Why legacy PNOZ relays are becoming hard to source
The PNOZ X family established Pilz as the standard for machine safety at a time when hardwired safety relays were the normal solution. Tens of thousands of units went into packaging lines, presses, conveyors and machine tools, and a great many are still running. As with any electromechanical product, the family has moved through its lifecycle toward the newer generations — the compact PNOZ s range and the configurable PNOZmulti platform — and the older variants have moved toward stock-only availability.
Electromechanical relays also wear. Contact life is finite, and a relay that has been switching safety circuits daily for two decades is simply closer to the end of its service life than a control relay on the same panel. That makes spare parts planning for safety circuits more urgent, not less.
A safety relay is not interchangeable with a control relay of similar contact rating. It embodies a specific safety function with a defined performance level, redundancy structure, monitoring behaviour and reaction time. Substituting an unverified equivalent compromises the machine's safety integrity — and, in most jurisdictions, invalidates the machine's conformity documentation. If you cannot confirm equivalence, do not fit it.
First, work out what the relay is actually doing
Before sourcing anything, establish the functional requirement. The part number alone does not tell you how the relay is configured on this machine.
- Which safety functions does it monitor? Emergency stop, safety gate, light curtain, two-hand control, or several of these together.
- How many safety contacts are used, and are any of them delayed? Delayed outputs are common on drive run-down circuits and are a frequent source of mismatch.
- What is the start-up behaviour? Manual monitored start against automatic start is a wiring-level distinction, and getting it wrong changes the machine's behaviour.
- Is there a feedback loop from external contactors? This monitoring path has to exist in the replacement too.
- What performance level is claimed in the documentation? This is what must be preserved or improved upon.
If the original wiring diagram is still available, use it. If it is not — which is common on machines of this age — then reverse-engineering the existing circuit carefully is part of the job, not an optional extra.
The three realistic routes
1. Like-for-like replacement
Where a unit with the identical article number can still be sourced, this is by far the cheapest path: no re-engineering, no revalidation, no updated documentation, no retraining. Genuine new-old-stock and function-tested units both serve here. Because availability is shrinking, holding one spare per critical machine is a low-cost way to remove a high-consequence failure mode.
2. Equivalent successor from the same manufacturer
When the original article number is unobtainable, the successor generation usually provides the same safety function with modern diagnostics. The complication is physical: terminal layout, housing width on the DIN rail and terminal numbering generally differ, so this becomes a wiring job with a documented before-and-after rather than a straight swap.
Two practical mitigations make this manageable. Choose the successor model that minimises the wiring delta — matching contact count and start-up behaviour matters more than matching the physical size. And do the change on a planned stop with the machine isolated, with the wiring diagram updated in the same session, because a relay swap whose documentation is never revised becomes an unmarked hazard for the next engineer.
3. Convert to a configurable safety controller
Where a machine carries several discrete safety relays, consolidating onto a configurable platform such as PNOZmulti can be a better long-term answer than replacing relays one by one as they fail. It reduces the spare parts tail, adds diagnostic visibility that hardwired relays cannot offer, and makes later functional changes possible in configuration rather than copper.
The trade-off is real: this is a safety project with functional testing, documentation and revalidation, not a repair. It makes sense on a machine with a long remaining life and a complex safety architecture. It is overkill for a single gate-monitoring relay.
- Isolate and lock off the machine, and verify isolation before touching safety wiring.
- Photograph every terminal before disconnecting anything — photographs cost nothing and prevent the classic rewiring error.
- Confirm the replacement's safety function, contact count, delayed outputs and start-up behaviour against the original.
- Verify the performance level claimed for the replacement is at least equal to the original.
- Function-test every safety circuit after the change, including the emergency stop path and any guard interlock.
- Update the machine documentation, wiring diagram and spares list in the same session.
The cost of getting this wrong
Safety circuits are one of the few areas where the cheapest available option is rarely the right one. An unverified substitute may function correctly and still leave the machine non-compliant, which surfaces at the next audit or, worse, at the next incident. Regulators and insurers treat safety function modification as a documented change with traceability requirements.
The practical rule: buy from a source that can supply traceability and condition information for the exact article number, and if the exact article number cannot be obtained, treat the replacement as an engineering change rather than a parts purchase. That means documentation, testing and sign-off — which is more work, and considerably less than the alternative.
How Austinovo can help
We supply genuine and function-tested Pilz safety relays, including legacy PNOZ article numbers and current successors. Send us the article number from the label — or a photograph of it — and we will confirm availability, condition and delivery time, and where a direct replacement is no longer available we will identify the closest successor with the same safety function.
For plants with a wide installed base of safety relays, we can review your list and flag which article numbers are still procurable and which have moved to stock-only, so you can prioritise the critical circuits first.
Need a Pilz PNOZ relay?
Send us the article number or a photo of the label. We confirm availability, condition and lead time within 24 hours.