CISPR 25:2016 CEC Limits

Conducted Emission – Current Probe Method (Table 6)

This table summarizes the Conducted Emission (CEC) current probe method limits (corresponding to Table 6) for automotive components and modules per CISPR 25, including complete data for Class 1-5, suitable for EMC pre-compliance and certification reference.

Limit Visualization Curve

Envelope

Class:

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Levels in dB(µA). Scroll horizontally to view more.

Service / Band	Frequency MHz	Class 5			Class 4			Class 3			Class 2			Class 1
Service / Band	Frequency MHz	Peak	QP	Avg	Peak	QP	Avg	Peak	QP	Avg	Peak	QP	Avg	Peak	QP	Avg
BROADCAST
LW	0.15 to 0.30	50	37	30	60	47	40	70	57	50	80	67	60	90	77	70
MW	0.53 to 1.8	26	13	6	34	21	14	42	29	22	50	37	30	58	45	38
SW	5.9 to 6.2	19	6	-1	25	12	5	31	18	11	37	24	17	43	30	23
FM	76 to 108	4	-9	-16	10	-3	-10	16	3	-4	22	9	2	28	15	8
TV Band I	41 to 88	0	-	-10	6	-	-4	12	-	2	18	-	8	24	-	14
DAB III	171 to 245	-2	-	-12	4	-	-6	10	-	0	16	-	6	22	-	12
MOBILE SERVICES
CB	26 to 28	10	-3	-10	16	3	-4	22	9	2	28	15	8	34	21	14
VHF	30 to 54	10	-3	-10	16	3	-4	22	9	2	28	15	8	34	21	14
VHF	68 to 87	4	-9	-16	10	1	-10	16	7	-4	22	13	2	28	15	8
VHF	142 to 175	4	-9	-16	10	1	-10	16	7	-4	22	13	2	28	15	8

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Details

Test Setup & Technical Overview

Detailed engineering guide for Conducted Emissions (CEC) by Current Probe Method

Technical Overview: CEC vs LISN

The Current Probe Method (CEC) and the LISN Voltage Method (CEV) are the two primary approaches for evaluating conducted emissions on automotive component power lines and signal harnesses.

While the LISN method measures RF noise voltage across a nominal 50 Ω impedance network directly connected to the power lines, the CEC method utilizes a specialized current clamp to measure the noise currents flowing through the entire wiring harness without physically breaking the circuits.

The current probe method is exceptionally effective for detecting RF current loops that can lead to cable radiation at high frequencies, serving as a critical indicator for potential radiated emission failures.

Test Configuration & Setup Details

Proper physical setup is paramount to ensure reproducibility. Under CISPR 25, the Equipment Under Test (EUT) is positioned on a non-conductive, low-dielectric support 50 mm above the ground plane (GP).

The ground plane itself must be a copper or galvanized steel sheet (minimum 0.5 mm thick) bonded securely to the shielded enclosure. The wiring harness should be 1700 - 2000 mm in length and routed parallel to the edge of the ground plane.

To capture standing wave resonances, current measurements are taken with the probe positioned at two distinct locations along the harness: 50 mm from the EUT connector (targeting high-frequency emissions) and 750 mm from the connector (targeting mid-to-low-frequency resonances).

Interpretation of Limits (Class 1-5)

CISPR 25 specifies five limit classes to accommodate different vehicle environments and installation configurations:

Class 5: The most stringent class, typically mandated by OEMs for safety-critical components (ADAS, steering, braking) or devices located near sensitive radio antennas.
Class 4 & 3: Applied to standard body electronics, powertrain control units, and infotainment displays.
Class 2 & 1: The least severe limits, reserved for simple, transient, or non-critical loads (e.g., seat adjusters, window motors) that present minimal risk to the vehicle's RF receivers.