Keep legacy lines running
Short answer. A spares shelf is a bet on two numbers you can actually look up: how long the line stops when this part fails, and how long the part takes to get here. Everything else — how critical the machine feels, how old it is, whether the platform is “current” — is a proxy for those two. Plan the shelf against downtime and lead time, and decide the migration at the same time, because the shelf is what buys you the time to migrate properly.
What belongs on the shelf
Failure stops the line, and delivery is slower than your tolerance
That is the whole test. Control components, drives and safety devices come first; the signal and interface modules around them next. Commodity items — terminals, contactors, sensors in current series — can be reordered inside a week and do not justify capital sitting on a shelf. A withdrawn CPU module cannot be reordered at all.
Quantities follow runtime, not superstition
If the platform has five more years of planned production and the article is obsolete, one spare covers one failure. Count the installed quantity, not the number of different part numbers — the shelf that gets you through a bad week is usually the one for the part that is in twelve cabinets.
Last time buy, and what it changes
A last-time-buy date is the manufacturer’s final order deadline before production closes, not a delivery deadline. After it, the only route to new-original stock is distribution, and lead times stop being predictable because nobody is making more. When you have an LTB date for a platform, size the shelf for the remaining runtime of the plant in one purchase decision, because the second chance does not exist.
We can check the current status of an article number and tell you whether it is still buildable, whether an LTB has been announced, and what the designated successor is. That answer costs you one enquiry and it is the input the whole shelf calculation needs.
A successor article is rarely a drop-in
A successor normally keeps the function and changes the interface: the memory concept, the fieldbus or the number of PROFINET ports, the terminal layout, or the engineering tool the project has to live in. One of our own catalogue entries shows the pattern plainly — the Siemens 6ES7288-1SR20-0AA0 is a CPU SR20 AC/DC/Relay with 12 digital inputs, 8 relay outputs, one industrial Ethernet interface and one RS 485 port, in IP20. Those five attributes are what a replacement has to reproduce for an existing cabinet, and a “newer” controller that differs in any of them is a migration project, not a spare.
Treat it that way and it is cheap: you find the difference on a test bench. Find it at 2 a.m. on a stopped line and it is the most expensive hour of the year.
Where we sit in this
Industriparts GmbH is an independent distributor, not an authorised one, and we say that on every product page rather than implying a partner status we do not have. What that means in practice for a legacy line: we can often still supply new-original parts for platforms that are no longer current, through a sourcing network rather than a price list — and we quote the actual condition and the real lead time instead of a stock symbol.
What we cannot honestly offer is a guarantee that an obsolete article will be available in three years. Anyone who offers you that is selling you a number, not a plan.
What to send us
A usable answer usually starts from a photo of the cabinet label plate. Then a list with:
- Manufacturer and type designation. As printed, not as remembered.
- Order number / material number. The single field that makes everything else checkable.
- Installed quantity. Twelve cabinets with the same module changes the shelf calculation.
- Required delivery date. Whether this is planning or already a breakdown.
- The platform’s planned runtime. How many years this line is meant to keep producing.