Abstract
Aim: Presentation of the results of experimental research on the reaction to fire of electric cables according to PN-EN 60332-1-2, as well as some additional tests. The aim of the study was to assess the influence of selected parameters, such as outer diameter, number of cores, the core material and the presence shielding on the fire spread through electric cables.
Project and methods: The study was performed on a testing stand, compliant with PN-EN 60332-1-2. In accordance with the typology presented in the classification standard PN-EN 13501-6, it constitutes a basic document for determining the Eca class reaction to fire, and an additional one for B1ca, B2ca, Cca, Dca classes. The tests were carried out on a group of electric cables with diameter between 7 mm and 17.5 mm, differing from each other in the amount of cores, as well as, in the core and insulation’s materials. Some of the cables had a screen made of galvanized wires. Testing methodology was supplemented with veins temperature measurements, carried out with the use of two thermo-couples positioned at both ends of the sample. Next to the tests based on normative methods, the authors also carried out some tests involving doubled and tripled flame exposure time.
Results: Shielded cables spread the fire in a much greater extent than their unscreened counterparts. Shielded cables’ maximum charring range increases proportionally to the wire’s thickness. There were no significant differences in the fire spread between the cables differing from each other in their core material. The highest temperature was recorded in case of the cables with the smallest diameter. Temperature measured at the end of the conductors located about 100 mm from the point of application of the burner reached its maximum of about 40°C during the normative flame application time, and about 150°C at a tripled application time. At the second measuring point, positioned about 500 mm from the flame application point, there were no temperature changes noticed, for none of the tested samples.
Conclusions: The main factor influencing the fire spread through an electric cable is the material of its insulation. In case of shielded cables the growth of charring range, along with the increase of cable diameter was caused by the greater amount of combustible material subjected to flame influence. The material of conductor does not have a major impact on the fire spread. For cables within tested diameters normative flame application time (i.e. 60 seconds) seems to be the most optimal. With extended exposure times there has been no significant increase of damage range, while there was a noticeable decrease of precision of the method.
Keywords: electric cables, reaction to fire, fire hazard
Type of article: short scientific report