as you would before swapping an NCU.
8. Count your DRIVE-CLiQ cables and add the ones that stayed in the old cabinet.

Related reading on Samonde

• SINAMICS fault codes: common causes and fixes
• SINUMERIK 840D alarm codes: how to read the number
• SINUMERIK 840D spare parts guide: NCU, PCU and OP panels
• The used industrial parts buying guide

Order numbers are the closest thing this trade has to a common language, and S120 booksize is one of the better designed examples once you stop reading the string as a serial number. These modules will outlast the catalogues that describe them. Learn where the four fields break and photograph the plate while the cabinet is still open. Then you spend the downtime fixing the machine instead of arguing with a parts desk about which 5 A module you meant.