Abstract: Mark of melting through copper plate is considered as one of key evidences to show ground short circuit occurring. But some similar melted marks often exist in fire scenes, which may be caused by solder alloying through copper plate. In the paper, the thermodynamic process of Cu- Sn alloy melting was analyzed by simultaneous thermal analyzer. According to actual fire scenario, the formation rule and typical characteristics of Cu-Sn alloy melting mark were researched. The results showed that O2 helped advance the Cu-Sn alloy melting reaction. When the temperature of copper plate was above 515 ℃ , the molten Sn could melt the copper plate and form the melting marks similar to melted marks caused by ground short circuit arc in appearance. As the temperature increased, the melting mark of Cu-Sn alloy changed from gold to black, and the size of alloying marks became larger and larger. This research result has certain theoretical reference value for the accurate identification of ground short circuit and the determination of temperature of molten copper in the field. 

Key words: fire investigation, penetration melted mark, arc through melting, alloy melting; mark characteristics