Model of a Reproduceable Flammability Test

The tests, requirements and areas of application of X and Y capacitors are defined in IEC 60384-14, version 2. This international standard which came into force in 1993 is in line with the European EN 132400 and is designed to make national symbols superfluous. The IEC lays down stricter peak voltage tests for several subclasses.

Despite the more stringent requirements for peak voltage strength called for by the IEC 60384-14/2, only limited conclusions can be drawn about the safety of radio interference suppression capacitors.

Model of a Reproduceable Flammability Test

A reproduceable test, which also takes a long life-time into account, is the DC-AC test.
The DC test simulates the pre-damaging of the capacitor by transients up to the first breakdown. An adjustable DC voltage is continually increased until the capacitor breaks down electrically. The sudden decrease in the voltage indicates the pre-damage of the capacitor (figure 1).

	Figure 1: Test circuit for DC test.		Figure 2: Test circuit for AC test

In the subsequent AC test, the same capacitor is subjected to a stress from zero up to its rated AC voltage at 50/60 Hz. The voltage should be applied to the capacitor for at least 5 minutes (figure 2).

The capacitor is considered to have passed the test if it stands up to the DC voltage load and the subsequent AC voltage stress without burning. The test results gained for standard commercial MKT plastic film and metallized paper capacitors are summarized in Table 1. These tests, which were carried out by an independent industrial user, showed that over 30% of the MKT capacitors were actively flammable. Not a single one of the 56 tested MP capacitors was flammable.

Table 1: Failure rate of MKT versus MP RFI capacitors.