Description of the differences on X1, X2,X3, Y1, Y2 & Y3 – Capacitor
Class X is for applications where failure could not lead to electric shock (hot to neutral). Class X1 capacitors are intended to operate safely even in the presence of spikes on the mains supply of up to 4 kV (installation category 3 or overvoltage category 3 according to IEC60664), which are normally industrial supplies, but some standards call up class X1 capacitors if they are connected directly to the mains supply upstream of the equipment fuse, irrespective of the type of mains supply. Class X2 capacitors are intended to operate safely even in the presence of spikes on the mains supply of up to 2.5 kV (installation category 2 or overvoltage category 2 according to IEC60060), which are normally residential, commercial and light industrial supplies. X capacitors can be found from 0.001 uF to at least 10 uF and are only made in film.
Class Y capacitors are for applications where failure could lead to electric shock if the ground connection were lost. This includes hot/neutral to ground, and antenna isolation capacitors. Because Y capacitors shunt current to ground, leakage-current limitations limit their size to a maximum of about 4700 pF in many commercial and industrial applications (but refer to the relevant standard for definite information) and about 470 pF in medical applications. Larger ones are available however. Y caps are available from 1000 pF to 0.1 uF and are made in both film and ceramic.
Because most applications require one X and two Y capacitors, multi-capacitor devices are available. Also available are a variety of metal or plastic housing styles, mounting options (pc mount, pigtail) and 4-wire connections. At least one manufacturer (WIMA) has X2 and Y2 capacitors in SMD, with more expected to follow. Line-filter capacitors are most often boxed and potted in epoxy. The box is usually polybutylene terephalate (PBT) for it´s superior flameability characteristics. This gives better moisture protection than an epoxy dip, or the common “wrap and fill” construction. Line-filter capacitors are also used as components in complete filter modules that include inductors and a bleeder resistor. Multi-capacitor modules can even use mixed dielectrics, such as a 3-phase module where the X capacitors are polyester, and the Ys are polypropylene.
Classes X1, X2, and Y were originally defined by the IEC in IEC 60384-14. CENELEC has adopted EN 132400 (technically equivalent to, but structurally different from IEC 384-14 2nd edition), which now defines seven classes of line-filter capacitors. Class X1 capacitors are impulse tested to 4 kV (higher for capacitors over 1.0 uF). Class X2 capacitors are impulse tested to 2.5 kV (higher for capacitors over 1.0 uF). Class Y1 capacitors are impulse tested to 8 kV, and Class Y2 are impulse tested to 5 kV. Classes X3, Y3, and Y4 are for lower-voltage capacitors, none of which are presently called up in safety standards. Other impulse tests also apply. These include a 1000 hour endurance test during which the capacitor is subjected to a continuous overvoltage condition, plus periodic 1000 VAC spikes, and a flammability test during which the capacitor is hit with a series of transients while under rated voltage. Capacitors conforming to IEC60384-14 normally also conform to EN132400, and vice versa, and should be accepted in all European countries.
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