Achieving the highest level of safety must be a prime factor whenever designing any device or machine. Safety capacitors are particularly important components in the field of electronics. Let’s have a look at what they’re made of.
At present, the electrical and/or electronic devices in our homes, factories, streets, etc., must comply with an electromagnetic interference (EMI) standard. This means that the equipment in question must not interfere with the other equipment around it and must be immune from the external interferences to which it is in turn subject, both carried over the grid and radiated.
To achieve this, one of the things that designers do is fit different types of filters inside the devices. Capacitors of different types and values make up a considerable part of such filters. EN 60384-14 and IEC 60384-14 Standards (Fixed capacitors for use in electronic equipment – Part 14: Fixed capacitors for electromagnetic interference suppression and connection to the supply mains) divide EMI suppression capacitors into two groups:
• X capacitors: for connection between phases and between phase and neutral.
• Y capacitors: for connection between phase and ground or between phase and neutral.
As can be seen from the above figures, the housing of electrical devices is normally connected to ground. The splitting into two groups required by the standard can be explained by the fact that:
In an X capacitor, the malfunctioning of the same cannot cause electrical shocks for the user, whereas this can occur in the case of Y capacitors. Let’s see what can happen.
In the event of an X capacitor failure, if its circuit is left open, the filter will not function properly even though the device may continue to work with or without too many problems (a piece of radio frequency equipment will probably work albeit not to the same level of quality, but we may not observe anything awry in other types of apparatus, even though we are most likely no longer complying with the EMI standard). If, on the other hand, the capacitor short-circuits on failing, the device will stop working and the fuse (if it has one) and/or the installation’s main power switch will trip. Take care, however: if the capacitor is not fire proof, a greater or lesser risk of fire arises depending on how long it takes aforementioned shut-off devices to kick in.
Let’s now have a look at what can happen if a Y capacitor fails. If it is left in open circuit, the housing will be left unconnected (and, once again, we will most likely not comply with the EMI standard). However, if it short-circuits, depending on the nature of the fault, either the neutral or the phase will be directly connected to the housing with the concomitant serious danger this represents should anyone touch it. If this happens, there would still be the installation’s residual-current device, but any failure of this or defective ground wiring could lead to a serious electrical accident. Moreover, the risk of fire would still remain, as in the previous case.
This is why both X and Y capacitors must pass a series of rigorous tests in order to comply with the EN 60384-14 Standard. The different sub-families provided for in that standard (X1, X2, X3 and Y1, Y2, Y3, Y4) refer to the higher or lower values applied when doing these tests (mainly with respect to surges: see the tables and figures given below). As a general rule, it can be said that X1s and Y1s are required for industrial purposes, whereas X2s and Y2s suffice for domestic use given the voltage of the Spanish national grid.
Among other tests, these components must faultlessly withstand a series of µsecond voltage peaks or surges (2500V for X2s and 5000V for Y2s), as well as an overvoltage of 1000V for 0.1 seconds, once an hour for one thousand working hours, withstanding 1.25 times their rated voltage.
Equally important, if not more so, is that they must be tested for their non-flammability, both in terms of active and passive flammability. That is to say, they must neither cause flames when they break down, nor become flammable when subject to flames.
Overvoltage endurance
Different tests to which X capacitors are subject
Different tests to which Y capacitors are subject
If they manage to pass all the tests, the manufacturer can mark them according to the corresponding category (e.g. X2) and the logo that indicates the standard with which they must comply. The standards indicated in the following table are similar or comparable to those in the countries shown.
Table with the different values indicated by the standard for each category
ELT uses the appropriate safety capacitors in all of its products. These capacitors come from suppliers whose products have passed all the tests, and therefore, carry the corresponding marking: X1, X2, Y1 etc. Accordingly, ELT complies with the standard because safety is a factor that always comes first, before considerations such as price, yield, or any other.
Alberto Peñaranda, quality department
