IEC 61558-2-19:2000 pdf free download – Safety of power transformers, power supply unitsand similar devices
19.1.2 For transformers with intermediate metal parts (e.g. the iron core) not connected to thebody and located between the input and output windings，the insulation between theintermediate metal part and the input windings or between the intermediate metal part andthe output windings, shall consist of at least basic insulation.
NOTE An intermediate metal part which is not separated from the input or output windings or the body by atleast basic insulation, is considered to be connected to the relevant part(s).
ln addition, the following applies:
– for class l transformers,the insulation between the input and output windings via the intermediate metal part shall consist of double or reinforced insulation;
– for class ll transformers,the insulation between the input and output windings via theintermediate metal part shall consist of double or reinforced insulation;the insulationbetween the input windings and the body,and between the output windings and thebody, via the intermediate metal part shall consist of double or reinforced insulation.
19.1.3 Class l transformers shall not have protective screening between input and outputwindings.
19.1.4 Transformers shall not be provided with capacitors which electrically connect inputand output circuits.
Addition:
19.101 There shall be no connection between the output circuit and the protective earth.
19.102 There shall be no connection between the output circuit and the body.
Compliance is checked by inspection.
19.103 The input and output terminals for the connection of external wiring shall be so locatedthat the distance measured between the points of introduction of the conductors into theseterminals is not less than 25 mm between the input and output terminals. If that distance isachieved by a barrier,this barrier shall be of insulating material and be permanently fixed tothe transformer.
19.111 For independent transformers,the socket-outlets if any，shall be part of thetransformer. For associated transformers, the connection to the appliance is ensured by acable or a flexible cable with double insulation.
19.112 The output winding shall be provided with a mid-point connection to the earthingterminal of the socket-outlets, if any.For transformers with more than one output winding, thewindings shall be separated by double or reinforced insulation. Alternatively, the mid-pointtapping of the windings can be connected together to a common point connected to the earthing terminal in all the socket-outlets, if any.The earthing terminals of the socket-outlets inthe output circuits shall not be connected to the protective earth.
Compliance is checked by inspection,by the tests of 18.1 and by measurements according toclause 26.
NOTE Perturbation attenuation transformers can be provided with enclosures of both metal and insulationmaterial.
19.113 The transformer shall be provided with a disconnecting protective device as shown infigure 101, breaking the output circuit in case of a short circuit in the connected appliancebetween the phase conductor and the conductor connected to the mid-point or between the twophase conductors. In this case，the disconnecting protective device shall operate within thetime stated in table 101.
NOTE This table has been extracted from table 41A of lEC 60364-4-41.Compliance is checked by inspection and by the following tests:
Disconnecting protective devices are checked by connecting the input of the transformer to avoltage of 0,94 to 1,06 times the rated voltage, whichever is the more severe,and the terminalsin the output,one at a time,are connected to the mid-point and then with each other.Thedisconnecting protective device shall then operate within the time stated in table 101.