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Since January 1996 all manufacturers have to design their equipment to comply with the protection requirements of the electro-magnetic compatibility (EMC) directive 89/336/EEC of the European Commission. The protection requirements define, that the manufacturer has to minimise the probability of causing or suffering from electromagnetic disturbances. Manufacturers of power drive systems (PDS) normally define a rated input voltage range, rated power range as well as a climatic ambient within which the PDS has to operate. The EMC product standard EN 61800-3 for adjustable speed electrical PDS, on the other hand accepts light load or unloaded test condition during the conducted emission measurement according to the emission standard EN 55011. This paper looks at the EMC behaviour of PDS, especially in combination with an input electromagnetic interference (EMI) filter in function of the supply voltage and its real load condition. Investigation shows direct influence of real ambient and load conditions on EMI filter performance. Therefore in many cases passing the EMC tests in laboratory conditions does not mean fulfilling protection requirements in the field.