电气线路中的裸导线或绝缘导线的绝缘体破损后，火线与零线，或火线与地线(包括接地从属于大地)在某一点碰在一起，引起电流突然大量增加的现象就叫短路，俗称碰线、混线或连电。
When the insulator of bare conductor or insulated conductor is damaged, the fire line and zero line, or the fire line and ground line (including ground subordinate to the earth) collide at a certain point, causing a sudden increase in current is called short circuit, commonly known as touching line, mixing line or connecting electricity.
由于短路时电阻突然减少，电流突然增大，其瞬间的发热量也很大，大大超过了线路正常工作时的发热量，并在短路点易产生强烈的火花和电弧，不仅能使绝缘层迅速燃烧，而且能使金属熔化，引起附近的易燃可燃物燃烧，造成火灾。
Because of the sudden decrease of resistance and the sudden increase of current when short circuit occurs, the instantaneous calorific value is also very large, which greatly exceeds the calorific value of the normal operation of the line. It is easy to generate strong sparks and arcs at the short circuit point. It can not only make the insulating layer burn rapidly, but also make the metal melt, and cause the flammable combustibles nearby to burn. A fire broke out