Various standards attempt to test the flammability of the insulation materials used by means of simulation in situations that are as close to reality as possible. This may be, for example, by means of the hot wire ignition test (overheating of a wire) or flame impingement (electric arc for tracking). There are also tests that simulate the real situation in rooms or control cabinets with chimney-like test designs. The results from the various methods can vary significantly and must be used in the context of specific objectives.
Flammability is tested according to the following standards, among others: UL94, IEC 60707, IEC 60695-11, DIN 40633-4.7, VDE 0340, UL 510, IEC 60454-2, DIN 4102, DIN EN 13501, etc.
(Definition: test of a device or material regarding its capacity not to become flammable or not to cause a fire (or smouldering fire) in the event e.g. of a short circuit or external application of heat. For example, classification of flammability under DIN EN 13501; flammability class (fire class) B1 = low flammability).
The procedures for plastic differ generally in the positioning of the test sample: horizontal, vertical or wound round a metal rod (films/adhesive tapes).
In this test of the fire behaviour of materials, the samples are clamped horizontally in a holder. The sample size is around 360 x 100 mm with a maximum thickness of 13 mm.
The first measurement mark (start of speed measurement) is at 38 mm, the second at 76 mm.
The sample is exposed to a Bunsen burner flame for 15 seconds on one edge. The speed at which the flame spreads is measured from the measurement mark. The test results are documented as follows:
DNI - non-flammable
SE - self-extinguishing (material burns but goes out before the measurement mark is reached)
SE/NBR - self-extinguishing with no burning rate (material burns, but goes out within 60 seconds and burning path is below 76 mm)
SE/B - self-extinguishing, the flame goes out within the measurement distance above the first 76 mm; the burning rate is given as 60xburning path/burning time (mm/min).
B - the flame covers the whole burning path (a total of 360 mm). The burning rate is given as 60xburning path/burning time (mm/min).
The HWI (hot wire ignition) test is used as one of the specifications for insulation materials. This classifies the products more finely in terms of their flammability. An overcurrent caused e.g. by a short circuit is simulated, causing a wire (coil, supply cable) to glow. Under the IEC 60695 standard, the test is carried out at temperatures of 550 °C, 650 °C, 750 °C, 850 °C and 960 °C. The test determines if the material ignites or continues to glow (test time 30 sec.). The temperature (+25K) at which the test is passed is specified. On the other hand, under the UL 746A standard, the time at which the test sample ignites is given.
HWI Range Mean time to inflammation in sec.
|120 and more
|60 to 119
|30 to 56
|15 to 29
|7 to 14
|less than 7
You will find details of the products in the respective E-files for the materials at UL. For example, the value for Nomex and Kapton PLC is 0.
Other tests include, for example, resistance to ignition when electric arcs are applied. These can come about if the surface of the insulating materials is so dirty or has become so conductive because of the voltage load that an electric arc ignites. One measure of the resistance of an insulating material (among others!) is the tracking resistance.
Tracking is brought about by the formation of a conductive pathway on the surface of an insulating material, caused by the simultaneous effect of electrical and electrolytic factors (in the absence of moisture).
In the case of electrical erosion, electrical discharges erode parts of the insulating material from the surface. An electrically conductive pathway is created by this and by the degradation products. In many insulating materials, the CTI test can result in spontaneous ignition. The CTI value is a figure without unit.
Standard measurement set-up: Two platinum electrodes are placed on the surface of the insulating material (3 mm thick or more) with a gap of 4 mm. An ammonium chloride solution is gradually dripped between them and voltage is applied. The CTI value indicates the maximum voltage at which there is no tracking path formation (definition of comparative tracking index: highest figure for voltage at which there is no failure in five samples after 50 drops in each case).
CTI = 1 (400-599V); Polyester, PEN, PP CTI = 2 (250-399V)
CTI = 3 (175-249V); PPS; PC, FR4-sheets (mostly)
CTI = 4 (100-174V); PI, PEI, PEEK
According to IEC 60112 and IEC 60664 (test method) the comperative tracking index is comparable with the classifications of the cti value in UL 746A as follows:
600 ≤ CTI: I 400 ≤ CTI < 600: II 175 ≤ CTI < 400: IIIa 100 ≤ CTI < 175: IIIb
As evidence of the efficiency of our adhesive insulation tapes, a few years ago we had a mandrel test carried out in accordance with EN 61558 Section 26.3 by the VDE testing body. The CMC 10966, CMC 10160, CMC 10262, CMC 10165, CMC 10858, CMC 10260 and CMC 70100 products passed the test with respect to the (reduced) distance through the insulating films (two layers). If you wish, we will send you the test report by e-mail.
In conjunction with the very good CTI values for the polyester film, compact insulation is possible in situations where small clearance and tracking distances are required.