Anyone serious about OEE needs to classify stoppages correctly. The difference between planned downtime and unplanned downtime sounds straightforward – in practice it's one of the most common weak points in availability analysis.
Planned downtime covers periods when equipment is deliberately not supposed to run. This includes scheduled maintenance and TPM intervals, planned changeovers, cleaning and validation, fixed breaks where lines intentionally stand, and line shutdowns or plant holidays.
Planned downtime is not a failure – it's part of the production concept. That said, it's worth watching: changeovers that consistently run too long or maintenance windows that open more often than necessary are legitimate optimization targets.
Unplanned downtime happens when equipment should be running but can't. Typical causes: technical failures, material shortages, quality holds, missing approvals, operator errors. Unplanned downtime is the hardest loss driver in OEE availability – and the primary target of most OEE and continuous improvement programs.
Classic OEE calculation uses planned production time as its base. Unplanned downtime reduces availability within that window. Classifying too much as "planned" makes OEE look artificially good. Lumping everything as "unplanned" makes targeted steering impossible – you can't separate changeover optimization from failure reduction if both sit in the same bucket.
A clear, plant-wide downtime taxonomy is not a nice-to-have. It's the prerequisite for comparable metrics.
Changeovers booked as planned on one line, unplanned on another. Maintenance logged as a breakdown. Breaks modeled differently across lines. "Waiting for material" disappearing into the catch-all "fault" category. The result: lines and plants become incomparable, improvement actions miss their target.
Start by defining plant-wide what planned and unplanned means – with a fixed stoppage list and category assignment. Capture machine states automatically, let operators select reasons at a terminal. Group reasons into clusters: technical, material, quality, organization, changeover, cleaning. Review definitions regularly – at least annually.
An MES enforces this logic systematically: shift schedules define when production is expected, stoppages are captured and classified automatically, OEE and availability are calculated consistently on that basis. Gut feeling becomes a hard steering metric.
Does planned downtime affect the OEE value? In classic OEE calculation, no – planned stoppages are excluded from the base. But tracking their volume and trends still matters: too much planned downtime eats capacity even if the OEE figure stays untouched.
What if stoppage reasons are booked inconsistently? That's an organizational issue, not a system issue. Clear written definitions, a short briefing and a manageable reason code catalog fix 80 percent of inconsistency. Systems offering hundreds of codes reliably produce bad data.
How detailed do stoppage reasons need to be? For operational steering, cluster level is usually enough. Five to eight main categories cover daily management and improvement work. Anyone needing deeper granularity – for predictive maintenance for example – can go further within categories without breaking comparability.