Požárně nebezpečné poruchy zásuvek v domácnostech

Abstract

This master's thesis deals with the issue of fire-hazardous failures of household electrical sockets. The aim of the thesis is to theoretically analyze and experimentally quantify the processes leading to thermal degradation and subsequent ignition of electrical connections. The theoretical part describes in detail the mechanisms of contact resistance formation, material fatigue, and thermodynamic instability, including the specific phenomenon of a glowing connection. The practical part consists of a set of interconnected laboratory measurements on socket samples of varying ages. It includes the analysis of the decline in mechanical properties (tightening torques, contact forces), precise four-wire measurement of contact resistances, and thermal load tests simulating fault conditions at rated current. The conclusion of the thesis is dedicated to the forensic analysis of microscopic traces, such as arc beads, metal weldings, and typical chemical degradation of the insulator, which serve in practice to unambiguously identify the primary cause of a fire. The results of the experiments prove that a loose connection can generate a critical amount of heat leading to destruction and fire even in the absence of an overcurrent, and this is true even for completely new devices.