Electrical engineers understand that electromagnetic disturbances are potential sources of malfunctions for all electronic equipment from PLCs and inverter drives to measuring and processing devices.  They can affect the performance of equipment causing it to malfunction and possibly crash.  Because problems due to electrical noise are often transient they are notoriously difficult to identify and correct and good practice is recommended.

In Europe, individual electrical components and devices are generally CE marked to show compliance with the EMC Directive  Directive 2004/108/EC.  The EMC Directive first limits electromagnetic emissions of equipment in order to ensure that, when used as intended, such equipment does not disturb radio and telecommunication as well as other equipment. The Directive also governs the immunity of such equipment to interference and seeks to ensure that this equipment is not disturbed by radio emissions when used as intended.

Conducted interference of various frequencies can be superimposed on the original signal. The signal may then be unreadable by the equipment that receives it and consequently its processing will be uncertain or impossible.  If a processing device such as a microprocessor is disturbed by high-frequency waves it can crash or produce abnormal results: when it restarts there is no apparent reason for the problem.

Variable speed drives may affect other equipment by causing interference problems conducted through cables or radiated by the device.  The most appropriate treatment is to arrange a filter on the disturbed line, as close as possible to the drive.  The appropriate filter characteristics are given by the manufacturers according to the voltage, the line current and the frequency of the disturbance to be reduced.

In addition to the performance of the individual devices, the control panel will also have an EMC footprint affected by panel layout, cabling and type of enclosure use.   To help equipment users, Schneider Electric UK has produced a 24 page booklet on “How to protect a machine from malfunctions due to electromagnetic disturbance”.  It comprises three sections covering:

– Panel design in accordance with EMC rules

– Assembly – panel wiring

– Guide for selection of “EMC” products

A new  EMC Directive 2014/30/EU of the European Parliament and of the Council of 26 February 2014  on the harmonisation of the laws of the Member States relating to electromagnetic compatibility (recast) (all languages), aligned to the New Legislative Framework, will be applicable from 20 April 2016.

Download the Schneider Electric EMC booklet from 999 Inverters

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