ISO 10816-3 Vibration Severity: Zones, Limits and How to Read Them

ISO 10816-3, now published as ISO 20816-3, is the international standard for deciding whether an industrial machine's vibration is acceptable. You measure broadband vibration on the bearing housings and compare the reading to defined severity zones. It answers the question every reliability team asks: how much vibration is too much?

How the standard measures vibration

Instead of analysing individual frequencies, ISO 10816-3 uses a single broadband number: the root-mean-square (RMS) vibration velocity in millimetres per second, measured over roughly 10 to 1000 Hz on the non-rotating parts of the machine. In practice that means a sensor on each bearing housing, read in the horizontal and vertical directions. Axial readings help diagnosis, but the zone limits only apply to axial vibration measured at thrust bearings.

Velocity is used because, across normal industrial running speeds, it tracks the fatigue-causing energy in a machine better than displacement or acceleration alone.

The four evaluation zones

Every reading lands in one of four zones:

• Zone A: the vibration of a newly commissioned machine in good condition.
• Zone B: acceptable for unrestricted long-term operation.
• Zone C: unsatisfactory for long-term running. The machine may operate for a limited period while you plan the repair.
• Zone D: severe enough to cause damage. Investigate and correct without delay.

The three figures that separate the zones are the A/B, B/C and C/D boundaries.

Machine groups and support conditions

The limits depend on machine size and mounting:

• Group 1: large machines, above about 300 kW (roughly 400 hp), or electric motors with a shaft height of 315 mm or more.
• Group 2: medium machines, about 15 kW to 300 kW, or electric motors with a shaft height from 160 mm up to 315 mm.
• Rigid or flexible support: a foundation counts as rigid when the machine-and-foundation system's lowest natural frequency is at least 25 percent above its main exciting frequency (usually running speed); otherwise it is flexible, and flexible mounts are allowed higher readings.

ISO 20816-3 covers machines running between 120 and 30,000 rpm. The withdrawn ISO 10816-3 stopped at 15,000 rpm.

The vibration velocity limits (RMS, mm/s)

So a 150 kW motor on a rigid base reading 3.0 mm/s RMS sits in Zone C: keep it running, but schedule the fix. The same reading on a large machine with a flexible support would sit in Zone A, below the 3.5 mm/s A/B boundary for that class.

ISO 10816 versus ISO 20816

ISO 20816 is the current, consolidated series. It merges the older ISO 10816 (vibration on non-rotating parts) and ISO 7919 (shaft vibration) into one family, with clearer machine-group definitions and updated guidance on where to measure. The zone concept and the familiar velocity limits carry over, so a reading judged against ISO 10816-3 gives the same verdict under ISO 20816-3.

What the number does not tell you

A severity zone tells you a machine is in trouble, not why. A rising broadband velocity is the trigger to look deeper with a spectrum: unbalance shows up at running speed, misalignment at twice running speed, and bearing faults at their own defect frequencies. For the two most common causes, see dynamic balancing, and how vibration compares with other techniques in thermography vs vibration analysis.

From a reading to a work order

A severity chart only prevents failures if a Zone C or D reading turns into action. That is where continuous monitoring beats a quarterly route: a system that watches the trend and can trigger a follow-up task the moment a machine crosses a boundary closes the gap between detecting a problem and fixing it.

Fabrico reads machine condition and OEE from the line and lets a threshold breach trigger a prioritized follow-up task, so a vibration alarm becomes a completed repair rather than a note in a spreadsheet.

Request a Fabrico demo to see the path from detection to fix on your equipment, and read breakdown vs preventive maintenance for the wider picture.

Related reading: condition monitoring software.

Setting ALARM and TRIP limits

ISO 20816-3 also tells you where to put the alarms. Set the ALARM above the machine's own steady baseline by 25 percent of the upper limit of Zone B, and do not normally let it exceed 1.25 times that limit. For a Group 2 machine on a rigid base the upper limit of Zone B is 2.8 mm/s, so a motor that normally runs at 1.2 mm/s gets an alarm at 1.9 mm/s, and no alarm on that class should sit above 3.5 mm/s.

TRIP limits depend on the machine design, but the standard recommends they do not exceed 1.25 times the upper limit of Zone C, which is about 5.6 mm/s for the same machine.

A change is a finding even inside Zone B

The zones are only the first test. The second, called Criterion II, looks at change: when a steady reading rises or falls by more than 25 percent of the B/C boundary, the standard treats it as significant, especially if it is sudden, and calls for a diagnostic investigation. On a Group 2 machine on a rigid base that is a step of 0.7 mm/s. A pump that jumps from 1.0 to 1.8 mm/s is still in Zone B, but it has moved more than the threshold and needs a spectrum.

Acceptance after installation or overhaul, and slow machines

For a new or overhauled machine, acceptance values are normally set in Zone A or B and usually do not exceed 1.25 times the A/B boundary, which is 1.75 mm/s for a Group 2 machine on a rigid base.

For machines running below 600 rpm, measure from 2 Hz instead of 10 Hz. Where the spectrum is expected to contain low frequency components, judge displacement as well as velocity: the standard also gives r.m.s. displacement limits, for example 22, 45 and 71 micrometers at the A/B, B/C and C/D boundaries for Group 2 on a rigid base.

Frequently Asked Questions

Is ISO 10816-3 still current?

It has been superseded by ISO 20816-3, but the two share the same zones and velocity limits, and ISO 10816-3 is still widely referenced in the field. A reading evaluated against either gives the same result.

Where do I place the sensor?

On the bearing housings, as close to the bearing as practical, measuring in the horizontal, vertical and axial directions. The velocity limits in the table apply to the non-rotating parts of the machine. ISO 20816-3 also gives separate limits for shaft relative vibration, measured peak to peak with proximity probes, in its Annex B.

What vibration level is acceptable?

It depends on machine size and mounting. For a medium machine on a rigid foundation, up to 2.8 mm/s RMS is acceptable for long-term operation (Zone B), 2.8 to 4.5 mm/s is Zone C, and above 4.5 mm/s is the damage zone.

Why velocity rather than acceleration or displacement?

Across the typical 10 to 1000 Hz industrial range, RMS velocity correlates best with the energy that fatigues a machine, which is why the standard uses it for the overall severity number. Acceleration is more useful for high-frequency bearing and gear defects, and displacement for slow-speed machines.

A severity reading tells you a machine is heading for trouble. It does not tell you what the trouble has already cost. Set next to equipment downtime per asset, a Zone C machine either explains the stops on that line or it does not, and availability tracking is where the two numbers meet.