1.电气火灾的原因和危害性我国的电气火灾大部分都是因漏电和短路而引发的，在低压配电系统中， 电气线路的漏电和短路是导致电气火灾发生的根源和重要原因之一， 并对国家经济和人民生命财产构成了很大的威胁，应引起大家高度的警惕和重视。

1. The electrical fire causes and harmfulness of the electrical fires were mostly caused by the leakage and the short circuit, in the low-voltage distribution system, leakage of electric circuit and short circuit is the root cause of electrical fires and one of the important reasons, and the national economy and people's life and property constitutes the great threat, should cause everyone to a high degree of attention and vigilance. 

　　当电气线路和电气设备的绝缘受到损伤而导致接地故障，主要是指相线对地或与地有联系的导电体之间的短路，包括相线与大地、PE 线、PEN 线、配电和用电设备的金属外壳、敷线钢管、桥架线槽、建筑物金属构件、上下水和采暖、通风等管道以及金属屋面、水面等之间的短路。当发生接地短路时在接地故障持续的时间内， 与它有关联的电气设备和管道的外露可导电部分对地和装置外的可导电部分间存在故障电压。

When the insulation of the electrical circuits and electrical equipment damage caused by ground fault, is mainly refers to phase line to ground or are associated with the short circuit between the conductive body, including the line with the earth, PE line and PEN line, distribution and metal casing of electrical equipment, apply the wiring groove line pipe, bridge, building hardware, plumbing and heating, ventilation and other short circuit between pipe and metal roofing, surface, etc. When grounding short circuit occurs within the duration of the ground fault, it linked with electrical equipment and the pipeline can be exposed conductive parts to ground and device can be conductive part between the breakdown voltage. 

　　此电压可使人身遭受电击， 也可因对地的电弧或火花引起火灾或爆炸，造成严重的经济和生命财产损失。

This voltage may cause an electric shock to the person, or a fire or explosion caused by an electric arc or spark in the ground, causing serious economic and loss of life and property. 

　　电气短路主要包括金属性短路和接地电弧性短路两种：

Electrical short circuit consists mainly of the gold attribute short circuit and earth arc short circuit two kinds: 

　　金属性短路是由导体间直接接触，如相与相之间、相与N 线之间短路，其短路电流大，短路点往往被高温熔焊，金属线芯产生高温以至炽热，绝缘被剧烈氧化而自燃，火灾危险甚大，但金属性短路产生的大短路电流能使断路器瞬时动作切断电源，火灾往往得以避免；接地电弧性短路是因短路电流受阻抗影响，电弧长时间延续，而电弧引起的局部温度可高达2000℃以上，足以引燃附近可燃物质引起火灾，但由于接地故障引起的短路电流较小，不足以使一般断路器动作跳闸切断电源，可见接地电弧性短路引起的火灾危险远远大于金属性短路。电气短路以单相接地故障居多， 电气火灾的危险则以接地电弧性短路为最严重。另外不论是TN 系统还是TT 系统，接地故障回路的阻抗都大于带电导体短路回路的阻抗， 这也是形成接地电弧性短路的一个重要原因。

Metallicity short-circuit is by direct contact between a conductor, such as short circuit between phase and phase N line, with its large short-circuit current, short circuit point tends to be high temperature fusion welding, high temperature and hot wire core, insulation is severe oxidation and spontaneous combustion, fire danger, but large short-circuit current produced by the metallicity short-circuit instantaneous action can make the circuit breaker to cut off the power supply, fire tend to avoid; Grounding short circuit arc sex is affected by the impedance due to short circuit current, arc long continuance, and arc caused by local temperature can be as high as 2000 ℃ above, enough to cause fire ignites near flammable materials, but caused by earth fault short-circuit current is small, not enough to make the general circuit breaker trip to cut off the power supply, visible arc grounding sex fire danger than metallicity short-circuit caused by short circuit. Electrical short circuit is centered on single phase ground fault, and the danger of electric fire is the most serious fault of ground arc. Moreover both TN system and TT system, the earth fault loop impedance is greater than that of a charged conductor short-circuit loop impedance, which is form the grounding arc sex is an important cause of short circuit.