Overview
ISO 20816-3:2022 provides guidance for evaluating vibration severity on industrial machines with rated power above 15 kW and operating speeds between 120 rpm and 30,000 rpm. This standard replaces ISO 10816-3:2009.
ISO 20816-3 maintains the same zone boundaries but introduces clearer machine group definitions, updated measurement location guidance, and better alignment with ISO 20816-1 general principles.
The Four Severity Zones
Vibration severity is classified into four zones based on measured velocity (mm/s RMS):
Zone A
New machines
Zone B
Acceptable for operation
Zone C
Limited operation
Zone D
Damage may occur
Machine Groups
Machines are classified into two groups by rated power or shaft height. The support (rigid or flexible) is a separate axis and changes the limits below.
| Group | Description | Examples |
|---|---|---|
| Group 1 | Large machines: above 300 kW or shaft height of 315 mm or more | Large motors, compressors, generators |
| Group 2 | Medium machines: 15-300 kW or shaft height of 160-315 mm | Medium motors, fans, blowers |
Zone Boundaries (mm/s RMS)
Velocity zone boundaries for broadband vibration measurement:
| Zone Boundary | Group 1 rigid support | Group 2 rigid support | Group 1 flexible support | Group 2 flexible support |
|---|---|---|---|---|
| A/B | 2.3 | 1.4 | 3.5 | 2.3 |
| B/C | 4.5 | 2.8 | 7.1 | 4.5 |
| C/D | 7.1 | 4.5 | 11.0 | 7.1 |
Zone Interpretation
| Zone | Condition | Recommended Action |
|---|---|---|
| Zone A | Excellent - New or recently overhauled machines | Continue monitoring at normal intervals |
| Zone B | Acceptable - Normal for unrestricted long-term operation | Monitor and trend; investigate significant changes |
| Zone C | Alert - Acceptable only for limited periods | Plan corrective action; increase monitoring frequency |
| Zone D | Not Acceptable - Damage may occur | Take immediate corrective action |
Measurement Requirements
Measurement Locations
- Horizontal (H): In plane of axis, toward coupling
- Vertical (V): Top of bearing housing
- Radial: two orthogonal radial directions on each bearing housing; axial at the thrust bearing
- Axial (A): Parallel to shaft axis
Measurement Parameters
- Velocity: mm/s RMS (primary parameter)
- Frequency range: 10-1,000 Hz above 600 rpm; 2-1,000 Hz from 120 to 600 rpm
- Averaging: RMS over measurement period
ISO 20816-3 zone boundaries apply to broadband (overall) vibration. Spectral analysis with narrowband data provides additional diagnostic value but uses different evaluation criteria.
Quick Reference Summary
Rigid support. For flexible support use the limits table above.
| If velocity is... | Group 2 Status | Group 1 Status |
|---|---|---|
| < 1.4 mm/s | Zone A - Excellent | Zone A - Excellent |
| 1.4 - 2.3 mm/s | Zone B - Acceptable | Zone A - Excellent |
| 2.3 - 2.8 mm/s | Zone B - Acceptable | Zone B - Acceptable |
| 2.8 - 4.5 mm/s | Zone C - Alert | Zone B - Acceptable |
| 4.5 - 7.1 mm/s | Zone D - Danger | Zone C - Alert |
| > 7.1 mm/s | Zone D - Danger | Zone D - Danger |
Sources
ISO 20816-3 is a paid standard. The limits above were checked against these three secondary sources, which agree with each other.