Conducted Emissions
Conducted emissions are unwanted electromagnetic disturbances that travel through power and signal cables, potentially causing interference with other devices on the same electrical network. Understanding and controlling these emissions is critical for EMC compliance and product approval in regulated markets.
Conducted emissions testing is a fundamental requirement under electromagnetic compatibility (EMC) regulations worldwide and applies to most electronic equipment intended for residential, commercial, or industrial use.
Why Conducted Emissions Matter
Electronic devices with switching circuits, digital logic, or power conversion generate high-frequency noise that can propagate through connected cables. Without proper filtering or design measures, these disturbances may:
Disrupt the operation of nearby devices
Cause data errors or system instability
Violate regulatory emission limits
Regulatory Impact:
Products exceeding conducted emission limits cannot be sold in regulated markets
Retrofitting fixes after mass production is expensive and time-consuming
Early detection through pre-compliance testing saves development costs
Measurement Setup
Line Impedance Stabilization Network (LISN)
Provides a defined impedance between the device under test (DUT) and the power source
Decouples the test setup from external mains variations
Couples high-frequency emissions to the measurement receiver
Required Equipment
EMI receiver or spectrum analyzer for signal detection
LISN for power line measurements
Shielded test environment to minimize ambient interference
Test Procedure
The DUT is operated in typical or worst-case modes
Emissions are measured across the specified frequency range (typically 150 kHz to 30 MHz)
Results are compared against applicable limits
Frequency Range and Limits
Conducted emissions are typically assessed from 150 kHz to 30 MHz, with measurement results expressed in dBµV.
Limits vary depending on:
Product category (e.g., residential vs. industrial)
Applicable regulatory framework
Operating environment classification
Applicable Standards
Conducted emission limits are defined in regional and international standards:
Europe:
EN 55032 (CISPR 32) – Multimedia equipment
EN 61000-6-3 – Generic standard for residential, commercial, and light industrial environments
EN 61000-6-4 – Generic standard for industrial environments
United States:
FCC Part 15 Subpart B – Unintentional radiators
International:
CISPR 11 – Industrial, scientific, and medical equipment
CISPR 22 – Information technology equipment (superseded by CISPR 32)
Common Causes of Non-Compliance
Typical sources of excessive conducted emissions include:
Inadequate input filtering on power supplies
High-frequency switching without sufficient damping
Poor PCB layout or grounding practices
Missing or undersized common-mode chokes
Insufficient shielding of internal cabling
Design Recommendations:
Use X/Y capacitors and common-mode chokes at power input
Implement RC snubbers on high-frequency switching nodes
Minimize current loop areas in PCB layout
Apply ferrite beads to I/O and signal cables
Identifying and addressing these issues during the design phase reduces the risk of compliance failures during formal testing.
Need Support?
Need conducted emission testing? Our ISO 17025 accredited laboratory performs EMC compliance testing to CISPR, EN, and FCC standards: → EMC Testing