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Measurment Method for EMC Filter

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Measurment method

Measurement of the leakage current (simplified).

The leakage current is measured from every pole of the network:

  • to all accessible metal parts

  • to metal parts of protection class II equipment which is separated

only by the base material from parts under voltage.

The test is made with AC at 250 V / 50 Hz.

Measurements are made in both switch positions (see diagram).

Protection class l

Devices are fitted with a special grounding conductor to provide protection against electrical shocks (L,N,PE wire cable). SCHURTER filters correspond to protection class I.

Insertion loss acc. CISPR 17 (common- and differential mode)

Asymmetrical measurement

In common mode measurements, the line and neutral conductors are measured with respect to earth. Line (L) and neutral (N) are measured to earth (E).

Symmetrical measurement

In differential mode measurements, the insertion transmission loss is measured between line and neutral through a balancing transformer; the earth wire is not used.

4-pole network with integrated balancing transformer for the measurement of insertion transmission loss in the symmetric case.

Measurement method

The insertion loss D is defined as that loss which results when a four-pole network is inserted into an existing layout, having a surge impedance Z, assuming that the LHS and the RHS terminal impedances of the four-pole network are equal in magnitude and real, the insertion transmission loss and the overall loss are the same.

The insertion transmission loss, in decibels, can be obtained as follows:

Insertion loss “alternate test method”

Asymmetrical measurement

Symmetrical measurement

The alternate test method allows the measurement in the GHz frequency range whereas the CISPR 17 method does not cover frequencies above 30MHz. The insertion loss is measured in a throughput method (common mode) and a cross coupled method (differential mode). The differential mode measurement of the alternate test method is not directly comparable to the conventional measurement acc. CISPR 17.

Voltage tests on noise suppression filters complying to EN 133200 II

IEC / UL 60939-3

Nominal voltage

Between L - N / L - L

Inner and outer insulation L/N - PE


Inner and outer insulation L/N - PE


150 ≤ UR ≤ 300 VAC

4.3 UR VDC

1500 VAC or 2250 VDC

4.3 UR VDC

300 ≤ UR ≤ 520 VAC

4.3 UR VDC

2 kVAC or 3 kVDC

4.3 UR VDC

520 ≤ UR ≤ 760 VAC

4.3 UR VDC

3 kVAC or 4 kVDC

4.3 UR VDC

*) C is the capacity measured between the connection block to which the high voltage is connected for test.

UL 1283 (Appliance filters)

Nominal voltage

Between connection

Between connection and case

UR ≤ 250 VAC

1250 VAC or 1768 VDC

1500 VAC or 2121 VDC

Application classes (IEC 60068-1)

The aim of this standard is to create a basis for classification of telecommunication engineering electrical components according to application classes which correspond to their climatic and mechanical suitability.


* relative humidity


The high reliability of the products can be excelled from MTBF (meantime between failures). These values are according MIL-HB-217-F class GB at an ambient temperature 40°C at rated voltage and current.

3-stage filter

1st stage

A differential mode acting filter with high energy absorption. Discharging resistors are normally used for Cx capacitors > 100 nF. The capacitors are tested and approved as so-called class X noise suppression capacitors. The 1st stage serves as dl/dt limitation.

2nd stage

A common mode acting filter with a high, broad band attenuation ratio. A ZNR varistor surge serves as the overvoltage suppression component. The earthed capacitors are tested and approved as so-called class Y noise suppression capacitors.

3rd stage

Common mode as well as differential mode acting filter in the HF range up to 300 MHz. Feedthrough capacitors make high attenuation values possible up to the gigahertz range. These capacitors are also class Y type. SCHURTER uses only approved noise suppression capacitors (MKP, MKT) according to IEC 60384-14.


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