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Industrial Mains Filters

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Power entry modules with filter

Same requirements are valid for filters as for RF suppression chokes.

Industrial mains filters

Frequency range 0.01 MHz ... 1000 MHz

General information

Electromagnetic compatibility (EMC) is the capability of electrical equipment (installations, devices, assemblies) to operate effectively in its electromagnetic environment (Immunity), without in turn irresponsibly affecting this environment (Emission). 

Mains filters of various types are used for the protection of electronic circuits, components and equipment against transients or similar interference, on the mains power supply. A suitable filter can be selected from the existing product range for each equipment type in accordance with electromagnetic conditions of its environment.

Mains interference can be classified into four categories:

A) Fluctuations in the industrial mains supply

 (magnetic voltage stabilizer)

B) Harmonic wave interference in the frequency range 100 Hz ... 2 kHz

 (filter type selective harmonic)

C) Transient interference signals in the frequency range up to

 300 MHz (filter type low-pass)

D) Sinusoidal interference signals in the frequency range up to

 1 GHz (filter type broad band, low-pass) 

In practice, however, interference is mainly found in the last three categories B, C and D. Superimposed on the high-voltage mains supply, such interference can affect the performance of electronic circuits, or even cause them damage. An optimally-designed mains filter can perform a double function:

Function 1

The filter protects an electronic control circuit from voltage spikes in the mains supply, which may be generated, for example, by electromechanical switches and relays.

Function 2

The same filter also acts simultaneously in the opposite direction. The HF interference generated in the unit by thyristor control is attenuated such that the boundary values Class B, (EN 55011/55022) are maintained.

Filters are usually made up of capacitors and inductance coils. Components such as leakage resistors, surge dissipators and VHF chokes can also be integrated into the filter. Broad band filters

which meet the highest requirements are often composed of 2 or 3 single stages put together to make one filter unit:


Leakage current

The leakage current of a device is mainly determined by the capacity value of the Y-capacitor.

According to international standards (IEC 60335-1) the following regulations with respect to leakage current can be assumed:

Type of appliance

Protection class

IL max. [mA]



Portable appliances





Stationary motor appliances *





Stationary heating appliances


0.75/kW (max. 5.0)









I, 0I, III




* Stationary appliances fixed or weighing in excess of 18 kg (without carrying handle).

For other applications:





Test equipment


0.5 mA
(UL 61010-1)

0.1 mA
(UL 60601-1)

5.0 mA
(UL 62368-1)

5.0 mA
(UL 61010-1)



0.1 mA
(IEC 60601-1)

5.0 mA
(IEC 62368-1)

3.5 mA
(IEC 61010-1)

Further details about leakage currents are also described under filter classification.

Rated voltage UR (Umax)max

The rated voltage UR is the maximum RMS alternating line to line voltage (Umax) which may be applied continuosly to the terminals of the filter. The rated voltage is the nominal voltage including 10% tolerances.


Filter with UR = 440 VAC is made for a power system with nominal voltage 400 VAC +10%.

For standard three phase filters the voltage between phase and earth is intended UR/√3 (example 440/250 VAC).

Filters made for IT power systems withstand a voltage between phase and earth equal to UR.

SCHURTER filters for IT systems have code endingwith „I“: ex. FMAC-0932-2512I.

The line frequency fN (50/60 Hz) may be exceeded under certain conditions. We recommend the users to consult in any case our technical department. DC power operation is possible in most cases.

Power distribution system

There are three main types of power distribution systems according to IEC 60364-1: TN, TT, IT.

The TN POWER SYSTEM is a power distribution system having one point directly earthed, the exposed conductive parts of the installation being connected to that point by protective earth conductors. Three types of TN POWER SYSTEMS are recognized according to the arrangement of neutral and protective earth conductors: TN-S, TN-C-S, TN-C.

Example of a TN-C-S system

TN-C-S is in a system which neutral and protective functions are combined in a single conductors in a part of the system.

Example of a TT system

A TT POWER SYSTEM is a power distribution system having one point directly earthed, the exposed conductive parts of the installation being connected to earth electrodes electrically indipendent of the earth electrodes of the power system.

Example of a IT system

The IT POWER SYSTEM is a power distribution system having no direct connection to earth, the exposed conductive parts of the electrical installation being earthed. In this case the voltage between phase and earth can reach the line to line voltage.

Nominal Current INN

The technical data gives the max continuous supply current in function of the ambient temperature IN/νa. The SCHURTER range generally differentiates between two types of filters:

- High-current filter: νa at IN = 40°CN

   νamax = 100°Cmax

- All other filters: νa at IN = 40°CN

   νamax = 85°Cmax 

The permissible working current at higher ambient temperatures can be read from the following graph.

Permissible working current as a function of ambient temperature

Up to the approved nominal ambient temperature a the filter can be operated continuously at its nominal current. Above this temperature the square of the nominal current drops off linearly and reaches its zero point at Tmax (85 or 100 °C).

Derating curve (approx.)


I = admissible operating current at elevated ambient air temperature

In = rated currentn

Tmax = max. allowable ambient air temperature Ta (85 °C)max

Ta = ambient air temperaturea

Tn = allowable ambient air temperature at rated current (40 °C)n

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