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Downtime Reason Code Hierarchy Reference

Downtime data is only useful if reasons are consistent. This table gives a starter hierarchy of reason codes, tied to the six big losses so each stop lands in the right loss bucket.

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Level 1 group	Level 2 reason	Big loss	Planned or unplanned	Example
Equipment failure	Mechanical breakdown	Breakdowns	Unplanned	Broken drive belt on conveyor
Equipment failure	Electrical fault	Breakdowns	Unplanned	Contactor failure on a spindle motor
Equipment failure	Controls or software fault	Breakdowns	Unplanned	PLC fault that needs reset and restart
Equipment failure	Tool breakage	Breakdowns	Unplanned	Broken end mill mid cycle
Setup and changeover	Product changeover	Setup and adjustments	Planned	Switch from part A to part B
Setup and changeover	Tooling change	Setup and adjustments	Planned	Fixture swap
Setup and changeover	First off approval wait	Setup and adjustments	Unplanned	Waiting for quality to approve the first piece
Setup and changeover	Adjustment after setup	Setup and adjustments	Unplanned	Re-zeroing offsets after a trial part
Material	Material shortage	Breakdowns	Unplanned	Bar stock not delivered to the cell
Material	Wrong or incorrect material	Breakdowns	Unplanned	Wrong lot staged
Material	Material jam or feed fault	Small stops	Unplanned	Part jam at the feeder
Minor stoppage	Sensor blocked or misread	Small stops	Unplanned	Dust on a photo eye
Minor stoppage	Cleaning during run	Small stops	Unplanned	Chip clearing
Minor stoppage	Operator intervention	Small stops	Unplanned	Manual reset of an alarm
Speed	Running below rated speed	Reduced speed	Unplanned	Feed rate reduced to avoid chatter
Speed	Worn equipment	Reduced speed	Unplanned	Machine run slower to hold tolerance
Quality	Startup rejects	Startup rejects	Unplanned	Scrap until the process warms up
Quality	Production rejects	Production rejects	Unplanned	Out of tolerance part found at inspection
Quality	Rework	Production rejects	Unplanned	Part sent for secondary operation
People	No operator available	Breakdowns	Unplanned	Operator pulled to another line
People	Shift change handover	Setup and adjustments	Planned	Scheduled handover time
Planned stop	Scheduled maintenance	Not a loss in OEE	Planned	Preventive maintenance slot
Planned stop	Break or meal	Not a loss in OEE	Planned	Scheduled break
Planned stop	No demand or no order	Not a loss in OEE	Planned	Nothing scheduled
Utilities	Power or air supply loss	Breakdowns	Unplanned	Compressed air pressure drop

Keep the list short enough that operators can pick a reason in a few seconds. Whether a reason counts against OEE depends on your planned time rules, so confirm before you load the codes into a system.

Review your downtime code set

Optional review of your reason code list and how stops flow into reports.

Optional. The tool and every export work without this. No spam.

How to use the table

Start from level 1 groups, then trim level 2 reasons to those that happen on your equipment. Operators should see no more than about ten choices per screen. Copy the result to Excel as the reason code master for your MES, your ERP downtime posting or a paper log.

Delete reasons that never happen
Add equipment specific faults at level 3
Mark each code planned or unplanned

Mapping to the six big losses

The six big losses are breakdowns, setup and adjustments, small stops, reduced speed, startup rejects and production rejects. The first two are availability losses, the next two are performance losses and the last two are quality losses. Mapping each code to one of these keeps reports consistent and lets you see which factor is dragging OEE.

Making the codes usable

Short names beat long descriptions. Avoid an Other code, or limit it and review it weekly, because it grows quickly and hides the real causes. Require a reason for any stop longer than your threshold and let small stops be counted automatically if the machine can report them.

Common mistakes

Plants often build too many codes, mix causes with symptoms and let supervisors assign reasons days later from memory. Capture the reason at the time of the stop, and review code use monthly so the list stays honest.

Frequently Asked Questions

How many reason codes should I have?

Most plants do well with 20 to 40 codes in two or three levels. Operators should see a short list on screen. Add detail only where a loss is large enough to justify the extra data entry.

Should changeovers count as downtime?

Yes for improvement work. Changeovers are an availability loss that SMED projects target. If you exclude them from OEE, still record them separately so the time is visible.

What about small stops of a few seconds?

Operators cannot log them by hand. Use machine signals to count them automatically, or sample them in a short observation study. Group them under a single minor stoppage reason with a note.

Can I load these codes into my ERP?

Many ERPs and MES products support configurable downtime or non-production reason codes. Check the field names and length limits in your own system before loading, and keep a single master list.

If you want downtime reasons captured against ERP work orders and reported without double entry, we can help design the posting flow.

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