How to read a Siemens order number

A Siemens article number — the Bestellnummer or MLFB — is not a serial number and not a random code. It is a structured description of the article, and once you can read it you can tell from the number alone whether two parts are interchangeable.

The shape of the number

Most Siemens automation numbers follow the same layout:

6ES7 315-2EH14-0AB0
│    │   │    │  └── variant / packaging
│    │   │    └───── functional version
│    │   └────────── type within the family
│    └────────────── family / series
└─────────────────── product group

The first block identifies the product group and is the fastest way to know what you are looking at:

Reading an S7 CPU number

Take 6ES7 315-2EH14-0AB0.

• 6ES7 — SIMATIC S7.
• 315 — CPU 315, an S7-300 CPU.
• -2 — the interface variant: 2 here denotes the two-interface version (MPI/DP plus PROFINET on the EH types).
• EH — the specific execution. 2EH is the CPU 315-2 PN/DP; 2AG is the CPU 315-2 DP.
• 14 — the functional version. This is the number people ignore and should not. A -0AB0 part with functional version 13 and one with 14 differ in firmware baseline and sometimes in supported I/O; the higher number is generally a functional superset, but not always, and a machine program compiled against a specific CPU version can refuse to load on a different one.
• -0AB0 — packaging and variant. 0AB0 is the standard single unit.

Where the traps are

Spaces and hyphens are cosmetic. 6ES7315-2EH14-0AB0, 6ES7 315-2EH14-0AB0 and 6ES7315 2EH14 0AB0 are the same article. Any search worth using normalises them; ours does.

The functional version is not optional. Buying "a 315-2 PN/DP" without the 14 can get you a part that will not run the program you have. When a supplier lists a part without the last blocks, ask for a photo of the rating plate before ordering.

SIPLUS is a different article. A 6AG1 number is the extended-temperature, conformal-coated version of the matching 6ES7. They are functionally equivalent and physically interchangeable, but the price and the environmental rating differ substantially. A supplier offering a 6AG1 against a 6ES7 request should say so.

"-0AB0" is not always "-0AB0". Some families use the final block for bundle variants (with or without memory card, with or without front connector). Check what is in the box.

Refurbished parts may carry an older functional version. This is normal on the surplus market and usually fine; it is a problem only when your project is version-locked.

Using the number to search

The practical workflow is: type the number with or without spaces, look at what comes back, and check three things on the part page before you request a quote — the functional version matches, the lifecycle status is what you expected, and the suppliers offering it list a condition you can accept.

If the number on your drawing returns nothing, it is usually one of three things: a legacy number that has been superseded, an ordering code for a configured assembly rather than a single article, or a distributor's own SKU. All three are worth searching anyway — cross-reference tables map many of them — and if nothing matches, a request with the number and a photo of the plate will usually be identified by a supplier who carries the family.