ISO 10816 Vibration Thresholds Explained for Plant Managers

ISO 10816is the standard that turns a raw vibration reading into a decision. It sorts a machine's overall vibration velocity (measured in mm/s RMS) into four zones — A, B, C and D — that run from "newly commissioned and healthy" to "damage is likely." The catch: the exact limits depend on the machine's size and how it's mounted, which is where most people get it wrong.

The Four ISO 10816 Zones

Whatever the machine class, the zones always mean the same thing. Only the numeric boundaries between them shift.

• Zone A — vibration of a newly commissioned machine in good condition. Nothing to do.
• Zone B — acceptable for unrestricted long-term operation. Normal running.
• Zone C — unsatisfactory for long-term operation. The machine can run, but plan an intervention. This is your warning line.
• Zone D — vibration severe enough to cause damage. This is your alarm line — investigate before failure.

Why the Numbers Change: Machine Class

ISO 10816-3 groups machines by power and foundation type, because a small pump and a large motor simply don't vibrate the same way at the same health. Roughly, the A/B and C/D boundaries widen as machines get bigger and as the mounting gets more flexible:

• Small machines (up to ~15 kW) sit in the tightest band — even modest velocities matter.
• Medium machines (~15–300 kW) tolerate more before crossing into the warning zone.
• Large machines (300 kW and up) have the widest bands, and rigid-mount vs flexible-mount changes the limits again.

The practical takeaway: a single site-wide "alarm at X mm/s" rule is almost always wrong. It will nag on large machines that are fine and stay silent on small machines that are already in trouble. The thresholds have to be set per machine class.

From Threshold to Alert

Knowing the zones is only useful if they drive action. The move most plants make:

• Set the C/D boundary as your alarm and the B/C boundary as your warning, per machine class.
• Watch the trend, not just the absolute value — a reading climbing steadily through Zone B often matters more than one that's sat flat in Zone C for years.
• Pair the overall level with a frequency spectrum so you know why vibration rose — bearing, misalignment or imbalance each show a different signature.

Overall RMS velocity tells you a machine is getting worse. It doesn't tell you what's wrong. That's the difference between a threshold alarm and diagnosis, and it's covered in our companion post on how vibration sensors catch failures.

How Vexron Uses ISO 10816

Vexronapplies ISO 10816 zones per machine class automatically, so you don't hand-set a threshold for every asset. Its VMI-1 model goes a step past the standard: instead of only flagging that overall velocity crossed into Zone C, it separates the bearing, alignment and imbalance signatures behind that rise and ranks the alert by severity and trend — so your team knows both how urgent it is and what to check first.