Why did the Mercury 200 electricity meter melt?

Good afternoon. Reflow what? If the contacts around them are melted, the cause of the melting is always an elevated temperature. And the cause of the fever is poor contact. As a result, the screw in the terminal block was loosely clamped or eventually loosened and the contact worsened and began to warm up. From heating there was an expansion and reverse narrowing of metals, coating them with soot. All this led to the fact that the contact became worse and worse. As a result, the temperature of the contacts in operating mode reaches such a temperature that the insulation begins to go off and the cases of electrical appliances melt.