SDAA522 September   2026 ISO6020 , ISOM8110 , ISOM8110-Q1 , ISOM8113-Q1 , ISOM8610 , ISOM8710 , ISOW6441

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Introduction
    1. 1.1 Why Magnetic Field Immunity Matters for Isolators
  5. 2 Magnetic Field Units at a Glance
  6. 3 IEC 61000-4-8 — Power Frequency Magnetic Field Immunity
    1. 3.1 What IEC 61000-4-8 Test Simulates
    2. 3.2 Test Levels for IEC 61000-4-8 Continuous Power Frequency Fields
    3. 3.3 Environment Classes — How a Level is Chosen
    4. 3.4 Field Strengths Observed in Actual Installations
  7. 4 IEC 61000-4-9 — Pulse Magnetic Field Immunity
    1. 4.1 What IEC 61000-4-9 Test Simulates
    2. 4.2 Impulse Current Waveform for Pulse Magnetic Field
    3. 4.3 Test Levels for IEC 61000-4-9 Pulse Magnetic Fields
  8. 5 Summary of Class 5 Testing— What We Are Targeting
  9. 6 What "PASS" Means — Performance Criteria
  10. 7 Test Setup Details
  11. 8 Test Results and Summary
    1. 8.1 Test Conditions for Both Standards:
  12. 9 System Design Considerations for End Equipment Performance
  13. 10Summary
  14. 11References

3.4 Field Strengths Observed in Actual Installations

IEC 61000-4-8 Annex D contains field strength measurements from real-world installations. These values help in understanding the level of headroom one can have by meeting Class 5 requirements.

Equipment Installation Location Typical field strength observed
Household appliances, 0.3m from surface 0.03 – 10A/m (max ≅ 20A/m)
Household appliances, 1.5m from surface < 0.1A/m (max 0.4A/m)
Directly under HV lines 10 – 16A/m per 1000A of line current
30m laterally from HV lines 3 – 5A/m per 1000A of line current
HV substation (220/400kV), near a 500A line 9 – 14A/m
HV substation relay room 1 – 7A/m
HV substation equipment room ≅ 0.7A/m
Power/industrial plant, 0.3–1.5m from a 2200A bus bar 6 – 85A/m
Other industrial plant sources 4 – 30A/m

Since field strength diminishes rapidly with distance, proximity is as critical as current magnitude. Which is why the isolator—positioned directly at the power boundary—is the component that requires the greatest margin and highest level of immunity.