For the copper bar under 630A circuit breaker in 500 KVA box transformer, see the second circuit breaker from the left in the figure. The temperature of the corresponding area above the molded case of the circuit breaker is obviously higher than that of the other two corresponding areas, and the other two phases are also hot. Moreover, the copper bar of this phase has been burnt to white, and there is no sense. The clamp meter does not measure the current of each phase. Judging from the phenomenon, it should be phase deviation, which leads to the high current of this phase, However, the equipment of this box transformer is three-phase air compressor, hoist, submersible pump and so on. There are only a few iodine tungsten lamps, so it is impossible to determine the specific reason of phase deviation

Analysis: the normal connection of the line temperature is too high, the cause of burning as long as one: line resistance is higher than the normal range!

The cause of line burning is that there is a large current in the line, but if the line resistance is very low or not, the temperature of the line will increase at most, and it will not burn. So the current itself is no problem - the problem is what makes the line temperature rise? Obviously - resistance.

So the conclusion is that the line connection is not reliable, or the line itself has quality problems, resulting in higher resistance than other lines. But if not, it means that the line diameter is too small, and the whole line is the smallest, so it will burn here.