Planned vs unplanned downtime and what counts against OEE

Breaks, changeovers and planned maintenance all count as downtime, because the machine is stopped, but they don’t all count against availability. Under the common OEE convention, a break with nobody meant to run the machine comes out of planned production time first. A changeover or a maintenance job inside a scheduled shift stays in and lowers availability, even though you planned it.

One test decides where each stop goes, and a decision table applies it to the stops plants argue about. One shift on a molding press, worked three ways, shows how far the convention moves the number.

Planned vs unplanned downtime#

NIST’s maintenance survey report puts the first point in one line: “PM is planned downtime which is still downtime.”^[3] The planned downtime glossary entry shows how IoTFlows marks those stops.

Planned or unplanned answers one question: did you choose this stop? Availability asks a different one: was the machine meant to be making parts at the time? Keep the two questions apart and most arguments about planned time settle quickly.

What counts against availability?#

Availability is run time divided by planned production time. Planned production time is the shift minus any time with no intention of running production, and Vorne’s OEE primer names breaks as the usual example.^[1]

Stop time is the rest of the time the machine was meant to run and didn’t. It includes unplanned stops, such as breakdowns, and planned stops, such as changeovers.^[1] The six big losses file planned stops under setup and adjustments, an availability loss: setups, changeovers, cleaning, warm-up, planned maintenance and quality inspections.^[2]

That leaves one test. Take time out of planned production time only when nobody intended to run the machine. Keep it in when the machine was scheduled to run and didn’t, whatever the reason and whoever chose it.

For example, the press above runs a 480-minute day shift with a 30-minute lunch, so planned production time is 450 minutes. The mold change and the lubrication PM were both on the schedule, and both stay in. The guide to calculating OEE from one shift carries the same structure through performance and quality.

Where each stop goes#

The table covers ten stops that plants argue about. Read each row with the one test: was the machine meant to run?

Breaks and meetings#

A break comes out only when the machine sits idle by plan. If a relief operator is meant to cover lunch, the machine was scheduled to run, and every stop in that slot is unplanned downtime.

A 10-minute shift-start meeting follows the same test. Take it out when the machine is meant to sit through it, and keep it in when the machine was meant to run.

Changeovers#

A changeover written into the schedule is planned and still counts. Vorne calls changeovers the usual largest source of setup and adjustment time,^[2] so taking them out of the denominator hides the loss you most want to shrink.

A changeover swapped in mid-shift for a rush job is unplanned. When you have to think about whether a stop was scheduled, it was not.

Planned maintenance#

Preventive maintenance inside a scheduled shift is a planned stop, and it lowers availability. The same job moved to a Saturday with no shift sits outside planned production time, so it costs OEE nothing.

That’s a reason to move PM into non-production hours where your plant has them. It isn’t a reason to relabel in-shift PM as excluded time.

Overruns#

A 45-minute mold change that takes 70 minutes is two records: 45 planned minutes and 25 unplanned ones. Both stay in availability. The split tells you whether the plan was too tight or the changeover went wrong.

Work one shift three ways#

The convention is a choice, and on one shift it moves availability by 16.6 points. Here is the shift from the figure above, with three different denominators.

The middle row follows the common OEE convention. The bottom row answers a different question, how much of the time you meant to produce went to stops nobody chose, and it isn’t OEE availability.

That reliability question has its own ratio: unplanned downtime as a share of planned production time. NIST’s survey of US discrete manufacturers asked for exactly this, and the average answer was 7.8%.^[3] On this press it’s 45 ÷ 450 = 10.0%.

Standards don’t settle the line either. ISO 22400 gives two definitions of OEE, and a 2020 review found they seem to diverge from each other and from Nakajima’s original TPM formulation.^[4] SEMI E10, written for the semiconductor and related industries, defines six mutually exclusive equipment states and names unscheduled downtime as the failed one.^[6]

Hours with no shift belong to a different metric. TEEP multiplies OEE by utilization, planned production time over all time, so it is the one that counts the weekend.^[5] The guide to utilization, OEE and TEEP on one calendar lines these metrics up hour by hour.

Why keep planned stops in availability?#

Planned stops cost the same minutes as unplanned ones. A 45-minute mold change is 45 minutes the press made no parts, whether you scheduled it or not. Keeping planned stops in the denominator keeps them on the list of losses you work on.

Datwyler’s injection molding plant shows why. With a reason on every stop, it cut shift-changeover downtime in half and material-changeover downtime by 30% within six months. Both are stops a plant plans for, and both gains would be invisible on an availability figure that left them out.

Track planned and unplanned stops automatically#

IoTFlows detects every stop from a sensor on the machine, with no PLC connection, and sorts it into the shift it fell in. Set your shifts and timezone first, since they decide which hours count at all.

Mark each downtime category planned or unplanned once, with the Planned downtime toggle. Operators then see a calendar icon on planned reasons when they classify a stop, and changeovers and maintenance rank by hours next to breakdowns.

A scheduled break window classifies every stop in your lunch slot automatically. Give that break category the None severity, and Exclude None on the Advanced Report takes it out of both uptime and downtime, matching the convention above. See how downtime tracking works.

Set your plant’s convention#

1. List what leaves planned production time

   Write down every kind of time with no plan to run: unstaffed breaks, hours with no shift and days with no orders. Everything else stays in.

2. Flag every reason code

   Mark each reason planned or unplanned when you build the list, then set its severity separately. The starter list of reason codes shows both settings on every code.

3. Split overruns from the plan

   Record a changeover’s scheduled minutes as planned and the rest as unplanned. Cut the stop record in two at the end of the scheduled slot and give each half its own reason.

4. Print the convention on the report

   Put one line under every OEE number saying what came out of planned production time. A reader in another plant can then compare like with like.

5. Shrink the planned stops too

   Rank planned stops by hours next to breakdowns and start on the largest. Measure changeover time before you try to cut it.