What is all the fuss about EMC?

When's it all happening and what can happen to me?

On the 1st of January, 1996 all electronic and electrical equipment must comply to the European Communities EMC directive 89/336/EEC. Failure to comply will be a criminal offence, and may lead to severe fines or imprisonment.

What does the directive cover?

The directive covers products connected to the public mains electricity supply and radio and telecomms communication systems. The directive covers both emissions and immunity in the bandwidth of 150kHz to 1GHz. See limit levels below.

Conducted Emissions

Radiated Emissions

When are suppression components needed?

If interference levels above those defined by the directive are experienced during normal equipment operation.

Immunity Wa?

In this condition the equipment is set up to operate normally and is subject to incident interference of different types at specified levels. Should the equipment malfunction under the required conditions then its immunity to the incident interference must be increased by adding suppression components to the point where the equipment is made immune to upset by the mandatory interference levels.

To ensure compliance with these limits it is usually necessary to design suppression components into equipment.

This need can be met in many ways from designing components such as chokes and capacitors into circuits or using a suitable mains filter pre packaged as a single component.

What standards apply?

The European Norms (EN) most frequently referred to are listed below:

Emissions. What's this then?

The specifications on EN55022 and EN55011 on emissions are frequency domain - based and specify the total amount of noise permitted in a given frequency band - width of 150kHz to 1000MHz. It has been agreed in the specification that the frequency range from 150kHz to 30MHz is concerned with conducted emission and the part of the spectrum from 30MHz to 1000MHz is devoted to radiated emissions.

How are emissions measurements made?

In order to ensure repeatability and consistency of measurements. the conducted emissions are measured with a standard receiver with defined time constants, impedance and attenuators against a standard mains supply Line Impedance Stabilisation Network (LISN), the radiated measurements are made using standard receivers with calibrated antennae against a specified ground plane in an open site of set minimum size and distances.

The flicker and harmonic distortion specification set out in EN60555 sets limits on the amount of flicker caused by voltage dips and distortion of the main current supply harmonics.

Where do I find information about Immunity?

The immunity to interference levels are covered by the IEC 1004 series, the main areas of interest being the conducted electrical fast transient and electrical surge requirements of parts 4 and 5 with the electrostatic discharge (part 2) and electro magnetic radiated energy (part 3) being the complementary parts.

What is filter made of?

Typically inductors and capacitors are used within filters in various combinations to allow RFI current to flow into harmless loops and selectively block RFI currents.

What are a filter's requirements?

The prime requirements for a filter intended to suppress interference on the mains supply lines are firstly that is shall pass the supply current which may be from dc to 400Hz, it also has to withstand the supply voltages and meet earth leakage current and all other safety aspects for IP, climatic category and IEC 950 requirements and rating, and secondly that it will provide a high degree of attenuation to all frequencies from 150kHz upwards.

It is important to remember when choosing a filter that for performance above 5MHz installation and integration can play a significant and decisive part.

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Terms and Conditions of Sale | Legal Notices Copyright © Reserved Whilst every effort has been made to ensure the accuracy of this information, we operate a policy of continuous improvement, and reserve the right to alter models and specifications without notice.  All values and specifications are nominal rather than exact, and where applicable, are with the rated supply voltage only, using new lamps and components.  All information is given in good faith but without guarantee to performance figures.  Where shown all dimensions are in mm unless specifically indicated otherwise.  E&OE

23/06/09